JP2008243828A - Negative electrode and manufacturing method for secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for a secondary battery capable of improving battery characteristics such as cycle characteristics. <P>SOLUTION: A negative electrode active material layer 12B including at least one kind among a group of a simple substance such as silicon, an alloy, and a compound is formed on a negative electrode current collector 12A by a gas phase method. The negative electrode active material layer 12B is set up to make alloy with the negative electrode current collector 12A. Lithium of 5 to 40% of negative electrode capacity is occluded on the negative electrode active material layer 12B as metal lithium is deposited or the like on the surface of the negative electrode active material layer 12B by the gas phase method. Thus, the electrochemically-active lithium is to remain on the negative electrode active material layer 12B after discharging at least at an initial charging and discharging cycle. Consequently, lithium can be replenished even though the lithium is consumed by reaction with an electrolyte, and electrical potential rise of the negative electrode 12 can be restrained at the final stage of discharging. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a negative electrode having a negative electrode active material layer on a negative electrode current collector, and a method for manufacturing a secondary battery including the negative electrode.

  2. Description of the Related Art In recent years, as mobile devices have higher performance and more functions, there is a strong demand for higher capacities of secondary batteries that are power sources thereof. There is a lithium secondary battery as a secondary battery that meets this requirement. However, when lithium cobaltate is used for the positive electrode and graphite is used for the negative electrode, which is a typical form of the present lithium secondary battery, the battery capacity is in a saturated state, and it is extremely difficult to increase the capacity significantly. . Therefore, the use of metallic lithium (Li) for the negative electrode has been studied for a long time, but in order to put this negative electrode into practical use, it is necessary to improve the precipitation dissolution efficiency of lithium and control the dendrite-like precipitation form. is there.

  On the other hand, secondary batteries using a high-capacity negative electrode using silicon (Si), germanium (Ge), tin (Sn), or the like have recently been actively studied. However, when these high-capacity negative electrodes are repeatedly charged and discharged, they are pulverized and refined by vigorous expansion and contraction of the active material, resulting in a decrease in current collection and an accelerated decomposition reaction of the electrolyte due to an increase in surface area. The cycle characteristics were extremely poor. Therefore, if a negative electrode in which an active material layer is formed on a current collector by a vapor phase method, a liquid phase method, or a sintering method is used, a conventional coated negative electrode coated with a slurry containing a particulate active material and a binder is used. Compared to miniaturization, the current collector and the active material layer can be integrated, so the electron conductivity in the negative electrode is extremely good, and the capacity and cycle life are improved. Is expected. In addition, since it is possible to reduce or eliminate the conductive material, binder, voids, and the like that existed in the conventional negative electrode, the negative electrode can be made essentially thin.

  However, even this negative electrode cannot be said to have sufficient cycle characteristics due to the irreversible reaction of the active material accompanying charge / discharge. Further, like the conventional high-capacity negative electrode, the reactivity with the electrolyte is still high, and the capacity is greatly deteriorated particularly in the initial cycle due to the reaction with the electrolyte accompanying charging and discharging. Further, in these high-capacity negative electrodes, the negative electrode potential increases remarkably with the desorption of lithium particularly at the end of discharge, which is one of the factors causing characteristic deterioration.

  In order to solve these problems, a method in which lithium involved in the battery reaction is previously occluded in the negative electrode can be considered. In addition, even in a conventional lithium ion secondary battery using carbon as a negative electrode, many techniques have been reported in which a predetermined amount of lithium is occluded in advance in the negative electrode. For example, an alkali metal is electrochemically supported on a negative electrode using particles having a structure in which metallic lithium layers and carbon layers are alternately stacked (see Patent Document 1), a transition metal chalcogen compound, or a thin layer of a carbon material. A negative electrode (see Patent Document 2), a negative electrode (see Patent Document 3) in which a lithium metal foil is attached and diffused and held in a carbon material, and an electrolytic solution is injected to short-circuit the metal lithium and the carbon material. Lithium secondary battery in which an aromatic hydrocarbon that forms a complex with metallic lithium is added to a negative electrode in which lithium is introduced by the above (see Patent Document 4), and a negative electrode in which metallic lithium is short-circuited to a carbon material (see Patent Document 5). There has been a report of a lithium secondary battery (see Patent Document 6) having a metallic lithium supply member provided in the battery container without being in electrical contact with the negative electrode.

  However, in such a carbon-based negative electrode, it is possible to improve the irreversible capacity of the carbon material by preliminarily storing lithium, but in general, the carbon-based negative electrode has a charge / discharge efficiency unlike the high-capacity negative electrode described above. Since it is high and the amount of occlusion of lithium is small, occlusion of lithium in advance leads to a large decrease in negative electrode capacity, and there are few advantages in terms of actual energy density.

Also, in the negative electrode other than carbon, for example, a negative electrode material made of silicon or germanium is previously subjected to lithium implantation using an ion implantation apparatus (see Patent Document 7), and both the positive electrode and the negative electrode are alkali metal ions. A battery in which an alkali metal is inserted by contact with a dispersion in which the alkali metal is dispersed in an organic solvent containing a compound that can be solvated or complexed with an alkali metal ion (see Patent Document 8) .) Has been reported.
JP-A-7-326345 Japanese Patent No. 3255670 Japanese Patent No. 3063320 JP-A-10-270090 Japanese Patent Laid-Open No. 11-185809 Japanese Patent Laid-Open No. 2001-277797 JP 2002-93411 A Japanese Patent Laid-Open No. 11-219724

However, in the technique described in Patent Document 7, since the lithium ion concentration to be implanted in advance is a very small amount of about 1 × 10 ¹⁶ ions / cm to 1 × 10 ¹⁸ ions / cm 3, the role as a reservoir for compensating cycle deterioration Does not work and its effect is small. Furthermore, an ion implantation apparatus that performs a very small amount of doping using plasma, as illustrated in Patent Document 7, complicates the apparatus configuration, and can easily dope an effective amount of lithium. difficult. Patent Document 8 is one in which both the positive electrode and the negative electrode are produced in a state in which an active material can insert an alkali metal, that is, a discharge-initiating positive electrode is used, which is excessive compared to the amount of lithium involved in the battery reaction. It is not intended to improve the characteristics by preliminarily storing lithium in the negative electrode.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a battery that can improve battery characteristics such as cycle characteristics by including excess lithium in the negative electrode.

  The method for producing a negative electrode of the present invention comprises a group consisting of a simple substance, an alloy and a compound of silicon or germanium on at least one method selected from the group consisting of a vapor phase method, a liquid phase method and a sintering method. A step of forming a negative electrode active material layer containing at least one of the above, and a step of occluding 5% to 40% of lithium in the negative electrode capacity in the negative electrode active material layer.

  The method for producing a secondary battery according to the present invention comprises applying a negative electrode current collector from a simple substance, an alloy, and a compound of silicon or germanium by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method. A step of forming a negative electrode active material layer containing at least one member of the group consisting of, and a step of making the negative electrode active material layer occlude lithium of 5% or more and 40% or less of the negative electrode capacity; The positive electrode current collector includes a step of producing a positive electrode by forming a positive electrode active material, and a step of inserting the negative electrode and the positive electrode together with an electrolyte into an exterior member.

  According to the negative electrode and secondary battery manufacturing method of the present invention, since the negative electrode active material layer formed on the negative electrode current collector has electrochemically active lithium remaining on the negative electrode after discharge, Even if lithium is consumed by the above reaction or the like, lithium can be replenished and deterioration can be suppressed. In addition, an increase in potential of the negative electrode at the end of discharge can be suppressed, and deterioration due to an increase in potential of the negative electrode can be suppressed. Therefore, battery characteristics such as cycle characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First embodiment)
FIG. 1 shows the configuration of the secondary battery according to the first embodiment of the present invention. This secondary battery is a so-called coin-type battery, in which a negative electrode 12 accommodated in an exterior cup 11 and a positive electrode 14 accommodated in an exterior can 13 are laminated via a separator 15 impregnated with an electrolytic solution. Has been. The peripheral portions of the outer cup 11 and the outer can 13 are sealed by caulking through an insulating gasket 16. The exterior cup 11 and the exterior can 13 are made of, for example, a metal such as stainless steel or aluminum.

  The negative electrode 12 includes, for example, a negative electrode current collector 12A and a negative electrode active material layer 12B provided on the negative electrode current collector 12A. The negative electrode active material layer 12B may be formed on both surfaces of the negative electrode current collector 12A, or may be formed on one surface.

  The anode current collector 12A is preferably made of a metal material containing at least one metal element that does not form an intermetallic compound with lithium. When lithium and an intermetallic compound are formed, they expand and contract with charge / discharge, structural breakdown occurs, current collection performance decreases, and the ability to support the negative electrode active material layer 12B decreases, so that the negative electrode active material layer 12B becomes a negative electrode. This is because it is easy to drop off from the current collector 12A. Note that in this specification, the metal material includes not only a single metal element but also an alloy composed of two or more metal elements or one or more metal elements and one or more metalloid elements. Examples of the metal element that does not form an intermetallic compound with lithium include copper (Cu), nickel (Ni), titanium (Ti), iron (Fe), and chromium (Cr).

  Among these, a metal element that is alloyed with the negative electrode active material layer 12B is preferable. As will be described later, when the negative electrode active material layer 12B includes at least one member selected from the group consisting of simple substances, alloys, and compounds such as silicon, germanium, and tin that are alloyed with lithium, the negative electrode active material accompanies charging / discharging. Although the layer 12B expands and contracts greatly and easily falls off the negative electrode current collector 12A, the negative electrode active material layer 12B and the negative electrode current collector 12A are alloyed and firmly bonded to suppress the drop off. Because it can. Metal element that does not form an intermetallic compound with lithium and that forms an alloy with negative electrode active material layer 12B, for example, a metal element that forms an alloy with at least one member selected from the group consisting of silicon, germanium, and tin as a simple substance, alloy, and compound Examples include copper, nickel, and iron. In particular, copper, nickel, or iron is preferable from the viewpoint of alloying with the negative electrode active material layer 12B, strength, and conductivity.

  The negative electrode current collector 12A may be composed of a single layer, but may be composed of a plurality of layers. In that case, the layer in contact with the negative electrode active material layer 12B is made of a metal material that forms an alloy with at least one of the group consisting of a simple substance such as silicon, germanium, or tin, an alloy, and a compound, and the other layer is made of another metal. You may make it comprise with material. The negative electrode current collector 12A is preferably composed of a metal material made of at least one metal element that does not form an intermetallic compound with lithium, except for the interface with the negative electrode active material layer 12B.

  The negative electrode active material layer 12B includes, for example, at least one selected from the group consisting of simple elements, alloys, and compounds of elements capable of forming an alloy with lithium as the negative electrode active material. Among them, the negative electrode active material preferably includes at least one member selected from the group consisting of silicon, germanium, or tin as a simple substance, an alloy, and a compound. In particular, a silicon simple substance, an alloy, or a compound is preferable. This is because they have a large ability to occlude and release lithium, and depending on the combination, the energy density of the negative electrode 12 can be made higher than that of conventional graphite. Among them, silicon alone, alloys or compounds are particularly low in toxicity and inexpensive.

Examples of silicon alloys or compounds include SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi. ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2) or LiSiO.

Examples of the germanium compound include Ge ₃ N ₄ , GeO, GeO ₂ , GeS, GeS ₂ , GeF _{4, and} GeBr ₄ . Examples of the tin compound or alloy include an alloy of tin and an element included in groups 4 to 11 of the long-period periodic table. In addition, Mg ₂ Sn, SnO _w (0 <w ≦ 2), SnSiO ₃ or LiSnO can be used.

  The negative electrode active material layer 12B is preferably formed by at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method. The negative electrode active material layer 12B can be prevented from being destroyed due to expansion / contraction due to charging / discharging, and the negative electrode current collector 12A and the negative electrode active material layer 12B can be integrated, and electrons in the negative electrode active material layer 12B can be integrated. This is because the conductivity can be improved. Moreover, it is because a binder, a space | gap, etc. can be reduced or eliminated and the negative electrode 12 can also be thinned. As used herein, “forming an active material layer by a sintering method” means that a layer formed by mixing a powder containing an active material and a binder is heat-treated in a non-oxidizing atmosphere or the like, This means that a denser layer having a higher volume density than before the heat treatment is formed.

  The negative electrode active material layer 12B is preferably alloyed with the negative electrode current collector 12A at least at a part of the interface with the negative electrode current collector 12A so that the negative electrode active material layer 12B does not fall off from the negative electrode current collector 12A due to expansion and contraction. . Specifically, the constituent elements of the negative electrode current collector 12A are diffused into the negative electrode active material layer 12B, the constituent elements of the negative electrode active material layer 12B are diffused into the negative electrode current collector 12A, or they are mutually diffused at the interface. preferable. This alloying often occurs at the same time when the anode active material layer 12B is formed by a vapor phase method, a liquid phase method, or a sintering method, but it may also be caused by further heat treatment. Note that in this specification, the above-described element diffusion is also included in one form of alloying.

  In the negative electrode active material layer 12B, electrochemically active lithium remains even after discharge at least in the initial charge / discharge cycle. Thereby, in this secondary battery, even if lithium is consumed due to reaction with the electrolytic solution, lithium can be replenished and the potential increase of the negative electrode 12 at the end of discharge can be suppressed. . The electrochemically active lithium may remain at least after the first discharge, and more preferably remains after the discharge up to the third cycle. This is because the negative electrode 12 has a significant capacity deterioration at the beginning of about three cycles. Of course, electrochemically active lithium may remain after discharge in the subsequent cycles.

  Whether or not electrochemically active lithium remains in the negative electrode 12 is determined by, for example, disassembling the discharged secondary battery, taking out the negative electrode 12, and using a metal foil or the like on which metallic lithium can be deposited as a counter electrode. A battery is manufactured, and it is confirmed by whether lithium can be desorbed from the negative electrode 12 and metallic lithium can be deposited on the counter electrode. That is, if lithium desorption from the negative electrode 12 is observed, electrochemically active lithium remains in the negative electrode 12, and if lithium desorption from the negative electrode 12 is not observed, the negative electrode 12 is electrochemically detected. It is determined that no active lithium remains. At that time, the electrolyte solution and the half battery used may have any shape as long as energization can be confirmed. Examples of the metal foil used for the counter electrode include lithium foil, copper foil, and nickel foil. After removing the negative electrode 12 from the battery, the negative electrode 12 may be washed with an organic solvent having low reactivity with lithium and dried.

  Thus, in order to allow electrochemically active lithium to remain in the negative electrode active material layer 12B after discharging, for example, in the negative electrode active material layer 12B during assembly, that is, before the first charge (before the first charge / discharge). It is preferable to occlude lithium beforehand. If lithium is occluded in advance, a coating film can be formed on the negative electrode 12 by the reaction between lithium and the electrolyte before charging and discharging, so that consumption of lithium in the initial cycle can be suppressed and charging and discharging are accompanied. This is because the stress applied to the negative electrode current collector 12A can be relaxed by expansion and contraction. Further, when the negative electrode active material layer 12A includes at least one member selected from the group consisting of silicon, germanium, a simple substance, an alloy, and a compound, dangling bonds existing in the negative electrode active material layer 12A, hydrogen, oxygen, or the like This is because the impurities can be reduced.

  The amount of lithium previously occluded in the negative electrode active material layer 12B is preferably 5% to 40% of the negative electrode capacity. If it is less than 5%, it is difficult to leave electrochemically active lithium in the negative electrode 12 even after discharge. If it exceeds 40%, not only the capacity is reduced, but also accompanying the alloying of the negative electrode active material and lithium. This is because the negative electrode 12 is bent by the stress, and the handleability and manufacturability are lowered. Even if the amount of lithium previously occluded in the negative electrode active material layer 12B is less than 5% of the negative electrode capacity, electrochemically active lithium may remain in the negative electrode 12 even after discharge. Even when active lithium does not remain after discharge, if the negative electrode 12 is preliminarily occluded with lithium, the above-described effects can be obtained although the degree is smaller than that in the case of remaining lithium. Therefore, it is preferable. In that case, the amount of lithium previously occluded in the negative electrode active material layer 12B is preferably 0.5% or more of the negative electrode capacity.

  The amount of lithium previously occluded in the negative electrode active material layer 12B is more preferably 0.02 μm or more and 20 μm or less per unit area in terms of the thickness of metallic lithium. Although it depends on the production method, if it is less than 0.02 μm per unit area, lithium is deactivated by oxidation in the handling atmosphere, and a sufficient effect cannot be obtained. On the other hand, if the thickness exceeds 20 μm, the negative electrode active material layer 12 becomes thick, the stress applied to the negative electrode current collector 11 becomes remarkably large, and the handleability and manufacturability are extremely reduced depending on the production method. It is.

  The positive electrode 14 includes, for example, a positive electrode current collector 14A and a positive electrode active material layer 14B provided on the positive electrode current collector 14A so that the positive electrode active material layer 14B side faces the negative electrode active material layer 12B. Is arranged. The positive electrode current collector 14A is made of, for example, aluminum, nickel, stainless steel, or the like.

The positive electrode active material layer 14B includes, for example, any one or two or more positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material such as a carbon material and the like as necessary. A binder such as polyvinylidene fluoride may be included. As the positive electrode material capable of inserting and extracting lithium, for example, a lithium-containing metal composite oxide represented by the general formula Li _x MIO ₂ is preferable. This is because the lithium-containing metal composite oxide can generate a high voltage and has a high density, so that the capacity of the secondary battery can be further increased. MI is one or more kinds of transition metals, and for example, at least one of cobalt and nickel is preferable. x varies depending on the charge / discharge state of the battery and is usually a value in the range of 0.05 ≦ x ≦ 1.10. Specific examples of such a lithium-containing metal composite oxide include LiCoO _{2 and} LiNiO ₂ .

  The separator 15 separates the negative electrode 12 and the positive electrode 14 and allows lithium ions to pass through while preventing a short circuit of current due to contact between both electrodes. The separator 15 is made of, for example, polyethylene or polypropylene.

  The electrolytic solution impregnated in the separator 15, that is, the liquid electrolyte includes, for example, a solvent and a lithium salt that is an electrolyte salt dissolved in the solvent, and may include an additive as necessary. . Examples of the solvent include organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, and any one of these or a mixture of two or more thereof may be used.

Examples of the lithium salt include LiPF ₆ , LiCF ₃ SO _{3, and} LiClO ₄ , and any one of these or a mixture of two or more thereof may be used.

  For example, the secondary battery can be manufactured as follows.

  First, for example, a negative electrode current collector 12A made of a metal foil is prepared, and a negative electrode active material layer 12B is formed on the negative electrode current collector 12A by depositing a negative electrode active material by a vapor phase method or a liquid phase method. . Further, after forming a precursor layer containing a particulate negative electrode active material on the current collector 12A, the negative electrode active material layer 12B may be formed by a sintering method in which the current layer is sintered. The negative electrode active material layer 12B may be formed by combining two or three of the phase method and the sintering method. Thus, by using at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, in some cases, at least part of the interface with the negative electrode current collector 12A, the negative electrode current collector A negative electrode active material layer 12B alloyed with 12A is formed. In order to further alloy the interface between the negative electrode current collector 12A and the negative electrode active material layer 12B, heat treatment may be further performed in a vacuum atmosphere or a non-oxidizing atmosphere. In particular, when the negative electrode active material layer 12B is formed by plating, it may be difficult to form an alloy. Therefore, it is preferable to perform this heat treatment as necessary. In addition, even in the case of forming a film by a vapor phase method, characteristics may be improved by further alloying the interface between the negative electrode current collector 12A and the negative electrode active material layer 12B. It is preferable to perform this heat treatment.

  Examples of the vapor phase method include a physical deposition method and a chemical deposition method. Specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, a CVD (Chemical Vapor Deposition; Phase growth) method. As the liquid phase method, a known method such as electrolytic plating or electroless plating can be used. As for the sintering method, a known method can be used, for example, an atmosphere sintering method, a reaction sintering method, or a hot press sintering method can be used.

  Next, for example, it is preferable that 0.5% to 40% of lithium of the negative electrode capacity be occluded in the negative electrode active material layer 12B. Any known technique may be used for the method of occluding lithium. For example, metal lithium may be deposited on the surface of the negative electrode active material layer 12B by a vapor phase method and occluded, or lithium metal foil may be attached or lithium powder may be applied by applying powdered metal lithium. May be occluded. Alternatively, an aromatic compound that forms a complex with metallic lithium may be used, and the lithium complex may be brought into contact with the negative electrode active material layer 12B so that lithium is occluded. You may make it insert lithium in.

  Among them, a method of depositing metallic lithium by a vapor phase method and occluding lithium is preferable. It is very dangerous to handle highly active powdered metallic lithium, and if a solvent is used, such as when lithium is inserted electrochemically, the negative electrode will be handled poorly, and it will be applied to the battery manufacturing process. It is because the nature also gets worse. Furthermore, according to the vapor phase method, the amount of lithium to be occluded can be easily controlled, lithium can be occluded uniformly over a large area, and roll-shaped electrodes can be continuously processed. Because.

  As the vapor phase method, for example, a film formed by heating raw materials such as a vacuum deposition method or an ion plating method is preferable, but a sputtering method or the like may be used. For example, when the negative electrode active material layer 12B is formed by a vapor phase method, depending on the apparatus used, metallic lithium may be continuously deposited without opening to the atmosphere. It is preferable to carry out in this way continuously, since the presence of excess adsorbed water and the formation of an oxide film can be suppressed. In this case, the negative electrode active material layer 12B and the deposition of metallic lithium may be performed by the same method such as a vacuum evaporation method. The negative electrode active material layer 12B is formed by a sputtering method, and the metallic lithium is deposited. You may make it carry out by different methods, such as depositing by vacuum evaporation.

  When the vapor phase method is used, the deposited metal lithium is diffused into the negative electrode active material layer 12B in the process of deposition, depending on the amount or deposition rate, and is alloyed and occluded. In order to promote diffusion and alloying of lithium into the negative electrode active material layer 12B, heat treatment may be further performed in a non-oxidizing atmosphere.

  In particular, when the vapor phase method is used, the occlusion amount of lithium is preferably 0.02 μm or more and 20 μm or less per unit area in terms of the thickness of metallic lithium. As described above, if the thickness is less than 0.02 μm, a sufficient effect cannot be obtained due to the deactivation of lithium due to oxidation, and if it exceeds 20 μm, the productivity decreases.

  Further, for example, the positive electrode 14 is prepared by mixing a positive electrode active material, a conductive material, and a binder to prepare a mixture, and this is dispersed in a dispersion medium such as N-methylpyrrolidone to form a positive electrode current collector 14A as a mixture slurry. The positive electrode active material layer 14 </ b> B is formed by applying and compression molding.

  After that, for example, the negative electrode 12, the separator 15 impregnated with the electrolytic solution, and the positive electrode 14 are laminated and placed in the outer cup 11 and the outer can 13, and they are caulked. Thereby, the secondary battery shown in FIG. 1 is obtained.

  In this secondary battery, when charged, for example, lithium ions are released from the positive electrode 14 and inserted in the negative electrode 12 through the electrolytic solution. When the discharge is performed, for example, lithium ions are released from the negative electrode 12 and inserted in the positive electrode 14 through the electrolytic solution. At that time, electrochemically active lithium remains in the negative electrode 12 even after discharge at least in the initial charge / discharge cycle. Therefore, lithium is replenished from the negative electrode 12 even if lithium is consumed by reaction with the electrolytic solution or the like. In addition, the potential increase of the negative electrode 12 is also suppressed at the end of discharge. Therefore, excellent charge / discharge cycle characteristics can be obtained.

  As described above, in the present embodiment, since the negative electrode 12 has lithium that is electrochemically active even after discharge in at least the initial charge / discharge cycle, lithium is consumed even if lithium is consumed due to reaction with the electrolytic solution or the like. In particular, it is possible to suppress deterioration that occurs remarkably in the initial charge / discharge cycle. In addition, the potential increase of the negative electrode 12 at the end of discharge can be suppressed, and deterioration due to the potential increase of the negative electrode 12 can also be suppressed. Therefore, battery characteristics such as cycle characteristics can be improved.

  In particular, if the negative electrode 12 is preliminarily occluded with lithium before the first charge (before the first charge / discharge), a film can be formed on the surface of the negative electrode 12 with the preliminarily occluded lithium. It is possible to suppress consumption of lithium due to a reaction with the electrolytic solution. Further, the stress applied to the negative electrode current collector 11 can be relaxed by the expansion and contraction of the negative electrode active material layer 12 due to the discharge. Further, when the negative electrode active material layer 12A includes at least one member selected from the group consisting of silicon, germanium, a single substance, an alloy, and a compound, dangling bonds existing in the negative electrode active material layer 12A, hydrogen, oxygen, etc. Impurities can be reduced.

  Further, when the amount of lithium previously occluded in the negative electrode active material layer 12B is 0.5% or more and 40% or less of the negative electrode capacity, the cycle characteristics can be further improved and the capacity can be increased.

  Furthermore, if the amount of lithium previously occluded in the negative electrode active material layer 12B is converted to the thickness of metallic lithium and is within the range of 0.02 μm or more and 20 μm or less per unit area, higher effects can be obtained. , Handling and manufacturability can be improved.

  In addition, if metal lithium is deposited on the negative electrode active material layer 12B by a vapor phase method to occlude lithium, the amount of occluded lithium can be easily controlled, and lithium can be uniformly distributed over a large area. It can also be occluded. Further, since the lithium can be occluded in the negative electrode active material layer 12B in the process of depositing metallic lithium, the negative electrode 12 can be easily handled. Furthermore, when the negative electrode active material layer 12B is formed by a vapor phase method, continuous film formation is possible, and the manufacturing process can be simplified.

(Second Embodiment)
FIG. 2 shows a configuration of a secondary battery according to the second embodiment of the present invention. In this secondary battery, the wound electrode body 30 to which the leads 21 and 22 are attached is housed inside the film-like exterior members 40A and 40B, and can be reduced in size, weight, and thickness. Yes.

  The leads 21 and 22 are led out, for example, in the same direction from the inside of the exterior members 40A and 40B to the outside. The lead 21 and the lead 22 are each made of a metal material such as aluminum, copper, nickel, or stainless steel, and each have a thin plate shape or a mesh shape.

  The exterior members 40A and 40B are made of, for example, a rectangular aluminum laminate film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. The exterior members 40A and 40B are disposed, for example, so that the polyethylene film side and the electrode winding body 30 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesion film 41 for preventing the entry of outside air is inserted between the exterior members 40A and 40B and the leads 21 and 22. The adhesion film 41 is made of a material having adhesion to the leads 21 and 22, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior members 40A and 40B may be made of a laminate film having another structure, a polymer film such as polypropylene, or a metal film instead of the above-described aluminum laminate film.

  FIG. 3 shows a cross-sectional structure taken along line II of the electrode winding body 30 shown in FIG. The electrode winding body 30 is obtained by stacking and winding a negative electrode 31 and a positive electrode 32 via a separator 33 and an electrolyte layer 34, and the outermost peripheral portion is protected by a protective tape 35.

  The negative electrode 31 has a structure in which a negative electrode active material layer 31B is provided on one surface or both surfaces of a negative electrode current collector 31A. The positive electrode 32 also has a structure in which a positive electrode active material layer 32B is provided on one surface or both surfaces of the positive electrode current collector 32A, and the positive electrode active material layer 32B side is disposed so as to face the negative electrode active material layer 31B. Yes. The specific configurations of the negative electrode current collector 31A, the negative electrode active material layer 31B, the positive electrode current collector 32A, the positive electrode active material layer 32B, and the separator 33 are the same as those of the negative electrode current collector 12A, the negative electrode active material layer in the first embodiment. 12B, the same as the positive electrode current collector 14A, the positive electrode active material layer 14B, and the separator 15.

  The electrolyte layer 34 is configured by a so-called gel electrolyte in which an electrolytic solution is held in a holding body. A gel electrolyte is preferable because it can obtain high ionic conductivity and can prevent battery leakage or swelling at high temperatures. The configuration of the electrolytic solution (that is, the solvent and the electrolyte salt) is the same as that in the first embodiment. The holding body is made of, for example, a polymer material. An example of the polymer material is polyvinylidene fluoride.

  For example, the secondary battery can be manufactured as follows.

  First, on each of the negative electrode 31 and the positive electrode 32, an electrolyte layer 123 in which an electrolytic solution is held in a holding body is formed. After that, the lead 21 is attached to the end of the negative electrode current collector 31A by welding, and the lead 22 is attached to the end of the positive electrode current collector 32A by welding. Next, the negative electrode 31 and the positive electrode 32 on which the electrolyte layer 34 is formed are laminated via a separator 33 to form a laminated body, and then the laminated body is wound in the longitudinal direction to attach the protective tape 35 to the outermost peripheral portion. Thus, the electrode winding body 30 is formed. Finally, for example, the electrode winding body 30 is sandwiched between the exterior members 40A and 40B, and the outer edges of the exterior members 40A and 40B are sealed and sealed by thermal fusion or the like. At that time, the adhesive film 41 is inserted between the leads 21 and 22 and the exterior members 40A and 40B. Thereby, the secondary battery shown in FIGS. 2 and 3 is completed.

  This secondary battery operates in the same manner as in the first embodiment, and has the same effect as in the first embodiment.

  Further, embodiments of the present invention will be specifically described with reference to the drawings. In the following examples, the symbols and symbols used in the above embodiment are used in correspondence with each other.

(Examples 1-1 to 1-4)
A secondary battery as shown in FIGS. 2 and 3 was produced. First, a negative electrode active material layer 31B made of silicon was formed on a negative electrode current collector 31A made of a copper foil having a thickness of 15 μm by a sputtering method. Next, metallic lithium was deposited on the negative electrode active material layer 31B by vacuum evaporation. The atmosphere for depositing metallic lithium was less than 1 × 10 ⁻³ Pa, and the deposition rate was greater than 5 nm / s. The amount of metallic lithium to be deposited, that is, the amount of lithium previously occluded in the negative electrode active material layer 31B is 5% and 10% of the lithium occlusion capacity of the negative electrode active material layer 31B in Examples 1-1 to 1-4. , 20%, and 30%. In addition, the thickness of the negative electrode active material layer 31B was made constant by subtracting the lithium capacity previously stored from the capacity of the negative electrode active material layer 31B. That is, the thickness of the negative electrode active material layer 31B was 5.26 μm in Example 1-1, 5.56 μm in Example 1-2, 6.25 μm in Example 1-3, and 7.14 μm in Example 1-4. did.

  After depositing metallic lithium, argon gas was injected into the vacuum chamber to atmospheric pressure and the negative electrode 31 was taken out. At that stage, the metallic lithium was already alloyed and occluded in the negative electrode active material layer 31B. It did not exist as lithium. This obtained the negative electrode 31 of Examples 1-1 to 1-4.

Subsequently, lithium cobaltate (LiCoO ₂ ) powder having an average particle diameter of 5 μm as a positive electrode active material, carbon black as a conductive material, and polyvinylidene fluoride as a binder, lithium cobaltate: carbon black: polyfluoride Vinylidene was mixed at a mass ratio of 92: 3: 5, and this was added to N-methylpyrrolidone as a dispersion medium to form a mixture slurry. Thereafter, the mixture slurry was applied to a positive electrode current collector 32A made of aluminum having a thickness of 15 μm, dried, and pressurized to form a positive electrode active material layer 32B, whereby the positive electrode 32 was produced.

After forming the anode 31 and the cathode 32, on these, 42.5 wt% ethylene carbonate and propylene carbonate 42.5% by weight and, LiPF ₆ 15 wt% and an electrolytic solution 30 wt% lithium salt A precursor solution in which 10% by mass of polyvinylidene fluoride, which is a block copolymer having a weight average molecular weight of 600,000, and 60% by mass of dimethyl carbonate were mixed and dissolved was applied, and allowed to stand at room temperature for 8 hours. The electrolyte layer 34 was formed by volatilizing.

  After the electrolyte layer 34 is formed, the negative electrode 31 and the positive electrode 32 on which the electrolyte layer 34 is formed are stacked via the separator 33, wound in the longitudinal direction, and the protective tape 35 is adhered to the outermost peripheral portion, thereby winding the electrode. 30 was formed. A polypropylene film was used for the separator 33. After that, the electrode winding body 30 was sandwiched and enclosed inside the exterior members 40A and 40B made of an aluminum laminate film. Thereby, the secondary batteries of Examples 1-1 to 1-4 were obtained.

About the produced secondary battery of Examples 1-1 to 1-4, the charge / discharge test was done on 25 degreeC conditions, and the capacity | capacitance maintenance factor of the 50th cycle was calculated | required. At that time, the charge is then made in a constant current density of 1 mA / cm ² until the battery voltage reached 4.2V, carried out at constant voltage of 4.2V until the current density reached 0.02 mA / cm ^2, discharge Was performed at a constant current density of 1 mA / cm ² until the battery voltage reached 2.5V. In addition, when performing charging, the initial utilization of the capacity obtained by subtracting the amount of lithium previously occluded from the capacity of the negative electrode 31 was set to 90% so that metallic lithium was not deposited on the negative electrode 31. . The capacity maintenance rate at the 50th cycle was calculated as the ratio of the discharge capacity at the 50th cycle to the initial discharge capacity, that is, (discharge capacity at the 50th cycle / initial discharge capacity) × 100. The obtained results are shown in Table 1.

Moreover, about the produced secondary battery of Examples 1-1 to 1-4, the battery was disassembled after the end of the third cycle discharge, the negative electrode 31 was taken out and washed with dimethyl carbonate, and this was used as a coin type A half cell was prepared. At that time, an electrolytic solution in which LiPF ₆ as a lithium salt was dissolved at 1.0 mol / dm ³ in a solvent in which ethylene carbonate and dimethyl carbonate were mixed at a mass ratio of 1: 1 was used as an electrolyte. A polypropylene film was used for the counter electrode, and a metal lithium foil was used for the counter electrode.

The produced half-cell was electrolyzed at a constant current density of 0.06 mA / cm ² until the potential difference between both electrodes reached 1.4 V so that lithium was desorbed from the working electrode, and then a constant voltage of 1.4 V When the current density reached 0.02 mA / cm ² , an amount of electricity corresponding to lithium desorption from the working electrode was observed. That is, in the secondary batteries of Examples 1-1 to 1-4, it was found that electrochemically active lithium remained in the negative electrode 31 even after discharge. In Table 1, “Yes” is shown in the column of remaining Li.

  As Comparative Example 1-1 with respect to Examples 1-1 to 1-4, secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-4 except that lithium was not previously stored in the negative electrode. For the secondary battery of Comparative Example 1-1, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-4, and the capacity retention ratio at the 50th cycle was obtained. The results are also shown in Table 1. Further, in the same manner as in Examples 1-1 to 1-4, after the discharge of the first cycle was completed, the negative electrode was taken out to prepare a half cell, and it was confirmed whether lithium was desorbed from the working electrode. As a result, the amount of electricity corresponding to lithium desorption from the working electrode was not observed, and it was found that no electrochemically active lithium remained in the negative electrode after discharging in the secondary battery of Comparative Example 1-1. It was. In Table 1, “None” is shown in the column of residual Li.

  As can be seen from Table 1, according to Examples 1-1 to 1-4 in which electrochemically active lithium remains in the negative electrode 31 even after discharge, compared to Comparative Example 1-1 in which no remaining lithium remains. A high capacity retention rate was obtained. That is, it was found that the cycle characteristics can be improved if the negative electrode 31 has electrochemically active lithium even after discharge.

(Examples 2-1 to 2-4)
Except that the negative electrode active material layer 31B was formed of germanium by a sputtering method, the negative electrodes 31 of Examples 2-1 to 2-4 were produced in the same manner as in Examples 1-1 to 1-4, and the same manner was performed. A secondary battery was manufactured. Moreover, as Comparative Example 2-1 with respect to Examples 2-1 to 2-4, except that lithium was not occluded in advance in the negative electrode, the negative electrode was produced in the same manner as in Examples 2-1 to 2-4, A secondary battery was produced. For the fabricated secondary batteries of Examples 2-1 to 2-4 and Comparative Example 2-1, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-4, and the capacity was maintained at the 50th cycle. The rate was determined. Moreover, the negative electrode 31 after discharge was taken out to produce a half-cell, and in Examples 2-1 to 2-4, whether or not electrochemically active lithium remained in the negative electrode 31 after the third cycle discharge. In Comparative Example 2-1, it was confirmed whether electrochemically active lithium remained in the negative electrode after the first cycle discharge. The results are shown in Table 2.

  As shown in Table 2, in Examples 2-1 to 2-4, electrochemically active lithium remained after discharge, but in Comparative Example 2-1, it was electrochemically active after discharge. Lithium did not remain. Moreover, according to Examples 2-1 to 2-4, a capacity retention rate higher than that of Comparative Example 2-1 was obtained as in Examples 1-1 to 1-4. That is, even when germanium is used as the negative electrode active material, cycle characteristics can be improved if electrochemically active lithium remains in the negative electrode 31 even after discharge, as in the case of using silicon. I understood.

(Examples 3-1 to 3-4)
The anode active material layer 31B having a thickness of 5μm composed of tin by vacuum evaporation on the anode current collector 31A made of a copper foil having a thickness of 15μm was formed, followed by 200 ° C. under an inert atmosphere is performed for 12 hours heat treatment Thereafter, a secondary battery was produced in the same manner as in Examples 1-1 to 1-4 except that the negative electrode 31 was produced by depositing metallic lithium on the negative electrode active material layer 31B by a vacuum evaporation method. did. Further, as Comparative Example 3-1 with respect to Examples 3-1 to 3-4, a negative electrode was produced in the same manner as in Examples 3-1 to 3-4 except that lithium was not previously stored in the negative electrode. A secondary battery was produced. For the fabricated secondary batteries of Examples 3-1 to 3-4 and Comparative Example 3-1, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-4, and the capacity was maintained at the 50th cycle. The rate was determined. Moreover, the negative electrode 31 after discharge was taken out to produce a half battery, and in Examples 3-1 to 3-4, whether or not electrochemically active lithium remained in the negative electrode 31 after the third cycle discharge. In Comparative Example 3-1, it was confirmed whether electrochemically active lithium remained in the negative electrode after the first cycle discharge. The results are shown in Table 3.

  As shown in Table 3, in Examples 3-1 to 3-4, electrochemically active lithium remained after discharge, but in Comparative Example 3-1, it was electrochemically active after discharge. Lithium did not remain. Moreover, according to Examples 3-1 to 3-4, a capacity retention rate higher than that of Comparative Example 3-1 is obtained as in Examples 1-1 to 1-4 and 2-1 to 2-4. It was. That is, even if tin is used for the negative electrode active material, cycle characteristics can be improved if electrochemically active lithium remains in the negative electrode 31 even after discharge, as in the case of using silicon or germanium. I found out that

  A secondary battery was fabricated and evaluated in the same manner as in Examples 3-1 to 3-4 except that the negative electrode active material layer 31B was formed by plating instead of the vacuum evaporation method. Results similar to 1-3-4 were obtained.

(Examples 4-1 to 4-5)
A coin-type secondary battery as shown in FIG. 1 was produced. The negative electrode 12 was produced in the same manner as in Examples 1-1 to 1-4. At that time, the amount of metallic lithium to be deposited, that is, the amount of lithium previously occluded in the negative electrode active material layer 12B was 5% of the lithium occlusion capacity of the negative electrode active material layer 12B in Examples 4-1 to 4-5, 10 %, 20%, 30%, and 40%. In addition, the thickness of the negative electrode active material layer 12B is 5.26 μm in Example 4-1 so that the capacity obtained by subtracting the capacity of lithium stored in advance from the capacity of the negative electrode active material layer 12B is constant. -2 was 5.56 μm, Example 4-3 was 6.25 μm, Example 4-4 was 7.14 μm, and Example 4-5 was 8.33 μm.

The positive electrode 14 was also produced in the same manner as in Examples 1-1 to 1-4. Next, the produced negative electrode 12 and positive electrode 14 were laminated via a separator 15 impregnated with an electrolytic solution, placed in the outer cup 11 and the battery can 13 and sealed by caulking. For the electrolytic solution, a solution obtained by dissolving LiPF ₆ as a lithium salt in a solvent obtained by mixing ethylene carbonate and dimethyl carbonate at a mass ratio of 1: 1 to 1.0 mol / dm ³ is used for the separator 50. Used a polypropylene film. This obtained the secondary battery of Examples 4-1 to 4-5. The size of the battery was 20 mm in diameter and 16 mm in thickness.

  As Comparative Example 4-1, with respect to Examples 4-1 to 4-5, a negative electrode was produced in the same manner as in Examples 4-1 to 4-5 except that lithium was not previously stored in the negative electrode. A battery was produced. Further, as Comparative Examples 4-2 to 4-4 with respect to Examples 4-1 to 4-5, the amount of lithium previously stored in the negative electrode was 0.3% of the lithium storage capacity of the negative electrode active material layer, 0.5% A negative electrode was produced in the same manner as in Examples 4-1 to 4-5, except that the content was changed to% or 1%, and a secondary battery was produced.

  For the fabricated secondary batteries of Examples 4-1 to 4-5 and Comparative Examples 4-1 to 4-4, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-4, and 50 cycles were performed. The eye capacity retention rate was determined. Further, the negative electrode 12 after the first cycle discharge was taken out to prepare a half battery, and it was confirmed whether or not electrochemically active lithium remained in the negative electrode 12. The results are shown in Table 4.

  As shown in Table 4, in Examples 4-1 to 4-5, electrochemically active lithium remained after discharge, but in Comparative Examples 4-1 to 4-4, electrochemical after discharge. No active lithium remained, and Examples 4-1 to 4-5 were higher in capacity retention than Comparative Examples 4-1 to 4-4. In addition, from the results of Comparative Examples 4-1 to 4-4, even when electrochemically active lithium does not remain after discharge, cycle characteristics can be improved by preliminarily storing lithium in the negative electrode. It turns out that it can improve. It has also been found that it is more preferable if the amount of lithium previously stored in the negative electrode is 0.5% or more of the lithium storage capacity of the negative electrode active material layer.

(Examples 5-1 to 5-5)
Except that the negative electrode active material layer 12B was formed of germanium by a sputtering method, the negative electrode 12 was produced in the same manner as in Examples 4-1 to 4-5, and a secondary battery was produced in the same manner. Further, as Comparative Example 5-4 with respect to Examples 5-1 to 5-5, Examples 5-1 to 5-5 were the same except that the amount of lithium previously occluded in the negative electrode was changed as shown in Table 5. A negative electrode was produced in the same manner as in −5, and a secondary battery was produced. For the fabricated secondary batteries of Examples 5-1 to 5-5 and Comparative Examples 5-1 to 5-4, a charge / discharge test was performed in the same manner as in Examples 1-1 to 1-4, and 50 cycles were performed. The eye capacity retention rate was determined. Further, the negative electrode 12 after the first cycle discharge was taken out to prepare a half battery, and it was confirmed whether or not electrochemically active lithium remained in the negative electrode 12. The results are shown in Table 5.

  As shown in Table 5, in Examples 5-1 to 5-5, electrochemically active lithium remained after discharge, but in Comparative Examples 5-1 to 5-4, electrochemical after discharge. No active lithium remained, and Examples 5-1 to 5-5 were higher in capacity retention than Comparative Examples 5-1 to 5-4. In addition, from the results of Comparative Examples 5-1 to 5-4, when germanium is used as the negative electrode active material, cycle characteristics can be obtained by previously storing lithium in the negative electrode, as in the case of using silicon. It has been found that it is more preferable that the amount of lithium stored in advance is 0.5% or more of the lithium storage capacity of the negative electrode active material layer.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the above embodiments and examples, and various modifications can be made. For example, in the above-described embodiments and examples, the case where a polymer material is used as an electrolyte holding member has been described. However, an inorganic conductor containing lithium nitride or lithium phosphate may be used as a holding member. And an inorganic conductor may be mixed and used.

  Moreover, although the said embodiment and Example demonstrated the negative electrodes 12 and 31 by which the negative electrode collector 12A and 31A were provided with the negative electrode active material layers 12B and 31B, the negative electrode collector and negative electrode active material layer You may have another layer in between.

  Further, in the above embodiments and examples, a coin type or wound laminate type secondary battery has been described. However, the present invention is not limited to a cylindrical type, a square type, a button type, a thin type, a large size, and a laminated laminate type. The same applies to the secondary battery. Moreover, not only a secondary battery but a primary battery is applicable.

It is sectional drawing showing the structure of the secondary battery which concerns on the 1st Embodiment of this invention. It is a disassembled perspective view showing the structure of the secondary battery which concerns on the 2nd Embodiment of this invention. It is sectional drawing showing the structure along the II line | wire of the electrode winding body shown in FIG.

Explanation of symbols

11 ... exterior cup, 12, 31 ... negative electrode, 12A, 31A ... negative electrode current collector, 12B, 31B
... negative electrode active material layer, 13 ... outer can, 14, 32 ... positive electrode, 14A, 32A ... positive electrode current collector, 14
B, 32B ... positive electrode active material layer, 15, 33 ... separator, 16 ... gasket, 21, 22 ...
Lead, 30 ... wound electrode body, 34 ... electrolyte layer, 35 ... protective tape

Claims (8)

The negative electrode current collector is subjected to at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, from the group consisting of a simple substance, an alloy, and a compound of silicon (Si) or germanium (Ge). Forming a negative electrode active material layer containing at least one kind;
And a step of occluding 5% to 40% of lithium in the negative electrode capacity in the negative electrode active material layer. The method for producing a negative electrode according to claim 1, wherein in the step of occluding lithium, metallic lithium is deposited on the surface of the negative electrode active material layer by a vapor phase method. 3. The method for producing a negative electrode according to claim 2, wherein the storage amount of lithium is 0.02 μm or more and 20 μm or less per unit area in terms of the thickness of metallic lithium. The method for producing a negative electrode according to claim 1, wherein in the step of occluding lithium, a metal lithium foil is attached to or applied to the surface of the negative electrode active material layer. The method for producing a negative electrode according to claim 1, wherein in the step of occluding lithium, a lithium complex of an aromatic compound that forms a complex with metallic lithium is brought into contact with the negative electrode active material layer. The method for producing a negative electrode according to claim 1, further comprising a step of performing a heat treatment in a vacuum atmosphere or a non-oxidizing atmosphere after the step of forming the negative electrode active material layer. The method for producing a negative electrode according to claim 1, further comprising a step of performing a heat treatment in a non-oxidizing atmosphere after the step of occluding lithium. The negative electrode current collector is subjected to at least one method selected from the group consisting of a vapor phase method, a liquid phase method, and a sintering method, from the group consisting of a simple substance, an alloy, and a compound of silicon (Si) or germanium (Ge). Forming a negative electrode active material layer containing at least one kind;
Producing a negative electrode by occluding 5% to 40% of lithium in the negative electrode capacity in the negative electrode active material layer;
Forming a positive electrode by forming a positive electrode active material on the positive electrode current collector;
A step of inserting the negative electrode and the positive electrode together with an electrolyte into an exterior member.

Images