JP2008135379A - Lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte lithium secondary battery capable of achieving cycling characteristics higher than conventional solid electrolyte lithium secondary batteries. <P>SOLUTION: A lithium secondary battery has a positive electrode, a negative electrode and a solid electrolyte, wherein the positive electrode contains a positive electrode active material particle which is composed of a particle made of a material capable of being doped/dedoped with lithium ions and a compound containing an element M which is placed on the surface of the particle in the form of fine particles or a layer (where the compound containing an element M is composed of one or more compounds selected from oxides, hydroxides, oxyhydroxides and carbonates containing one or more elements selected from B, Al, Mg, Co, Cr, Mn and Fe as the element M). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium secondary battery. Specifically, the present invention relates to a lithium secondary battery having a solid electrolyte.

  Lithium secondary batteries have already been put into practical use as power sources for mobile phones, notebook computers, etc., and are also being applied to medium and large applications such as automobile applications and power storage applications. Among lithium secondary batteries, lithium secondary batteries having a solid electrolyte (hereinafter sometimes referred to as solid electrolyte type lithium secondary batteries) are attracting attention in terms of safety.

  As a conventional solid electrolyte type lithium secondary battery, a lithium ion conductive inorganic solid electrolyte mainly composed of sulfide is used as a solid electrolyte, and lithium chloride is supported on the surface of a lithium-containing transition metal oxide as a positive electrode. Patent Document 1 discloses a lithium secondary battery using a positive electrode active material.

JP 2001-52733 A

  However, although the initial capacity of the conventional solid electrolyte lithium secondary battery is improved, the cycle performance of maintaining the capacity as much as possible after repeated charging and discharging is sufficient. I can't say that. An object of the present invention is to provide a solid electrolyte type lithium secondary battery capable of achieving high cycle performance as compared with a conventional solid electrolyte type lithium secondary battery.

The inventor of the present invention has made extensive studies to solve the above-mentioned problems, and has reached the present invention.
That is, the present invention provides the following inventions.
<1> A lithium secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode is mounted on the surface of the particle as a particle or in a layered manner on a particle capable of doping / dedoping lithium ions. Element M-containing compound (wherein element M-containing compound is a compound containing one or more elements selected from B, Al, Mg, Co, Cr, Mn and Fe as element M, and oxide) A lithium secondary battery characterized by comprising positive electrode active material particles comprising: one or more compounds selected from hydroxide, oxyhydroxide and carbonate.
<2> The lithium secondary battery according to <1>, wherein the element M is Al.
<3> The lithium secondary battery according to <1> or <2>, wherein the material capable of doping and dedoping lithium ions is a composite oxide containing lithium and nickel.
<4> The lithium secondary battery according to any one of <1> to <3>, wherein the positive electrode further contains solid electrolyte particles.
<5> The lithium secondary battery according to <4>, further including a sheet-like solid electrolyte.

  The lithium secondary battery of the present invention can achieve high cycle performance without causing a decrease in the initial capacity as compared with the conventional solid electrolyte lithium secondary battery. Very useful.

  The present invention relates to a lithium secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode has particles of a material capable of doping and dedoping lithium ions, and the surface of the particles as particles or in layers. Mounted element M-containing compound (wherein element M-containing compound is a compound containing one or more elements selected from B, Al, Mg, Co, Cr, Mn and Fe as element M, and oxidized) A lithium secondary battery characterized in that it comprises positive electrode active material particles consisting of a compound, a hydroxide, an oxyhydroxide, and a carbonate. In the above-described conventional positive electrode, a positive electrode active material in which lithium chloride is supported on the surface of a lithium-containing transition metal oxide is used, and excess lithium ions are present on the surface of the lithium-containing transition metal oxide. Therefore, in the present invention, the element M-containing compound is made of a material that can be doped / undoped with lithium ions. It is considered that it can be placed on the surface of the particle as a particle or in a layered manner, suppressing the presence of excess lithium ions, reducing the internal resistance of the positive electrode, and improving the cycle performance of the lithium secondary battery. It is done.

In the present invention, the lithium ion-doped / undopeable material (hereinafter sometimes referred to as a core material) is a lithium-containing material, and examples thereof include oxides and sulfides. Lithium and cobalt-containing composite oxide typified by LiCoO ₂ , lithium and nickel-containing composite oxide typified by LiNiO ₂ , LiMn ₂ O ₄ , LiNiVO ₄ , LiMn _1.5 Ni _0.5 O ₄ , Li (Mn, Co) O ₂ , LiCoPO ₄ , LiFePO ₄ , LiTiS ₂ , LiMoS ₂ , LiMo ₆ S _8, etc., and some of the transition metal elements in these oxides or sulfides may be different from each other. Mention may also be made of compounds substituted with elements.

  From the viewpoint of further improving the initial capacity of the lithium secondary battery, the core material is preferably a composite oxide containing lithium and nickel. Specific examples of the composite oxide containing lithium and nickel include composite oxides represented by the following formula (1) or formula (2).

Li _x Ni _1-y M ¹ _y O ₂ (1)
(Where x and y are 0.9 ≦ x ≦ 1.2 and 0 ≦ y ≦ 0.5, respectively, and M ¹ is B, Al, Ga, In, Si, Ge, Sn, Mg, and transition One or more elements selected from metal elements.)
In the sense of further improving the initial capacity of the lithium secondary battery, M ¹ in the formula (1) is preferably one or more elements selected from B, Al, Mg, Co, Cr, Mn, and Fe. In the formula (1), y is preferably in the range of 0.001 to 0.4, and more preferably in the range of 0.01 to 0.3.

Li _x Ni _1-z M ² _z O ₂ (2)
(Where x and z are 0.9 ≦ x ≦ 1.2 and 0.3 ≦ z ≦ 0.9, respectively, and M ² is B, Al, Si, Sn, Mg, Mn, Fe and Co. 2 or more elements selected from
In order to further improve the initial capacity of the lithium secondary battery, z in the formula (2) is preferably a value in the range of 0.4 to 0.8, and more preferably 0.5 to 0.00. It is a value in the range of 7 or less, and M ² is preferably two or more elements selected from B, Al, Mn, Fe and Co, more preferably two kinds selected from B, Mn, Fe and Co These elements are more preferably two or more elements selected from Mn, Fe and Co.

The element M-containing compound in the present invention may be a compound different from the core material in the present invention. For example, even if it is a compound not containing lithium or a compound containing lithium, it is not possible to dope / dedope lithium ions. Examples of such compounds include compounds that do not store energy in lithium secondary batteries by themselves. In the element M-containing compound, the element M is preferably Al in terms of battery cycle performance and safety. As the element M-containing compound in the present invention, when the element M is Al, the Al-containing compound may be alumina or a compound containing Li and Al. Examples of the compound containing Li and Al include LiAlO ₂ . The element M-containing compound may be a compound different from the core material, but a compound that is not capable of doping and dedoping lithium ions such as LiAlO ₂ is from the viewpoint of further improving the cycle performance of the obtained lithium secondary battery. This is a preferred embodiment.

  In the present invention, the element M-containing compound (B) is placed on the surface of the core material (A) as particles or in a layered form, that is, (B) is on the surface of the particles of (A) as particles. Or it shows that it adheres in layers. This adhesion may be one in which (A) and (B) are chemically bonded or physically adsorbed. Moreover, (B) should just adhere to a part of surface of the particle | grains of (A). (B) may adhere to the surface of the particle of (A) as a particle, or may coat the surface of the particle of (A) as a particle or in layers. (B) preferably covers the entire surface of the particles of (A). When (B) coats the surface of the particles of (A) as particles or in layers, the thickness of the coating is preferably 1 nm to 500 nm, more preferably 1 nm to 100 nm.

  In the present invention, when the element M-containing compound is in the form of particles, in order to coat the particle surface of the core material more efficiently, it is preferably finer than the particles of the core material. The BET specific surface area of the compound is preferably 5 times or more, more preferably 20 times or more of the BET specific surface area of the core material. In addition, even if the element M-containing compound is not in the form of particles, the element M-containing compound can be placed in layers on the surface of the core material particles by using a technique such as sputtering.

Next, a method for producing positive electrode active material particles in the present invention will be described.
First, the core material in the positive electrode active material particles can be produced by firing a metal compound mixture that can become a core material by firing. That is, a compound containing a corresponding metal element is weighed so as to have a predetermined composition and can be produced by firing a metal compound mixture obtained after mixing. For example, a composite oxide represented by Li _1.11 [Ni _0.36 Mn _0.43 Co _0.21 ] O ₂ , which is one of the preferred compositions, includes lithium hydroxide, dinickel trioxide, manganese carbonate, and cobalt oxide. : Co can be obtained by firing the metal compound mixture obtained by weighing and mixing so that the molar ratio of Co is 1.11: 0.36: 0.43: 0.21.

  Examples of the compound containing the metal element include oxides, hydroxides, oxyhydroxides, carbonates, nitrates, acetates, halides, oxalates, alkoxides, sulfides, and the like. Those that can be decomposed and / or oxidized at high temperatures to form oxides can be used. Among these, the compound containing Li is preferably a hydroxide and / or carbonate, the compound containing Ni is preferably a hydroxide and / or oxide, and the compound containing Mn is a carbonate and / or carbonate. Oxides are preferred, and the compounds containing Co are preferably oxides and / or hydroxides. Moreover, you may use the complex compound containing 2 or more types of said corresponding metal element.

  In order to increase the crystallinity of the core material, the metal compound mixture before firing may further contain a compound containing boron. The content of the boron-containing compound is usually 0.00001 mol% or more and 5 mol% or less in terms of boron with respect to the total moles of metal elements excluding lithium in the metal compound mixture. . Preferably, it is 0.0001 mol% or more and 3 mol% or less in terms of boron. Examples of the compound containing boron include boron oxide and boric acid, and boric acid is preferable. Further, the boron further contained in the metal compound mixture here may remain in the fired core material, or may be removed by washing, evaporation or the like.

  The compound containing the metal element may be mixed by either dry mixing or wet mixing, but simpler dry mixing is preferable, and examples of the dry mixing apparatus include a V-type mixer, a W-type mixer, and a ribbon mixer. , Drum mixer, dry ball mill and the like.

  In addition, from the viewpoint of promoting the solid phase reaction during firing, the volume-based average particle diameter of the metal compound mixture is preferably a value in the range of 1 μm to 20 μm. Here, the volume-based average particle size of the metal compound mixture is a value of D50 measured by a laser diffraction scattering method particle size distribution measuring apparatus, that is, 50% cumulative in the volume-based cumulative particle size distribution of the metal compound mixture. It means the particle size (D50) viewed from the minute particle side of the hour.

  After the metal compound mixture is compression-molded as necessary, a fired product is obtained by, for example, holding and firing in a temperature range of 600 ° C. to 1200 ° C. for 2 to 30 hours. In firing, it is preferable to rapidly reach the holding temperature as long as the firing vessel containing the metal compound mixture is not damaged. As the firing atmosphere, when the core material is an oxide, air, oxygen, nitrogen, argon, or a mixed gas thereof can be used, but an atmosphere containing oxygen is preferable. When the core material is a sulfide, the firing atmosphere can include an atmosphere containing sulfur such as hydrogen sulfide. The atmosphere may contain the above air, oxygen, nitrogen, argon or a mixed gas thereof.

  The fired product may be pulverized using a pulverizer such as a vibration mill, a jet mill, or a dry ball mill as necessary to obtain a core material. In the case of a jet mill, since the particles constituting the fired product are accelerated by a jet stream and pulverized by collision between particles, there is little distortion of the crystal structure due to collision, and pulverization is easy in a short time. Generation of particles other than the intended purpose can be suppressed. In place of the jet mill, pulverization may be performed using a vibration mill or a dry ball mill. However, in that case, the process may be complicated, for example, requiring an air classification operation. Moreover, it is more preferable to use a fluidized bed jet mill with a built-in classifier as the jet mill. Examples of the jet mill include a counter jet mill (manufactured by Hosokawa Micron Corporation, product name).

  The core material manufactured by the above is comprised from particle | grains. Next, a method for producing positive electrode active material particles in the present invention by using the core material and placing an element M-containing compound on the surface of the core material particles will be described. The positive electrode active material particles in the present invention can be produced by dry mixing using a core material and an element M-containing compound. The dry mixing method is not particularly limited, but a simple method is a method in which a predetermined amount of each of the core material and the element M-containing compound is put in a container and shaken. Moreover, what is necessary is just to carry out by industrially used apparatuses, such as mixers, such as a V type, W type, and a double cone type, a powder mixer which has a screw and a stirring blade inside, a ball mill, and a vibration mill.

  The amount of the element M-containing compound used depends on the BET specific surface area of the core material, but when the core material is a composite oxide containing lithium and nickel, the element M is 0. An amount of 005 to 0.15 mol is preferable in terms of further improving the cycle performance of the lithium secondary battery of the present invention, and an amount of element M of 0.01 to 0.10 mol with respect to 1 mol of the core material is more preferable. .

  In addition, in the dry mixing described above, if the mixing is insufficient, the cycle performance of the lithium secondary battery of the present invention may be deteriorated, so that the aggregate of the element M-containing compound cannot be visually confirmed. It is preferable to do. Addition of a mixing process using media to dry mixing improves the mixing efficiency, allows the element M-containing compound to adhere firmly to the particle surface of the core material, and makes the secondary lithium more excellent in cycleability and output characteristics. There is a tendency to give batteries.

  By holding the positive electrode active material particles produced as described above in an atmosphere containing water, the element M-containing compound can be more firmly attached to the particle surface of the core material. Examples of the holding method include a method of filling a container with positive electrode active material particles and holding the container in a temperature-controlled and humidity-controlled atmosphere. At this time, the weight increase rate of the positive electrode active material particles is controlled to be in the range of 0.1 wt% to 5.0 wt%, preferably in the range of 0.3 wt% to 3.0 wt%. Is good. The method for measuring the rate of weight increase is not particularly limited. For example, before filling the positive electrode active material particles, the weight of the container is measured, and a predetermined amount of the positive electrode active material particles is filled therein and maintained in the atmosphere. By measuring the total weight before and after, the weight increase rate of the positive electrode active material particles can be calculated.

  When the positive electrode active material particles are held in an atmosphere containing water, the temperature is 20 ° C. or more and 90 ° C. or less, and the relative humidity is 20% or more and 90% or less. This is preferable because it tends to provide a lithium secondary battery having excellent characteristics and the weight increase rate can be easily controlled. A temperature of 30 ° C. to 70 ° C. and a relative humidity of 50% to 80% are further preferable ranges. Further, it is preferable to supply carbon dioxide gas into the system while holding from the viewpoint of shortening the holding time. In particular, when the amount of carbon dioxide gas is 0.05 to 50 mg / h / (g-positive electrode active material particles), it is preferable because the achievement time of the weight increase rate is short and the control of the weight increase rate is relatively easy. At this time, as a carbon dioxide supply method, a gas containing carbon dioxide may be continuously supplied during holding, or carbon dioxide may be introduced in advance before holding. Examples of the gas containing carbon dioxide include pure carbon dioxide, inert gas such as air, nitrogen, oxygen, and argon, and gas obtained by diluting carbon dioxide with a mixed gas thereof. On the other hand, when the amount of carbon dioxide gas is more than 50 mg / h / (g-positive electrode active material particles), the time to reach a predetermined weight increase becomes too short, and the weight increase rate control tends to be difficult. It is a preferred embodiment that the amount of carbon dioxide gas is 0.1 to 10 mg / h / (g-positive electrode active material particles).

  Further, the positive electrode active material particles may be fired after the above holding. As firing conditions, a firing temperature of 600 ° C. or higher and a firing time of 30 minutes or longer are preferable. Note that the firing temperature and time here are the maximum temperature and holding time at the maximum temperature in the temperature raising program, respectively. In the case of temperature, if there is a difference between the program temperature and the actual temperature, the actual temperature will be Use the converted temperature. Here, the firing is not particularly limited as long as the temperature and the holding time are such that the crystal structure of the core material particles does not substantially change. At this time, either the temperature in firing or the holding time is in a range not exceeding the temperature or holding time in the firing step of the production of the core material, but lithium having an excellent balance between initial capacity, cycleability, and output characteristics It tends to give a secondary battery, which is preferable. In addition to air, the firing atmosphere at this time is exemplified by oxygen, nitrogen, carbon dioxide, water vapor, nitrogen oxide, hydrogen sulfide, or a mixed gas thereof, or under a reduced pressure, such as lithium nickelate. When a core material made of a material that requires a high-concentration oxygen atmosphere at the time of firing is preferably fired in an atmosphere having an oxygen concentration of 90% by volume or more so that the crystallinity of the core material does not deteriorate. In addition, even if the element M-containing compound and the core material may partially react due to the firing after holding in the portion where the element M-containing compound and the core material are in contact with each other, The element M-containing compound is still placed.

  Moreover, when the BET specific surface area of the powder composed of the positive electrode active material particles obtained after firing is 0.7 to 2 times the BET specific surface area of the core material, a lithium secondary battery excellent in cycle performance and output characteristics is obtained. In terms of giving, it is preferably 0.8 times or more and 1.2 times or less.

  Next, production examples of the lithium secondary battery of the present invention will be described. The lithium secondary battery of the present invention has a positive electrode, a negative electrode, and a solid electrolyte. The positive electrode can include a positive electrode composed of a positive electrode mixture and a positive electrode current collector, and the negative electrode can include a negative electrode composed of a negative electrode material and a negative electrode current collector.

  Examples of the positive electrode material mixture include powders composed of positive electrode active material particles obtained as described above, a carbonaceous material as a conductive material, a thermoplastic resin as a binder, and the like. Examples of the carbonaceous material include natural graphite, artificial graphite, coke, carbon black, and the like, and spherical materials may be used. As the conductive material, the above carbonaceous materials may be used alone or in combination. For example, artificial graphite and carbon black can be mixed and used. In addition to reducing the resistance in the positive electrode, in addition to the conductive agent, a solid electrolyte having lithium ion conductivity is mixed in the positive electrode mixture in an amount of about 1 to 70 parts by weight with respect to 100 parts by weight of the positive electrode mixture. You may do it.

Examples of the thermoplastic resin include polyvinylidene fluoride (hereinafter sometimes referred to as PVDF), polytetrafluoroethylene (hereinafter sometimes referred to as PTFE), tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride. Examples thereof include a copolymer, a hexafluoropropylene / vinylidene fluoride copolymer, and a tetrafluoroethylene / perfluorovinyl ether copolymer. These may be used alone or in combination of two or more. Note that these binders may be those dissolved in an organic solvent in which the binder is soluble, such as 1-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP).
Further, a fluororesin and a polyolefin resin are used in combination as a binder so that the ratio of the fluororesin in the positive electrode mixture is 1 to 10% by weight and the ratio of the polyolefin resin is 0.1 to 2% by weight. And may be excellent in binding properties with the current collector.

  As the positive electrode current collector, Al, Ni, stainless steel, or the like can be used, but Al is preferable because it is easily processed into a thin film and is inexpensive. Examples of the method of supporting the positive electrode mixture on the positive electrode current collector include a method of pressure molding, or a method of pasting using a solvent or the like, and applying and drying on the current collector and then fixing. .

  As a negative electrode material of the lithium secondary battery of the present invention, for example, a lithium metal, a lithium alloy, or a material that can be doped / undoped with lithium ions can be used. Materials that can be doped / undoped with lithium ions include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired organic polymer compounds; lower potential than the positive electrode And chalcogen compounds such as oxides and sulfides for doping and dedoping lithium ions. As a carbonaceous material, graphite materials such as natural graphite and artificial graphite are mainly used in that a lithium secondary battery having a large energy density is obtained when combined with a positive electrode because of high potential flatness and low average discharge potential. A carbonaceous material as a component is preferable.

  The shape of the carbonaceous material may be, for example, a flake shape such as natural graphite, a spherical shape such as mesocarbon microbeads, a fibrous shape such as graphitized carbon fiber, or an aggregate of fine powder. Then, a thermoplastic resin as a binder can be added. Examples of the thermoplastic resin include PVDF, polyethylene, and polypropylene.

  Examples of the chalcogen compounds such as oxides and sulfides used as the negative electrode material include crystalline materials mainly composed of Group 13, 14 and 15 elements of the periodic table, such as amorphous compounds mainly composed of tin compounds. Or an amorphous oxide etc. are mentioned. Also in these cases, a carbonaceous material as a conductive material and a thermoplastic resin as a binder can be added as necessary.

  As the negative electrode current collector, Cu, Ni, stainless steel, or the like can be used. In particular, in a lithium secondary battery, Cu is preferable because it is difficult to form an alloy with lithium and it can be easily processed into a thin film. As a method of supporting the mixture containing the negative electrode material on the negative electrode current collector, a method of pressure molding, or a method of pasting using a solvent or the like, and applying and drying on the current collector and then fixing the current collector Is mentioned. Moreover, in order to reduce the resistance in an electrode, you may mix about 1-70 weight part of solid electrolyte which has lithium ion conductivity with respect to 100 weight part of negative mix in the mixture containing negative electrode material.

In the present invention, the solid electrolyte to be used includes, for example, a polyethylene oxide polymer compound, a polymer compound containing at least one of a polyorganosiloxane chain or a polyoxyalkylene chain, and the electrolyte includes LiClO ₄ , LiPF ₆ , LiBF. ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , lithium salt of lower aliphatic carboxylic acid, LiAlCl ₄ , LiB (C ₂ O ₄ ) ₂ A polymer solid electrolyte in which one kind or a mixture of two or more kinds can be used.

In the present invention, a gel electrolyte obtained by holding a non-aqueous electrolyte solution in the polymer compound is also treated as a solid electrolyte. As the non-aqueous electrolyte solution retained in the gel electrolyte, a solution obtained by dissolving an electrolyte in an organic solvent is used. Examples of the electrolyte include LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , lower aliphatic carboxylic acid lithium salt, LiAlCl ₄ , LiB (C Among the lithium salts such as ₂ O ₄ ) ₂ , one or two or more kinds can be mentioned. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1 Carbonates such as 1,3-dioxolan-2-one and 1,2-di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3 , 3-tetrafluoropropyl difluoromethyl ether, Ethers such as trahydrofuran and 2-methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformamide, N, N-dimethylacetamide and the like Amides; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; or those obtained by further introducing a fluorine substituent into the above organic solvent Usually, two or more of these may be used in combination. Among these, a mixed solvent containing carbonates is preferable, and a mixed solvent of cyclic carbonate and acyclic carbonate or cyclic carbonate and ether is more preferable. As a mixed solvent of cyclic carbonate and acyclic carbonate, ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate are used in that they are hardly decomposable even when a graphite material such as natural graphite or artificial graphite is used as the negative electrode active material. The mixed solvent containing is preferable.

  When a gel electrolyte is used as the solid electrolyte, a separator may be used in combination in order to prevent a short circuit between the positive and negative electrodes. As the separator, for example, a material having a form such as a porous film, a nonwoven fabric, or a woven fabric, which is made of an olefin resin such as fluororesin, polyethylene, or polypropylene, nylon, or aromatic aramid can be used. The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced, and is usually about 5 to 100 μm.

Moreover, you may use the solid electrolyte of an inorganic compound from a viewpoint of raising the safety | security of a lithium secondary battery more. Examples of the solid electrolyte of the inorganic compound include Li ₂ S—SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—P ₂ S ₅ , Li ₂ S—B ₂ S ₃ , Li ₂ S—Al ₂ S _3. Or sulfide glasses such as Li ₂ O—SiO ₂ , Li ₂ O—GeO ₂ , Li ₂ O—P ₂ O ₅ , Li ₂ O—B ₂ O ₃ , or sulfides thereof. Lithium halide LiX (X = F, I, Cl, Br), Li ₃ PO ₄ , Li ₂ SO ₄ , Li ₂ O ₃ , Li ₃ BO ₃ , Li ₂ CO ₃ , Li ₃ N , Li ₄ SiO ₄ , Li ₂ SiO ₃ and other lithium compounds have been added to improve lithium ion conductivity, and sulfide glass and oxide glass have been combined to improve chemical stability. Can be mentioned. Further, lanthanum-containing perovskite oxides such as La _0.51 Li _0.34 TiO _2.94 and Li _0.1 La _0.3 NbO ₃ , LiTi (PO ₄ ) ₃ , Li ₁₄ Zn (GeO ₄ ) ₄ , Li ₃ N, Li _3.6 Si _0.6 P _0.4 Inorganic compounds such as O ₄ , Li _3.4 V _0.6 Si _0.4 O ₄ , Li ₄ GeS ₄ , Li ₄ SiS ₄ , and LiPON _x (where x is greater than 0 and less than 1) may be used as the solid electrolyte. it can.

  In the present invention, as the solid electrolyte, two or more of the above polymer solid electrolyte, gel electrolyte, and inorganic compound solid electrolyte may be mixed or combined.

The shape of the lithium secondary battery of the present invention is not particularly limited, and may be any of a paper type, a coin type, a cylindrical type, a square type, and the like.
Moreover, you may use the bag-shaped package which consists of a laminated sheet etc. which contain aluminum, without using the metal hard case which serves as a negative electrode or a positive electrode terminal as an exterior.

Hereinafter, the present invention will be described more specifically with reference to examples.
In addition, as evaluation conditions of the obtained battery, battery characteristics such as cycle characteristics are confirmed using the following two conditions as a charge / discharge test by constant current charge and constant current discharge. The following evaluation condition 1 is a method for confirming the cycle characteristics of the battery, and evaluation condition 2 is for confirming the output characteristics of the battery, that is, to obtain the same capacity at the time of large current discharge as at the time of small current discharge. It is a method to check whether or not.

Evaluation condition 1
Maximum charging voltage: 4.2V
Charging current: 0.1 mA / cm ²
Discharge minimum voltage: 2.5V
Discharge current: 0.1 mA / cm ²
Number of charge / discharge cycles: 50 evaluation conditions 2
At the first cycle Maximum charging voltage: 4.2V
Charging current: 0.1 mA / cm ²
Discharge minimum voltage: 2.5V
Discharge current: 0.1 mA / cm ²
2nd to 6th cycles Maximum charging voltage: 4.2V
Charging current: 0.1 mA / cm ²
Discharge minimum voltage: 2.5V
Discharge current: 0.1 mA / cm ² (2 cycles), 0.5 mA / cm ² (3 cycles), 1 mA / cm ² (4 cycles), 5 mA / cm ² (5 cycles), 10 mA / cm ² (6 cycles)

Production Example 1 (Production of positive electrode active material)
Lithium hydroxide (LiOH.H ₂ O; manufactured by Honjo Chemical Co., Ltd., pulverized product, average particle size 10 to 25 μm) and nickel hydroxide (Ni (OH) ₂ ; manufactured by Kansai Catalysts Chemical Co., Ltd., product name is nickel hydroxide No. 3) and cobalt oxide (Co ₃ O ₄ ; manufactured by Shodo Chemical Industry Co., Ltd., product name is cobalt oxide (HCO)) are weighed so that the atomic ratio of each metal is the following molar ratio, The raw material mixed powder was obtained by mixing using a Digue mixer (Musbo Co., Ltd. make, M-20 type).
Li: Ni: Co = 1.05: 0.85: 0.15
The raw material mixed powder obtained above is dried at 120 ° C. for 10 hours, and is pulverized and mixed under the following conditions using a dynamic mill (Mitsui Mining Co., Ltd., MYD-5XA type) to obtain a pulverized powder. It was.
Grinding media: 5mmφ high alumina (6.1kg)
Number of rotations of agitator shaft: 650 rpm
Supply amount of dry raw material mixed powder: 12.0kg / h
The pulverized powder obtained above is filled in an alumina sheath and baked at 730 ° C. for 15 hours in an oxygen stream to obtain a lump, and this lump is dried using a 15 mmφ nylon-coated steel ball as a pulverization medium. Grinding with a ball mill until the volume-based average particle size becomes 5.5 μm (measured with a laser diffraction particle size distribution analyzer SALD-1100 (manufactured by Shimadzu Corporation)), and core material C1 (BET ratio) The surface area was 1.0 m ² / g).

The core material C1 (900 g) and aluminum oxide (manufactured by Nippon Aerosil Co., Ltd., primary particle diameter 13 nm, BET specific surface area 113 m ² / g, product name is alumina C) 37.4 g (C1 (1 mol)) , Al element is set to 0.08 mol) into a polyethylene pot with an internal volume of 5 L, and a dry ball mill is mixed at 80 rpm for 30 minutes using 4.2 kg of 15 mmφ nylon-coated steel balls as media. 720 g of the obtained powder is divided into four stainless steel trays (400 × 240 × 66 mmt) and filled (180 g in each stainless steel tray). The stainless steel tray is adjusted to a temperature of 50 ° C. and a relative humidity of 60%. It was set in a humidity-controlled thermostat (internal volume 225 L), and the powder was held in an atmosphere containing water. At this time, carbon dioxide gas was introduced into the system at 19 ml / min (20 ° C.). After holding for 3 hours, the stainless steel tray was taken out of the thermo-hygrostat (at this time, the weight increase rate of the powder was 1.5% by weight), and fired in an oxygen stream at 725 ° C. for 1 hour. A powder S1 made of material particles was obtained.

Production Example 2 (Production of solid electrolyte)
When a solid electrolyte of an inorganic compound is used as the solid electrolyte, it can be manufactured by the following method. That is, lithium phosphate (Li ₃ PO ₄ ), lithium sulfide (Li ₂ S), and silicon sulfide (SiS ₂ ) are weighed so as to have the following molar ratio and mixed sufficiently to prepare a mixed raw material. The mixed raw material is filled in a glassy carbon crucible and melt-reacted at 1000 ° C. for 2 hours in an argon gas stream. The obtained melt is rapidly cooled using a twin roller to form a glassy solid electrolyte (0.01 Li ₃ PO ₄ -0.63Li ₂ S-0.36SiS ₂₎ to give the can was further pulverized to obtain a powder (E1) consisting of the solid electrolyte particles.
Li ₃ PO ₄ : Li ₂ S: SiS ₂ = 0.01: 0.63: 0.36

Example 1
Regarding the positive electrode, the positive electrode active material powder S1 obtained in Production Example 1, acetylene black as a conductive material, and PVDF as a binder are in a weight ratio of S1: conductive material: binder = 85: 10: 5. In this way, dehydrated 1-methyl-2-pyrrolidone (hereinafter sometimes referred to as NMP) is added to the resulting mixture to knead to obtain a paste of a positive electrode mixture, and a positive electrode current collector made of aluminum foil It was prepared by applying on the body, drying and rolling.
As the negative electrode, a lithium foil having a thickness of 0.1 mm is used.
For the solid electrolyte, the solid electrolyte powder E1 of Production Example 2 and polytetrafluoroethylene (hereinafter sometimes referred to as PTFE) as a binder are weighed to a weight ratio of 98: 2, mixed, An elastic body is pressure-molded to obtain a solid electrolyte (sheet-like).
Lamination obtained by sandwiching a sheet-shaped solid electrolyte between a positive electrode (a surface coated with a mixture) and a negative electrode (a surface coated with a mixture) using the positive electrode, the negative electrode, and the sheet-shaped solid electrolyte The sheet is pressure-molded to increase the degree of contact, and accommodated in a battery can to produce the battery 1. By evaluating the battery 1 under the above evaluation conditions, battery characteristics such as cycle characteristics can be confirmed.

Example 2
The positive electrode active material powder S1 obtained in Production Example 1, acetylene black as a conductive agent, PVDF as a binder, and solid electrolyte powder E1 in Production Example 2 in a weight ratio, S1: Conductive material: Binder: Weigh and mix so that E1 = 50: 10: 5: 35, add dehydrated NMP to the resulting mixture, knead to make a paste of the positive electrode mixture, and apply on the positive electrode current collector made of aluminum foil And drying and rolling to produce a positive electrode.
As the negative electrode and the solid electrolyte, the same ones as in Example 1 were used, and the battery 2 was produced in the same manner as in Example 1. By evaluating the battery 2 under the above evaluation conditions, battery characteristics such as cycle characteristics can be confirmed.

Example 3
Spherical graphite as a negative electrode material, acetylene black as a conductive agent, and PVDF as a binder are weighed and mixed so that the negative electrode material: conductive material: binder = 85: 10: 5 by weight ratio. A dehydrated NMP is added to the resulting mixture and kneaded to form a paste of a negative electrode mixture, which is applied onto a negative electrode current collector made of copper foil, dried and rolled to produce a negative electrode.
As the positive electrode and the solid electrolyte, the same ones as in Example 1 are used, and the battery 3 is produced in the same manner as in Example 1. By evaluating the battery 3 under the above evaluation conditions, battery characteristics such as cycle characteristics can be confirmed.

Example 4
The positive electrode active material powder S1 obtained in Production Example 1, acetylene black as a conductive agent, PVDF as a binder, and solid electrolyte powder E1 in Production Example 2 in a weight ratio, S1: Conductive material: Binder: Weigh and mix so that E1 = 40: 10: 5: 45, add dehydrated NMP to the resulting mixture, knead to make a paste of the positive electrode mixture, and apply on the positive electrode current collector made of aluminum foil And drying and rolling to produce a positive electrode.
Spherical graphite as a negative electrode material, acetylene black as a conductive agent, PVDF as a binder, and solid electrolyte powder E1 of Production Example 2 in a weight ratio, negative electrode material: conductive material: binder: E1 = 40: 10 : Weighed and mixed so as to be 5:45, added dehydrated NMP to the resulting mixture, kneaded to form a paste of negative electrode mixture, applied on the negative electrode current collector made of copper foil, dried, rolled Thus, a negative electrode is produced.
Using the above positive electrode and negative electrode, the surfaces coated with the respective mixtures are overlapped to obtain a laminated sheet, further rolled to increase the degree of contact, and housed in a battery can. 4 is produced. By evaluating the battery 4 under the above evaluation conditions, battery characteristics such as cycle characteristics can be confirmed.

Example 5
Spherical graphite as a negative electrode material, acetylene black as a conductive agent, PVDF as a binder, and solid electrolyte powder E1 of Production Example 2 in a weight ratio, negative electrode material: conductive material: binder: E1 = 50: 10 : Weighed and mixed so as to be 5:35, added dehydrated NMP to the resulting mixture, kneaded to form a paste of negative electrode mixture, applied on the negative electrode current collector made of copper foil, dried, rolled Thus, a negative electrode is produced.
The same positive electrode as in Example 2 is used as the positive electrode, and the same solid electrolyte as in Example 1 is used. By evaluating the battery 5 under the above evaluation conditions, battery characteristics such as cycle characteristics can be confirmed.

  The lithium secondary battery of the present invention is the embodiment of Examples 2, 4 and 5 in the above embodiment, that is, a lithium secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, and the positive electrode contains lithium ions. Particles of a material that can be doped / dedoped, and an element M-containing compound placed on the surface of the particle as particles or in a layered form (wherein the element M-containing compound includes elements M, B, Al, Mg, A compound containing one or more elements selected from Co, Cr, Mn, and Fe, and one or more compounds selected from oxides, hydroxides, oxyhydroxides, and carbonates). By using a lithium secondary battery containing positive electrode active material particles and solid electrolyte particles, the initial capacity can be further increased. Furthermore, the embodiment of Examples 2 and 5 above, that is, a lithium secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode is made of particles of a material capable of doping and dedoping lithium ions, Element M-containing compound placed on the surface of the particle as a particle or in a layered form (wherein the element M-containing compound is selected from B, Al, Mg, Co, Cr, Mn and Fe as the element M) A compound containing the above elements, and one or more compounds selected from oxides, hydroxides, oxyhydroxides and carbonates.) And containing positive electrode active material particles and solid electrolyte particles, Furthermore, the effect of the present invention can be further enhanced by the lithium secondary battery having a sheet-like solid electrolyte.

Claims (5)

  A lithium secondary battery having a positive electrode, a negative electrode, and a solid electrolyte, wherein the positive electrode is placed as particles or in layers on the surface of the particles that can be doped / undoped with lithium ions Element M-containing compound (Here, element M-containing compound is a compound containing, as element M, one or more elements selected from B, Al, Mg, Co, Cr, Mn, and Fe, oxide, hydroxide A positive electrode active material particle comprising: an oxide, an oxyhydroxide, and a carbonate.   The lithium secondary battery according to claim 1, wherein the element M is Al.   The lithium secondary battery according to claim 1 or 2, wherein the material capable of doping and dedoping lithium ions is a composite oxide containing lithium and nickel.   The lithium secondary battery according to claim 1, wherein the positive electrode further contains solid electrolyte particles.   The lithium secondary battery according to claim 4, further comprising a sheet-like solid electrolyte.