JP5103698B2 - Non-aqueous electrolyte secondary battery and manufacturing method thereof - Google Patents

Description

【０１１７】
表１から明らかなように、正極活物質としてリチウムマンガン複合酸化物とリチウムニッケル系複合酸化物との混合物を用い、且つ保存するときの電圧を３．４Ｖ〜３．７５Ｖの範囲内とした実施例１〜実施例１２では、高い初期容量を示すとともに、容量回復率も９０％を上回る高い値を示した。
【０１１８】
しかし、保存するときの電圧が３．３Ｖである比較例１、比較例３及び比較例５では、容量回復率が低い値を示し、保存特性に劣ることがわかった。
【０１１９】
逆に、保存するときの電圧が３．７８Ｖである比較例２、比較例４及び比較例６は、実施例１〜実施例１２に比べて容量回復率に劣るとともに、初期容量が低い値を示した。
【０１２０】
以上の結果から、保存するときの電圧を３．４Ｖ〜３．７５Ｖの範囲内とすることで、高容量と保存特性とを両立可能な非水電解液二次電池を実現できることがわかった。
【０１２１】
なお、表１の結果から、正極活物質のリチウムマンガン複合酸化物とリチウムニッケル系複合酸化物との混合比率を変えた場合であっても、保存するときの電圧を３．４Ｖ〜３．７５Ｖの範囲内とすることで、良好な結果を得られることがわかった。
【０１２２】
また、正極活物質として含有するリチウムニッケル系複合酸化物の組成を変えた場合であっても、保存するときの電圧を３．４Ｖ〜３．７５Ｖの範囲内とすることで、良好な結果を得られることがわかった。
【０１２３】
また、正極活物質として、リチウムマンガン複合酸化物またはリチウムニッケル系複合酸化物を単独で用いた実施例１３及び実施例１４も、高い初期容量及び容量回復率を示した。この結果から、正極活物質が、リチウムマンガン複合酸化物またはリチウムニッケル系複合酸化物の一方のみを含有する場合であっても、電圧を規定の範囲内にすることにより、優れた保存特性を示す非水電解液二次電池を得られることがわかった。
【０１２４】
【発明の効果】
以上の説明からも明らかなように、本発明に係る非水電解質二次電池は、正極活物質としてリチウムマンガン複合酸化物及びリチウムニッケル系複合酸化物のうち少なくとも一方を含有し、且つ保存するときの電圧を３．４Ｖ〜３．７５Ｖの範囲内に設定している。このため、非水電解質二次電池は、５０％程度の適度な充電状態とされ、これにより、正極表面に良質な被膜が形成される。したがって、本発明によれば、高エネルギー密度を確保しつつ良好な保存特性を実現する非水電解質二次電池を提供することが可能である。
【０１２５】
また、本発明に係る非水電解質二次電池の製造方法は、正極活物質としてリチウムマンガン複合酸化物及びリチウムニッケル系複合酸化物のうち少なくとも一方を含有し、且つ保存するときの電圧が３．４Ｖ〜３．７５Ｖの範囲内となるように充電を行っている。これにより、非水電解質二次電池の充電状態を５０％程度の適度なものとし、正極表面に良質な被膜を形成する。したがって、本発明によれば、高エネルギー密度を確保するとともに良好な保存特性を実現する非水電解質二次電池を製造することが可能である。
【図面の簡単な説明】
【図１】本発明を適用した非水電解液二次電池の一構成例を示す断面図である。
【図２】正極活物質としてリチウムマンガン複合酸化物及びリチウムニッケル系複合酸化物を用いた電池Ａ、及び正極活物質としてリチウムコバルト複合酸化物を用いた電池Ｂの放電曲線を示す特性図である。
【符号の説明】
１ 電池缶、２ 正極、３ 負極、４ セパレータ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nonaqueous electrolyte secondary battery having a positive electrode containing a positive electrode active material, a negative electrode containing a material that can be doped and dedoped with lithium, and a nonaqueous electrolyte.
[0002]
[Prior art]
In recent years, due to advances in electronic technology, electronic devices have become higher performance, smaller, and more portable, and batteries used in these electronic devices are increasingly required to have higher energy density.
[0003]
Conventionally, as secondary batteries used in these electronic devices, aqueous secondary batteries such as lead batteries and nickel / cadmium batteries are mainly used. However, these aqueous secondary batteries have a low discharge potential and energy. It is hard to say that the density is satisfactory.
[0004]
On the other hand, recently, lithium secondary batteries using metallic lithium or lithium alloy as a negative electrode and using a lithium compound as a positive electrode have been attracting attention as a battery system that satisfies requirements such as discharge potential and energy density. Research and development is actively conducted.
[0005]
However, it has been recognized that this lithium secondary battery has problems in terms of cycle life, safety, quick chargeability, and the like, which is a major obstacle to practical use. This is considered to be caused by the formation of dendrites by dissolution and precipitation of metallic lithium as the negative electrode and the miniaturization of the negative electrode. For this reason, the above-mentioned lithium secondary battery is merely put into practical use as a part of coin-type lithium secondary batteries.
[0006]
In order to solve these problems, a so-called lithium ion secondary battery has been proposed as a nonaqueous electrolyte secondary battery using a carbonaceous material such as coke as a negative electrode active material.
[0007]
In this lithium ion secondary battery, since lithium does not exist in a metal state, there is no deterioration in cycle characteristics due to the metal lithium negative electrode and safety problems, and a lithium compound having a high redox potential is used for the positive electrode. Thus, the battery voltage can be increased and a high energy density can be obtained.
[0008]
Further, the lithium ion secondary battery has a lower self-discharge than the nickel-cadmium battery, and is a very excellent battery as a secondary battery.
[0009]
For this reason, this lithium ion secondary battery has already been commercialized as a power source for portable electronic devices such as an 8 mm video tape recorder (VTR), a compact disc (CD) player, a laptop computer, a mobile phone, etc. It is highly expected in the future.
[0010]
[Problems to be solved by the invention]
However, although a lithium ion secondary battery can obtain a high energy density, there is a problem that the storage characteristics due to the positive electrode are poor.
[0011]
Therefore, the present invention has been proposed in view of such a conventional situation, and an object thereof is to provide a nonaqueous electrolyte secondary battery having a high energy density and excellent storage characteristics, and a method for manufacturing the same. .
[0012]
[Means for Solving the Problems]
  In order to achieve the above object, a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode containing a positive electrode active material, and can be doped and dedoped with lithium.CarbonaceousA negative electrode containing a material and a non-aqueous electrolyte, the positive electrode active material containing at least one of a lithium manganese composite oxide and a lithium nickel composite oxide;Lithium manganese composite oxide has the general formula Li _x Mn ₂ O _Four (Wherein x ≧ 0.95), and the lithium nickel composite oxide is represented by the general formula LiNi _x Co _y Al _z O ₂ (However, in the formula, x + y + z = 1. Also, 0.4 ≦ x ≦ 0.985, 0.01 ≦ y ≦ 0.4, and 0.005 ≦ z ≦ 0.2. )The voltage is maintained in the range of 3.4V to 3.75V by the initial charge.
[0013]
  The non-aqueous electrolyte secondary battery configured as described above contains at least one of a lithium manganese composite oxide and a lithium nickel composite oxide as a positive electrode active material, andFirst chargeIs set within the range of 3.4V to 3.75V. For this reason, the non-aqueous electrolyte secondary battery is appropriately charged at about 50%, thereby forming a good-quality film on the surface of the positive electrode.
[0014]
The nonaqueous electrolyte secondary battery according to the present invention preferably contains a lithium manganese composite oxide and a lithium nickel composite oxide as the positive electrode active material. When the positive electrode active material is a mixture of a lithium manganese composite oxide and a lithium nickel composite oxide, the non-aqueous electrolyte secondary battery has excellent cycle characteristics.
[0015]
  In addition, the method for manufacturing a non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode containing a positive electrode active material, and can be doped and dedoped with lithium.CarbonaceousA negative electrode containing a material and a non-aqueous electrolyte;_xMn₂O_Four(Where x ≧ 0.95) and a lithium manganese composite oxide and LiNi_xCo_yAl_zO₂(Where x + y + z = 1, 0.4 ≦ x ≦ 0.985, 0.01 ≦ y ≦ 0.4, and 0.005 ≦ z ≦ 0.2). An assembly step for producing a battery precursor of a non-aqueous electrolyte secondary battery containing at least one of the lithium nickel-based composite oxides, and at least charging the battery precursor,By first chargeVoltage within the range of 3.4V to 3.75VTo maintainAnd a charging step.
[0016]
  In the method for producing a non-aqueous electrolyte secondary battery as described above, the positive electrode active material contains at least one of a lithium manganese composite oxide and a lithium nickel composite oxide, andFirst chargeIs charged so as to be within a range of 3.4V to 3.75V. As a result, the state of charge of the nonaqueous electrolyte secondary battery is moderated to about 50%, and a high-quality film is formed on the surface of the positive electrode.
[0017]
In the method for producing a nonaqueous electrolyte secondary battery according to the present invention, it is preferable to use a lithium manganese composite oxide and a lithium nickel composite oxide as the positive electrode active material. When the positive electrode active material is a mixture of a lithium manganese composite oxide and a lithium nickel composite oxide, a nonaqueous electrolyte secondary battery having excellent cycle characteristics can be manufactured.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a nonaqueous electrolyte secondary battery to which the present invention is applied and a manufacturing method thereof will be described in detail with reference to the drawings. Hereinafter, a nonaqueous electrolyte secondary battery generally called a lithium ion secondary battery will be described as an example of a nonaqueous electrolyte secondary battery to which the present invention is applied.
[0019]
FIG. 1 shows a cross-sectional configuration of a non-aqueous electrolyte secondary battery to which the present invention is applied. This nonaqueous electrolyte secondary battery is a so-called cylindrical type, and is formed by applying a positive electrode mixture containing a positive electrode active material to a positive electrode current collector inside a substantially hollow cylindrical battery can 1. A spiral electrode in which a strip-shaped positive electrode 2 and a strip-shaped negative electrode 3 formed by applying a negative electrode mixture containing a negative electrode active material to a negative electrode current collector are wound many times through an ion-permeable separator 4 Have a body. The battery can 1 is made of, for example, iron plated with nickel, and has one end closed and the other end open. In addition, a pair of insulating plates 5 and 6 are arranged inside the battery can 1 perpendicular to the peripheral surface so as to sandwich the spiral electrode body.
[0020]
At the open end of the battery can 1, a battery lid 7, a safety valve device 8 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 9 provided inside the battery lid 7 are provided via a sealing gasket 10. The battery can 1 is attached by being caulked, and the inside of the battery can 1 is sealed. The battery lid 7 is made of, for example, the same material as the battery can 1. The safety valve device 8 is electrically connected to the battery lid 7 via the heat-sensitive resistance element 9, and when the internal pressure of the battery exceeds a certain level due to internal short circuit or external heating, the safety lid device 8 and the battery lid 7 are swirled. A so-called current interrupting mechanism for disconnecting the electrical connection with the mold electrode body is provided. The heat-sensitive resistor element 9 limits the current by increasing the resistance value when the temperature rises, and prevents abnormal heat generation due to a large current. The sealing gasket 10 is made of, for example, an insulating material, and asphalt is applied to the surface.
[0021]
The spiral electrode body has, for example, a center pin 11 as a center. A positive electrode lead 12 made of aluminum or the like is connected to the positive electrode 2 of the spiral electrode body, and a negative electrode lead 13 made of nickel or the like is connected to the negative electrode 3. The positive electrode lead 12 is electrically connected to the battery lid 7 by being welded to the safety valve device 8, and the negative electrode lead 13 is welded to and electrically connected to the battery can 1. The separator 4 between the positive electrode 2 and the negative electrode 3 is impregnated with, for example, an electrolytic solution as a nonaqueous electrolyte.
[0022]
As the negative electrode active material constituting the negative electrode 3, a material capable of doping and dedoping lithium can be used. As a material capable of doping and dedoping lithium, for example, a carbonaceous material can be used.
[0023]
Specific carbonaceous materials include carbonaceous materials such as non-graphitizable carbon materials and graphite materials. More specifically, carbonaceous materials such as pyrolytic carbons, cokes, graphites, glassy carbon fibers, organic polymer compound fired bodies, carbon fibers, activated carbon and the like can be mentioned. Examples of the cokes include pitch coke, knee coke, and petroleum coke. Moreover, the organic polymer compound fired body is obtained by firing and carbonizing a phenol resin, a furan resin or the like at an appropriate temperature.
[0024]
Examples of materials that can be doped and dedoped with lithium include conductive polymers such as polyacetylene and polypyrrole, and SnO.₂Oxides such as these can also be used. Moreover, a lithium-aluminum alloy etc. can be used as a lithium alloy.
[0025]
In addition to the negative electrode active material as described above, the negative electrode mixture may contain a known binder or a known additive that is usually used for this type of battery.
[0026]
In the non-aqueous electrolyte secondary battery to which the present invention is applied, at least one of a lithium manganese composite oxide and a lithium nickel composite oxide is used as the positive electrode active material constituting the positive electrode 2.
[0027]
As a specific lithium manganese composite oxide, the general formula Li_xMn_2-yM ’_yO₄(However, in the formula, x ≧ 0.9 and 0.01 ≦ y ≦ 0.5. Further, M ′ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, A compound represented by Ti, Mg, Ca, Sr, B, Ga, In, Si, or Ge). In particular, as a lithium manganese composite oxide, the general formula Li_xMn₂O₄However, it is preferable to use a compound represented by the formula (where x ≧ 0.95).
[0028]
As a specific lithium nickel-based composite oxide, a general formula LiNi_1-zM ”_zO₂(However, in the formula, 0.01 ≦ z ≦ 0.5. M ″ is Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, which are one or more elements.) In particular, as a lithium nickel-based composite oxide, a general formula LiNi_xCo_yAl_zO₂(However, in the formula, x + y + z = 1. Also, 0.4 ≦ x ≦ 0.985, 0.01 ≦ y ≦ 0.4, and 0.005 ≦ z ≦ 0.2. It is preferable to use a compound represented by
[0029]
Since the lithium manganese composite oxide and the lithium nickel composite oxide have a high redox potential, by using at least one of them as a positive electrode active material, a non-aqueous electrolyte solution having a high battery voltage and a high energy density can be obtained. A secondary battery can be realized. For example, lithium manganese composite oxide has advantages such as a low raw material price and raw material supply stability.
[0030]
Further, as the positive electrode active material, it is preferable to use a mixture of these lithium manganese composite oxide and lithium nickel composite oxide. Thereby, cycle characteristics can be improved.
[0031]
The reason for this is shown below.
[0032]
That is, a non-aqueous electrolyte comprising a positive electrode using a lithium manganese composite oxide and a lithium nickel-based composite oxide as a positive electrode active material, a negative electrode containing a negative electrode active material capable of doping and dedoping lithium, and a non-aqueous electrolyte In the secondary battery, lithium is dedoped from the positive electrode in the charging reaction. At that time, the crystal structure lattice of the lithium manganese composite oxide contracts, but the crystal structure lattice of the lithium nickel composite oxide expands. Conversely, in the discharge reaction, the crystal structure lattice of lithium manganese composite oxide expands, but the crystal structure lattice of lithium nickel composite oxide contracts. Therefore, when viewed as the whole positive electrode active material, volume change due to contraction / expansion associated with charge / discharge is reduced. As a result, even if charging / discharging is repeated, the positive electrode active material is hardly subjected to stress due to volume change, and as a result, the contact with the conductive agent or the like is maintained in a good state.
[0033]
When a lithium manganese composite oxide is used alone as the positive electrode active material, a high energy density can be obtained, but the volume change of the lithium manganese composite oxide accompanying charge / discharge increases, and the cycle characteristics may be deteriorated.
[0034]
In addition, when a lithium nickel composite oxide is used alone as the positive electrode active material, a high energy density can be obtained, but the volume change of the lithium nickel composite oxide accompanying charge / discharge increases, resulting in deterioration of cycle characteristics. There is a fear.
[0035]
When a lithium manganese composite oxide and a lithium nickel composite oxide are mixed and used as the positive electrode active material, the weight mixing ratio is preferably in the range of 20:80 to 80:20. When the mixing ratio of the lithium manganese composite oxide is excessive from the above range, the cycle characteristics may be impaired. Conversely, when the mixing ratio of the lithium nickel composite oxide is excessive from the above range, the cycle characteristics may be impaired.
[0036]
In addition to the positive electrode active material as described above, the positive electrode mixture may contain a known binder or a known additive that is usually used for this type of battery.
[0037]
As the positive electrode current collector, for example, an aluminum foil or the like can be used.
[0038]
As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution obtained by dissolving an electrolyte salt in a non-aqueous solvent can be used.
[0039]
As electrolyte salt, the well-known electrolyte salt used for the normal electrolyte solution for batteries can be used. Specifically, LiPF₆, LiBF₄, LiAsF₆LiClO₄, LiCF₃SO₃, LiN (CF₃SO₂)₂, LiC (CF₃SO₂)₃LiAlCl₄, LiSiF₆, LiB (C₆H₅)₄, LiCl, LiBr, CF₃SO₃Lithium salts such as Li can be mentioned. Among these, from the viewpoint of oxidation stability, LiPF₆Or LiBF₄Is preferably used.
[0040]
Non-aqueous solvents include propylene carbonate, ethylene carbonate, dimethoxyethane, dimethyl carbonate, diethyl carbonate, γ-butyllactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane. , Diethyl ether, sulfolane, methyl sulfolane, methyl sulfolane butyrate, acetonitrile, propiononitrile, methyl propionate, and the like can be used. These non-aqueous solvents may be used alone or in combination of two or more.
[0041]
By the way, as described above, by using at least one of the lithium manganese composite oxide and the lithium nickel composite oxide as the positive electrode active material, a high battery voltage is exhibited, and a high energy density non-aqueous electrolyte secondary battery is obtained. realizable. Furthermore, cycle characteristics can be improved by using a mixture of lithium manganese composite oxide and lithium nickel composite oxide.
[0042]
However, even when, for example, a lithium manganese composite oxide and a lithium nickel composite oxide are mixed and used as the positive electrode active material, this non-aqueous electrolyte secondary battery has a problem of poor storage characteristics. . That is, the actual situation is that a technique for improving both cycle characteristics and storage characteristics has not yet been established.
[0043]
Therefore, after the non-aqueous electrolyte secondary battery is manufactured, the voltage of the non-aqueous electrolyte secondary battery when it is left, that is, stored, is set within the range of 3.4V to 3.75V. By using a predetermined positive electrode active material and keeping the voltage at the time of storage within a specified range, the nonaqueous electrolyte secondary battery is brought into an appropriate charged state of about 50%. Thereby, a good-quality thin film is formed on the surface of the positive electrode 2, and a decrease in capacity is suppressed even after long-term storage. Therefore, the nonaqueous electrolyte secondary battery to which the present invention is applied has excellent cycle characteristics and good storage characteristics.
[0044]
When the voltage when storing the non-aqueous electrolyte secondary battery is less than 3.4 V, the film formed on the surface of the positive electrode 2 is too thin, and the effect of improving the storage characteristics becomes insufficient. On the other hand, when the voltage when storing the nonaqueous electrolyte secondary battery exceeds 3.75 V, the film formed on the surface of the positive electrode 2 becomes too thick, so that the heavy load characteristic is deteriorated.
[0045]
The voltage when storing the non-aqueous electrolyte secondary battery is more preferably in the range of 3.5V to 3.73V. Thereby, the improvement effect of the storage characteristic of a non-aqueous-electrolyte secondary battery can be acquired further more reliably.
[0046]
Further, the voltage when storing the non-aqueous electrolyte secondary battery is set within the range of 3.4 V to 3.75 V, and a lithium manganese composite oxide and a lithium nickel composite oxide are mixed as a positive electrode active material. By using it, the storage characteristic improvement effect of the nonaqueous electrolyte secondary battery can be remarkably obtained.
[0047]
Here, the reason why the voltage when storing the nonaqueous electrolyte secondary battery is set within the range of 3.4 V to 3.75 V will be described in more detail with reference to FIG.
[0048]
Incidentally, in a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, the state of charge of the battery can be determined by detecting the voltage across the terminals of the non-aqueous electrolyte secondary battery. In other words, in a nonaqueous electrolyte secondary battery, the battery can be controlled to a desired state of charge by controlling the voltage between the terminals of the battery.
[0049]
In a conventional non-aqueous electrolyte secondary battery using a lithium cobalt composite oxide as a positive electrode active material, deterioration of storage characteristics is suppressed by making a charged state of about 50%.
[0050]
A nonaqueous electrolyte secondary battery (hereinafter referred to as battery A) using a mixture of lithium manganese composite oxide and lithium nickel composite oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material. The discharge curve is shown by a solid line in FIG. Further, a discharge curve of a nonaqueous electrolyte secondary battery (hereinafter referred to as battery B) using a conventional lithium cobalt composite oxide as a positive electrode active material and a carbonaceous material as a negative electrode active material is shown in FIG. Shown with dotted lines. In FIG. 2, the vertical axis represents the battery voltage, and the horizontal axis represents the state of charge of the battery.
[0051]
As is clear from FIG. 2, the battery B using the conventional lithium cobalt composite oxide as the positive electrode active material has an intersection with a line indicating 50% charge state in the vicinity of 3.8V to 3.9V. .
That is, by controlling the voltage when storing the battery B to 3.8 V to 3.9 V, the state of charge of the battery B can be set to about 50%, and the storage characteristics can be improved.
[0052]
However, when a voltage of about 3.8 V to 3.9 V optimum for the battery B is directly applied to the battery A containing the lithium manganese composite oxide and the lithium nickel composite oxide as the positive electrode active material, it is clear from FIG. Thus, the battery A is in a charged state of about 70% to 80%. As a result, in the battery A, the film formed on the surface of the positive electrode becomes thick, and the heavy load characteristics are deteriorated.
[0053]
Therefore, in accordance with the characteristics of the positive electrode active material to be used, by setting the voltage when storing the battery A within the range of 3.4V to 3.75V, the state of charge of the battery A is about 50%. It can be. As a result, a good-quality film is formed on the surface of the positive electrode, and the storage characteristics of the battery A can be improved.
[0054]
As described above, by using at least one of lithium manganese composite oxide and lithium nickel composite oxide as the positive electrode active material and setting the voltage within the range of 3.4 V to 3.75 V, the state of charge is 50 % Can be moderate. Therefore, it is possible to secure a high energy density and improve the storage characteristics of the non-aqueous electrolyte secondary battery.
[0055]
Further, by using a lithium manganese composite oxide and a lithium nickel composite oxide in combination as the positive electrode active material, it becomes possible to improve the cycle characteristics, and the effect of improving the storage characteristics can be obtained more reliably.
[0056]
Next, a method for producing the above non-aqueous electrolyte secondary battery will be described.
[0057]
First, the components of the nonaqueous electrolyte secondary battery are assembled as follows to produce a battery precursor.
[0058]
First, the positive electrode 2 is produced. A positive electrode active material is mixed with a binder, a conductive agent, and the like to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent to form a slurry (paste). The positive electrode mixture slurry is applied to both surfaces of the positive electrode current collector, dried, and then compression-molded at a constant pressure to obtain a belt-like positive electrode 2.
[0059]
As a specific lithium manganese composite oxide, the general formula Li_xMn_2-yM ’_yO₄(However, in the formula, x ≧ 0.9 and 0.01 ≦ y ≦ 0.5. Further, M ′ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Or a compound represented by one or more of Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge. In particular, as lithium manganese composite oxide, Li_xMn₂O₄However, it is preferable to use a compound represented by the formula (where x ≧ 0.95).
[0060]
Further, as a specific lithium nickel-based composite oxide, a general formula LiNi_1-zM ”_zO₂(However, in the formula, 0.01 ≦ z ≦ 0.5. M ″ is Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, or Ge, which is a compound represented by 1) or more._xCo_yAl_zO₂(However, in the formula, x + y + z = 1. Also, 0.4 ≦ x ≦ 0.985, 0.01 ≦ y ≦ 0.4, and 0.005 ≦ z ≦ 0.2. It is preferable to use a compound represented by
[0061]
At this time, at least one of the lithium manganese composite oxide and the lithium nickel composite oxide as described above is used as the positive electrode active material. Moreover, it is more preferable to use a mixture of lithium manganese composite oxide and lithium nickel composite oxide as the positive electrode active material.
[0062]
Next, the negative electrode 3 is produced. A negative electrode active material capable of doping and dedoping lithium and a binder are mixed to prepare a negative electrode mixture, and the negative electrode mixture is dispersed in a solvent to form a slurry (paste). The negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector, dried, and then compression-molded at a constant pressure to obtain a strip-shaped negative electrode 3.
[0063]
The positive electrode 2 and the negative electrode 3 obtained in this way are stacked via a microporous separator 4 and wound many times to produce a spiral electrode body.
[0064]
Next, the obtained spiral electrode body is sandwiched in the battery can 1 in a state where the pair of insulating plates 5 and 6 are arranged above and below the spiral electrode body so as to be sandwiched from the direction perpendicular to the winding peripheral surface. Accommodate. Further, the positive electrode lead 12 is led out from the positive electrode current collector, and the negative electrode lead 13 is led out from the negative electrode current collector to the battery lid 7 and welded to the battery can 1 to ensure electrical connection.
[0065]
Next, for example, a nonaqueous electrolytic solution obtained by dissolving an electrolyte in a nonaqueous solvent at a predetermined concentration is injected into the battery can 1.
[0066]
Next, the battery can 1 is caulked through a sealing gasket 10 to fix the safety valve device 8, the heat-sensitive resistor element 9 and the battery lid 7, and the inside of the battery can 1 is sealed to produce a battery precursor. .
[0067]
Next, at least charging is performed on the battery precursor assembled in this manner, and the voltage is stored in the range of 3.4 V to 3.75 V. Thereby, a non-aqueous electrolyte secondary battery is obtained.
[0068]
By setting the voltage at the time of storage within the above range, the non-aqueous electrolyte secondary battery is appropriately charged at about 50%, and a good-quality film is formed on the surface of the positive electrode 2. Thereby, while ensuring a high energy density, the non-aqueous-electrolyte secondary battery by which the deterioration of the storage characteristic resulting from a positive electrode was suppressed can be produced.
[0069]
In particular, by using a mixture of lithium manganese composite oxide and lithium nickel composite oxide as the positive electrode active material, it is possible to improve the cycle characteristics and improve the storage characteristics more reliably. A battery can be produced.
[0070]
In the above description, a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte as a non-aqueous electrolyte is taken as an example, but the present invention is not limited to this. For example, in the present invention, any of a polymer solid electrolyte containing an electrolyte salt as a nonaqueous electrolyte and a gel electrolyte obtained by impregnating an organic polymer with a nonaqueous solvent and an electrolyte salt can be used.
[0071]
Examples of the polymer material used for the polymer solid electrolyte include silicone, polyether-modified siloxane, polyacryl, polyacrylonitrile, polyphosphazene-modified polymer, polyethylene oxide, polypropylene oxide, and composite polymers, cross-linked polymers, and modified polymers thereof. Polymers, acrylonitrile-butadiene rubber, polyacrylonitrile-butadiene styrene, acrylonitrile-polyethylene chloride-propylene-diene-styrene resin, acrylonitrile-vinyl chloride resin, acrylonitrile-methacrylate resin, acrylonitrile-acrylate resin, polyethylene oxide And ether polymers. Moreover, you may use it, mixing 2 or more types among these.
[0072]
Polymer materials include acrylonitrile, vinyl acetate, methyl methacrylate, butyl methacrylate, methyl acrylate, butyl acrylate, itaconic acid, methyl hydroxide acrylate, ethyl hydroxide acrylate, acrylamide, vinyl chloride, fluoride Copolymer with vinylidene or the like, or poly (vinylidene fluoride), poly (vinylidene fluoride-co-hexafluoropropylene), poly (vinylidene fluoride-co-tetrafluoroethylene), poly (vinylidene fluoride-co- Fluoropolymers such as trifluoroethylene, etc., and mixtures thereof can be used.
[0073]
Further, the nonaqueous electrolyte secondary battery according to the present invention is not particularly limited with respect to its shape, such as a cylindrical shape, a square shape, a coin shape, a button shape, and various sizes such as a thin shape and a large size. Can be.
[0074]
【Example】
Hereinafter, specific examples to which the present invention is applied will be described based on experimental results.
[0075]
First, a lithium manganese composite oxide and a lithium nickel composite oxide were prepared as follows.
[0076]
(1) Method for preparing lithium nickel composite oxide
Cobalt oxide, nickel oxide, aluminum hydroxide, and lithium hydroxide were mixed so that Li / Ni / Co / Al = 1 / 0.985 / 0.01 / 0.005, and in oxygen at a temperature of 750 ° C. By firing for 5 hours, LiNi_0.985Co_0.01Al_0.005O₂Got.
[0077]
(2) Method for preparing lithium nickel composite oxide
Cobalt oxide, nickel oxide, aluminum hydroxide, and lithium hydroxide were mixed so that Li / Ni / Co / Al = 1 / 0.4 / 0.4 / 0.2, and in oxygen at a temperature of 750 ° C. By firing for 5 hours, LiNi_0.4Co_0.4Al_0.2O₂Got.
[0078]
(3) Method for preparing lithium manganese composite oxide
Manganese dioxide and lithium carbonate are mixed so that Li / Mn = 1/2, and fired in the atmosphere at a temperature of 900 ° C. for 5 hours.₂O₄Got.
[0079]
Example 1
First, the graphite powder used for a negative electrode was produced.
[0080]
100 parts by weight of coal-based coke and 30 parts by weight of coal tar-based pitch as a binder were added and mixed at about 100 ° C., followed by compression molding with a press to obtain a carbon molded body precursor. This carbon molded body precursor was heat-treated at 1000 ° C. or lower to obtain a carbon molded body.
[0081]
The carbon molded body was impregnated with a binder pitch dissolved at 200 ° C. or lower, and then a pitch impregnation / firing step in which heat treatment was performed at 1000 ° C. or lower was repeated several times. Thereafter, this carbon molded body was heat-treated at 2800 ° C. in an inert gas stream to obtain a graphitized molded body, and then pulverized and classified to prepare a graphite powder.
[0082]
Using the graphite powder produced as described above, a negative electrode was produced as follows. After mixing 90 parts by weight of graphite powder and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder, it is dispersed in N-methylpyrrolidone serving as a solvent to form a slurry to obtain a negative electrode mixture slurry. It was. The negative electrode mixture slurry was uniformly applied to both sides of a 10 μm-thick strip-shaped copper foil as a negative electrode current collector and dried, followed by compression molding with a roll press at a constant pressure to produce a strip-shaped negative electrode.
[0083]
Next, a positive electrode was produced as follows.
[0084]
Lithium manganese composite oxide (LiMn) obtained by the preparation method of (3) described above₂O₄) And 80% by weight of lithium nickel composite oxide (LiNi) obtained by the preparation method of (1) described above_0.985Co_0.01Al_0.005O₂) Was mixed with 20% by weight, and this mixture was used as a positive electrode active material.
[0085]
A positive electrode mixture was prepared by mixing 91% by weight of this positive electrode active material, 6% by weight of graphite as a conductive agent, and 3% by weight of polyvinylidene fluoride, and dispersed in N-methylpyrrolidone to form a slurry. A negative electrode mixture slurry was obtained. This negative electrode mixture slurry was uniformly applied to both surfaces of a 20 μm-thick belt-like aluminum foil as a positive electrode current collector and dried, and then compression-molded with a roll press at a constant pressure to produce a belt-like positive electrode.
[0086]
The strip-shaped negative electrode and the strip-shaped positive electrode prepared as described above were laminated through a separator made of a microporous polyethylene film having a thickness of 25 μm and wound many times to prepare a spiral electrode body.
[0087]
This spiral electrode body was housed in a nickel-plated iron battery can, and insulating plates were disposed on both the upper and lower surfaces of the spiral electrode body. In order to collect the positive electrode and the negative electrode, the aluminum lead is led out from the positive electrode current collector to lead to a safety valve device having a current interrupt device and a thermal resistance element, and the nickel lead is led out from the negative electrode current collector. Welded each battery can.
[0088]
Next, in a battery can, an equal volume mixed solvent of ethylene carbonate and diethyl carbonate, LiPF₆A non-aqueous electrolyte obtained by dissolving 1 mol of was injected.
[0089]
Next, the battery lid was fixed to the battery can by caulking through a gasket coated with asphalt to produce a battery precursor of a cylindrical nonaqueous electrolyte secondary battery having a diameter of 18 mm and a height of 65 mm.
[0090]
Finally, the non-aqueous electrolyte secondary battery was obtained by setting the charging voltage to 3.4 V and charging the battery precursor with a constant current of 500 mA. The obtained nonaqueous electrolyte secondary battery is maintained at a voltage of 3.4 V, that is, stored.
[0091]
Example 2
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the charging voltage was set to 3.5V.
[0092]
Example 3
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the charging voltage was set to 3.73V.
[0093]
Example 4
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the charging voltage was set to 3.75V.
[0094]
Comparative Example 1
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the charging voltage was set to 3.3V.
[0095]
Comparative Example 2
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the charging voltage was set to 3.78V.
[0096]
Example 5
The mixing ratio of the positive electrode active material was determined using the lithium manganese composite oxide (LiMn) obtained by the preparation method of (3) described above.₂O₄) And 20% by weight of lithium nickel-based composite oxide (LiNi) obtained by the preparation method of (1) described above._0.985Co_0.01Al_0.005O₂) Was set to 80% by weight, and a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1.
[0097]
Example 6
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 5 except that the charging voltage was set to 3.5V.
[0098]
Example 7
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 5 except that the charging voltage was set to 3.73V.
[0099]
Example 8
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 5 except that the charging voltage was set to 3.75V.
[0100]
Comparative Example 3
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 5 except that the charging voltage was set to 3.3V.
[0101]
Comparative Example 4
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 5 except that the charging voltage was set to 3.78V.
[0102]
Example 9
The mixing ratio of the positive electrode active material was determined using the lithium manganese composite oxide (LiMn) obtained by the preparation method of (3) described above.₂O₄) 80% by weight and the lithium nickel composite oxide (LiNi) obtained by the preparation method of (2) described above._0.4Co_0.4Al_0.2O₂) Was mixed with 20% by weight, and a non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this mixture was used as a positive electrode active material.
[0103]
Example 10
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9 except that the charging voltage was set to 3.5V.
[0104]
Example 11
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9 except that the charging voltage was set to 3.73V.
[0105]
Example 12
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9 except that the charging voltage was set to 3.75V.
[0106]
Comparative Example 5
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9 except that the charging voltage was set to 3.3V.
[0107]
Comparative Example 6
A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 9 except that the charging voltage was set to 3.78V.
[0108]
Example 13
As a positive electrode active material, lithium manganese composite oxide (LiMn) obtained by the preparation method of (3) described above₂O₄A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 4 except that only a) was used.
[0109]
Example 14
As a positive electrode active material, a lithium nickel composite oxide (LiNi obtained by the preparation method of (1) described above)_0.985Co_0.01Al_0.005O₂A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 4 except that only a) was used.
[0110]
About the Example 1- Example 14 produced as mentioned above and the comparative example 1- comparative example 6, the preservation | save test was done as follows.
[0111]
That is, first, each nonaqueous electrolyte secondary battery was fully charged under conditions of a voltage of 4.20 V, a charging current of 1000 mA, and a charging time of 2.5 hours, and then a discharge current of 1500 mA and a final voltage of 3.0 V. Discharging was performed under the conditions, and the initial capacity A at this time was measured.
[0112]
Next, the batteries fully charged under the above-described conditions were stored at 60 ° C. for 2 weeks, and then each non-aqueous electrolyte secondary battery was discharged under conditions of a discharge current of 1500 mA and a final voltage of 3.0V.
[0113]
Next, after charging again under the above conditions, discharging was performed under the above conditions, and the capacity B at this time was measured.
[0114]
And the capacity | capacitance B with respect to the initial stage capacity A was represented by the percentage as a capacity | capacitance recovery rate.
[0115]
The above results are shown in Table 1 below.
[0116]
[Table 1]

[0117]
As is clear from Table 1, a mixture of a lithium manganese composite oxide and a lithium nickel composite oxide was used as the positive electrode active material, and the voltage during storage was within a range of 3.4 V to 3.75 V. In Examples 1 to 12, a high initial capacity was exhibited, and a capacity recovery rate was a high value exceeding 90%.
[0118]
However, in Comparative Example 1, Comparative Example 3 and Comparative Example 5 in which the voltage during storage was 3.3 V, the capacity recovery rate was low and it was found that the storage characteristics were inferior.
[0119]
On the contrary, Comparative Example 2, Comparative Example 4 and Comparative Example 6 in which the voltage at the time of storage is 3.78 V are inferior to the capacity recovery rate compared to Examples 1 to 12, and the initial capacity is low. Indicated.
[0120]
From the above results, it was found that a non-aqueous electrolyte secondary battery capable of achieving both high capacity and storage characteristics can be realized by setting the voltage during storage within the range of 3.4 V to 3.75 V.
[0121]
In addition, from the result of Table 1, even when the mixing ratio of the lithium manganese composite oxide and the lithium nickel composite oxide of the positive electrode active material is changed, the voltage at the time of storage is 3.4 V to 3.75 V. It turned out that a favorable result can be obtained by making it in the range of this.
[0122]
In addition, even when the composition of the lithium nickel composite oxide contained as the positive electrode active material is changed, by setting the voltage during storage within the range of 3.4 V to 3.75 V, good results are obtained. It turns out that it is obtained.
[0123]
In addition, Example 13 and Example 14 using lithium manganese composite oxide or lithium nickel composite oxide alone as the positive electrode active material also showed high initial capacity and capacity recovery rate. From this result, even when the positive electrode active material contains only one of the lithium manganese composite oxide or the lithium nickel composite oxide, excellent storage characteristics are exhibited by keeping the voltage within the specified range. It was found that a nonaqueous electrolyte secondary battery can be obtained.
[0124]
【Effect of the invention】
As is clear from the above description, the nonaqueous electrolyte secondary battery according to the present invention contains and stores at least one of a lithium manganese composite oxide and a lithium nickel composite oxide as a positive electrode active material. Is set within the range of 3.4V to 3.75V. For this reason, the non-aqueous electrolyte secondary battery is appropriately charged at about 50%, thereby forming a good-quality film on the surface of the positive electrode. Therefore, according to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that realizes good storage characteristics while ensuring a high energy density.
[0125]
In addition, the non-aqueous electrolyte secondary battery manufacturing method according to the present invention contains at least one of a lithium manganese composite oxide and a lithium nickel composite oxide as a positive electrode active material, and the voltage when stored is 3. Charging is performed so as to be within the range of 4V to 3.75V. As a result, the state of charge of the nonaqueous electrolyte secondary battery is moderated to about 50%, and a high-quality film is formed on the surface of the positive electrode. Therefore, according to the present invention, it is possible to manufacture a non-aqueous electrolyte secondary battery that ensures high energy density and realizes good storage characteristics.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing one structural example of a non-aqueous electrolyte secondary battery to which the present invention is applied.
FIG. 2 is a characteristic diagram showing discharge curves of a battery A using a lithium manganese composite oxide and a lithium nickel composite oxide as a positive electrode active material, and a battery B using a lithium cobalt composite oxide as a positive electrode active material. .
[Explanation of symbols]
1 battery can, 2 positive electrode, 3 negative electrode, 4 separator

Claims (8)

A positive electrode containing a positive electrode active material, a negative electrode containing a carbonaceous material that can be doped and dedoped with lithium, and a non-aqueous electrolyte,
As the positive electrode active material, containing at least one of lithium manganese composite oxide and lithium nickel composite oxide,
The lithium manganese composite oxide is represented by the general formula Li _x Mn ₂ O ₄ (where x ≧ 0.95).
The lithium nickel composite oxide is represented by the general formula _{LiNi x Co y Al z O 2} ( where in the formula, is x + y + z = 1. In addition, a 0.4 ≦ x ≦ 0.985, 0.01 ≦ y ≦ 0.4, 0.005 ≦ z ≦ 0.2.)
A non-aqueous electrolyte secondary battery characterized in that the voltage is maintained within a range of 3.4 V to 3.75 V by initial charging.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the voltage is maintained within a range of 3.5 V to 3.73 V by the initial charging.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains the lithium manganese composite oxide and the lithium nickel composite oxide. The non-aqueous electrolyte secondary battery according to claim 3 , wherein a weight mixing ratio between the lithium manganese composite oxide and the lithium nickel composite oxide is in a range of 20:80 to 80:20. It has a positive electrode containing a positive electrode active material, a negative electrode containing a carbonaceous material that can be doped and dedoped with lithium, and a non-aqueous electrolyte. As the positive electrode active material, the general formula Li _x Mn ₂ O ₄ (however, , where a x ≧ 0.95.) lithium-manganese composite oxide represented by the general formula _{LiNi x Co y Al z O 2} ( where in the formula, is x + y + z = 1. Further, 0.4 ≦ x ≦ 0.985, 0.01 ≦ y ≦ 0.4, and 0.005 ≦ z ≦ 0.2.) At least one of the lithium nickel composite oxides represented by An assembly process for producing a battery precursor of a non-aqueous electrolyte secondary battery containing;
The battery precursor is charged at least, and has a charging step in which the voltage is maintained in the range of 3.4 V to 3.75 V by the initial charging, and manufacturing a non-aqueous electrolyte secondary battery Method. 6. The method for producing a nonaqueous electrolyte secondary battery according to claim 5 , wherein the voltage is maintained within a range of 3.5V to 3.75V by the initial charging. 6. The method for producing a nonaqueous electrolyte secondary battery according to claim 5 , wherein the lithium manganese composite oxide and the lithium nickel composite oxide are used as the positive electrode active material. 8. The nonaqueous electrolyte secondary battery according to claim 7 , wherein a weight mixing ratio of the lithium manganese composite oxide and the lithium nickel composite oxide is within a range of 20:80 to 80:20. 9. Production method.

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