JP5376640B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries consist of a carbonaceous material that can be doped and dedoped with lithium, a negative electrode using lithium and a metal material that forms an alloy with lithium, lithium cobaltate, lithium nickelate, manganate A positive electrode using a composite oxide of lithium and a transition metal, such as lithium, as an active material is used. Each of the strip-shaped negative electrode current collector and the positive electrode current collector is laminated with a separator interposed therebetween. It is manufactured by covering a battery or the like with a film or the like covered with an outer package or by laminating them in a spiral shape.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have been widely used as power sources for mobile phones, notebook personal computers, camcorders and the like. These non-aqueous electrolyte secondary batteries have a larger volume or weight capacity density and can take out a higher voltage than secondary batteries using aqueous electrolyte such as conventional lead storage batteries and alkaline storage batteries. Therefore, it is widely adopted as a power source for small devices, and greatly contributes to the development of today's mobile devices.

  On the other hand, in recent years, the shift to a clean energy society and the establishment of environmental technologies have been attracting attention due to the growing awareness of environmental issues, and it is suitable for power storage applications, uninterruptible power supply (UPS) applications, and mobile power supply applications. Early realization of high performance secondary batteries is required. Lithium ion secondary batteries are being actively studied for such large-scale batteries due to the above-mentioned characteristics of high energy density. However, in order to spread a wide range of applicable products, the life cycle cost of existing products is high. Superiority is essential, and price reduction is an indispensable element.

  In other words, in a lithium ion secondary battery with a high operating voltage, if the charge / discharge current value can be increased using a low-cost material, it can be expressed as a high-performance UPS, hybrid vehicle (HEV), or electric vehicle (EV). Can contribute to the realization of advanced information society and clean energy society. Against this background, low-cost, high capacity and high output of lithium ion secondary batteries are being actively studied.

  For example, in the past, lithium cobaltate was mainly used as the positive electrode active material in small portable applications, but as an alternative material for lithium cobaltate, an attempt was made to replace cobalt in lithium cobaltate with other elements, or an iron-based material having an olivine structure. Development of materials etc. is accelerated.

  When lithium cobaltate is used for the positive electrode, vigorous research has been conducted since an electromotive force exceeding 4 V has been obtained. Conventionally, lithium cobaltate has been mainly used in small portable applications. Lithium cobalt oxide is widely used as a positive electrode active material in today's lithium ion secondary batteries because it exhibits good characteristics such as potential flatness, capacity, discharge potential, and cycle characteristics.

However, cobalt, which is an element contained in lithium cobaltate, has a small amount of crust and is an expensive material, so there is a problem in supply stability and price of raw materials. Moreover, since lithium cobaltate has a layered rock salt structure (α-NaFeO ₂ structure), an oxygen layer having a large electronegativity is adjacent to the lithium due to the release of lithium during charging. For this reason, it is necessary to limit the amount of lithium extracted during actual use, and if too much lithium is extracted, such as in an overcharged state, the structure will change due to electrostatic repulsion between oxygen layers and heat will be generated. In order to ensure the safety of the battery, a large protection circuit is required outside, and a positive electrode material with higher safety is demanded.

Although lithium nickelate has a capacity greater than that of lithium cobaltate, the crystal structure is the same layered structure as lithium cobaltate, which is due to the instability of Ni ⁴⁺ during charging, resulting in oxygen desorption from lithium cobaltate. The temperature is low and safety is more difficult to secure. Furthermore, considering that the discharge potential is lower than that of lithium cobaltate and the environmental load of Ni is high, it is not attractive as an alternative material for lithium cobaltate.

  On the other hand, lithium manganate is a material that is highly expected as one of positive electrode materials for lithium ion secondary batteries. Manganese has abundant crustal abundance compared to cobalt, is an inexpensive element, and there is no problem with the supply stability of raw materials.

This lithium manganate has a spinel structure represented by the chemical formula LiMn ₂ O ₄ and functions as a 4V-class positive electrode material between the composition and λ-MnO ₂ . Since spinel lithium manganate has a three-dimensional host structure different from the layered rock salt structure of lithium cobaltate, etc., most of the theoretical capacity can be used, and excellent cycle characteristics are expected.

Lithium manganate LiMn ₂ O ₄ is a complex oxide that is highly anticipated as an alternative to the current mainstream positive electrode active material lithium cobaltate. However, conventional secondary batteries using lithium manganate are charged and discharged at high temperatures. There are problems with its practical application in two respects: capacity deterioration due to repetition and reduction in storage capacity due to self-discharge.

  The cause of the capacity deterioration due to the charge / discharge cycle is that the average valence of Mn ions changes between trivalent and tetravalent as charge compensation accompanying Li in / out, so that Jahn-Teller distortion occurs in the crystal, In addition, elution of Mn from lithium manganate or impedance rise due to Mn elution. In other words, the causes of capacity deterioration in which the charge / discharge capacity decreases by repeating the charge / discharge cycle include the influence of impurities, elution of Mn from lithium manganate, precipitation of eluted Mn on the negative electrode active material or separator, The inactivation due to the release of the substance particles, the influence of the acid generated by the contained water, the deterioration of the electrolyte solution due to the release of oxygen from lithium manganate, and the like can be considered.

  Assuming that a single spinel phase is formed, the elution of Mn is caused by the disproportionation of trivalent Mn in the spinel structure into tetravalent Mn and divalent Mn. It can be easily dissolved, elution is caused by a relative shortage of Li ions, and repeated charge / discharge promotes generation of irreversible capacity and disorder of atomic arrangement in the crystal. At the same time, the eluted Mn ions are likely to be deposited on the negative electrode or the separator to prevent the movement of Li ions.

  Further, when Mn ions are deposited on the negative electrode or the separator, a coating having low conductivity is formed on the negative electrode or the separator, so that the direct current resistance value of the battery is increased, which causes a decrease in output. Further, when lithium manganate is put in and out of Li ions, the cubic symmetry is distorted by the Jahn-Teller effect and accompanied by expansion / contraction of several percent of the unit cell length. Therefore, by repeating the cycle, it is expected that a partial electrical contact failure occurs or that the released particles do not function as an electrode active material.

  In addition, it is considered that oxygen release from lithium manganate is facilitated along with elution of Mn. Lithium manganate having many oxygen defects has a 3.3 V plateau capacity that increases as the cycle progresses, resulting in deterioration of cycle characteristics. Further, it is presumed that a large amount of oxygen release affects the decomposition of the electrolytic solution, which may cause cycle deterioration due to deterioration of the electrolytic solution. To solve this problem, improvement of the synthesis method, addition of other transition metal elements, excess Li composition, etc. have been studied so far. To satisfy both of the increase in discharge capacity and the improvement in cycle life at the same time. Not reached.

  Therefore, reducing Mn elution, reducing lattice distortion, reducing oxygen vacancies, etc. are derived as countermeasures.

  Next, measures to reduce storage capacity after high-temperature storage are as follows. It is considered effective to improve the stability of lithium manganate, that is, to suppress the elution of Mn, the reaction with the electrolyte, the release of oxygen, and the like.

In particular, when used in a high-temperature environment, both of these deteriorations are accelerated, which is a major obstacle to expanding applications. However, the charge / discharge capacity is limited because there are limited material systems that can be expected to satisfy the performance required for current high performance secondary batteries such as high electromotive force, voltage flatness during discharge, cycle characteristics, energy density, etc. There is a need for a new spinel lithium manganate that does not deteriorate and has excellent cycle and storage characteristics.

Various methods have been investigated as methods for improving these problems. For example, in Patent Document 1, when a material represented by the formula LixMn ₂ O ₄ and 1.025 ≦ x ≦ 1.185 is used as the positive electrode active material, Li of more than 1 is contained in the spinel. It is described that the cycle characteristics are improved because it is considered to be in the vacant oxygen tetrahedron.

In Patent Document 2, a hydrogen ion scavenger reacts with hydrogen ions (H ⁺ ) present in an organic electrolyte, and can effectively reduce the hydrogen ion concentration. It is described that the elution of Mn from manganese oxide and the change in Li concentration in the electrolytic solution are suppressed, so that the charge / discharge cycle, particularly the charge / discharge life at high temperatures, is greatly improved.

JP-A-2-270268 Japanese Patent No. 2996234

  However, although these disclosed techniques have certain effects, further improvements are required to improve long-term reliability. The charge / discharge characteristics of lithium-manganese composite oxide, particularly the cycle characteristics and capacity storage characteristics at high temperatures, may not always be satisfactory.

  Therefore, the present invention has been made in view of the above improvements, and is excellent in battery characteristics, particularly high-temperature cycle characteristics and storage characteristics, in which case the volume increase is small, and the heat dissipation is excellent during large current charge / discharge. An object of the present invention is to provide a film exterior laminated type lithium ion secondary battery.

  That is, the technical problem of the present invention is to provide a laminated lithium ion secondary battery having a laminate film that is excellent in high temperature cycle characteristics and storage characteristics, in which volume increase is small and heat dissipation is excellent. There is to do.

The lithium ion secondary battery of the present invention is a laminated lithium ion secondary battery having a laminate film as an outer package, and the positive electrode mixture is a part of manganese of lithium manganate having a spinel structure as an active material Chemical formula (1) in which is substituted with lithium, aluminum, magnesium and boron
_{Li 1 + x Mn 2-x} -y-z-γ Al y Mg z B γ O 4 ······· (1)
(0.02 ≦ x ≦ 0.08, 0.02 ≦ y ≦ 0.2, 0.02 ≦ z ≦ 0.1, 0.002 ≦ γ ≦ 0.1) and at least a hydrogen ion scavenger Chemical formula (2) having a layered structure containing nickel
LiNi _1-x M _x O ₂ (2)
(M includes at least one of Co, Mn, and Al, 0 ≦ x ≦ 2/3), and the weight ratio is represented by chemical formula (1): chemical formula (2) = (100−a): a (25 ≦ a ≦ 90).

  According to the present invention, it has become possible to provide a laminated lithium ion secondary battery having a laminate film that is excellent in high-temperature cycle characteristics and storage characteristics, in which volume increase is small and heat dissipation is excellent.

The schematic diagram which shows the structure of the lithium ion secondary battery of this invention. The figure which shows the X-ray-diffraction pattern of the positive electrode active material for lithium ion secondary batteries of this invention.

  An embodiment of the present invention will be described.

  The present inventors have scrutinized the prior art and made various studies in order to achieve the above object. As a result, the manganese (Mn) site of lithium manganate was changed to lithium (Li), aluminum (Al), magnesium. Li-rich lithium / manganese composite oxides with simultaneous substitution of (Mg) and boron (B) have specific charge / discharge characteristics, particularly charge / discharge capacity, by using composite oxides in a specific composition region of the oxides. Improved heat cycle characteristics, storage characteristics, and extremely large effects on the volume increase at that time, and improved heat dissipation by making a laminated lithium ion secondary battery with a laminate film as the outer package As a result, the present invention has been found.

  The positive electrode active material for a lithium ion secondary battery of the present invention includes an aluminum / magnesium / boron-containing lithium / manganese composite oxide represented by the chemical formula (1). It is thought that lithium and magnesium doped to bismuth stabilize the crystal by lowering the lattice constant of the spinel structure, and aluminum and boron have a stable trivalent oxidation degree to stabilize the structure. It is done.

  Furthermore, when a hydrogen ion scavenger is included in the chemical formula (1) which is the positive electrode active material for the lithium ion secondary battery of the present invention, the crystal structure is stabilized by lithium overdoping and aluminum / magnesium / boron substitution. As a result, the elution of manganese, reaction with the electrolyte, oxygen release, etc. are suppressed compared to conventional lithium-manganese composite oxides, so the effect of the hydrogen ion scavenger is longer than that of conventional lithium ion secondary batteries. Cycle characteristics and storage characteristics under high-temperature environments that are expected to be practical, improve the volume increase at that time, and increase the current capacity compared to conventional cylindrical batteries by using a laminated laminate film as an exterior body. A lithium ion secondary battery having excellent heat dissipation during discharge, improved high-rate cycle characteristics, light weight and high long-term reliability can be obtained.

  It is important to reduce the weight of the battery including the exterior body to increase the energy density, and it is very important as a power source for driving an electric vehicle or the like. It is extremely effective to use a laminate film rather than a metal can as a lightweight battery outer package.

  Also, the battery is more likely to rise in temperature when charging and discharging a large current than when charging and discharging at a low current, and there is a possibility that the battery characteristics deteriorate due to the temperature rise. In particular, it is an important problem in a battery used at a high rate, such as a hybrid vehicle (HEV), and is required to have high heat dissipation even during large current discharge. The structure of the power generation element composed of the positive electrode, the negative electrode, and the separator is generally a wound structure or a laminated structure, but the laminated structure has a lower heat resistance than the wound structure, and thus has excellent heat dissipation.

  FIG. 1 is a schematic diagram showing the configuration of the lithium ion secondary battery of the present invention. A layer 12 containing a positive electrode active material on the positive electrode current collector 11 and a layer 13 containing a negative electrode active material on the negative electrode current collector 14 are arranged to face each other with a separator 15 containing an electrolytic solution interposed therebetween.

  The lithium ion secondary battery of the present invention has a positive electrode using a positive electrode active material containing an aluminum / magnesium / boron-containing lithium / manganese composite oxide, and a negative electrode using a negative electrode active material capable of occluding and releasing lithium. A separator that does not cause electrical connection is sandwiched between the positive electrode and the negative electrode, and is immersed in a lithium ion conductive non-aqueous electrolyte, which is sealed in a laminate film.

  By applying a voltage to the positive electrode and the negative electrode, lithium ions are desorbed from the positive electrode active material, and the lithium ions are occluded in the negative electrode active material, resulting in a charged state. In addition, by connecting the positive electrode and the negative electrode to a device outside the battery for output, lithium ions are released from the negative electrode active material, and the lithium ion is occluded in the positive electrode active material, which is opposite to that during charging. .

(Positive electrode)
The positive electrode active material for a lithium ion secondary battery according to the present invention preferably contains an aluminum / magnesium / boron-containing lithium / manganese composite oxide represented by the chemical formula (1).

Next, a method for manufacturing the positive electrode active material will be described. As a raw material for producing the positive electrode active material, Li ₂ CO ₃ , LiOH, Li ₂ O, Li ₂ SO _{4 and the} like can be used as the Li raw material, but Li ₂ CO ₃ , LiOH, and the like are suitable. As the Mn raw material, various manganese oxides such as electrolytic manganese dioxide (EMD) · Mn ₂ O ₃ , Mn ₃ O ₄ , chemically synthesized manganese dioxide (CMD), MnCO ₃ , MnSO _{4 and the} like can be used.

As the Al raw material, Al ₂ O ₃ , AlCl ₃ , Al (OH) ₃ , Al ₂ (SO ₄ ) ₃ , Al ₂ (CO ₃ ), Al (NO ₃ ) _3, or the like can be used. As the Mg raw material, MgO, Mg (OH) ₂ , MgCl ₂ , Mg (NO ₃ ) ₂ , Mg ₃ (PO ₄ ) ₂ , MgCO _3, etc. can be used. As the B raw material, B ₂ O ₃ , H ₃ BO ₃ , a lithium boron compound, orthoboric acid, boron oxide, boron phosphate, or the like can be used.

  Mn raw materials and substitutional element raw materials may hardly cause element diffusion during firing, and Mn oxides and substitutional element oxides may remain as different phases after firing the raw materials. For this reason, Mn raw material, Al raw material, Mg raw material, B raw material are dissolved and mixed in an aqueous solution, and then precipitated in the form of hydroxide, sulfate, carbonate, nitrate, etc. A mixture of Al, Mg, B, and Mn containing a substitution element can be used as a raw material. It is also possible to use Al, Mg, B, Mn oxide or Al, Mg, B, Mn mixed oxide obtained by firing such a mixture.

  When such a mixture is used as a raw material, Mn, Al, Mg, and B are well diffused at the atomic level, and Al, Mg, and B can be easily introduced into the 16d site of the spinel structure.

  These raw materials are weighed and mixed so as to have a target metal composition ratio. The mixing is performed by pulverizing and mixing with a ball mill, a jet mill or the like. The mixed powder is fired in air or oxygen at a temperature of 600 ° C. or higher and 950 ° C. or lower to obtain a positive electrode active material containing an aluminum / magnesium / boron-containing lithium / manganese composite oxide.

  The firing temperature is desirably high for diffusing each element, but if the firing temperature is too high, oxygen deficiency may occur, which may adversely affect battery characteristics. Therefore, the firing temperature is particularly preferably 650 ° C. or higher and 850 ° C. or lower. A positive electrode active material synthesized by a liquid system method such as a sol-gel process or hydrothermal synthesis can also be used in the same manner if the final composition is a predetermined one.

The specific surface area of the obtained aluminum / magnesium / boron-containing lithium / manganese composite oxide is preferably 0.01 m ² / g or more and 10 m ² / g or less. And a specific surface area of 0.01 m 2 / ^g less, there is a possibility that the charge-discharge characteristics inferior for insertion and desorption of Li from the positive electrode active material is inhibited, and the specific surface area is greater than 10 m 2 / ^g, the binder This is because a large amount of the agent is necessary and there is a risk that it may be disadvantageous in terms of the capacity density of the positive electrode active material. More preferably 0.05 m ² / g or more, or less ^2m 2 / g.

  The positive electrode for a lithium ion secondary battery of the present invention preferably contains a lithium / nickel composite oxide having a layered structure containing at least nickel represented by the chemical formula (2) as a hydrogen ion scavenger.

The lithium / nickel composite oxide may be, for example, LiNi _0.8 Co _0.2 O ₂ . These materials are considered to have an effect of capturing hydrogen ions generated in the electrolytic solution, and have an effect of improving battery life.

The hydrogen ion scavenger is not limited to the lithium / nickel composite oxide, but may react with hydrogen ions (H ⁺ ) present in the organic electrolyte solution to reduce the hydrogen ion concentration. There is no particular limitation, and any hydrogen ion scavenger can be used. Moreover, if it can function also as an electrode material, it can mix with said positive electrode active material, and can comprise the electrode excellent in electroconductivity.

  In the positive electrode active material of the present invention, the effect of the hydrogen ion scavenger is more remarkable than the conventional lithium manganese oxide due to the simultaneous substitution of excess lithium and aluminum / magnesium / boron. It is considered that elution of Mn from the boron-containing lithium manganese oxide is suppressed, and the high-temperature cycle characteristics and the storage characteristics are further improved.

  This hydrogen ion scavenger may be either an inorganic compound or an organic compound. Examples thereof include lithium / nickel composite oxides, hydrogen storage alloys, and carbon that can store hydrogen. These can be used in powder form.

  When the electrolyte contains a composition that can react with water to generate hydrogen ions, combined with a technology that improves the cycle characteristics and storage characteristics at high temperatures by placing a hydrogen ion scavenger at the place in contact with the electrolyte in the battery In addition, each characteristic improvement effect can be obtained synergistically. This is because the presence of the hydrogen ion scavenger causes various actions such as reducing the concentration of hydrogen ions in the secondary battery, and suppresses the decomposition and deterioration of the electrolyte. As a result, the cycle characteristics of the secondary battery at high temperatures This is because the storage characteristics can be improved.

  In the above-described positive electrode for a lithium ion secondary battery, the content of the aluminum / magnesium / boron-containing lithium / manganese composite oxide in the positive electrode is (100-a) parts by mass, and the lithium / nickel composite oxide When the content is a part by mass, this a preferably satisfies 25 ≦ a ≦ 90.

  Regarding the composition ratio of the aluminum-magnesium-boron-containing lithium-manganese composite oxide and the lithium-nickel composite oxide, if a is less than 25 or greater than 90, the cycle characteristics and storage characteristics of the lithium ion secondary battery at high temperature This is because there is a possibility that the ratio is not improved or the volume increase rate is large.

  The method for producing the positive electrode is not particularly limited. For example, a powder of lithium / manganese composite oxide containing aluminum / magnesium / boron and a powder of lithium / nickel composite oxide together with a conductivity-imparting agent and a binder are used. Is mixed with a suitable dispersion medium capable of dissolving (slurry method), coated on a current collector such as an aluminum foil, dried after the solvent is dried, and then compressed by a press or the like to form a film.

  In addition, there is no restriction | limiting in particular as an electroconductivity imparting agent, Carbon black, acetylene black, natural graphite, artificial graphite, carbon fiber, etc. can be used. As the binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like can be used.

  The addition amount of the conductivity imparting agent is preferably 1% by weight or more and 10% by weight or less with respect to the weight of the mixture, and the addition amount of the binder is also 1% by weight or more and 10% by weight with respect to the weight of the mixture. It is preferable that: This is because when the conductivity-imparting agent and the binder exceed 10% by weight, the proportion of the positive electrode active material for the lithium ion secondary battery is decreased, and the capacity per weight may be decreased. This is because if the conductivity-imparting agent and the binder are less than 1% by weight, the conductivity may not be maintained or a problem of electrode peeling may occur.

Moreover, it is preferable that the density of the mixture which comprises the formed lithium ion secondary battery positive electrode except the collector is 2.5 g / cm ³ or more and 3.5 g / cm ³ or less. This is because if the density of the mixture is less than 2.5 g / cm ³ or more than 3.5 g / cm ³ , the discharge capacity during use at a high discharge rate may decrease.

(Negative electrode)
The negative electrode active material is made of a material that can occlude and release lithium, such as lithium metal, silicon-based material, tin-based material, transition metal-containing oxide, or carbon material. As the carbon material, graphite storing lithium, amorphous carbon, diamond-like carbon, fullerene, carbon nanotube, carbon nanohorn, or a composite thereof can be used.

  When lithium metal is used as the negative electrode active material, a melt cooling method, a liquid quenching method, an atomizing method, a vacuum deposition method, a sputtering method, a plasma CVD method, a photo CVD method, a thermal CVD method, a sol-gel method, etc. Thus, a layer containing the negative electrode active material can be obtained. In the case of carbon materials, carbon and a binder such as polyvinylidene fluoride (PVDF) are mixed and dispersed and kneaded in a solvent such as N-methyl-2-pyrrolidone (NMP). The layer containing the negative electrode active material can be obtained by a method such as coating on a current collector such as copper foil or a method such as a vapor deposition method, a CVD method, or a sputtering method.

(Current collector)
Aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used as the positive electrode current collector, and copper, stainless steel, nickel, titanium, or an alloy thereof can be used as the negative electrode current collector.

(Separator)
As the separator, a woven fabric, a nonwoven fabric, a porous film, or the like can be used. In particular, a polypropylene or polyethylene-based porous film is preferably used in terms of a thin film and a large area, film strength and film resistance.

  Solvents for the electrolyte include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate. (EMC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-di Chain ethers such as ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethyl Formamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- Aprotic organic solvents such as oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, and fluorinated carboxylic acid esters can be used singly or in combination. . Of these, propylene carbonate, ethylene carbonate, γ-butyl lactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate and the like are preferably used alone or in combination.

A lithium salt is dissolved as a supporting salt in these organic solvents. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO _{2) 2, LiN (C 2} F 5 SO 2) 2, LiB 10 Cl 10, lithium lower aliphatic carboxylic acids, chloroborane lithium, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, and imides like . Further, a polymer electrolyte may be used instead of the electrolytic solution, or an ionic liquid containing a quaternary ammonium salt or the like may be used.

  The electrolyte concentration is preferably 0.5 mol / L or more and 1.5 mol / L. This is because if the concentration is lower than 0.5 mol / L, the electrical conductivity decreases, and if the concentration is higher than 1.5 mol / L, the density and the viscosity may increase.

  In the lithium ion secondary battery according to the present invention, in a dry air or inert gas atmosphere, a negative electrode and a positive electrode are laminated through a separator, and then inserted into a laminate film, impregnated with an electrolytic solution, and the laminate film is sealed. It is obtained by stopping.

  As the outer package of a lithium ion secondary battery, a laminate film characterized by being lighter than a metal can and excellent in heat dissipation is used. It is preferable in terms of heat dissipation.

  Examples of the present invention will be described in detail below, but the present invention is not limited to the following examples.

(Synthesis of positive electrode active material)
First, lithium carbonate (Li ₂ CO ₃ ) pulverized and classified to an average particle size of 5 μm or less, manganese oxide (Mn ₂ O ₃ ), aluminum hydroxide (Al (OH) ₃ ) pulverized and classified to an average particle size of 10 μm or less. ), Magnesium hydroxide (Mg (OH) ₂ ), and boron oxide are prepared in a predetermined ratio, mixed for 2 hours by a planetary ball mill, the mixture is put in a crucible, Primary firing was performed at a temperature of 0 ° C.

  The primary fired product was crushed and remixed, followed by secondary firing at 600 ° C. in air. Next, the obtained fired product was pulverized using an Ishikawa-type Reika machine to obtain an aluminum / magnesium / boron-containing lithium / manganese composite oxide having an average particle size of 10 μm.

  FIG. 2 is a diagram showing an X-ray diffraction pattern of the positive electrode active material for a lithium ion secondary battery of the present invention.

This is the result of X-ray diffraction measurement of the obtained powdered positive electrode active material using CuKα rays. FIG. 2 shows Li _1.02 (Mn _1.938 Al _0.02 Mg _{0.02) used} as the positive electrode active material in Example 1. B _0.002 ) shows the X-ray diffraction pattern of O ₄ .

  This positive electrode active material belongs to the space group Fd3m, and a diffraction pattern that can be indexed in the space group Fd3m is obtained by matching the peak in FIG. 2 with the peak of Fd3m, and as a result of detailed verification, It was confirmed that the synthesized powder had no spinel structure and basically had a spinel structure.

(Preparation of laminated laminate film exterior lithium ion secondary battery)
In the N-methyl-2-pyrrolidone (NMP) in which the obtained powdered positive electrode active material, LiNi _0.8 Co _0.02 O ₂ and a conductivity-imparting agent were dry-mixed to dissolve polyvinylidene fluoride (PVDF) as a binder The slurry was uniformly dispersed in the slurry. Carbon black was used as the conductivity imparting agent.

The slurry was applied on an aluminum metal foil (thickness 20 μm) serving as a positive electrode current collector, and NMP was evaporated to prepare a positive electrode having a thickness of 85 μm. The solid content ratio in the positive electrode was positive electrode active material: LiNi _0.8 Co _0.2 O ₂ : conductivity imparting agent: PVDF = 67.5: 22.5: 4: 6 (mass%). The solid content ratio in the negative electrode was mixed so as to be a ratio of carbon: PVDF = 90: 10 (mass%), dispersed in NMP, and coated on a copper foil (thickness 10 μm) serving as a negative electrode current collector. A negative electrode having a thickness of 47 μm was produced.

  The negative electrode was cut into a shape in which a negative electrode active material layer of 30 mm × 14 mm and a current collector of 5 mm × 5 mm extended to the right short side thereof. Similarly, the positive electrode was cut into a shape in which a positive electrode active material layer of 28 mm × 13 mm and a current collector of 5 mm × 5 mm extended to the left short side portion thereof. The separator was cut into a shape of 4 mm × 3 mm on one long side portion of the separator as a separator convex portion of 32 mm × 16 mm. Six, five, and ten negative electrodes, positive electrodes, and separators were prepared, and the negative electrode and the positive electrode were sequentially laminated via the separator so that the upper and lower outermost layers of the laminate were negative electrodes.

  Further, the uncoated portions of the positive electrode and the uncoated portions of the negative electrode overlap each other so that the positive electrode current collector is positioned on the left side of the laminate and the negative electrode current collector is positioned on the right side. A tab with an aluminum sealant having a width of 5 mm, a length of 20 mm, and a thickness of 0.1 mm is used as a positive electrode current collector, a tab with a nickel sealant of the same size is used as a negative electrode current collector, a tab, a current collector, and a current collector. They were integrated by ultrasonic welding so that they were electrically connected to each other.

Next, an aluminum laminate film made of 70 mm × 70 mm polypropylene and aluminum foil with a thickness of 125 μm was folded in two as a battery outer package, the laminate was inserted, and the sides except one side for injecting the electrolyte were bonded by thermal fusion. . An electrolyte solution using 1 mol / L LiPF ₆ as an electrolyte was injected and impregnated under reduced pressure, and then the opening was vacuum sealed to produce a laminated laminate type lithium ion secondary battery. .

(Evaluation of high-temperature characteristics of laminated laminate film-coated lithium-ion secondary battery)
High-temperature cycle characteristics were evaluated using the produced laminated laminate type lithium ion secondary battery. The conditions for cycle evaluation were a charge rate of 1.0 C, a discharge rate of 1.0 C, a charge end voltage of 4.2 V, and a discharge end voltage of 3.0 V at a temperature of 60 ° C. The capacity retention rate (%) was a value obtained by dividing the discharge capacity (mAh) after 1000 cycles by the discharge capacity (mAh) at the 10th cycle. The volume increase rate was a value obtained by dividing the volume after 1000 cycles by the volume at the 10th cycle, and the volume was measured by the Archimedes method.

  In addition, the storage characteristics were evaluated using the produced laminated laminate type lithium ion secondary battery. At a temperature of 20 ° C., the battery was charged to 4.2 V at a charge rate of 0.5 C. After reaching 4.2 V, the battery was charged by constant voltage charging for 2 hours and discharged to 3.0 at a discharge rate of 0.1 C. Thereafter, the battery was charged under the same conditions, discharged at 0.1 C to a depth of discharge (DOD) of 60%, and allowed to stand at a temperature of 60 ° C. for 12 weeks, and the capacity was measured under the same charge / discharge conditions. A value obtained by dividing the discharge capacity after storage by the discharge capacity before storage was defined as a capacity recovery rate. The volume increase rate was a value obtained by dividing the volume after storage by the volume before storage, and the volume was measured by the Archimedes method.

  Tables 1 to 4 do not contain at least one of the aluminum element amount y, the magnesium element amount z, and the boron element amount γ of the chemical formula (1), which is the positive electrode active material, and the ratio is changed. About Example 1-148, the result of a high temperature cycling characteristic and a storage characteristic is shown.

  In Tables 5 to 7, all of the aluminum element amount y, the magnesium element amount z, and the boron element amount γ of the chemical formula (1) as the positive electrode active material are contained, and the proportion of the content was changed. About 16 and Comparative Examples 149 to 240, the results of the high-temperature cycle characteristics and the storage characteristics are shown.

  Among the results in Tables 5 to 7, when the results were better than all the results in Tables 1 to 4, it was judged that the high temperature cycle characteristics and the storage characteristics were excellent. That is, the capacity retention rate of the high-temperature cycle characteristics exceeds 55.4% (Comparative Examples 43 and 56), the volume increase rate is less than 8.3% (Comparative Examples 80, 82 and 102), and the capacity recovery of the storage characteristics When the rate exceeded 58.1% (Comparative Example 54) and the volume increase rate was less than 6.8% (Comparative Example 148), it was judged that the high temperature cycle characteristics and the storage characteristics were excellent.

  Examining Tables 5 to 7, Li amount x is 0.02 or more and 0.08 or less, Al amount y is 0.02 or more and 0.2 or less, Mg amount z is 0.02 or more and 0.10 or less, It was found that the high temperature cycle characteristics and the storage characteristics were good when the B content γ was 0.002 or more and 0.10 or less.

  Laminated laminate type lithium produced using a positive electrode obtained by mixing lithium manganese oxide and a nickel-containing lithium layered compound, which is a positive electrode active material of Example 7 in which lithium excess of the present invention and aluminum, magnesium, and boron are simultaneously substituted Laminate laminate prepared using an ion secondary battery and a positive electrode obtained by mixing lithium manganese oxide and a nickel-containing lithium layered compound, which are positive electrode active materials of Comparative Example 1 in which lithium excess, aluminum / magnesium / boron are not substituted The capacity retention rate and the volume increase rate of the cycle characteristics after 1000 cycles of the lithium ion secondary battery of the type, and the capacity recovery rate and the volume increase rate of the storage characteristics after storage at DOD 60%, temperature 60 ° C. for 12 weeks were investigated.

Here, along with changing the weight ratio of LiNi _0.8 Co _0.2 O ₂ is the compound nickel-containing lithium layer were investigated with storage characteristics high-temperature cycle characteristics by changing the type of nickel-containing lithium layered compound. The survey results are shown in Table 8.

  When Example 7 and Comparative Example 1, Example 17 and Comparative Example 246, and Example 18 and Comparative Example 247 are compared, the capacity retention rate of the high-temperature cycle characteristics is higher in each Example than in each Comparative Example. It was found that the volume increase rate was low, the capacity recovery rate of the storage characteristics was high, and the volume increase rate was low.

  As a result, the positive electrode active material of the present invention has a lithium ion, aluminum, magnesium, and boron substituted at the same time, so that the effect of the hydrogen ion scavenger is more remarkable than the conventional lithium manganese oxide. -As a result of suppressing the elution of Mn from the magnesium-boron-containing lithium manganese oxide, it is considered that the high-temperature cycle characteristics and the storage characteristics were further improved.

  Among the results in Table 8, when the results were better than all the results in Tables 1 to 4, it was judged that the high temperature cycle characteristics and the storage characteristics were excellent. That is, the capacity retention rate of the high-temperature cycle characteristics exceeds 55.4% (Comparative Examples 43 and 56), the volume increase rate is less than 8.3% (Comparative Examples 80, 82 and 102), and the capacity recovery of the storage characteristics When the rate exceeded 58.1% (Comparative Example 54) and the volume increase rate was less than 6.8% (Comparative Example 148), it was judged that the high temperature cycle characteristics and the storage characteristics were excellent.

  From the results of Table 8, it was found that the weight ratio of the nickel-containing lithium layered compound was particularly good at 25% or more and 90% or less.

It was found that when the amount of LiNi _0.8 Co _0.2 O ₂ was less than 25% or more than 95%, the volume increase rate of the storage characteristics was increased. Further, it was found that nickel-containing lithium layered compounds other than LiNi _0.8 Co _0.2 O ₂ have good high-temperature cycle characteristics and storage characteristics other than LiCoO _{2 of} Comparative Example 249. By mixing a nickel-containing lithium layered compound represented by the chemical formula LiNi _1-x M _x O ₂ (M is at least one of Co, Mn, and Al, 0 ≦ x ≦ 2/3) The properties and storage properties were found to be good.

  Using the same electrode active material and electrode composition as in Example 7, a 18650 type cylindrical battery in which the structure of the power generation element was a wound type and the outer package was an aluminum can was produced as Comparative Example 250. The batteries of Example 7 and Comparative Example 250 were charged to 4.2 V at a charging rate of 0.5 C at a temperature of 20 ° C., and after reaching 4.2 V, charging was performed by performing constant voltage charging for 2 hours, with a discharge rate of 10 C. Was measured with a thermograph when discharged to 3.0V. Further, the capacity retention rate of the cycle characteristics after 1000 cycles was measured at a temperature of 20 ° C. with a charge rate of 5.0 C, a discharge rate of 5.0 C, a charge end voltage of 4.2 V, and a discharge end voltage of 3.0 V.

  The capacity retention rate (%) is a value obtained by dividing the discharge capacity (mAh) after 1000 cycles by the discharge capacity (mAh) at the 10th cycle. Table 9 shows the relationship between the temperature rise at the time of 10 C discharge and the capacity retention rate of the cycle characteristics of the battery of Example 7 and the battery in which the power generation element structure and the exterior body are changed.

  Table 9 shows that a lithium ion secondary battery with a laminated laminate film using lithium manganese oxide in which lithium excess of the present invention is simultaneously substituted with aluminum, magnesium, and boron and a 18650 cylindrical lithium ion secondary battery are compared. It was found that the film exterior laminate type lithium ion secondary battery had a low temperature rise during 10 C discharge and a high capacity retention rate of cycle characteristics.

  From this, it was found that when the structure of the power generation element is a laminate type and the exterior body is a laminate film, the heat dissipation is excellent and the capacity retention rate of cycle characteristics is high.

  From the results of the examples, it is possible to provide a laminated lithium ion secondary battery having an outer package made of a laminate film that is excellent in high-temperature cycle characteristics and storage characteristics, and has a small volume increase rate and excellent heat dissipation. I understood it.

  In the above, this invention was demonstrated based on the Example. This is merely an example, and it will be understood by those skilled in the art that various modifications are possible and that such modifications are within the scope of the present invention.

11 Positive Electrode Current Collector 12 Layer Containing Positive Electrode Active Material 13 Layer Containing Negative Electrode Active Material 14 Negative Electrode Current Collector 15 Separator Containing Electrolyte

Claims (1)

A laminated lithium ion secondary battery with a laminate film as the outer package, where the positive electrode mixture is replaced with lithium, aluminum, magnesium, and boron, part of the manganese in the lithium manganate having the spinel structure as the active material Chemical formula (1)
_{Li 1 + x Mn 2-x} -y-z-γ Al y Mg z B γ O 4 ······· (1)
(0.02 ≦ x ≦ 0.08, 0.02 ≦ y ≦ 0.2, 0.02 ≦ z ≦ 0.1, 0.002 ≦ γ ≦ 0.1) and at least a hydrogen ion scavenger Chemical formula (2) having a layered structure containing nickel
LiNi _1-x M _x O ₂ (2)
(M includes at least one of Co, Mn, and Al, 0 ≦ x ≦ 2/3), and the weight ratio is represented by chemical formula (1): chemical formula (2) = (100−a): a A lithium ion secondary battery characterized by being (25 ≦ a ≦ 90).

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