JP4085243B2 - Non-aqueous secondary battery - Google Patents

Description

【００６３】
表１に示す結果から明らかな様に、実施例１および２において製造した電池は、サイクル特性に優れ、且つ高い安全性を示した。
【００６４】
実施例において製造した電池は、十分な電池容量を示すと共に、電解液の分解によるものと推測される充放電効率の低下が実質的に抑制され、負極活物質中の黒鉛構造の破壊も防止される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous secondary battery.
[0002]
[Prior art]
In recent years, in the field of small-sized secondary batteries for portable devices, nickel hydride batteries, lithium secondary batteries, etc. have been rapidly developed to meet the conflicting needs of miniaturization and high capacity, for example, 180 Wh / l. Batteries having the above volume energy density are commercially available. In particular, lithium ion batteries have the potential to achieve a volume energy density exceeding 350 Wh / l, and are more reliable in terms of safety and cycle characteristics than lithium secondary batteries that use metallic lithium as the negative electrode. Because of its superiority, its market is expanding dramatically.
As a positive electrode active material of such a lithium ion battery, a material having an electromotive force exceeding 4 V, such as a lithium cobalt composite oxide, a lithium nickel composite oxide, or a lithium manganese composite oxide, is used. Among these, lithium cobalt composite oxides that are excellent in battery characteristics and easy to synthesize are currently used in the largest amount.
[0003]
However, since cobalt, which is a raw material, has a small recoverable reserve and is expensive, the use of lithium nickel composite oxide as an alternative material has been studied. The lithium nickel composite oxide has a layered rock salt structure like the lithium cobalt composite oxide, and is a high capacity material exceeding 200 mAh / g.
[0004]
However, lithium-nickel composite oxide is produced by Ni ⁴⁺ Oxygen desorption from the crystal lattice due to the chemical instability and the unstable structure of the lithium-nickel composite oxide in a highly charged state where a large amount of lithium is extracted from the structure. There is a problem that the separation start temperature is low. For example, Solid State Ionics, 69, No. 3/4, 265 (1994) reports that “the start of oxygen desorption of lithium nickel composite oxide in the charged state is lower than that of conventional lithium cobalt oxide”. Has been. For these reasons, a battery using a lithium nickel composite oxide alone as a positive electrode active material has a problem in terms of thermal stability in a high charge state even though a high capacity can be obtained. It has not been put to practical use until now because sufficient properties cannot be secured.
On the other hand, since lithium manganese composite oxide has a spinel crystal structure, it is structurally different from lithium cobalt composite oxide and lithium nickel composite oxide having a layered rock salt structure. Due to the difference in structure, the oxygen desorption start temperature in the high charge state of the lithium manganese composite oxide is higher than that of the lithium cobalt composite oxide and the lithium nickel composite oxide. That is, the lithium manganese composite oxide is a highly safe positive electrode material.
However, a lithium secondary battery using a lithium-manganese composite oxide as a positive electrode causes so-called “capacity deterioration” in which the capacity is gradually reduced by repeated charge and discharge. For this reason, its practical use has been difficult.
Generally, lithium ion batteries are required to have safety and excellent cycle life. However, a battery using a lithium nickel composite oxide as a positive electrode active material has a problem in that it lacks thermal stability during high charge. In addition, although the battery using lithium manganese composite oxide is highly safe, (1) it is difficult to achieve both high energy density (high charge / discharge capacity) and high cycle life, and (2) self-discharge. There are two problems that the storage capacity decreases.
First, in a battery using a lithium-manganese composite oxide, the reasons why high capacity cannot be realized include non-uniform reaction during composite oxide synthesis and the influence of mixed impurities. In addition, as a cause of capacity deterioration due to charge / discharge cycles, the average valence of Mn ions changes between trivalent and tetravalent as charge compensation accompanying Li in / out, and therefore the Jahn-Teller strain is crystallized. That occurs in, that Mn from the lithium manganese composite oxide is eluted, that the eluted Mn is precipitated on the negative electrode active material or on the separator, and further, the influence of impurities, The inactivation due to the release of the active material particles, the influence of the acid generated in the electrolyte due to the water content, and the deterioration of the electrolyte due to the release of oxygen from the lithium manganese composite oxide are considered. When a spinel single phase is formed, the cause of elution of Mn is that trivalent Mn in the spinel structure is easily dissolved in the electrolytic solution by partially disproportionating to tetravalent and divalent It may be shaped, or it may be eluted due to the relative shortage of Li ions. As a result, generation of irreversible capacity due to repeated charge and discharge, and disorder of atomic arrangement in the crystal are promoted, and eluted Mn ions are deposited on the negative electrode or separator, preventing the movement of Li ions. Guessed. In addition, the lithium manganese composite oxide is distorted by the Jahn-Teller effect and is expanded and contracted by several% of the unit cell length by taking in and out Li ions. Therefore, by repeating the charge / discharge cycle, it is assumed that the particles do not function as an active material due to partial electrical isolation of the particles.
Furthermore, it is considered that the release of oxygen from the lithium manganese composite oxide becomes easier with the elution of Mn. When the amount of released oxygen increases, it is presumed that the decomposition of the electrolytic solution is promoted, and it is presumed that the charge / discharge cycle deterioration due to the deterioration of the electrolytic solution also occurs.
Realizing such suppression of Mn elution, reduction of lattice distortion, reduction of oxygen vacancies, etc. is important in improving the cycle characteristics of lithium batteries. Japanese Patent Laid-Open No. 2-270268 proposes to improve the cycle characteristics by making the composition of Li sufficiently excessive with respect to the stoichiometric ratio. Furthermore, a proposal has been made to improve the cycle characteristics by replacing a part of the Mn element of the lithium manganese composite oxide with addition or doping of Co, Ni, Fe, Cr, Al or the like (Japanese Patent Laid-Open No. 4-141954). JP, 4-160758, JP-A-4-69076, JP-A-4-237970, JP-A-4-825560, JP-A-4-89662, etc.). These techniques such as excessive Li composition and addition of metal elements are effective in improving cycle characteristics, but conversely are accompanied by a reduction in charge / discharge capacity, so both high cycle life and high capacity are satisfied. It has not reached.
[0005]
As a negative electrode active material for small batteries, Japanese Patent Application Laid-Open Nos. 57-208079 and 63-24555 are excellent in flexibility and have no risk of lithium being deposited in a dendritic shape during a charge / discharge cycle. Proposes graphite. Currently, graphite-based materials such as natural graphite, artificial graphite, graphite with reduced impurities by acid treatment, mesocarbon microbeads, and graphitized carbon fiber have the property of forming intercalation compounds based on a unique layer structure. As a secondary battery electrode material utilizing this property, it has been put to practical use. Furthermore, the use of materials with low crystallinity has also been proposed. For example, JP-A-63-24555 discloses various carbon materials having a turbostratic structure and selective orientation obtained by thermally decomposing hydrocarbons in the gas phase in order to suppress decomposition of the electrolyte. is doing.
[0006]
However, these highly crystalline materials have advantages and disadvantages.
[0007]
It is known that when a highly crystalline carbon material typified by graphite is used as the negative electrode material, theoretically, the change in potential associated with insertion and extraction of lithium is reduced, and the capacity usable as a battery is increased. It has been.
[0008]
However, as the crystallinity of the carbon material increases, the charge / discharge efficiency, which is believed to be associated with the decomposition of the electrolyte, is reduced, and the carbon material is destroyed due to the expansion / contraction of the crystal that accompanies repeated charge / discharge. To.
[0009]
Moreover, when these graphite-type carbon materials are used for a negative electrode and the positive electrode containing lithium manganese complex oxide with high safety | security is used, cycle capacity falls significantly. This phenomenon is remarkable when the utilization factor of the negative electrode active material is 255 mAh per 1 g of the active material. The cause of this is not clear, but the graphite-based material has a low potential during charging / discharging, so manganese eluate present in the electrolyte during charging / discharging deposits on the surface, and is involved in decomposition of the electrolyte, gas generation, etc. It seems to be.
[0010]
[Problems to be solved by the invention]
The present invention has been made in view of the problems of the prior art, and has as its main object to provide a non-aqueous secondary battery having a long cycle life and excellent safety.
[0011]
[Means for Solving the Problems]
As a result of conducting research while paying attention to the current state of the technology as described above, the present inventor succeeded in achieving the above object by using a specific active material or the like.
That is, the present invention relates to the following non-aqueous secondary battery.
1. In a nonaqueous secondary battery in which a nonaqueous electrolyte containing a positive electrode, a negative electrode, and a lithium salt is contained in a battery container, the positive electrode active material in the positive electrode is a mixture composed of a lithium manganese composite oxide and a lithium nickel composite oxide. And the negative electrode active material in the negative electrode is an amorphous carbon layer having a surface spacing of (002) planes (d002) of 0.34 nm or less by an X-ray wide angle diffraction method with a surface spacing of 0.34 nm or more. A non-aqueous secondary battery comprising at least double-structured graphite particles coated with lithium and storing lithium at 200 mAh to 255 mAh per gram of negative electrode active material when fully charged.
2. 2. The nonaqueous secondary battery according to 1 above, wherein the negative electrode active material further contains graphitized mesocarbon microbeads.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
In the nonaqueous secondary battery of the present invention, a mixture of a lithium manganese composite oxide and a lithium nickel composite oxide is used as the positive electrode active material.
[0013]
As the lithium manganese composite oxide used in the present invention, for example, lithium manganese composite oxide (LiMn ₂ O _Four ), A composite oxide obtained by adding at least one dissimilar metal element to a lithium manganese composite oxide (Li _{1 + a} Mn _2-ab MA _b O _Four ), Lithium manganese composite oxide (Li _{1 + x} Mn _2-x O _Four ) And the like.
[0014]
Lithium manganese complex oxide with at least one dissimilar metal element added (Li _{1 + a} Mn _2-ab MA _b O _Four ), MA in the formula represents a dissimilar metal element. As MA, for example, Al, Mg, Cr, Fe, Co, Ni and the like can be exemplified, and among these, Al, Mg, Cr and the like are preferable. The value of a in the above formula is usually about 0.01 to 0.2, preferably about 0.03 to 0.15. The value of b in the above formula is usually about 0.01 to 0.2, preferably about 0.03 to 0.15.
[0015]
Lithium manganese composite oxide Li containing lithium in excess of the stoichiometric ratio _{1 + x} Mn _2-x O _Four In the formula, x in the formula is usually about 0.01 to 0.2, preferably about 0.03 to 0.15.
[0016]
As the lithium nickel composite oxide used in the present invention, for example, a composite oxide obtained by adding at least one different metal element to a lithium nickel composite oxide (LiNi _1-c MB _c O ₂ ) And the like.
[0017]
Lithium nickel composite oxide with at least one different metal element added (LiNi _1-c MB _c O ₂ ), MB represents a different metal element. Examples of MB include Co, Al, Mn, and the like. C in the formula is usually about 0.01 to 0.5, preferably about 0.1 to 0.3.
[0018]
The proportion of the lithium manganese composite oxide in the mixture used as the positive electrode active material in the present invention is usually 70 to 95 when the total of the lithium manganese composite oxide and the lithium nickel composite oxide is 100 parts by weight. About part by weight, preferably about 70 to 85 parts by weight. The proportion of the lithium nickel composite oxide is usually about 5 to 30 parts by weight, preferably about 15 to 30 parts by weight when the total of the lithium manganese composite oxide and the lithium nickel composite oxide is 100 parts by weight. It is. By setting it within the above range, it is possible to more reliably obtain an effect of improving the capacity and cycle characteristics, and it is possible to obtain a more stable battery.
[0019]
The average particle diameter of the positive electrode active material is not particularly limited, and can be approximately the same as the particle diameter of the conventional active material. The average particle diameter of the positive electrode active material is usually about 1 to 60 μm, preferably about 5 to 40 μm, more preferably about 10 to 30 μm. In the present specification, the “average particle size” means the center particle size in the volume particle size distribution obtained by the dry laser diffraction measurement method.
[0020]
The specific surface area of the positive electrode active material is not particularly limited, but is usually 1 m ² / g or less, more preferably 0.2 to 0.7 m ² It is about / g. In the present specification, “specific surface area” refers to a value measured by the BET method using nitrogen gas.
[0021]
The negative electrode active material used in the present invention includes at least double-structure graphite particles in which the surface of the core portion made of graphite particles is coated with amorphous carbon. That is, only the double structure graphite particles may be used as the negative electrode active material, or a mixture of the double structure graphite particles and other components may be used as the negative electrode active material. For example, a mixture of the double-structured graphite particles and graphitized mesocarbon microbeads can be exemplified.
[0022]
The graphite particles that are the core of the double-structured graphite particles have a (002) plane spacing (d002) of about 0.34 nm or less, more preferably about 0.3354 to 0.338 nm, more preferably about 0.3354 to 0.338 nm. Preferably, it is about 0.3354 to 0.336 nm. When this value is too large, the crystallinity of the core portion becomes low, so that the potential change accompanying the release of lithium ions becomes large, and the effective capacity that can be used as a battery becomes low.
[0023]
The interplanar spacing of the amorphous carbon layer covering the graphite-based particle core is such that the interplanar spacing (d002) of the (002) plane by X-ray wide angle diffraction method exceeds 0.34 nm, more preferably 0.34 nm More than 0.38 nm, more preferably more than 0.34 nm and not more than 0.36 nm. If this value in the coating layer is too small, the crystallinity is too high, resulting in a decrease in charge / discharge efficiency presumed to be due to the decomposition of the electrolyte solution, and expansion of the interplanar spacing of crystals due to repeated charge / discharge / Shrinking increases the risk of destruction of the carbon material. On the other hand, when the surface interval (d002) of the (002) plane is too large, lithium ions are difficult to move, and the capacity that can be used as a battery is reduced. The production method of the double structure graphite particles used in the present invention is not particularly limited, and for example, a known method described in WO97 / 18160 or the like can be used.
[0024]
In the graphitized mesocarbon microbeads, the distance between both surfaces (d002) of the (002) plane by the X-ray wide angle diffraction method is usually less than about 0.34 nm, more preferably about 0.3354 to 0.338 nm, and still more preferably 0.3354 to It is about 0.336 nm. The method for producing graphitized mesocarbon microbeads is not particularly limited, and for example, a known method such as the method described in JP-A-9-151382 can be used.
[0025]
When a mixture of double structure graphite particles and graphitized mesocarbon microbeads (MCMB) is used as the negative electrode active material, the mixing ratio is not particularly limited. When the total of the double structure graphite particles and the graphitized mesocarbon microbeads is 100 parts by weight, the double structure graphite particles are usually about 50 to 95 parts by weight, and preferably about 60 to 80 parts by weight. When MCMB is included, adhesion to the current collector is improved, so that the amount of binder used can be reduced. As a result, the battery capacity can be increased. By setting the amount of MCMB to be in the above range, the battery capacity can be increased more reliably.
[0026]
The average particle diameter of the negative electrode active material is not particularly limited, and can be the same as, for example, the particle diameter of a conventional active material. The average particle size is usually about 1 to 60 μm, preferably about 5 to 40 μm, more preferably about 10 to 30 μm.
[0027]
The specific surface area of the negative electrode active material is not particularly limited, but is usually 0.2 to 3 m. ² / g, preferably 0.2 to 2.5 m ² It is about / g.
[0028]
The lithium occlusion amount of the negative electrode active material in the present invention is about 200 mAh to 255 mAh per gram of active material when fully charged. When the lithium storage capacity of the negative electrode active material is too small, the capacity of the battery becomes too small. On the other hand, when it is too large, the cycle life at high temperatures is extremely reduced.
[0029]
The nonaqueous secondary battery of the present invention may include a separator. The separator is not particularly limited, and a known separator can be used, and can be appropriately determined according to the heat resistance of the battery, desired safety, and the like. Examples of the material of the separator include microporous membranes such as polyolefin-based materials (polyethylene, polypropylene, etc.); non-woven fabrics such as polyamide, kraft paper, glass, and cellulose-based materials (rayon, etc.).
[0030]
The structure of a separator is not specifically limited, For example, a single layer or a multilayer separator can be used. In the case of a multilayer, it is preferable to use at least one nonwoven fabric. When at least one nonwoven fabric is used, cycle characteristics are improved.
[0031]
The secondary battery of the present invention uses a non-aqueous electrolyte containing a lithium salt. The lithium salt contained in the non-aqueous electrolyte is not particularly limited, and is appropriately selected from known lithium salts according to a conventional method in consideration of the types of positive electrode material, negative electrode material, usage conditions such as charging voltage, etc. Can be determined. For example, LiPF ₆ , LiClO _Four , LiBF _Four , LiAsF ₆ , LiSbF ₆ Etc., LiPF ₆ , LiBF _Four Is preferred.
[0032]
The solvent contained in the non-aqueous electrolyte can be appropriately determined according to a conventional method in consideration of the types of positive electrode material and negative electrode material, usage conditions such as charging voltage, and the like. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dimethoxyethane, γ-butyrolactone, methyl acetate, methyl formate and the like can be exemplified. A solvent may be used individually by 1 type, or may use 2 or more types together.
[0033]
The concentration of the lithium salt is not particularly limited, but is usually about 0.5 to 2 mol per liter of solvent.
[0034]
As a matter of course, the non-aqueous electrolyte preferably has a water content as low as possible, specifically, a water content of about 100 ppm or less. The term “non-aqueous electrolyte” used in the present specification includes a non-aqueous electrolyte solution and an organic electrolyte solution, and further includes a gel-like or solid electrolyte.
[0035]
The non-aqueous electrolyte used in the present invention may contain a known additive such as a disulfide derivative, if necessary. The blending amount of these additives is not particularly limited as long as the effect of the present invention is exhibited, but is usually about 0.01 to 5% by weight with respect to the whole non-aqueous electrolyte.
[0036]
The positive electrode and the negative electrode of the present invention can be prepared by a known method (for example, molding) in consideration of the shape and characteristics of a desired nonaqueous secondary battery. More specifically, a method of applying a mixture containing an active material, a binder, and, if necessary, a conductive material and an organic solvent to a current collector, drying and molding can be exemplified.
[0037]
The binder is not particularly limited, and specific examples include fluorine resins such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene; rubber materials such as fluoro rubber and SBR; polyolefins such as polyethylene and polypropylene; acrylic resins and the like Polyvinylidene fluoride (PVDF) -based material is preferable, and modified PVDF in which a —COOH group or the like is introduced into the PVDF structure is particularly preferable.
[0038]
The blending amount of the binder may be appropriately determined according to the type, particle size, shape, target electrode thickness, strength, etc. of the positive electrode or negative electrode active material of the present invention, and is not particularly limited. When the active material or negative electrode active material is 100 parts by weight, it is usually about 1 to 30 parts by weight. When a mixture of double-structured graphite particles and graphitized mesocarbon microbeads is used as the negative electrode active material, the negative electrode can be produced with a smaller amount of binder. When using the said mixture as a negative electrode active material, the compounding quantity of a binder is good also as about 1-10 weight part normally, when a negative electrode active material is 100 weight part.
[0039]
As the conductive material, a conductive material known in the art can be used, and examples thereof include acetylene black, natural graphite, artificial graphite, and ketjen black.
[0040]
The usage-amount of the electrically conductive material in a positive electrode is not restrict | limited in particular, It can set suitably according to the kind etc. of active material. The amount of conductive material used in the positive electrode is usually about 20 parts by weight or less when the positive electrode active material is 100 parts by weight. In the negative electrode, even if a conductive material is not used or mixed, the effect of the present invention can be easily obtained by reducing the amount to about 0.1 to 10 parts by weight with respect to 100 parts by weight of the negative electrode active material.
[0041]
Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide (DMF) and the like.
[0042]
The current collector is not particularly limited, and examples of the positive electrode current collector include aluminum foil, and examples of the negative electrode current collector include copper foil and stainless steel foil. Furthermore, what can form an electrode on metal foil or a metal gap, for example, expanded metal, mesh, etc., can be used as a current collector for a positive electrode and a negative electrode.
[0043]
The shape, size, etc. of the non-aqueous secondary battery of the present invention are not particularly limited, and an arbitrary shape such as a cylindrical shape, a rectangular shape, a thin shape, a box shape, etc., is selected according to each application. Can do. Also, the dimensions can be appropriately selected depending on the application.
[0044]
【The invention's effect】
According to the present invention, a nonaqueous secondary battery having an excellent cycle life can be provided. That is, a non-aqueous secondary battery that can maintain a high discharge capacity when used repeatedly can be provided.
[0045]
According to the present invention, a non-aqueous secondary battery excellent in safety can be provided.
[0046]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. The present invention is not limited by the description of these examples.
[0047]
Example 1
(1) Li as the lithium manganese complex oxide _1.1 Mn _1.8 Al _0.1 O _Four LiNi as a lithium nickel composite oxide _0.82 Co _0.18 O ₂ Then, acetylene black as a conductive material was dry mixed. A slurry 1 was prepared by uniformly dispersing the obtained mixture in N-methyl-2-pyrrolidone (NMP) in which polyvinylidene fluoride (PVDF) as a binder was dissolved. Next, slurry 1 was applied to both surfaces of an aluminum foil serving as a current collector, dried, and then pressed to obtain a positive electrode. The solid content ratio (weight ratio) in the positive electrode was lithium manganese composite oxide: lithium nickel composite oxide: acetylene black: PVDF = 72: 18: 4: 6.
[0048]
In this example, the positive electrode coating area (W1 × W2) is 50 × 30 mm. ² It is. In addition, the electrode is provided with a current collector not coated with the slurry 1.
[0049]
(2) Double-structure graphite particles (interplanar spacing of (002) plane of graphite particle core (d002) = 0.34 nm, interplanar spacing of (002) plane of coating layer (d002) = 0.34 nm) and conductive material The acetylene black which is is dry mixed. The obtained mixture was uniformly dispersed in NMP in which PVDF as a binder was dissolved to prepare slurry 2. Next, slurry 2 was applied to both sides of a copper foil serving as a current collector, dried, and then pressed to obtain a negative electrode. The amount of negative electrode active material applied here was such that the amount of lithium occlusion when the battery was fully charged was equivalent to 230 mAh per gram of active material.
[0050]
The solid content ratio (weight ratio) in the negative electrode was set to double-structured graphite particles: acetylene black: PVDF = 93: 2: 6.
[0051]
Negative electrode application area (W1 x W2) is 52 x 32 mm ² It is. In addition, the electrode is provided with a current collecting portion to which the slurry 2 is not applied.
[0052]
Further, the slurry 2 was applied only on one side by the same method as described above, to produce a single-sided electrode (negative electrode). A single-sided electrode is arrange | positioned outside in the electrode laminated body mentioned later.
[0053]
(3) Eight positive electrodes obtained in the above item (1) and seven negative electrodes (two inner surfaces) obtained in the above item (2) were separated into separators (polyethylene microporous membrane; basis weight 13.3 g / m). ² ) Were alternately laminated to produce an electrode laminate.
[0054]
(4) After the aluminum positive electrode terminal is attached to the positive electrode current collector of the electrode laminate obtained in the above (3) and the nickel negative electrode terminal is attached to the negative electrode current collector by spot welding, the thickness is 0.11. The aluminum-resin laminated film (aluminum layer 0.02mm) of mm is housed in a container with an outer casing, and LiPF is added at a concentration of 1 mol / l in a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 30:70. ₆ The electrolyte solution in which the solution was dissolved was injected and impregnated. Thereafter, the container was sealed so that the internal pressure was 0.1 atm, and a flat non-aqueous secondary battery was obtained.
[0055]
(5) Using this battery, after charging to 4.2V with a current of 120mA, perform constant current and constant voltage charging to apply a constant voltage of 4.2V for a total of 8 hours, then discharge to 2.5V with a constant current of 120mA. The charging / discharging cycle was set to 1 cycle, and 100 cycles were performed. Further, in order to evaluate the cycle characteristics, the capacity retention rate was calculated from the discharge capacities at 1 cycle and 100 cycles. The results are shown in Table 1.
[0056]
In addition, as a safety evaluation test, an overcharge test was performed according to UL-1642. In the overcharge test, the battery was charged to 4.2 V with a current of 120 mA, followed by constant current and constant voltage charging that applied a constant voltage of 4.2 V for a total of 8 hours, and then overcharged with 1 C current. The battery was charged to an amount of 250%. The results are shown in Table 1.
[0057]
Example 2
The negative electrode active material in Example 1 (2) is a mixture of double-structured graphite particles and graphitized mesocarbon microbeads, and the solid content ratio (weight ratio) in the negative electrode is determined as double-structured graphite particles: acetylene black: PVDF = 64.4: 27.6: 2: 6 A battery was prepared in the same manner as in Example 1, except that the cycle characteristics and capacity retention rate were measured, and an overcharge test was performed. The results are shown in Table 1.
[0058]
Comparative Example 1
A battery was prepared in the same manner as in Example 1 except that the amount of the negative electrode active material applied in (2) of Example 1 was set so that the lithium occlusion amount when the battery was fully charged was equivalent to 190 mAh per gram of active material. The cycle characteristics and capacity retention rate were measured, and an overcharge test was performed. The results are shown in Table 1.
[0059]
Comparative Example 2
A battery was prepared in the same manner as in Example 1 except that the amount of negative electrode active material applied in (2) of Example 1 was changed to an amount corresponding to 260 mAh per 1 g of active material of the lithium storage amount when the battery was fully charged. The cycle characteristics and capacity retention rate were measured, and an overcharge test was performed. The results are shown in Table 1.
[0060]
Comparative Example 3
The positive electrode active material in Example 1 (1) is a lithium cobalt composite oxide (LiCoO). ₂ Except for the above, a battery was prepared in the same manner as in Example 1, and the cycle characteristics and capacity retention rate were measured, and an overcharge test was performed. The results are shown in Table 1.
[0061]
Comparative Example 4
A battery was prepared by the same method as in Example 1 except that the negative electrode active material in (2) of Example 1 was only graphitized mesocarbon microbeads, and the cycle characteristics and capacity retention were measured. The test was conducted. The results are shown in Table 1.
[0062]
[Table 1]

[0063]
As is apparent from the results shown in Table 1, the batteries produced in Examples 1 and 2 were excellent in cycle characteristics and exhibited high safety.
[0064]
The batteries manufactured in the examples show sufficient battery capacity, and the decrease in charge / discharge efficiency presumed to be caused by the decomposition of the electrolyte is substantially suppressed, and the destruction of the graphite structure in the negative electrode active material is also prevented. The

Claims (2)

In a non-aqueous secondary battery in which a non-aqueous electrolyte containing a positive electrode, a negative electrode and a lithium salt is housed in a battery container,
The positive electrode active material in the positive electrode is a mixture composed of a lithium manganese composite oxide and a lithium nickel composite oxide,
The negative electrode active material in the negative electrode is coated with an amorphous carbon layer having a surface spacing of 0.34 nm or more on the surface of the graphite particles having a (002) plane spacing (d002) of 0.34 nm or less by X-ray wide angle diffraction method. Comprising at least double-structured graphite particles,
A non-aqueous secondary battery that stores 200 mAh to 255 mAh per gram of negative electrode active material as a chargeable / dischargeable lithium amount when fully charged under the designed charging conditions of the secondary battery. The nonaqueous secondary battery according to claim 1, wherein the negative electrode active material further contains graphitized mesocarbon microbeads.