JP4752372B2 - Positive electrode active material, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a method for producing a positive electrode active material and a positive electrode material.

  In recent years, with the widespread use of portable and cordless devices such as mobile phones and notebook computers, there is an increasing demand for batteries that supply power to these devices, and secondary batteries that can be repeatedly charged and discharged are required. In particular, there is a high expectation for a non-aqueous electrolyte secondary battery that can realize a small and lightweight battery with a higher operating voltage and energy density than an aqueous secondary battery.

There are various compounds as the positive electrode active material constituting the non-aqueous electrolyte secondary battery. In particular, lithium transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ and LiMn ₂ O ₄ are partially substituted with other elements. Alternatively, the solid solution has a high operating potential and is excellent in that a battery having a high operating voltage can be realized in combination with a negative electrode such as a carbon material, and some have already been put into practical use.

As described above, the nonaqueous electrolyte secondary battery has a feature that the battery voltage is higher than that of the aqueous solution type secondary battery. However, since the activity is high in addition to the high voltage, the electrolyte solution is oxidized and decomposed in the charged state. Gas is generated, the battery swells, leaks, the electrolyte is removed by the gas and the electrode reaction area decreases, so the battery characteristics also deteriorate, and it reacts directly with the mixed moisture. There existed a subject of causing decomposition of electrolyte solution through a product. Therefore, studies have been made to modify or modify the surface of the active material. For example, it has been proposed to form various compound layers on the surface of the positive electrode active material. (For example, see Patent Document 1)
Moreover, as a manufacturing method for surface modification / modification, although it is for improving the conductivity of the negative electrode material, utilizing a mechanochemical reaction that acts mechanical energy consisting of compressive force and grinding force, A method has been proposed in which a conductive material is rolled on the surface of active material particles to modify the surface of the active material. (For example, see Patent Document 2)
JP-A-8-222219 JP 2001-15101 A

  However, in the conventional technique such as Patent Document 1, it is possible to suppress the gas generation by covering the active material with the surface layer. However, for example, the surface layer made of an oxide having a high electron resistance inhibits ionic conduction. In addition, since the electron conductivity is poor, battery characteristics such as large current discharge characteristics are sacrificed, and the performance balance of the total battery is not sufficient.

  Therefore, when coating with a metal or nitride excellent in electron conductivity was examined, the surface layer was destroyed by pressure when the metal surface layer was rolled in the actual electrode manufacturing process, and the gas suppression effect was reduced. There was a problem to do. On the other hand, although the nitride surface layer has high hardness and durability against rolling, there is a problem that the nitride surface layer can not cope with the expansion and contraction of the active material due to charge and discharge and peels off from the active material.

Furthermore, also from the point of manufacturing method, when forming these surface layers, if a method of fusing mechanical energy such as mechanofusion is used, a part of the positive electrode active material is scraped off to produce fine particle powder. In addition, due to impurities mixed in from the device that gives mechanical energy, the amount of gas generated increases more than the effect of suppressing gas generation, or the voltage drops due to a micro short circuit of the battery. It was. The reason why micro short-circuiting due to impurities, which is hardly a problem in the negative electrode as in Patent Document 2, has become a major issue is that the potential of the negative electrode is different from that of the positive electrode of the present invention, and the solubility of the mixed metal is different. It is estimated that.

  As described above, the conventional technology does not consider the problem in the actual battery manufacturing process or the problem at the time of actual use, and is due to the destruction of the coating layer due to the rolling of the electrode or the expansion and contraction of the active material accompanying the charge / discharge. There was a problem such as peeling of the coating layer.

  The present invention has been made in view of the above problems, and the method for producing a positive electrode active material according to the present invention is a method in which a part of the surface of a lithium transition metal composite oxide particle capable of releasing and occluding lithium ions is coated with metal. It has the process of forming a layer, and the process of forming a nitride coating layer.

  Further, the positive electrode active material using the production method is characterized in that at least a part of the surface of the lithium transition metal composite oxide particles capable of releasing and occluding lithium ions is coated with a metal nitride. .

  Through such a manufacturing process, a part of the surface of the lithium transition metal composite oxide particles capable of releasing and occluding lithium ions can be coated with the metal nitride.

  Further, according to the manufacturing method of the present invention, the metal nitride coating layer is a gradient material having a nitrogen concentration, and a metal layer or a metal layer having a substantially zero nitrogen concentration exists at the interface with the lithium transition metal composite oxide. The positive electrode active material having Such a positive electrode active material maintains adhesion to the active material against expansion and contraction during charge and discharge by a layer having a small amount of metal or nitrogen solid solution, while a layer having a large amount of nitrogen solid solution functions as a hardened layer. Since the effect of the coating layer can be maintained even after experiencing the rolling process, it solves the problems of the battery manufacturing process and suppresses the generation of gas during charging / discharging and storage in a high temperature environment, and the reliability of the battery Can be improved.

  As described above, when the production method of the present invention is used, a positive electrode active material and a non-aqueous electrolyte that are excellent in charge and discharge characteristics and have high reliability that is difficult to generate gas even after charge and discharge cycles in a high temperature environment and after storage. A secondary battery can be obtained.

  As a result of intensive studies by the present inventors, it is effective to suppress gas generation without degrading battery performance by first coating a part of the lithium transition metal composite oxide with a metal and then nitriding. It has been found that a coating layer can be formed. It is not just a nitride coating, but an active material interface from the surface of the coating layer so that a layer with almost zero nitrogen or a metal layer is present at the interface between the lithium transition metal composite oxide and the coating nitride. It is more preferable to form a nitride coating layer having a structure in which the nitrogen element concentration is inclined toward the top.

  Some metal nitrides have high hardness, and the strong coating layer formed only of the metal nitrides was not broken even when the lithium transition metal composite oxide particles were rubbed with each other in the electrode rolling process. However, it could not withstand the repeated expansion and contraction associated with the charging / discharging of the battery, and as the charging / discharging cycle proceeded, it peeled off and the gas generation suppressing effect was reduced. On the other hand, when a nitride coating layer in which the concentration of nitrogen element increases from the interface with the lithium transition metal composite oxide of the present invention toward the coating layer surface, the inner metal or a portion having a composition close thereto is formed. However, it is possible to relieve the stress of expansion and contraction accompanying charging / discharging, prevent peeling of the coating layer, and maintain the gas generation suppressing effect.

  In order to form a coating layer having such a form, the nitride is simply fused to the lithium transition metal composite oxide by mechanical energy such as a mechano-fusion method, or the nitride itself is deposited and baked. The first step of forming a metal layer on the surface of the lithium transition metal composite oxide and the second step of nitriding the metal layer or forming a nitride layer thereon are provided. It is necessary to take a manufacturing method.

  Since the metal layer is easily adhered to the lithium transition metal composite oxide, the metal layer is preferably present at the interface between the coating layer and the lithium transition metal composite oxide. As a method for forming the metal layer, for example, a metal layer is formed by a plating method such as electroless plating, physical vapor deposition, chemical vapor deposition, sputtering, ion plating, thermal spraying, or a method using an organometallic compound such as alkylaluminum. be able to. The metal layer may be a single metal such as Ni, Co, Ti, Zn, Zr, Al, Nb, V, Ta, or Li, or an alloy such as an Al-Ti alloy. From the viewpoints of stability at the positive electrode potential, electron conductivity and hardness when nitrides are formed, at least one selected from the group consisting of Ti, Zn, Zr, Al, Nb, V, and Ta is preferable. .

  In addition, the formation of a nitride for suppressing side reactions and imparting strength can be performed by a method such as a gas nitriding method or a plasma nitriding method. As a gas used in the gas nitriding method, for example, ammonia gas, a mixed gas of ammonia and nitrogen, a mixed gas added with carbon monoxide, hydrogen, or the like can be used, and nitriding is possible from a temperature of several hundred degrees Celsius. For this reason, it is possible to prevent a decrease in battery capacity due to a decrease in crystallinity of the active material. Further, examples of the atmosphere of the plasma nitriding (ion nitriding) method include an atmosphere of nitrogen gas, a mixed gas of nitrogen and hydrogen, a mixed gas of nitrogen, ammonia, and an inert gas. Since this nitriding method can generally be performed at a relatively low temperature of 600 ° C. or lower, this method also prevents the occurrence of problems such as greatly changing the crystallinity of the active material or causing decomposition to lower the battery capacity. it can.

  The formation of the metal layer and the nitriding process as described above may be performed by separate apparatuses or may be an apparatus capable of continuous processing. As one method of continuous processing, an ion plating method which is a kind of physical vapor deposition can be considered. A metal nitride film can also be deposited by first depositing a metal in an argon plasma atmosphere and adding and introducing a reactive gas such as nitrogen or ammonia from the middle. Alternatively, in the sputtering method as well, a metal nitride can be deposited by introducing a reactive gas after depositing a metal in an argon atmosphere.

In addition, the nitriding process not only nitrides the metal coated on the surface but also simultaneously nitrides the surface of the uncoated active material, so that it is effective even if nitrogen element penetrates, diffuses or substitutes on the surface of the active material. Is. As a result of studies by the present inventors, even when the surface of the active material is nitrided by the above-described method, a gas generation suppressing effect is recognized, and nitrogen element is present on the surface, invading and dissolving. I understood. Although the mechanism for suppressing gas generation is not clear, it is possible that electrons are donated from nitrogen substituted for oxygen in the lithium transition metal complex oxide and the apparent valence of the transition metal at the time of charging is reduced. , Oxides, hydroxides and carbonates that may contribute to gas generation (eg NiO, Ni (OH) ₂ , CoO, Co ₃ O ₄ , Co (OH) ₂ , Li ₂ O, LiOH, Li ₂ CO ₃ etc.) may be inactivated by nitriding.

  As mentioned above, although the formation method of the coating layer of this invention was illustrated, it is not limited to these.

A lithium transition metal composite oxide can be used as the positive electrode active material for a non-aqueous electrolyte secondary battery used in the present invention. For example, the general formula Li _x Ni _(1-yz) Co _y M _z O ₂ (x is a variable that changes with charge and discharge, and 0 <x <1.1, 0 <y ≦ 0.5, 0 ≦ z < 0.5, M is Al
, Mn, Mg, Ca, Fe, Ti, Zn, Sr, Ba, Zr, Y, B, and a lithium transition metal composite oxide represented by at least one element selected from the group consisting of Ta are suitable. It is also possible to use a mixture of a plurality of different positive electrode materials. The average particle diameter of the positive electrode active material particles is not particularly limited, but is preferably 1 to 30 μm.

  The conductive agent for positive electrode used in the present invention may be anything as long as it is an electron conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, natural graphite (such as flake graphite), graphite such as artificial graphite, carbon black such as acetylene black, channel black, furnace black and thermal black, conductive fibers such as carbon fiber and metal fiber, fluorine Carbon oxides, metal powders such as aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or organic conductive materials such as polyphenylene derivatives are included alone or as a mixture thereof Can be made. Among these conductive agents, artificial graphite and acetylene black are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1-50 weight% is preferable with respect to positive electrode material, and 1-30 weight% is especially preferable. In the case of carbon or graphite, 2 to 15% by weight is particularly preferable.

  The positive electrode binder used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred materials in the present invention include polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

  As the current collector for the positive electrode used in the present invention, any electronic conductor that does not cause a chemical change in the charge / discharge potential of the positive electrode material to be used may be used, and generally known aluminum, conductive resin, etc. may be used. it can. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

  In addition to a conductive agent and a binder, a filler, a dispersant, an ionic conductor, a pressure enhancer, and other various additives can be used for the electrode mixture. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0 to 30 weight% is preferable with respect to an electrode mixture.

  In the configuration of the negative electrode plate and the positive electrode plate in the present invention, it is preferable that the negative electrode mixture surface is present at least on the opposite surface of the positive electrode mixture surface.

The main component of the negative electrode active material of the present invention is a graphite material or a non-graphitizable carbonaceous material. For the purpose of improving the characteristics, a conductive material can be used for the negative electrode, and any electron conductive material may be used. For example, natural graphite (such as flake graphite), artificial graphite, graphite such as expanded graphite, carbon black such as acetylene black, channel black, furnace black, and thermal black, conductive fiber such as carbon fiber and metal fiber , Metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives can be contained alone or as a mixture thereof. Among these conductive materials, artificial graphite, acetylene black, and carbon fiber are particularly preferable. The addition amount of the conductive material is not particularly limited, but is preferably 1 to 30% by weight, particularly preferably 1 to 10% by weight with respect to the negative electrode active material. The binder for the negative electrode used in the present invention may be either a thermoplastic resin or a thermosetting resin. Preferred binders include styrene butadiene rubber, polyvinylidene fluoride, and ethylene-acrylic acid copolymer. Or (Na ⁺ ) ion-crosslinked product of the material, ethylene-methacrylic acid copolymer or (Na ⁺ ) ion-crosslinked product of the material, ethylene-methyl acrylate copolymer, or (Na ⁺ ) ion-crosslinked product of the material , An ethylene-methyl methacrylate copolymer, or a (Na ⁺ ) ion-crosslinked product of the above material, alone or as a mixture.

  The negative electrode current collector used in the present invention may be anything as long as it is an electron conductor that is chemically stable in the constructed battery, and copper, titanium, or the like can be used. The thickness is not particularly limited, but a thickness of 1 to 500 μm is used.

  For the electrode mixture of the positive electrode and the negative electrode, a filler, a dispersant, an ionic conductor, a pressure enhancer, and other various additives can be used in addition to the conductive material and the binder. Any filler can be used as long as it is a fibrous material that does not cause a chemical change in the constructed battery. Usually, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0 to 10 weight% is preferable with respect to an electrode mixture.

  The shape of the battery can be applied to any of a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, a square type, a large type used for an electric vehicle, and the like. Further, the nonaqueous electrolyte secondary battery of the present invention can be used for a portable information terminal, a portable electronic device, a small electric power storage device for home use, a motorcycle, an electric vehicle, a hybrid electric vehicle, etc., but is not particularly limited thereto. I don't mean.

  Next, specific examples of the present invention will be described.

Example 1
The case of LiNi _0.81 Co _0.15 Al _0.04 O ₂ is taken as an example as the positive electrode active material to be coated. This positive electrode active material includes a composite hydroxide formed by coprecipitation of cobalt hydroxide Co (OH) ₂ and aluminum hydroxide when nickel hydroxide Ni (OH) ₂ is synthesized by a conventionally known method. Then, lithium hydroxide was mixed so as to have a molar ratio of Li / (Ni + Co + Al) = 1.05 and synthesized by firing at 750 ° C. for 24 hours in an oxygen stream. In addition, when adding Al or other elements, it can be added in the form of its hydroxide, oxide, nitrate, sulfate, metal, or composite hydroxide coprecipitated with Ni and Co. It can also be added as.

LiNi _0.81 Co _0.15 Al _0.04 O ₂ thus produced was coated with vanadium (V) metal by sputtering in Ar gas at 1 Pa. The state of the coating was confirmed by an analysis method such as SEM, EPMA, XPS. Furthermore, plasma nitriding (ion nitriding) treatment by glow discharge was performed in a low vacuum using a mixed gas of nitrogen and hydrogen. The conditions of the plasma nitriding treatment are as follows: an active material is charged on the cathode of the processing apparatus, and a mixed gas of nitrogen and hydrogen (50% each) adjusted so that the processing chamber becomes 1000 Pa is introduced into the processing chamber. Nitriding was performed by applying a voltage to generate a glow discharge. The active material was adjusted using a heater so that the temperature became about 500 ° C. and treated for 2 hours.

  The surface of the obtained active material was coated with vanadium nitride by an analysis method such as SEM, EPMA, XPS, etc., the nitrogen concentration was low near the interface with the active material surface, and the presence of metal vanadium was also confirmed.

Using the positive electrode active material thus obtained, a coin-type non-aqueous electrolyte secondary battery was produced as follows. A cross-sectional view of this coin-type non-aqueous electrolyte secondary battery is shown in FIG. Using positively dehydrated N-methylpyrrolidinone (NMP) as a dispersion solvent, a positive electrode active material, acetylene black (AB), and polyvinylidene fluoride (PVDF) are kneaded at a weight ratio of 100: 5: 4. Thus, an active material mixture paste was prepared. After applying and drying this paste on the positive electrode core material 1 made of aluminum foil, it was rolled using a roller to produce a positive electrode sheet. The density of the positive electrode 2 after rolling was 3.86 g / cc. This positive electrode sheet was punched into a disk shape having a diameter of 15 mm to obtain a positive electrode for a coin battery.

  On the other hand, a negative electrode core made of copper foil is prepared by kneading active material flaky graphite and binder styrene butadiene rubber at a weight ratio of 100: 3 using water as a dispersion solvent. It apply | coated and dried to the material 3, and it rolled with the roller to make the negative electrode sheet. This was vacuum-dried at 110 ° C. for 10 hours and punched into a disk shape having a diameter of 16 mm to obtain a negative electrode 4 for a coin battery.

Also, a polypropylene microporous membrane was used as the separator 5, and the electrolyte was used by dissolving 1 mol / L LiPF ₆ in ethylene carbonate and ethyl methyl carbonate having a volume ratio of 1: 3.

  These positive and negative electrodes, separator, and electrolyte were placed in a battery case 6 of a coin-type battery, covered with a sealing plate 7 and caulked through a gasket 8 to produce a coin-type battery having a diameter of 20 mm and a thickness of 1.6 mm. A positive current collector 9 made of aluminum mesh and a negative current collector 10 made of nickel mesh were previously welded to the battery case 6 and the sealing plate 7, respectively. This battery is designated as A1. The design capacity of this battery is 12 mAh.

  The handling environment at the time of synthesizing the active material or producing the battery was as low as possible.

Example 2
Cathode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was sputtered with vanadium metal, and instead of performing plasma nitriding treatment, the active material coated with this metal was put in a ring furnace, and flowing at 500 ° C. for 50 hours while flowing ammonia gas A coin-type battery was produced in the same manner as in Example 1 except that nitriding was performed and gas nitriding was performed. This battery is designated as A2.

Example 3
The positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with vanadium metal by sputtering in Ar gas at 1 Pa, and then further introduced with nitrogen gas during sputtering to coat vanadium nitride. A coin-type battery was produced in the same manner as in Example 1. This battery is designated as A3.

Example 4
The positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was charged into an ion plating apparatus into which 0.1 Pa of argon gas was introduced. Vanadium metal was first deposited, and then nitrogen gas was added during the deposition. A coin-type battery was produced in the same manner as in Example 1 except that vanadium nitride was deposited. This battery is designated as A4.

Example 5
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with titanium (Ti) metal by sputtering. This battery is designated as A5.

Example 6
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with an aluminum metal by a sputtering method. This battery is designated as A6.

Example 7
The positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with zinc (Z
n) A coin-type battery was produced in the same manner as in Example 1 except that the metal was coated. This battery is designated as A7.

Example 8
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with niobium (Nb) metal by sputtering. This battery is designated as A8.

Example 9
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with zirconium (Zr) metal by sputtering. This battery is designated as A9.

Example 10
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with a tantalum (Ta) metal by a sputtering method. This battery is designated as A10.

Example 11
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with nickel (Ni) metal by sputtering. This battery is designated as A11.

Example 12
A coin-type battery was produced in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with nickel (Ni) metal by an electroless plating method (basic bath). This battery is designated as A12. As components of the plating solution, NiSO ₄ .7H ₂ O, NaH ₂ PO ₂ , and NaOH were used, and the pH was about 9 and the solution temperature was 90 ° C.

<< Comparative Example 1 >>
A coin-type battery was fabricated in the same manner as in Example 1, except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was coated with vanadium metal by sputtering and an active material that did not form a nitride film was used. . This battery is designated as B1.

<< Comparative Example 2 >>
A coin-type battery was fabricated in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ was an active material in which vanadium nitride was adhered by a mechanofusion method. This battery is designated as B2.

<< Comparative Example 3 >>
A coin-type battery was fabricated in the same manner as in Example 1 except that the positive electrode active material LiNi _0.81 Co _0.15 Al _0.04 O ₂ after firing was used as it was. This battery is designated as B3.

  The batteries produced as described above are summarized in Table 1.

  Moreover, those batteries were evaluated.

  First, in order to evaluate the degree of destruction of the active material or the coating layer in the rolling process, the active material is put into a disk-shaped pellet molding die, a pressure of 60 Mpa is applied, and then taken out and crushed to obtain a particle size distribution. It was measured. Table 2 shows the presence or absence of fine powder of less than 1 micron.

  Moreover, about the completed battery, charge and discharge current 2mA and the constant current charge / discharge of voltage range 2.5V-4.2V were performed 3 cycles in 25 degreeC environment. Table 2 shows the ratio of voltage failure batteries when 10 cells of each example and comparative example were left in a charged state in a 45 ° C. environment for 3 days. A cell having a battery voltage of 3.9 V or less was regarded as defective.

  Separately from this, in order to evaluate the gas generation in the high-temperature charge / discharge cycle, first, the initial battery thickness was measured in the charged state (each n = 5 cells). Thereafter, under the environment of 45 ° C., a cycle test was performed in the same charge / discharge current value and voltage range as described above, and the thickness of the battery was measured in the charged state after 50 cycles. Table 2 shows the change in battery thickness and the maintenance rate of discharge capacity.

  As can be seen from Tables 1 and 2, not only in Comparative Example 3 using the fired active material as it is, but also in Comparative Example 1 in which only metal coating was performed and in Comparative Example 2 in which nitride was fused to the surface, More gas was generated than in the Examples, and the swelling of the battery was large. In the case of only metal coating, it is inferred that the coating layer or part of the active material collapsed due to the pressure during rolling because of the presence of fine powder after the press test. Nitride coating by the mechano-fusion method applies a great deal of pressure during the coating process, so that a portion of the active material may collapse before the hard nitride layer is formed, and fine powder may be generated. There is a possibility that the nitride layer could not follow and collapsed. Moreover, since voltage failures frequently occurred, it is assumed that a part of the used stainless steel container was mixed in the mechano-fusion treatment process and caused a problem.

  On the other hand, the active material produced by the production method of the present invention is less likely to produce fine powder even when pressed, and is expected to suppress gas generation under a high temperature environment. In fact, it was found that the swelling of the battery in the 45 ° C. cycle was very small, and the reaction with the electrolytic solution was suppressed by holding a strong coating despite the expansion and contraction of the active material during charging and discharging. Moreover, since gas generation was suppressed, gas did not accumulate between the electrodes, and the capacity retention rate after cycling was high.

Furthermore, experiments were performed with active material compositions other than this example, that is, LiCoO ₂ , LiNiO _2, and LiMnO ₂ , and similar results were obtained.

  Similar results were obtained even when the above active material was used, and a cobalt (Co) metal and a lithium (Li) metal were coated by a sputtering method and a plasma nitriding method was used.

  In addition, this invention is not limited to the manufacturing method and conditions described in said Example.

  The positive electrode material for a non-aqueous electrolyte secondary battery of the present invention and a battery using the same are useful as a portable power source having excellent reliability and a long lifetime.

Sectional drawing of the nonaqueous electrolyte secondary battery of one Example of this invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode core material 2 Positive electrode 3 Negative electrode core material 4 Negative electrode 5 Separator 6 Battery case 7 Sealing plate 8 Gasket 9 Positive electrode collector 10 Negative electrode collector

Claims (7)

A positive electrode active material comprising: a step of forming a metal coating layer on a part of a surface of a lithium transition metal composite oxide particle capable of releasing and occluding lithium ions; and a step of forming a nitride coating layer. Manufacturing method. 2. The method for producing a positive electrode active material according to claim 1, wherein the step of forming the nitride coating layer nitrides both the metal layer and the surface of the lithium transition metal composite oxide particles not covered with the metal layer. . The positive electrode active produced by the production method according to claim 1 or 2, wherein at least a part of the surface of the lithium transition metal composite oxide particles capable of releasing and occluding lithium ions is coated with a metal nitride. material. The positive electrode active material according to claim 3, wherein the metal nitride is a gradient material having a nitrogen concentration, and a metal layer is present at an interface with the lithium transition metal composite oxide. The metal or nitride covering the surface of the lithium transition metal composite oxide particles is at least one selected from the group consisting of Ni, Co, Ti, Zn, Zr, Al, Nb, V, Ta, Li and nitrides thereof. The positive electrode active material according to claim 3, wherein the positive electrode active material is present. The positive electrode active material according to claim 3, wherein the lithium transition metal composite oxide is represented by LiMO ₂ (M is at least one of Ni, Co, and Mn). A non-aqueous electrolyte secondary battery using the positive electrode active material according to claim 3.

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