JP6611438B2 - Positive electrode material for non-aqueous electrolyte secondary battery, method for producing the same, and non-aqueous electrolyte secondary battery - Google Patents

Description

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

  In recent years, non-aqueous electrolyte secondary batteries mounted on portable electronic devices such as mobile phones and notebook computers are required to have a higher capacity in order to ensure a longer driving time.

  For example, it is known that increasing the end-of-charge voltage can increase the energy density and increase the output, but acceleration of the deterioration of the positive electrode and the decrease in battery safety are problems. The cause of these problems is largely due to side reactions occurring at the interface between the electrolytic solution and the positive electrode material, and improvement is achieved by changing the chemical state of the positive electrode surface.

  For example, in Japanese Patent Application Laid-Open No. 2011-96626 (Patent Document 1), a lithium ion battery using high lithium-containing transition metal oxide particles as a positive electrode material has a crystal structure from the central part of the positive electrode material toward the outermost surface part. It is proposed that the battery characteristics such as load characteristics, discharge capacity, and charge / discharge efficiency in high voltage charge / discharge as high as 4.8V based on Li can be improved by gradually changing the layer structure from the layered rock salt structure to the spinel structure. Has been.

  In addition, in US Pat. No. 5,693,435 (Patent Document 2), in a lithium ion battery using Li-containing cobalt oxide particles as a positive electrode material, by reducing only the outermost surface of the positive electrode material, It has been reported that deterioration due to a room temperature charge / discharge cycle at a charge end voltage of 4.4 V on the basis of Li can be suppressed.

JP 2011-96626 A US Pat. No. 5,693,435

  However, the lithium ion battery using the high lithium-containing transition metal oxide particles described in Patent Document 1 as a positive electrode material can be increased in capacity by high-voltage charging, but other Li-containing transitions have a large Li-containing capacity. True density is lower than metal oxide. In addition, since the average charge / discharge potential is low, there is a problem that it is difficult to improve the energy density per volume and the output density.

  Moreover, since the lithium ion battery using the lithium-containing cobalt oxide particles described in Patent Document 2 as a positive electrode material has a high true density and a high potential in a wide range of charged states, it has a high charge end voltage. By charging and discharging, high energy and high output can be expected. However, by continuing to maintain a high voltage in a high temperature environment, Co elution is promoted, resulting in a problem that the positive electrode material is structurally broken.

  Accordingly, the present invention provides a positive electrode material for a non-aqueous electrolyte secondary battery that can suppress the elution of Co in a high temperature environment while improving the energy density per volume and the output density by increasing the charge end voltage. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery using the manufacturing method and the positive electrode material.

  In order to solve the above problems, the present inventors conducted extensive research and found that the problem is solved by making the outermost surface of lithium-containing cobalt oxide particles having a predetermined composition a specific structure. Completed the invention. That is, the gist of the present invention is as follows.

(1) General composition formula Li _{1 + x} Co _1-y M _y O _2-δ (where M is Ni, Mn, Al, Mg, Zr, V, W, Mo, Cr, Bi, Cu, Ti, Si, One or more elements selected from the group consisting of Fe, P, F and Cl, and 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.1, and 0 ≦ δ ≦ 0.02. The positive electrode material for nonaqueous electrolyte secondary batteries containing the particle | grains containing the lithium containing cobalt oxide by which the outermost surface of the said particle | grain has a spinel structure.
(2) in the Raman ^spectrum, the positive electrode material for a nonaqueous electrolyte secondary battery according to (1) having a shoulder peak in the range of 650cm ^-1 ~700cm -1.
(3) The particles are further coated with an oxide or fluoride containing one or more elements selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn, and P; The positive electrode material for a nonaqueous electrolyte secondary battery according to (1) or (2), wherein the number of atoms is 10% or less of the number of molecules of the lithium-containing cobalt oxide.
(4) A method for producing a positive electrode material for a nonaqueous electrolyte secondary battery according to (1) above,
Synthesizing a lithium-containing cobalt oxide;
A step of mixing Li ₂ CO ₃ and / or LiOH with respect to the synthesized lithium-containing cobalt oxide;
A method for producing the positive electrode material for a non-aqueous electrolyte secondary battery, comprising a step of performing an annealing treatment within a temperature range of 950 ° C. to 1100 ° C. for 2 hours to 20 hours.
(5) A method for producing a positive electrode material for a nonaqueous electrolyte secondary battery according to (1) above,
Mixing Li ₂ CO ₃ and / or LiOH with a lithium-containing cobalt oxide raw material;
A method for producing the positive electrode material for a non-aqueous electrolyte secondary battery, comprising a step of performing an annealing treatment within a temperature range of 950 ° C. to 1100 ° C. for 5 hours to 48 hours.
(6) A nonaqueous electrolyte secondary battery comprising a positive electrode including the positive electrode material for a nonaqueous electrolyte secondary battery according to any one of (1) to (3), a negative electrode, a separator, and a nonaqueous electrolyte.
(7) In addition to the positive electrode material for nonaqueous electrolyte secondary batteries according to any one of (1) to (3) above, the positive electrode has a general composition formula Li _{1 + a} Ni _1-bcd Co _b Mn _c M ′ _d O _2-e (wherein M ′ is selected from the group consisting of Al, Mg, Zr, V, W, Mo, Cr, Ti, B, Si, Fe, P, F, S and Cl) One or more elements, 0 ≦ a ≦ 0.05, 0 ≦ b ≦ 0.02, 0.01 ≦ c ≦ 0.03, 0.001 ≦ d ≦ 0.03, 0 ≦ e ≦ 0. The lithium-containing nickel / cobalt / manganese oxide represented by 01) is in a proportion of 5% by mass to 50% by mass with respect to the total of the lithium-containing nickel / cobalt / manganese oxide and the lithium-containing cobalt oxide. The nonaqueous electrolyte secondary battery according to (6) above.
(8) The peak potential confirmed at the highest potential of the dQ / dV curve obtained by differentiating the charge curve of the positive electrode with voltage when charged to 5 V at a room temperature and a load factor of 0.1 C or less, The nonaqueous electrolyte secondary battery according to (6) or (7), which is 4.64 V or more.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode material for nonaqueous electrolyte secondary batteries which is high capacity | capacitance and excellent in the continuous charge characteristic at high temperature and a high voltage can be provided. Problems, configurations, and effects other than those described above will be clarified by the following description of the embodiments.

It is a figure which shows the Raman spectrum of the positive electrode material for nonaqueous electrolyte secondary batteries of Examples 1, 2, and 3 and Comparative Examples 1 and 2. It is a figure which shows the X-ray-diffraction measurement result of the positive electrode material for nonaqueous electrolyte secondary batteries of Example 1 and Comparative Examples 1 and 2. It is the schematic which shows one Embodiment of the nonaqueous electrolyte secondary battery which concerns on this invention.

  Hereinafter, a positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention, a manufacturing method thereof, and a non-aqueous electrolyte secondary battery using the positive electrode material will be described. In addition, this invention is not limited to what was shown below, In the range which does not change the summary, it can change suitably and can implement.

The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention is
General composition formula Li _{1 + x} Co _1-y M _y O _2-δ (1)
Wherein M is one or more selected from the group consisting of Ni, Mn, Al, Mg, Zr, V, W, Mo, Cr, Bi, Cu, Ti, Si, Fe, P, F and Cl Element containing particles containing lithium-containing cobalt oxide represented by 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.1, and 0 ≦ δ ≦ 0.02. It has a spinel structure. Here, the outermost surface of the particle refers to a region having a thickness within 100 nm of the surface portion of the particle. By using the positive electrode material, a nonaqueous electrolyte secondary battery having a high capacity and capable of continuous charging at a high temperature and a high voltage can be obtained.

  In order to produce a positive electrode of a nonaqueous electrolyte secondary battery using the positive electrode material, a positive electrode mixture slurry is prepared by dispersing the positive electrode material in a solvent together with a binder, a conductive auxiliary agent, and the like. Can be applied to the surface of the positive electrode current collector to form a positive electrode mixture layer.

  The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention is in the form of particles, is composed of secondary particles in which primary particles are aggregated, or primary particles, and each shape may be substantially spherical. The above shape can be confirmed by observing particles existing in a predetermined region with a scanning electron microscope. The diameter of the particles is preferably in the range of 5 μm to 50 μm, more preferably distributed so as to have peaks in the range of 5 μm to 15 μm and in the range of 20 μm to 50 μm. By having a plurality of peaks, the packing state of the particles in the positive electrode mixture layer is improved. The particle size distribution can be measured by a laser diffraction / scattering particle size distribution measuring apparatus.

The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention needs to reduce the interface with the non-aqueous electrolyte from the viewpoint of suppressing Co elution. Therefore, it is advantageous to have a small BET specific surface area. However, if the BET specific surface area of the particles is too small, the density at the time of stacking will be small, so that the battery capacity will be reduced and the discharge characteristics at high load will be reduced. Problem arises. For this reason, it is preferable that the BET specific surface area S is in the range of 0.01 ≦ S ≦ 1.0 [m ² / g]. The BET specific surface area can be obtained by measuring the surface area using the BET formula, which is a theoretical formula for multimolecular layer adsorption. Specifically, the BET specific surface area can be obtained using a specific surface area measuring apparatus by a nitrogen adsorption method.

  In the general composition formula (1), x related to Li is 0 ≦ x ≦ 0.1, and more preferably 0 ≦ x ≦ 0.03. When x is less than 0, the particles of the positive electrode material become small, and the diameter of the particles is less than 5 μm. When such a small particle is used to form the positive electrode mixture layer, the density is small, and thus a sufficient battery capacity cannot be obtained. Further, since the surface area is increased, Co elution is likely to occur. On the other hand, when x exceeds 0.1, a large amount of oxygen deficiency occurs. For this reason, the potential in the low charge state is lowered, and the output is lowered in the low charge state. In addition, since the oxygen is deficient, the structure is easily collapsed and the cycle life is shortened. Furthermore, since there is a large amount of lithium on the particle surface of the positive electrode material, the positive electrode mixture slurry prepared using such a positive electrode material becomes a gel, and the resistance of the formed positive electrode mixture layer is increased, or during the battery reaction. This is not preferable because gas is generated.

  X in the range of 0 ≦ x ≦ 0.1 means that Li is slightly in excess of the stoichiometric composition. In such a state, a phase transition phenomenon accompanied by structural collapse at a high voltage of 4.5 V or higher is suppressed, and Co elution is prevented. The average valence of Co in the positive electrode material is preferably 2.8 or more and 3.3 or less. The valence of Co is calculated from inductively coupled plasma emission analysis and iodometric titration, and can be obtained by quantifying the atomic ratio of Li and Co and the amount of oxygen.

  In the general composition formula (1), y related to M (Ni, Mn, Al, Mg, Zr, V, W, Mo, Cr, Bi, Cu, Ti, Si, Fe, P, F, and Cl) is 0. ≦ y ≦ 0.1. Regarding Ni, Mn, Al, Mg, Zr, V, W, Mo, Cr, Bi, Cu, and Ti, various battery characteristics can be improved by replacing part of Co. Moreover, Si, Fe, P, F, Cl, etc. may be inevitably contained as impurities.

  The addition of Ni as M is preferable because the effect of suppressing Co elution is increased. Although other element substitution can stabilize the structure of the lithium-containing cobalt oxide and suppress the Co elution, there is a problem that the charge / discharge capacity decreases. On the other hand, if Ni is within the range of the present invention, the change in charge / discharge capacity due to the increase / decrease of the addition amount is extremely small, and Ni is preferable as an additive element for suppressing Co elution while maintaining the battery at a high capacity. The addition amount y of Ni is preferably 0 <y ≦ 0.1, and more preferably 0 <y ≦ 0.05 in order to suppress a decrease in potential.

  Addition of Mg as M replaces Li and Co sites, stabilizes the structure of the lithium-containing cobalt oxide, increases the effect of suppressing Co elution, and improves heat resistance It is preferable because of the effect of If it is added excessively, the crystal lattice of the lithium-containing cobalt oxide is distorted, which may cause a decrease in battery capacity and a decrease in load characteristics due to a decrease in Li mobility. Further, when Mg is excessively contained, there is a problem that Mg is eluted with a charge / discharge cycle and the life of the battery is reduced. Therefore, the added amount y of Mg is 0 <y ≦ 0.1. Preferably, there is more preferably 0.005 ≦ y ≦ 0.01.

  Addition of Al as M has almost the same ionic radius of 6-coordinate Co ions and Al ions, so it is replaced with Co sites to stabilize the structure of lithium-containing cobalt oxides and elution of Co There is an effect to suppress. Moreover, there exists an effect which improves heat resistance. However, like Mg, if added excessively, the crystal lattice of the lithium-containing cobalt oxide is distorted, which may cause a decrease in battery capacity and a decrease in load characteristics due to a decrease in Li mobility. The addition amount y of Al is preferably 0 <y ≦ 0.1, and more preferably 0 <y ≦ 0.01.

  The addition of Zr has the effect of improving the high voltage charge / discharge cycle life at 4.3 V or higher in addition to the effect of increasing the potential in the low charge state and improving the output. The amount y of Zr is preferably 0 <y ≦ 0.1, and more preferably 0.001 ≦ y ≦ 0.005. When it exceeds 0.005, the growth of the positive electrode material particles is suppressed, and the particles may be small. When such a small particle is used to form the positive electrode mixture layer, there is a possibility that sufficient battery capacity cannot be obtained due to its low density. Further, since the surface area is increased, Co elution is likely to occur. Mn, V, W, Mo, Cr, Ti, and the like can exhibit the same effects as Zr.

  The addition of Bi promotes grain growth and has an effect of suppressing the Co elution reaction even at a high voltage. The amount y of Bi is particularly preferably 0.001 ≦ y ≦ 0.005. If it exceeds 0.005, a heterogeneous phase appears and the electrochemical characteristics may be deteriorated.

  In the general composition formula (1), δ relating to oxygen is 0 ≦ δ ≦ 0.02. The collapse of the crystal structure due to the desorption of oxygen is considered to be one cause of Co elution. If δ calculated from iodometric titration and ICP is 0.02 or less, oxygen deficiency is sufficiently small.

The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention has a layered rock salt structure in which the central part of the lithium-containing cobalt oxide particles represented by the general composition formula (1) belongs to the space group R3-m. There is a stepwise change to a spinel structure belonging to the space group Fd3m in the region of the thickness of 100 nm or less which is the outermost surface. Since the lamellar rock salt structure and the spinel structure are lattice-matched, the arrangement of oxygen remains the same, and the arrangement of metallic elements including Li, Co, and M is gradually changed, so a clear boundary is formed between the two types of structures. However, the influence on the diffusion of Li is small. Furthermore, the presence of a structure-stable spinel structure in the outermost shell suppresses deterioration of the surface of the lithium-containing cobalt oxide particles due to a disproportionation reaction or a side reaction with an electrolytic solution such as Co elution by reduction. The As a result, the continuous charging characteristics at high temperature and high voltage are dramatically improved. In the Raman spectrum of the particle surface of the lithium-containing cobalt oxide that provides such an effect, it has a shoulder peak in the range of 650 cm ^{−1 to} 700 cm ⁻¹ . The shoulder peak in the present invention, in the Raman spectrum, the peak shape is asymmetrical expressed in about 590 cm ^-1, and, in between the peak top of the 700 cm ^-1, higher spectral intensity than the background is held Refers to the part. An example of a Raman spectrum measurement method is as follows. A laser beam having a wavelength of 532 nm and an intensity of 0.7 mW to 1.0 mW is irradiated to one point on the particle surface of lithium-containing cobalt oxide, and the generated Raman scattered light is detected by a CCD. Can be obtained.

  The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention is an oxide in which particles contain one or more elements selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn, and P. It may be further coated with a product or fluoride. In this case, in addition to improving the deterioration suppressing effect due to the charge / discharge cycle, the Co elution suppressing effect is also improved. However, if the amount of oxide or fluoride to be coated is too large, the resistance may increase and the battery capacity may decrease. Therefore, the element contained in the oxide or fluoride to be coated is preferably 10% or less of the number of molecules of the lithium-containing cobalt oxide represented by the general composition formula (1).

<Preparation of positive electrode material for nonaqueous electrolyte secondary battery>
The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention can be produced, for example, by firing a mixture powder in which a Li compound, a Co compound, an M compound, and the like are mixed at an appropriate ratio. In addition, there is no particular limitation, and it is also possible to manufacture by mixing a precursor hydroxide excluding Li obtained by a coprecipitation method or the like with a Li compound and baking.

As the Li compound, LiOH, Li ₂ CO _3, LiCl, or the like can be used. Further, as the Co compound and the M compound, hydroxides or oxides of these elements can be used. The temperature during synthesis is 800 ° C. to 1100 ° C., the temperature holding time is 5 hours to 48 hours, the heating / cooling rate r is 1 ≦ r ≦ 5 ° C./min, and the atmosphere during synthesis is air or oxygen atmosphere. Is preferred.

Next, in order to make the outermost surface of the particles into a spinel structure, for example, the following procedure can be used. First, the lithium-containing cobalt oxide after combining, mixing _Li 2 CO ₃ and / or LiOH. It is preferable to mix at a molecular weight ratio of 0.5% to 10%. Next, annealing is performed at a temperature range of 950 ° C. to 1100 ° C. for 2 hours to 20 hours. At this time, the heating / cooling rate r is preferably 1 ≦ r ≦ 5 ° C./min, the atmosphere during annealing is an air or oxygen atmosphere, and the pressure is preferably atmospheric pressure or lower.

As another method, first, during the synthesis of the lithium-containing cobalt oxide, Li ₂ CO ₃ and / or LiOH is excessively mixed with the raw material of the lithium-containing cobalt oxide. It is preferable to mix at a molecular weight ratio of 0.5% to 10%. Next, the outermost surface of the particle can be formed into a spinel structure by performing an annealing treatment within a temperature range of 950 ° C. to 1100 ° C. for 5 hours to 48 hours. At this time, the heating / cooling rate r is preferably 1 ≦ r ≦ 5 ° C./min.

  By the above-described annealing treatment, lithium and oxygen on the surface of the lithium-containing cobalt oxide are evaporated to form a spinel structure.

  In the general composition formula (1), when the oxygen concentration is low, oxygen desorption easily occurs when the amount of Li addition is large. Moreover, when Ni was used as M, it turned out that Ni is easy to transfer to Li site partially. The oxygen concentration can be adjusted as appropriate according to the contents of Li and Ni. For example, x related to Li in the general composition formula (1) is 0.1, and y related to Ni is 0.05. In this case, the oxygen concentration is preferably 20% or more. By adjusting the firing atmosphere in this manner, oxygen deficiency and Ni transition are suppressed, and in the spectrum of the powder XRD, a layered rock salt structure belonging to the space group R3-m is observed, and it belongs to the (104) plane. The ratio of the diffraction intensity attributed to the (003) plane to the diffraction intensity is 1.5 to 30. By the above production method, a positive electrode material for a non-aqueous electrolyte secondary battery having improved capacity, output, heat resistance, storage at a high voltage, and continuous charge characteristics at a high voltage can be obtained.

  In the positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention, the particles are oxidized containing at least one element selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn, and P. In order to further coat with a product or fluoride, for example, the following procedure is used.

  When coating with Zr, Ti, Al, Ni, Mn, and Zn oxide, in an aqueous solution of sodium hydroxide or lithium hydroxide adjusted to a pH value of 9 to 11 and a temperature of 60 ° C. to 80 ° C. After the powder of the positive electrode material for a non-aqueous electrolyte secondary battery is stirred and dispersed, the covering element nitrate or sulfate is dropped. At this time, a coprecipitate is generated by simultaneously dropping ammonia water so that the pH value does not change. Thereafter, the coprecipitate and the positive electrode material powder are continuously stirred for 5 hours or more, and adjusted so that the pH value does not fluctuate with sodium hydroxide or lithium hydroxide as needed. In particular, when obtaining a coprecipitate such as Ni and Mn, it is more preferable to replace the dissolved oxygen in the aqueous solution with nitrogen. Next, the positive electrode material powder to which the coprecipitate is adhered and the aqueous solution are separated by suction filtration, washed with ultrapure water, and dried. By firing this powder, a positive electrode material for a non-aqueous electrolyte secondary battery in which a coating layer of Zr, Ti, Al, Ni, Mn, and Zn oxide is formed can be obtained.

  As another method for coating Zr, Ti, Al, Ni, Mn, and Zn oxide, an alkoxide of a desired element is dissolved in an alcohol solvent, and is stirred and dried at a temperature of 60 ° C. or higher and 80 ° C. or lower. There is also a method of adhering to a positive electrode material for a water electrolyte secondary battery and baking.

In addition, when coating Zr, Ti, Al, Ni, Mn, Zn, and P oxide containing Li, any of the above methods may be used to coat the surface of the particles of the positive electrode material for a non-aqueous electrolyte secondary battery. After attaching the precursor, LiOH or Li ₂ CO ₃ may be mixed and fired.

For example, when a fluoride such as AlF ₃ is coated, a non-aqueous electrolyte solution is added in an aqueous solution of sodium hydroxide or lithium hydroxide adjusted to a pH value of 9 to 11 and a temperature of 60 ° C. to 80 ° C. The powder of the positive electrode material for the next battery is stirred and dispersed, and then aluminum nitride hydrate is added. Ammonium fluoride aqueous solution is dripped little by little, and after stirring for 5 hours or more, it may be filtered, dried, and fired in an inert gas atmosphere.

  The firing temperature at the time of coating is preferably 400 ° C. or more and 600 ° C. or less, and the firing time is preferably 5 hours or more and 24 hours or less. The firing atmosphere is preferably an oxidizing atmosphere such as air or oxygen when obtaining an oxide, and an inert atmosphere such as nitrogen when obtaining a fluoride.

  In order to produce a positive electrode using the positive electrode material for a non-aqueous electrolyte secondary battery, the positive electrode material is mixed with a binder, a conductive auxiliary agent, etc., and dispersed in a solvent to prepare a positive electrode mixture slurry. The mixture slurry is applied to the surface of the positive electrode current collector to form a positive electrode mixture layer.

As the binder, any one of a thermoplastic resin and a thermosetting resin may be used as long as it is chemically stable in the nonaqueous electrolyte secondary battery. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Oroechiren copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or its Na ⁺ Ionic crosslinked body, ethylene-methacrylic acid copolymer or its Na ⁺ ion crosslinked body, ethylene-methyl acrylate copolymer or its Na ⁺ ion crosslinked body, ethylene-methyl methacrylate copolymer or its Na ⁺ ion crosslinked body Etc. are applicable. These may be used alone or in combination of two or more. Among these, PVDF or acrylic materials are particularly preferably used in consideration of stability in the nonaqueous electrolyte secondary battery, influence on characteristics, and the like.

  As the conductive assistant, any inorganic material or organic material may be used as long as it is chemically stable in the nonaqueous electrolyte secondary battery. For example, graphite such as natural graphite and artificial graphite, single or multi-walled carbon nanotubes, graphene, fullerene, VGCF, acetylene black, ketjen black (trade name), carbon such as channel black, furnace black, lamp black, thermal black, etc. Conductive fiber such as black, carbon fiber, metal fiber, metal powder such as aluminum powder, conductive whisker made of carbon fluoride, zinc oxide, potassium titanate, conductive metal oxide such as titanium oxide, polyphenylene derivative, etc. The organic conductive material or the like can be used. These may be used alone or in combination of two or more. Among these, graphite having high conductivity and carbon black excellent in liquid absorption are preferable.

  As a form of the conductive auxiliary agent, for example, when it is in the form of particles, it is not limited to only the primary particles, and those having the form of aggregates such as secondary particles and chain structures can also be used. In the case of a conductive additive having such an aggregate form, it is easier to handle and the productivity of the positive electrode can be increased.

  The mass of the positive electrode material in the positive electrode mixture layer is preferably 85% to 99%. If the content ratio of the positive electrode material is less than 85%, the battery capacity becomes small. Conversely, if the content ratio is more than 99%, the amount of the conductive auxiliary agent is relatively small and the resistance of the positive electrode may be increased.

As the positive electrode material, only the positive electrode material for the non-aqueous electrolyte secondary battery represented by the general formula (1) may be used, but may be combined with other positive electrode materials. Examples of the positive electrode material to be combined include, for example, the general composition formula Li _{1 + a} Ni _1-bcd Co _b Mn _c M ′ _d O _2-e (2)
(Wherein M ′ is one or more elements selected from the group consisting of Al, Mg, Zr, V, W, Mo, Cr, Ti, B, Si, Fe, P, F, S and Cl. 0 ≦ a ≦ 0.05, 0 ≦ b ≦ 0.02, 0.01 ≦ c ≦ 0.03, 0.001 ≦ d ≦ 0.03, and 0 ≦ e ≦ 0.01. Lithium-containing nickel-cobalt-manganese oxides. When combining the lithium-containing nickel / cobalt / manganese oxide, the lithium-containing nickel / cobalt / manganese oxide and the lithium-containing cobalt oxide are preferably contained in a proportion of 5% by mass or more and 50% by mass or less.

  By combining the positive electrode material represented by the general formula (2), the electrochemical characteristics and safety as a nonaqueous electrolyte secondary battery can be improved.

  The mass of the binder in the positive electrode mixture layer is preferably 0.2% by mass to 5% by mass. Moreover, it is preferable that the mass of the conductive support agent which occupies for a positive mix layer shall be 0.5 mass%-8 mass%.

A positive electrode material mixture including a positive electrode material for a nonaqueous electrolyte secondary battery according to the present invention as a positive electrode material, a binder, a conductive auxiliary agent, and the like is dispersed in N-methyl-2-pyrrolidone (hereinafter referred to as NMP) or the like. A positive electrode mixture slurry is prepared. After this positive electrode mixture slurry is applied to one or both surfaces of the positive electrode current collector, NMP is evaporated, and a press treatment is performed to form a positive electrode mixture layer on the current collector surface. The press treatment is for adjusting the thickness and density of the positive electrode mixture layer, and can be performed using, for example, a roll press machine or a hydraulic press machine. The density of the positive electrode mixture layer produced in this way is preferably 3.5 g / cm ³ or more and 4.5 g / cm ³ or less. The method for manufacturing the positive electrode is not limited to the above, and other manufacturing methods may be used.

  The material of the positive electrode current collector is not particularly limited as long as it is a chemically stable electron conductor in the nonaqueous electrolyte secondary battery. For example, in addition to aluminum, aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., aluminum, aluminum alloy, a composite material in which a carbon layer or a titanium layer is formed on the surface of stainless steel, or the like can be used. . Among these materials, aluminum or aluminum alloy is preferable because it is lightweight and has high conductivity. As a material of the positive electrode current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like of the above materials can be used. Further, the surface of the positive electrode current collector can be roughened by surface treatment. The thickness of the positive electrode current collector is not particularly limited, but is preferably 1 μm to 500 μm.

  As a method for applying the positive electrode mixture slurry to the current collector surface, various methods such as spin coating, dipping, and screen printing can be used.

  The nonaqueous electrolyte secondary battery according to the present invention has a positive electrode using the positive electrode material for a nonaqueous electrolyte secondary battery according to the present invention as a positive electrode material. There are no particular restrictions on the configuration and structure other than the positive electrode.

The positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention is less likely to transition to CoO ₂ (O1 structure). For example, for a non-aqueous electrolyte secondary battery using a lithium metal as a negative electrode and a positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention as a positive electrode, charging to 5 V at 0.1 C or less at room temperature, In the dQ / dV curve obtained by differentiating the charge curve of the positive electrode at this time, the peak potential due to the start of the phase transition to the O1 structure that appears on the highest potential side is 4.64 V or higher. . This indicates that the positive electrode material for a non-aqueous electrolyte secondary battery according to the present invention is not easily transferred to CoO ₂ (O1 structure).

  Next, although this invention is demonstrated further in detail based on an Example and a comparative example, it is not limited to these.

Example 1
<Synthesis of positive electrode material>
Li ₂ CO ₃ as the Li compound and Co ₃ O ₄ as the Co compound were mixed in a mortar at an appropriate mixing ratio, then solidified into a pellet shape, and using a muffle furnace in an atmospheric atmosphere at atmospheric pressure, Heat treatment was performed at 950 ° C. for 24 hours.

Next, the pellets are pulverized, and Li ₂ CO ₃ is added to the lithium-containing cobalt oxide by 1.5% in a molecular weight ratio, mixed using a mortar, and in an oxygen gas atmosphere (oxygen) using a tubular electric furnace. A positive electrode for a non-aqueous electrolyte secondary battery comprising lithium-containing cobalt oxide particles represented by the general composition formula LiCoO ₂ by performing an annealing treatment at 1000 ° C. for 10 hours at a gas flow rate of 0.5 L / min) The material was synthesized.

The composition was measured by an ICP (Inductivity Coupled Plasma) method and an iodometric titration method. The particle size was measured with a laser diffraction / scattering particle size distribution analyzer, and it was confirmed that the average diameter was 20 μm. Moreover, as a result of calculating | requiring the BET specific surface area using the specific surface area measuring apparatus by a nitrogen adsorption method, the specific surface area was 0.15 m < ² > / g.

Here, the Raman spectrum of the positive electrode material for a non-aqueous electrolyte secondary battery according to Example 1 was measured by irradiating a point on the particle surface with laser at a wavelength of 532 nm, an intensity of 0.8 mW, and an irradiation time of 30 seconds. As shown in FIG. 1, the Raman spectrum of the positive electrode material for a nonaqueous electrolyte secondary cell according to example ^1, a shoulder peak was confirmed in the range of 650cm ^-1 ~700cm -1. It is considered that a shoulder peak as shown in FIG. 1 appears as a result of overlapping spectra of LT-LiCoO ₂ and Co ₃ O _{4 having} a spinel structure, and it was confirmed that a spinel structure was present. Moreover, the X-ray diffraction of the positive electrode material for nonaqueous electrolyte secondary batteries according to Example 1 was measured. From the X-ray diffraction measurement result shown in FIG. 2, it was a layered rock salt structure belonging to the space group R3-m, and no heterogeneous phase was confirmed. This suggests that the spinel structure confirmed by the Raman spectrum does not have long-range order and exists in a state having lattice strain on the outermost surface of the particle.

<Preparation of positive electrode>
As a positive electrode material, a lithium-containing cobalt oxide powder of the above general composition formula LiCoO ₂ was dispersed in an NMP solution containing PVDF as a binder to prepare a mixed solution. The mass of PVDF in the mass of the NMP solution is 10%. The mass ratio of the lithium-containing cobalt oxide having the above composition and the NMP solution was 95: 5. To this mixed solution, 2.5 parts by mass of carbon black as a conductive assistant was added, kneaded in a mortar, and NMP was added to adjust the viscosity to prepare a positive electrode mixture slurry.

  The positive electrode mixture slurry was applied to a positive electrode current collector made of aluminum foil having a thickness of 15 μm using a baker-type applicator, and then dried at 80 ° C. for 1 hour. An agent layer was formed. The positive electrode current collector on which the positive electrode mixture layer was formed was processed into a disk shape having a diameter of 15 mm, then pressed at a pressure of about 30 MPa, and further dried at 100 ° C. for 20 hours in a vacuum dryer. A positive electrode was produced by such a process.

<Production of negative electrode>
A metal lithium rolled plate having a predetermined thickness was processed into a disk shape having a diameter of 16 mm to produce a negative electrode.

<Nonaqueous electrolyte>
A non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) at a molar concentration (mol / l) in a solvent in which ethylene carbonate and diethyl carbonate having a volume ratio of 1: 2 were mixed. .

<Assembly of nonaqueous electrolyte secondary battery>
A flat battery was assembled using the above positive electrode, negative electrode, and non-aqueous electrolyte. FIG. 3 schematically shows a cross section of the assembled nonaqueous electrolyte secondary battery 1. The assembly was performed as follows.

  After the insulating ring 8 was inserted into the side surface of the stainless steel container 13, the negative electrode 4, the separator 3, and the positive electrode 2 were laminated in this order, and the nonaqueous electrolyte was impregnated into the separator 3. As the separator 3, a microporous film made of polypropylene was used. An aluminum pressing plate 5 and a leaf spring 6 are sequentially stacked on the positive electrode 2, a stainless steel lid 7 is placed via an insulating packing 9, and tightened with a bolt 12 and a nut 11 via an insulating sleeve 10, A flat battery was constructed.

  The positive electrode 2 is electrically connected to the lid 7 via the pressing plate 5 and the leaf spring 6, and the negative electrode 4 is electrically connected to the bolt 12 via the container 13. Thereby, electrical energy can be taken out from the inside of the battery using the lid 7 and the bolt 12 as terminals.

(Example 2)
The synthesis conditions of the positive electrode material of Example 1 were changed, and the mixture ratio of Co ₃ O ₄ and Li ₂ CO ₃ was mixed at a ratio of Li / Co = 1.03, and was used in an air atmosphere using an electric furnace. A positive electrode material composed of lithium-containing cobalt oxide particles represented by the general composition formula LiCoO ₂ was synthesized as a positive electrode material by heat treatment at 1000 ° C. for 20 hours. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 2 was fabricated in the same procedure as in Example 1 above.

Results of the evaluation of the Raman spectrum in the same manner as in Example 1, a shoulder peak was confirmed in the range of ^{650cm -1 ~700cm} -1 as shown in FIG.

Example 3
The annealing conditions of Example 1 were changed, Li ₂ CO ₃ was added at a molecular weight ratio of 10%, mixed using a mortar, and in an oxygen gas atmosphere using a tubular electric furnace (oxygen gas flow rate 0.5 L / min) Then, a positive electrode material composed of lithium-containing cobalt oxide particles represented by a general composition formula Li _1.05 CoO _1.98 was synthesized as a positive electrode material by performing heat treatment at 1000 ° C. for 10 hours. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 3 was fabricated in the same procedure as in Example 1 above.

Results of the evaluation of the Raman spectrum in the same manner as in Example 1, a shoulder peak was confirmed in the range of ^{650cm -1 ~700cm} -1 as shown in FIG.

(Example 4)
Lithium represented by the general composition formula LiCo _0.95 Ni _0.05 O ₂ as the positive electrode material is the same as that of Example 1 except that Ni (OH) ₂ is added to Example 1 as the Ni compound. Containing cobalt oxide was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 4 was fabricated in the same procedure as in Example 1 above.

(Example 5)
A lithium-containing cobalt oxide represented by the general composition formula LiCo _0.98 Ni _0.02 O ₂ was synthesized as a positive electrode material in the same procedure as in Example 4. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 5 was fabricated in the same procedure as in Example 1 above.

(Example 6)
Instead of the Ni compound used in Example 4, Mg (OH) ₂ was used as the Mg compound, and the general composition formula LiCo _0.99 Mg _0.01 O was used as the positive electrode material in the same procedure as in Example 1 except that. A lithium-containing cobalt oxide represented by ₂ was synthesized. Using this positive electrode material, a non-aqueous electrolyte secondary battery according to Example 6 was fabricated in the same procedure as in Example 1 above.

(Example 7)
Instead of the Ni compound used in Example 4, Al (OH) ₃ was used as the Al compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.97 Al was used as the positive electrode material. A lithium-containing cobalt oxide represented by _0.03 O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 7 was fabricated in the same procedure as in Example 1 above.

(Example 8)
Instead of the Ni compound used in Example 4, Bi (OH) ₂ was used as the Bi compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.995 Bi was used as the positive electrode material. A lithium-containing cobalt oxide represented by _0.005 O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 8 was fabricated in the same procedure as in Example 1 above.

Example 9
Instead of the Ni compound used in Example 4, V ₂ O ₅ was used as the V compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.97 V ₀ was used as the positive electrode material. A lithium-containing cobalt oxide represented by _0.03 O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 9 was produced in the same procedure as in Example 1 above.

(Example 10)
Instead of the Ni compound used in Example 4, TiO ₂ was used as the Ti compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.97 Ti _0.03 was used as the positive electrode material. A lithium-containing cobalt oxide represented by O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 10 was fabricated in the same procedure as in Example 1 above.

(Example 11)
Instead of the Ni compound used in Example 4, Mn (OH) ₂ was used as the Mn compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.99 Mn was used as the positive electrode material. A lithium-containing cobalt oxide represented by _0.01 O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 11 was fabricated in the same procedure as in Example 1 above.

Example 12
Instead of the Ni compound used in Example 4, ZrO ₂ was used as the Zr compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.995 Zr _0.005 was used as the positive electrode material. A lithium-containing cobalt oxide represented by O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 12 was fabricated in the same procedure as in Example 1 above.

(Example 13)
In addition to the Ni compound used in Example 4, Mg (OH) ₂ was used as the Mg compound, and the other procedures were the same as in Example 1 except that the general composition formula Li _1.01 Co _0.97 Ni was used as the positive electrode material. A lithium-containing cobalt oxide represented by _0.02 Mg _0.01 O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 13 was fabricated in the same procedure as in Example 1 above.

(Example 14)
In addition to the Ni and Mg compounds used in Example 13, ZrO ₂ was used as the Zr compound, and the other procedures were the same as in Example 1 except that the general composition formula LiCo _0.965 Ni _0.02 Mg ₀ was used as the positive electrode material. A lithium-containing cobalt oxide represented by _.01 Zr _0.005 O ₂ was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 14 was fabricated in the same procedure as in Example 1 above.

(Example 15)
A lithium-containing cobalt oxide represented by a general composition formula Li _1.01 Co _0.97 Ni _0.02 Mg _0.01 O ₂ was synthesized as a positive electrode material in the same procedure as in Example 13. Next, the positive electrode material powder for a nonaqueous electrolyte secondary battery is stirred and dispersed in an aqueous lithium hydroxide solution adjusted to have a pH value of 9 or more and 11 or less and a temperature of 60 ° C. or more and 80 ° C. or less. NO ₃₎ was added dropwise ₃ · 9H ₂ O. At this time, Al (OH) ₃ coprecipitate was produced by simultaneously dropping ammonia water so that the pH value would not change. Thereafter, stirring was continued for 5 hours or longer, and the pH value was adjusted so as not to fluctuate with lithium hydroxide as needed. Next, the positive electrode material powder to which Al (OH) ₃ was adhered and the aqueous solution were separated by suction filtration, washed with ultrapure water, and vacuum-dried at 80 ° C. for 24 hours. The powder was fired at 400 ° C. for 10 hours in an air atmosphere. By such a process, an oxide-coated positive electrode material in which the number of Al atoms in the oxide film formed on the surface of the positive electrode material was 1% of the number of molecules of the lithium-containing cobalt oxide was produced. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 15 was fabricated in the same procedure as in Example 1.

(Example 16)
A lithium-containing cobalt oxide represented by a general composition formula Li _1.01 Co _0.97 Ni _0.02 Mg _0.01 O ₂ was synthesized as a positive electrode material in the same procedure as in Example 13. Next, zirconium isopropoxide was dissolved in an isopropyl alcohol solvent, stirred at 60 ° C. for 10 hours together with the positive electrode material powder for a non-aqueous electrolyte secondary battery, and dried at 80 ° C. This powder was fired at 400 ° C. in an air atmosphere for 10 hours. Through such a process, an oxide-coated positive electrode material in which the number of Zr atoms in the oxide film formed on the surface of the positive electrode material was 1% of the number of molecules of the lithium-containing cobalt oxide was produced. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 16 was produced in the same procedure as in Example 1.

(Example 17)
A lithium-containing cobalt oxide represented by a general composition formula Li _1.01 Co _0.97 Ni _0.02 Mg _0.01 O ₂ was synthesized as a positive electrode material in the same procedure as in Example 13. Next, after stirring and dispersing the positive electrode material powder for a non-aqueous electrolyte secondary battery in a lithium hydroxide aqueous solution adjusted to a pH value of 9 or more and 11 or less and a temperature of 60 ° C., aluminum nitride hydrate was added. I put it in. Ammonium fluoride aqueous solution was dropped there little by little, and after stirring for 10 hours or more, suction filtration was performed, followed by washing with ultrapure water, followed by vacuum drying at 80 ° C. for 24 hours. This powder was fired in a nitrogen gas atmosphere for 10 hours. By such a process, a fluoride-coated positive electrode material in which the number of Al atoms in the AlF ₃ coating formed on the surface of the positive electrode material was 1% of the number of molecules of the lithium-containing cobalt oxide was produced. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Example 17 was fabricated in the same procedure as in Example 1.

  Table 1 lists the compositions of the positive electrode materials of Examples 1 to 17 and elements covering the surface of the positive electrode material.

(Comparative Example 1)
The annealing treatment conditions were changed from Example 1, Li ₂ CO ₃ was added at a molecular weight ratio of 0%, mixed using a mortar, and in an oxygen gas atmosphere using a tubular electric furnace (oxygen gas flow rate 0.5 mL / min) Then, a positive electrode material for a non-aqueous electrolyte secondary battery composed of lithium-containing cobalt oxide particles represented by the general composition formula Li _0.98 CoO ₂ is synthesized as a positive electrode material by performing a heat treatment at 1000 ° C. for 10 hours. did. Using this positive electrode material, a non-aqueous electrolyte secondary battery according to Comparative Example 1 was produced in the same procedure as in Example 1.

As a result of evaluating the Raman spectrum in the same manner as in Example 1, as shown in FIG. 1, a shoulder peak in the range of 650 cm ^{−1 to} 700 cm ⁻¹ does not appear, and a Raman spectrum of a general lithium-containing cobalt oxide is obtained. It was. Also, from the X-ray diffraction measurement result shown in FIG. 2, it was confirmed that the layered rock salt structure belongs to the space group layer R3-m, and it was confirmed that there was no heterogeneous phase from the center of the particle to the surface.

(Comparative Example 2)
The annealing process conditions were changed from Example 1, Li ₂ CO ₃ was added at a molecular weight ratio of 1.5%, mixed using a mortar, and heat-treated at 1000 ° C. for 10 hours in an air atmosphere using a muffle furnace. As a result, a positive electrode material for a non-aqueous electrolyte secondary battery composed of lithium-containing cobalt oxide particles represented by the general composition formula LiCoO ₂ was synthesized as a positive electrode material. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Comparative Example 2 was produced in the same procedure as in Example 1.

As a result of evaluating the Raman spectrum in the same manner as in Example 1, as shown in FIG. 1, a shoulder peak in the range of 650 cm ^{−1 to} 700 cm ⁻¹ does not appear, and a Raman spectrum of a typical lithium-containing cobalt oxide is obtained. It was. Also, from the X-ray diffraction measurement result shown in FIG. 2, it was confirmed that the layered rock salt structure belongs to the space group layer R3-m, and it was confirmed that there was no heterogeneous phase from the center of the particle to the surface.

(Comparative Example 3)
Change the annealing conditions from Example 1, add 6% of Li ₂ CO ₃ by molecular weight ratio, mix using a mortar, and heat-treat at 1000 ° C. for 10 hours in an air atmosphere using a muffle furnace. Thus, a positive electrode material for a non-aqueous electrolyte secondary battery composed of lithium-containing cobalt oxide particles represented by the general composition formula Li _1.10 CoO _1.95 was synthesized as a positive electrode material. Using this positive electrode material, a non-aqueous electrolyte secondary battery according to Comparative Example 3 was produced in the same procedure as in Example 1.

(Comparative Example 4)
Non-water consisting of lithium-containing cobalt oxide particles represented by the general composition formula Li _0.99 Co _0.95 Ni _0.05 O ₂ as a positive electrode material, synthesized without carrying out the annealing treatment of Example 4 A positive electrode material for an electrolyte secondary battery was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Comparative Example 4 was produced in the same procedure as in Example 1.

(Comparative Example 5)
The annealing treatment conditions of Example 4 were changed, Li ₂ CO ₃ was added at a molecular weight ratio of 1.0%, mixed using a mortar, and in an oxygen gas atmosphere using a tubular electric furnace (oxygen gas flow rate 0.5 L / min) ), A non-aqueous solution comprising lithium-containing cobalt oxide particles represented by the general composition formula Li _0.97 Co _0.95 Ni _0.05 O ₂ as a positive electrode material by performing a heat treatment at 1000 ° C. for 10 hours. A positive electrode material for an electrolyte secondary battery was synthesized. Using this positive electrode material, a non-aqueous electrolyte secondary battery according to Comparative Example 5 was produced in the same procedure as in Example 1.

(Comparative Example 6)
A non-aqueous electrolyte secondary battery composed of lithium-containing cobalt oxide particles represented by the general composition formula LiCo _0.99 Mg _0.01 O ₂ as a positive electrode material, synthesized without performing the annealing treatment of Example 6 A positive electrode material was synthesized. Using this positive electrode material, a nonaqueous electrolyte secondary battery according to Comparative Example 6 was produced in the same procedure as in Example 1.

(Comparative Example 7)
A non-aqueous electrolyte secondary battery composed of lithium-containing cobalt oxide particles represented by the general composition formula LiCo _0.99 Mg _0.01 O ₂ as a positive electrode material, synthesized without performing the annealing treatment of Example 6 A positive electrode material was synthesized. Next, after coating the surface of the positive electrode material with Al oxide in which the number of Al atoms is 1% of the number of lithium-containing cobalt oxide in the same procedure as in Example 15, the same as in Example 1 A nonaqueous electrolyte secondary battery according to Comparative Example 7 was produced according to the procedure.

(Comparative Example 8)
Lithium-containing cobalt oxide particles represented by the general composition formula Li _1.01 Co _0.97 Ni _0.02 Mg _0.01 O ₂ as a positive electrode material synthesized without carrying out the annealing treatment of Example 13 A positive electrode material for a non-aqueous electrolyte secondary battery was synthesized. Next, after coating the surface of the positive electrode material with Al oxide in which the number of Al atoms is 1% of the number of lithium-containing cobalt oxide in the same procedure as in Example 15, the same as in Example 1 A nonaqueous electrolyte secondary battery according to Comparative Example 8 was produced according to the procedure.

Table 1 lists the compositions of the positive electrode materials of Comparative Examples 1 to 8 and elements covering the surface of the positive electrode material.

<Evaluation of non-aqueous electrolyte secondary battery>
About each nonaqueous electrolyte secondary battery of Examples 1-17 and Comparative Examples 1-8, initial charge capacity and cycle characteristics, a storage test, and continuous charge characteristics were measured in the following manner.

<Measurement of initial charge capacity>
At room temperature (25 ° C.), the battery is charged at a constant current until the battery voltage reaches 4.45 V at a current of 0.05 C, and then the current is applied at a constant voltage of 4.45 V vs Li / Li ^+. The battery was charged until it reached 0.005C. The measurement results are shown in Table 2.

<Evaluation of cycle characteristics>
After completion of the initial charging, the battery was left for 1 hour and discharged at a constant current until the battery voltage reached 2.5 V at a current of 0.05 C load. This process was repeated for 2 cycles and left to initialize for 1 day.

After aging, charging is started at a constant current of 0.2C load factor, charging is performed until the battery voltage reaches 4.5V vs Li / Li ⁺ , and then the current is loaded at a constant voltage of 4.5V vs Li / Li ^+. The battery was charged until the rate reached 0.02C. Thereafter, the battery was left for 1 hour, and discharged at a constant current until the battery voltage reached 2.5 V at a load factor of 0.2 C. The charge / discharge cycle was repeated 50 times, and the discharge capacity at the 50th cycle was compared with the discharge capacity at the first cycle.

<Evaluation of storage characteristics>
After completion of the initial charging, the battery was left for 1 hour and discharged at a constant current until the battery voltage reached 2.5 V at a current of 0.05 C load. This process was repeated for 2 cycles and left to initialize for 1 day.

Next, charging is started at a constant current of a load factor of 0.05 C, charging is performed until the battery voltage becomes 4.5 V vs Li / Li ⁺ , and then the current is loaded at a constant voltage of 4.5 V vs Li / Li ⁺ The battery charged to a rate of 0.005 C was left in a constant temperature bath at 60 ° C. for 7 days, and then discharged at a constant current until the battery voltage reached 2.5 V at a load factor of 0.05 C.

Furthermore, charging is started at a constant current of a load factor of 0.05 C, charging is performed until the battery voltage becomes 4.45 V vs Li / Li ⁺ , and then the current is applied at a constant voltage of 4.45 V vs Li / Li ^+. The battery was charged until it reached 0.005C. Thereafter, the battery was left for 1 hour and discharged at a constant current until the battery voltage reached 2.5 V at a current of 0.05 C load factor. The case where the final discharge capacity of the test was 80% or more of the discharge capacity after initialization was evaluated as ◯, and the case where it was less than 80% was evaluated as x. The evaluation results are shown in Table 2.

<Evaluation of continuous charging characteristics>
After completion of the initial charging, the battery was left for 1 hour and discharged at a constant current until the battery voltage reached 2.5 V at a current of 0.05 C load. This process was repeated for 2 cycles and left to initialize for 1 day.

After leaving the battery in a constant temperature bath at 60 ° C. for 30 minutes, charging is started at a constant current with a load factor of 0.05 C while maintaining the environment at 60 ° C., and the battery voltage becomes 4.5 V vs Li / Li ⁺ . Until charged. After the current value decays, the battery is continuously charged at a constant voltage of 4.5 V vs Li / Li ⁺ until the current value rises again to the load factor of 0.05 C. From the time when charging is started, the charge is again increased to 0.05 C. The time to reach was measured. The measurement results are shown in Table 2.

From the results shown in Table 2, the following can be understood.
The non-aqueous electrolyte secondary batteries according to Examples 1, 2, and 3 and Comparative Examples 1 and 2 each have an initial charge / discharge capacity of 188 mAh / g to 189 mAh / g, and the capacity retention rate after the cycle test is 80 %. On the other hand, there was a difference between the results of the storage test and the continuous charge characteristics. In Examples 1, 2, and 3, the capacity retention after the storage test was 80% or more, but in Comparative Examples 1 and 2, it was less than 80%. Regarding the continuous charging characteristics, Examples 1, 2, and 3 were about four times as long as Comparative Examples 1 and 2. The difference between the results of the storage test and the continuous charging characteristics is considered to be due to a plurality of deterioration modes. In particular, in the case of Examples 1, 2, and 3, the structurally stable spinel structure is the outermost shell. It is considered that the presence of the Co-elution due to disproportionation or reduction due to a side reaction with the electrolytic solution peculiar to the lithium-containing cobalt oxide is suppressed.

  In the nonaqueous electrolyte secondary battery according to Comparative Example 3, although the continuous charge characteristics were dramatically improved by increasing the lithium content, the initial charge capacity and the cycle characteristics were significantly decreased due to oxygen deficiency. The results of the storage test were also poor, and it was found that the unbalanced characteristic was that only the continuous charging characteristic was good as compared with Examples 1, 2, and 3.

  Example 4 and Comparative Examples 4 and 5 are all nonaqueous electrolyte secondary batteries using a positive electrode material having a composition in which 5% of Co is replaced by Ni. Although there was no difference in the initial charge capacity, cycle characteristics, and storage test results, the continuous charge characteristics were about 4 times better than Comparative Examples 4 and 5 in terms of continuous charge characteristics, reaching 582 hours. Thus, it was found that when Co was partially replaced by Ni, the structural stability of the spinel structure was present in the outermost shell, so that the characteristics could be further improved compared to the case of no substitution.

  Example 6 and Comparative Example 6 are non-aqueous electrolyte secondary batteries using a positive electrode material having a composition in which 1% of Co is replaced with Mg. Similar to Ni substitution, it was found that even when a part of Co was replaced with Mg, the structural stability of the spinel structure was present in the outermost shell, so that the characteristics could be further improved compared to the case of no substitution.

  An element M other than Ni and Mg is also effective. As shown in Examples 7 to 12, even when substituted with Al, Bi, V, Ti, Mn, and Zr, a structure-stable spinel structure exists in the outermost shell. As a result, it was found that the characteristics could be further improved as compared with the case of no substitution. Regarding M, the same effect can be obtained by using Cr, Mo, W instead of Mn, V, Ti. Moreover, these elements can also be mixed and used suitably.

  Examples 13 and 14 are non-aqueous electrolyte secondary batteries using a positive electrode material in which a part of Co is replaced by a plurality of M at a ratio of several percent. In particular, it has been found that the continuous charge characteristics when Ni, Mg and Zr are combined are dramatically improved and exceed 650 hours.

In addition to the addition of M, as shown in Examples 15 to 17, by using a positive electrode material coated with metal oxide and fluoride such as Al ₂ O ₃ , ZrO ₂ , or AlF ₃ on the surface, the cycle The characteristics were improved, and it was revealed that a nonaqueous electrolyte secondary battery excellent in all the characteristics shown in Table 2 was obtained. On the other hand, even when the surface was coated with an oxide, it was found that the continuous charge characteristics were inferior in the case of Comparative Examples 7 and 8 that were not spinel structured.

  As described above, according to the present invention, it is possible to provide a nonaqueous electrolyte secondary battery that has a high capacity and is excellent in continuous charge characteristics at a high voltage at a high temperature. In all the nonaqueous electrolyte secondary batteries described in the examples, the most of the dQ / dV curve obtained by differentiating the charging curve of the positive electrode with voltage when charged to 5 V at a load factor of 0.1 C or less at room temperature. It was confirmed that the peak potential confirmed to be a high potential was 4.64 V or more. The non-aqueous electrolyte secondary battery according to the present invention having such characteristics is excellent in the Co elution suppressing effect when charged until the positive electrode potential becomes 4.4 V or higher with respect to lithium.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Positive electrode 3 Separator 4 Negative electrode 5 Holding plate 6 Leaf spring 7 Lid 8 Insulating ring 9 Insulating packing 10 Insulating sleeve 11 Nut 12 Bolt 13 Container

Claims (4)

General composition formula Li _{1 + x} Co _1-y M _y O _2-δ (where M is Ni, Mn, Al, Mg, Zr, V, W, Mo, Cr, Bi, Cu, Ti, Si, Fe, P) 1 or more elements selected from the group consisting of F, Cl, and 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.1, and 0 ≦ δ ≦ 0.02. comprises particles containing cobalt oxide containing, outermost surface of the particles have a spinel structure, in the Raman spectrum, the positive electrode for a nonaqueous electrolyte secondary battery having a shoulder peak in the range of 650cm ^-1 ~700cm ^-1 materials, and the general formula _{Li 1 + a Ni 1-b} -c-d Co b Mn c M 'd O 2-e ( wherein, M' is Al, Mg, Zr, V, W, Mo, Cr, Ti 1 selected from the group consisting of B, Si, Fe, P, F, S and Cl These elements are as follows: 0 ≦ a ≦ 0.05, 0 ≦ b ≦ 0.02, 0.01 ≦ c ≦ 0.03, 0.001 ≦ d ≦ 0.03, 0 ≦ e ≦ 0.01 a positive electrode containing an acid compound represented by some),
A negative electrode,
A separator;
And a nonaqueous electrolyte, comprising the oxide, in a proportion of 50 mass% or more 5% by weight relative to the total of the oxides and lithium-containing cobalt oxides,
Non-aqueous electrolyte secondary battery.   The particles are further coated with an oxide or fluoride containing one or more elements selected from the group consisting of Li, Zr, Ti, Al, Mg, Ni, Mn, Zn and P, and the number of atoms of the elements is The nonaqueous electrolyte secondary battery according to claim 1, which is 10% or less of the number of molecules of the lithium-containing cobalt oxide.   The potential of the peak confirmed at the highest potential of the dQ / dV curve obtained by differentiating the charge curve of the positive electrode with voltage when charged to 5 V at a load factor of 0.1 C or less at room temperature is 4.64 V. The nonaqueous electrolyte secondary battery according to claim 1, which is as described above. General composition formula Li _{1 + x} Co _1-y M _y O _2-δ (where M is Ni, Mn, Al, Mg, Zr, V, W, Mo, Cr, Bi, Cu, Ti, Si, Fe, P) 1 or more elements selected from the group consisting of F, Cl, and 0 ≦ x ≦ 0.1, 0 ≦ y ≦ 0.1, and 0 ≦ δ ≦ 0.02. comprises particles containing cobalt oxide containing, outermost surface of the particles have a spinel structure, in the Raman spectrum, the positive electrode for a nonaqueous electrolyte secondary battery having a shoulder peak in the range of 650cm ^-1 ~700cm ^-1 A method of manufacturing a material,
Synthesizing a lithium-containing cobalt oxide;
A step of mixing Li ₂ CO ₃ and / or LiOH with respect to the synthesized lithium-containing cobalt oxide;
And a step of performing an annealing treatment in an oxygen atmosphere at a temperature range of from 950 ° C. to 1100 ° C. for 2 hours to 20 hours.

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