JP2016170958A - Positive electrode active substance material for lithium ion secondary battery, positive electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte battery improved in cycle discharge when a positive electrode active substance exhibiting basic properties is used, and excellent in cycle retention rate.SOLUTION: A positive electrode active substance material for a lithium ion secondary battery includes a positive electrode active substance exhibiting basic properties and a coating layer coating the surface of the positive electrode active substance and including a compound represented by formula 1 (where, R1 and R2 represent hydrocarbon or oxygen, and n represents 1-30).SELECTED DRAWING: None

Description

  The present disclosure relates to a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  Lithium ion secondary batteries have higher output and higher capacity than conventional nickel cadmium batteries and nickel metal hydride batteries, and are currently widely used as main power sources for portable devices. In recent years, attention has been paid not only to portable devices, but also to power supplies for large-sized devices such as electric vehicles and industrial machines, and higher performance is required and research and development have been widely conducted.

  In order to increase the capacity of lithium ion secondary batteries that are required in recent years, it has been studied to use lithium ion secondary batteries in a wider voltage range.

  However, in a positive electrode that is exposed to a high potential as the operating voltage range expands, the decomposition reaction of the electrolytic solution on the surface of the positive electrode active material is likely to occur, so that the deterioration of the positive electrode active material itself or the electrolytic solution is promoted. It is difficult to extend the life of ion secondary batteries.

  Therefore, attempts have been made to improve various characteristics of the lithium ion secondary battery by coating the surface of the positive electrode active material with an inorganic compound such as an oxide.

  Patent Document 1 reports that the cycle characteristics and thermal stability of a lithium ion secondary battery are improved by coating the surface of lithium cobalt oxide with aluminum oxide.

  Patent Document 2 reports that the initial interface resistance with the solid electrolyte material is reduced by coating the surface of the positive electrode active material with a coat layer having a polyanion structure.

JP 2001-143703 A JP 2012-99323 A

  However, the cycle characteristics of the lithium ion secondary battery using the positive electrode active material shown in these technologies are still insufficient, and further improvement of characteristics is required.

  One object of the present invention is to solve the above problems, and provide a positive electrode active material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery having excellent cycle characteristics. There is.

The positive electrode active material for a lithium ion secondary battery of the present invention (hereinafter referred to as “positive electrode material”) is a compound represented by Formula 1 that covers a basic positive electrode active material and the surface of the positive electrode active material. (Wherein R1 and R2 are hydrocarbons or oxygen, and n represents 1 to 30).

  By using the positive electrode material, the cycle characteristics of a lithium ion secondary battery using the positive electrode material are improved.

  When the coating layer including the compound represented by Formula 1 is present on the surface of the positive electrode active material, the oxidative decomposition reaction with the electrolytic solution on the surface of the positive electrode active material exhibiting basicity can be suppressed.

  In addition, since the coating layer has a higher affinity with the electrolytic solution than the positive electrode active material, when the decomposition reaction of the electrolytic solution on the surface of the positive electrode active material occurs, the coating layer and the electrolytic solution preferentially react and stabilize. This is considered to suppress the deterioration of the electrolytic solution.

  In the positive electrode material of the present invention, the particle size A indicated by D50 of the positive electrode active material is 5 μm ≦ A ≦ 25 μm, the thickness B of the coating layer is 1 nm ≦ B ≦ 100 nm, and the particles of the positive electrode active material The ratio B / A of the thickness B of the coating layer to the diameter A is preferably 0.0008 ≦ B / A ≦ 0.02.

  By using a positive electrode active material and a positive electrode material having a coating layer that satisfy the above relationship, cycle characteristics of a lithium ion secondary battery using the positive electrode material can be further improved.

  This is presumably because there is a phase difference between the particle diameter and the thickness of the coating layer, and in the above range, the effect of suppressing the oxidative decomposition reaction of the electrolytic solution on the positive electrode active material surface is particularly high.

The positive electrode active material of the present invention has a general formula Li _x Ni _(1-yz) Co _y M _z O ₂ (M is Mg, Ca, Sr, Ba, Ti, Al, Cr, Mn, Fe, Ge, W , Cu, Zn at least one element, 0.95 ≦ x ≦ 1.2, 0 <y ≦ 1.0, 0 ≦ z ≦ 0.5, 0 <y + z ≦ 1.0) It is preferable to consist of the lithium transition metal oxide represented.

  By using the positive electrode active material having the above composition, cycle characteristics of a lithium ion secondary battery using the positive electrode active material can be further improved.

  The positive electrode active material having the above composition has a high lithium desorption voltage among positive electrode active materials exhibiting basicity, and the oxidative decomposition reaction of the electrolytic solution easily occurs when the positive electrode active material is exposed to a higher potential in a charged state. . Therefore, it is considered that a remarkable effect can be obtained by the presence of the coating layer.

  ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material material for lithium ion secondary batteries which has the outstanding cycling characteristics, the positive electrode for lithium ion secondary batteries, and a lithium ion secondary battery can be provided.

It is a schematic cross section of the lithium ion secondary battery which concerns on this invention form.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Positive electrode active material for lithium ion secondary battery>
A positive electrode active material for a lithium ion secondary battery (hereinafter also referred to as “positive electrode material”) covers a basic positive electrode active material and the surface of the positive electrode active material, and is represented by Formula 1. And a coating layer comprising a compound (R1 and R2 are hydrocarbons or oxygen, and n is 1 to 30).

  The positive electrode active material showing basicity in the present embodiment is prepared by stirring a positive electrode active material-containing aqueous solution obtained by adding 2 mol of a positive electrode active material to 100 ml of water, and reaching the equilibrium pH of the positive electrode active material-containing aqueous solution. A value is greater than 7 at 22 ° C.

  In addition, although the stirring time until it reaches | attains equilibrium changes with positive electrode active materials, it is about 5 to 15 minutes, for example. Moreover, as a measuring method of pH, a pH meter, a litmus paper, etc. can be used.

  In the present embodiment, the pH of the positive electrode active material exhibiting basicity is preferably 8 or more at 22 ° C. as the pH value in the measurement method.

  The pH varies depending on the temperature. If the measured value at 22 ° C. is 8 or more, the pH can be shifted to the neutral or acidic side under the conditions for producing a lithium ion secondary battery using this positive electrode material. This makes it easier to obtain the effects of the present invention.

  The positive electrode active material in the present invention is not particularly limited as long as it shows basicity under the above measurement conditions, but among them, an oxide positive electrode active material is preferable. By using the oxide positive electrode active material, a lithium ion secondary battery with high energy density can be obtained.

The oxide positive electrode has a general formula Li _x Ni _(1-yz) Co _y M _z O ₂ (M is Mg, Ca, Sr, Ba, Ti, Al, Cr, Mn, Fe, Ge, W, Cu, It is at least one element of Zn and is represented by 0.95 ≦ x ≦ 1.2, 0 <y ≦ 1.0, 0 ≦ z ≦ 0.5, 0 <y + z ≦ 1.0) A positive electrode active material mainly containing a compound can be given. Specific examples of such compounds include LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _1/3 Co _{1 / 3} Mn _1/3 O _{2 and the} like.

Further, as another oxide positive electrode, the general formula LiMn _1-x M _x O ₄ (M is Ni, Co, Mg, Ca, Sr, Ba, Ti, Al, Cr, Fe, Ge, W, Cu, Zn) A positive electrode active material having a compound represented by 0 ≦ x) as a main component, or a general formula X (Li (Li _1/3 M _2/3 ) O ₂ ) · Y ( LiM′O ₂ ) (M is at least one selected from tetravalent metal elements, M ′ is at least one selected from transition metal elements, 0 <X <1, 0 <Y <1 And X + Y = 1, a compound represented by:

  In the present embodiment, “main component” means that the positive electrode active material contains the compound or composition represented by the above general formula to the extent that the effects of the present invention can be exhibited. . Specifically, the proportion of the compound or composition represented by the above general formula with respect to all the materials constituting the positive electrode active material is 50 mol% or more. Among these, in the present invention, the ratio is preferably 60 mol% or more, more preferably 70 mol% or more, further preferably 80 mol% or more, and particularly preferably 90 mol% or more. Moreover, in this invention, a positive electrode active material may consist only of a compound or composition represented by the said general formula.

  As the positive electrode active material in the present embodiment, those having a conventionally known particle shape such as a spherical shape and a polyhedral shape can be used. Of these, spherical or elliptical spheres are preferable. When an active material having these particle shapes is used, the thickness of the coating layer can be made uniform.

  The coating layer in this embodiment coat | covers the surface of the said positive electrode active material, and is provided with the compound (R1 and R2 are hydrocarbons or oxygen, and n shows 1-30) represented by Formula 1.

  The coating layer in the present embodiment may partially cover the surface of the positive electrode active material particles, or may cover the entire surface. In the present invention, the coating layer preferably covers 50% or more of the surface of the positive electrode active material, more preferably 70% or more.

The covering ratio C1 of the coating layer with respect to the positive electrode active material particle A1 is equal to the coating length L2 of the coating layer with respect to the peripheral length L1 of the active material particle when the cross section of the electrode produced using the positive electrode active material in the present invention is observed. The ratio is a value calculated as C = (L2 / L1) * 100. In the cross section of the electrode, the value of C _ave , which is the average value of the coverage C1-C100 of the coating layer with respect to the active material particles A1-A100, is defined as the coverage of the present positive electrode material.

  The positive electrode material in the present embodiment has a weight percentage of 50% in a cumulative particle diameter curve plotted with the weight percentage (%) passing through a sieve having a certain particle diameter on the vertical axis and the particle diameter on the horizontal axis of the logarithmic scale. The particle size A of the positive electrode active material indicated by the particle size D50 is 5 μm ≦ A ≦ 25 μm, the thickness B of the coating layer is 1 nm ≦ B ≦ 100 nm, and the thickness of the coating layer with respect to the particle size A of the positive electrode active material The ratio of B is preferably 0.0008 ≦ B / A ≦ 0.02, the thickness of the coating layer is 5 nm ≦ B ≦ 60 nm, and the thickness B of the coating layer with respect to the particle size A of the positive electrode active material The ratio is more preferably 0.002 ≦ B / A ≦ 0.012.

  The particle size A of the positive electrode active material can be determined using a known particle size distribution measuring method and apparatus such as a dynamic light scattering method, a laser diffraction method, and an image imaging method.

The particle diameter A of the active material particles and the thickness B of the coating layer in the present embodiment are the average thickness of the coating layer with respect to the active material particles A1 when the cross section of the electrode produced using the positive electrode active material in the present invention is observed. In the cross section of the electrode, the average particle diameter A _ave of the active material particles A1-A100 is defined as the particle diameter of the active part chamber particles, and the average value of the coating layer thickness B1-B100 with respect to the active material particles A1-A100 A certain value of B _ave is defined as the thickness of the coating layer.

<Method for producing positive electrode material>
Next, a method for manufacturing the positive electrode material will be described. The method for producing a positive electrode material of the present invention includes a positive active material having a basic active material and a coating layer formed so as to cover the surface of the positive active material and comprising a compound represented by Formula 1. And a coating compound synthesis step for synthesizing the compound represented by Formula 1 and a coating step for coating the surface of the positive electrode active material with a coating layer containing the compound. It is what.

<Coating compound synthesis process>
First, the coating compound synthesis step in the present invention will be described. The coating compound synthesis step in the present invention is a step of synthesizing the compound represented by Formula 1.

The compound used for the coating layer in this embodiment can be synthesized, for example, from the chemical reaction of Formula 2 using the following compound. In addition to the following chemical reactions, different raw material compounds may be used, and the synthesis method is not particularly limited.

  The compound used for the coating layer in the present embodiment includes infrared spectroscopy, Raman spectroscopy, liquid chromatography mass spectrometry (LC-MS), gas chromatography mass spectrometry (GC-MS), and nuclear magnetic resonance (NMR). It can be identified by combining general analysis techniques for identifying organic compounds represented by

As a compound used for the coating layer in the present embodiment, it is preferable to use a compound represented by formulas 3 to 6 below.

  As for the compound used for the coating layer in this embodiment, it is preferable that n which represents a repeating unit is 1-30.

  In addition, the compound used for the coating layer in the present embodiment may be a compound in which the single structures represented by the above formulas 3 to 6 are repeatedly bonded, or may be a compound in which the structures represented by a plurality of formulas are repeatedly bonded.

When n = 1, the compound used for the coating layer in this embodiment is preferably composed of hydrogen or fluorine at the ends, and both ends may be composed of the same element or different elements.
<Coating process>
Next, the coating process in the present invention will be described. The coating step in the present invention is a step of coating the surface of the positive electrode active material with the compound represented by Formula 1 obtained in the coating compound synthesis step.

  The coating layer can be formed by mixing the compound represented by Formula 1 with the positive electrode active material powder, and the dispersibility of the positive electrode active material powder is improved by mixing the compound when producing the electrode. Therefore, it is preferable because the coating layer can be formed with a high coverage. Moreover, it is more preferable to mix with the dispersion medium used when producing an electrode. In addition, an electrode may be prepared using a positive electrode active material powder having a coating layer formed in advance, or an electrode prepared using a positive electrode active material powder that does not form a coating layer is a solution in which a compound represented by Formula 1 is dispersed. You may form a coating layer by immersing in.

  For the formation of the coating layer, an existing dispersing device typified by a ball mill device or a bead mill device can be used.

<Positive electrode for lithium ion secondary battery>
Next, a positive electrode for a lithium ion secondary battery (hereinafter also referred to as “positive electrode”) according to the present embodiment will be described with reference to FIG.

  The positive electrode 10 according to the present embodiment includes a current collector 12 and a positive electrode active material layer 14 provided on the current collector 12 including the positive electrode active material.

  As the current collector 12 of the positive electrode 10, for example, a metal foil such as an aluminum foil can be used. The positive electrode active material layer 14 provided on the current collector 12 is a layer containing the positive electrode active material, the binder, and a conductive material in an amount as necessary.

  The binder is not particularly limited as long as the positive electrode active material can be bound to the positive electrode current collector 12, and a known binder can be used. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoro Fluorine such as ethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene copolymer Resin. These conductive aids not only bind constituent materials such as active materials and conductive materials, but also contribute to binding between the constituent materials and the current collector. In addition to the above, as the binder, for example, polystyrene, polypropylene, polyethylene terephthalate, aromatic polyamide, cellulose, styrene / butadiene rubber, isoprene rubber, butadiene rubber, ethylene / propylene rubber, or the like may be used. Also, styrene / butadiene / styrene block copolymer, its hydrogenation agent, styrene / ethylene / butadiene / styrene copolymer, styrene / isoprene / styrene block copolymer, thermoplastic elastomeric polymer such as hydrogenation, etc. It may be used. Further, syndiotactic 1,2-polybutadiene, ethylene / vinyl acetate copolymer, and propylene / α-olefin (having 2 to 12 carbon atoms) copolymer may be used. Further, a conductive polymer may be used.

  The conductive material is not particularly limited, and a known conductive material can be used. Examples thereof include carbon blacks, carbon materials, metal powders such as copper, nickel, stainless steel, and iron, mixtures of carbon materials and metal powders, and conductive oxides such as ITO.

<Method for producing positive electrode>
The positive electrode 10 described above includes, for example, the present positive electrode material, a binder, and an amount of a conductive material as required according to the type of the solvent, such as N-methyl-2-pyrrolidone in the case of PVDF, A slurry can be prepared by adding to a solvent such as N, N-dimethylformamide, and the slurry can be applied to the surface of the current collector 12 and dried.

<Lithium ion secondary battery>
Next, a lithium ion secondary battery including an electrode including the above-described positive electrode material will be briefly described with reference to FIG.

  The lithium ion secondary battery 100 mainly includes a stacked body 30, an exterior body 50 that accommodates the stacked body 30 in a sealed state, and a pair of leads 60 and 62 connected to the stacked body 30.

  The laminated body 30 is configured such that a pair of the positive electrode 10 and the negative electrode 20 are opposed to each other with the separator 18 interposed therebetween. The positive electrode 10 is as described above. The negative electrode 20 is a product in which a negative electrode active material layer 24 is provided on a negative electrode current collector 22. The positive electrode active material layer 14 and the negative electrode active material layer 24 are in contact with both sides of the separator 18. Leads 60 and 62 are connected to the end portions of the positive electrode current collector 12 and the negative electrode current collector 22, respectively, and the end portions of the leads 60 and 62 extend to the outside of the exterior body 50.

  As the negative electrode current collector 22, a copper foil or the like can be used. Moreover, as the negative electrode active material layer 24, the thing containing a negative electrode active material, a binder, and the quantity of electrically conductive material as needed can be used. As the binder and the conductive material, those exemplified for the positive electrode can be used.

Examples of the negative electrode active material include graphite, non-graphitizable carbon, graphitizable carbon, and low-temperature calcined carbon that can occlude / release (intercalate / deintercalate, or dope / dedope) lithium ions. Carbon materials, metals that can be combined with lithium such as Al, Si, and Sn, amorphous compounds mainly composed of oxides such as SiO ₂ and SnO ₂ , lithium titanate (Li ₄ Ti ₅ O ₁₂ ), etc. The particle | grains containing are mentioned.

  The manufacturing method of the negative electrode 20 should just adjust slurry and apply | coat to a collector like the manufacturing method of the positive electrode 10. FIG.

The electrolyte solution is contained in the positive electrode active material layer 14, the negative electrode active material layer 24, and the separator 18. The electrolyte solution is not particularly limited. For example, in the present embodiment, an electrolyte solution containing a lithium salt (electrolyte aqueous solution, electrolyte solution using an organic solvent) can be used. However, the electrolyte aqueous solution is preferably an electrolyte solution (non-aqueous electrolyte solution) using an organic solvent because the electrochemical decomposition voltage is low, and the withstand voltage during charging is limited to a low level. As the electrolyte solution, a lithium salt dissolved in a non-aqueous solvent (organic solvent) is preferably used. Examples of the lithium salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiCF ₃ , CF ₂ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , Salts such as LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiN (CF ₃ CF ₂ CO) ₂ , LiBOB (lithium bis (oxalate) borate) Can be used. In addition, these salts may be used individually by 1 type, and may use 2 or more types together.

Examples of the organic solvent include aprotic high dielectric constant solvents such as ethylene carbonate and propylene carbonate, and aprotic low viscosity such as acetic acid esters and propionic acid esters such as dimethyl carbonate and ethyl methyl carbonate. A solvent is mentioned. It is desirable to use these aprotic high dielectric constant solvents and aprotic low viscosity solvents in combination at an appropriate mixing ratio. Furthermore, ionic liquids using imidazolium, ammonium, and pyridinium type cations can be used. The counter anion is not particularly limited, and examples thereof include BF ₄ ⁻ , PF ₆ ⁻ , (CF ₃ SO ₂ ) ₂ N ^{− and the} like. The ionic liquid can be used by mixing with the organic solvent described above.
The concentration of the lithium salt in the electrolyte solution is preferably 0.5 to 2.0 M from the viewpoint of electrical conductivity. The conductivity of the electrolyte at 25 ° C. is preferably 0.01 S / m or more, and is adjusted by the type of electrolyte salt or its concentration.

  Moreover, you may add an additive to electrolyte solution. Examples of additives include vinylene carbonate derivatives typified by 1,3-dioxol-2-one, ethylene sulfate derivatives typified by sultone 3-hydroxy-1-propanesulfonate, 4-fluoro-1,3-dioxolane- Additives such as 2-one may be used. In addition, these additives may be used individually by 1 type, and may use 2 or more types.

  In the present embodiment, the electrolyte solution may be a gel electrolyte obtained by adding a gelling agent in addition to liquid. Further, instead of the electrolyte solution, a solid electrolyte (a solid polymer electrolyte or an electrolyte made of an ion conductive inorganic material) may be contained.

  The separator 18 may also be formed of an electrically insulating porous structure, for example, a single layer of a film made of polyethylene, polypropylene or polyolefin, a stretched film of a laminate or a mixture of the above resins, or cellulose. And a fiber nonwoven fabric made of at least one constituent material selected from the group consisting of polyester and polypropylene.

  The exterior body 50 seals the laminated body 30 and the electrolytic solution therein. The outer package 50 is not particularly limited as long as it can prevent leakage of the electrolytic solution to the outside and entry of moisture and the like into the lithium ion secondary battery 100 from the outside. For example, as the outer package 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the synthetic resin film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point such as polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is preferably polyethylene or polypropylene.

  The leads 60 and 62 are made of a conductive material such as aluminum.

<Method for producing lithium ion secondary battery>
Then, the manufacturing method of the lithium ion secondary battery which concerns on this embodiment is demonstrated. The manufacturing method of the lithium ion secondary battery according to the present embodiment includes a positive electrode 10 containing the active material, a negative electrode 20, a separator 18 interposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution containing a lithium salt. And a step of enclosing the outer body 50 in the exterior body 50.

  For example, the positive electrode 10 containing the active material described above, the negative electrode 20 and the separator 18 are stacked, and the positive electrode 10 and the negative electrode 20 are heated and pressed with a press tool from a direction perpendicular to the stacking direction. 10, the separator 18 and the negative electrode 20 are brought into close contact with each other. Then, for example, a lithium ion secondary battery can be manufactured by placing the laminate 30 in a bag-shaped outer package 50 prepared in advance and injecting a non-aqueous electrolyte solution containing the lithium salt. Instead of injecting the non-aqueous electrolyte solution containing the lithium salt into the outer package, the laminate 30 may be impregnated in advance with the non-aqueous electrolyte solution containing the lithium salt.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. Are included in the technical scope.

  Hereinafter, the present positive electrode material will be described more specifically based on examples and comparative examples.

Example 1
<Measurement of pH of positive electrode active material>
A positive electrode active material-containing aqueous solution prepared by adding 2 mol of LiNi _0.85 Co _0.10 Al _0.05 O ₂ (hereinafter referred to as NCA) used as the positive electrode active material of Example 1 to 100 ml of water was prepared. After stirring for a minute, the pH of the positive electrode active material-containing aqueous solution of Example 1 was measured using a pH meter, and pH was 11.2.
<Synthesis of coating compound>
As shown in the following formula 2, a halogenated sulfone compound, 2-chloropropionic acid and ethylene glycol were reacted in pyridine and chloroform, and the reaction solvent was separated to obtain a coating compound.

  When the obtained coating compound was identified using LCMS, GCMS, and NMR, it was confirmed that the desired coating compound was obtained.

<Preparation of positive electrode>
Using NCA as a positive electrode active material, a mixture of the above-mentioned coating compound and positive electrode active material in a ratio of 95 parts by weight: 5 parts by weight is used as a positive electrode active material, and together with acetylene black and PVDF (polyvinylidene fluoride), A coating for positive electrode was prepared by adding to NMP (N-methyl-2-pyrrolidone). The ratio of the positive electrode active material, carbon black, and PVDF, which are solids in the positive electrode paint, was adjusted to positive electrode active material: carbon black: PVDF = 90 parts by mass: 5 parts by mass: 5 parts by mass.

The positive electrode coating material was applied to an aluminum foil having a thickness of 20 μm. The applied positive electrode coating material was dried and then rolled to obtain a positive electrode. Next, the Li foil was cut into a predetermined size and attached to a copper foil (thickness: 15 μm) to obtain a negative electrode. The positive electrode and the negative electrode were laminated with a separator made of a polyethylene microporous film interposed therebetween to obtain a laminate (element body). The positive electrode and the negative electrode were ultrasonically welded with an aluminum foil (width 4 mm, length 40 mm, thickness 80 μm) and nickel foil (width 4 mm, length 40 mm, thickness 80 μm) as external lead terminals, respectively. Polypropylene (PP) previously grafted with maleic anhydride was wrapped around this external lead terminal and thermally bonded. This is to improve the sealing performance between the external terminal and the exterior body. The battery outer package was made of an aluminum laminate material, and the configuration was prepared as PET (12) / Al (40) / PP (50). PET is polyethylene terephthalate and PP is polypropylene. The value in parentheses represents the thickness of each layer (unit: μm). At this time, bags were made so that PP was inside. The upper laminate was put into a battery case, and 1 M LiPF ₆ / EC + DEC (30:70 volume ratio) as an electrolyte was injected into the battery case. Then, the battery case was vacuum heat sealed, and the electrode evaluation half cell of Example 1 was used. Was made.

  When an electrode cross section using the produced positive electrode material was observed with an SEM, it was confirmed that a coating layer was present on the surface of the positive electrode active material. Further, when the prepared electrode was subjected to cross-sectional observation at a plurality of points and the particle diameter A and the thickness B of the coating layer were confirmed for 100 positive electrode active material particles, the average particle diameter Aave of the positive electrode active material was 10.7 μm, and the coating layer The average thickness Bave was 20 nm and B / A = 0.187.

<Measurement of discharge capacity>
After charging the half cell of Example 1, the discharge capacity (unit: mAh / g) of the half cell of Example 1 was measured by discharging. In this measurement, the theoretical capacity of LiNi _0.85 Cl _0.10 Al _0.05 O _{2 as} the positive electrode active material was set to 190 mAh / g. In charging, the upper limit charging voltage was 4.3 V (VS. Li ^/ Li ⁺ ). Charging was performed until the positive electrode voltage reached the upper limit charging voltage and the charging current was attenuated to 1 / 20C. In the discharge, the lower limit discharge voltage was set to 3.0 V (VS. Li ^/ Li ⁺ ). The discharge rate was 0.1 C and 1 C, and after charging and discharging at 1 C, charging and discharging were performed at 1 C. 1C is a current value at which discharge is terminated by constant current discharge for one hour.

  From this measurement result, the ratio (cycle retention rate) of the discharge capacity per gram of active material at the 500th cycle of discharge rate 1C to the discharge capacity per gram of active material at the first cycle of discharge rate 1C is obtained. It was. The measurement temperature was 25 ° C. Table 1 shows the discharge maintenance ratio of the half cell of Example 1.

(Examples 2 to 30)
NCA having a different particle diameter as a positive electrode active material, or LiCoO ₂ (hereinafter referred to as LCO), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (hereinafter referred to as NCM) instead of NCA, Except having changed the addition amount, the half cell of Examples 2-30 was produced by the method similar to Example 1. FIG. Moreover, when the pH of the said active material was measured by the method similar to Example 1, LCO was 10.5 and NCM was 10.8, and it confirmed that an active material showed basicity.

(Comparative Example 1)
A half cell of Comparative Example 1 was produced in the same manner as in Example 1 except that the coating compound was not mixed.

(Comparative Example 2)
A half cell of Comparative Example 2 was produced in the same manner as in Example 20 except that the coating compound was not mixed.

(Comparative Example 3)
A half cell of Comparative Example 3 was produced in the same manner as in Example 26 except that the coating compound was not mixed.

About Examples 1-30 and Comparative Examples 1-3, the ratio (cycle maintenance factor) of the discharge capacity of the first cycle at the discharge rate 1C and the discharge capacity after 500 cycles at the discharge rate 1C was determined. The results are shown in Table 1.

  From the cycle maintenance rate of Examples 1 to 30, the positive electrode active material showing basicity and the surface of the positive electrode active material were coated, and the compound represented by Formula 1 (R1 and R2 are hydrocarbons or oxygen, n It was found that a positive electrode material for a lithium ion secondary battery including a coating layer provided with 1 to 30 exhibits an excellent cycle retention rate. On the other hand, in the positive electrode active material that does not exhibit basicity, no change was observed in the cycle retention rate regardless of the presence or absence of the coating layer and its thickness. Further, in the positive electrode material for a lithium ion secondary battery, the particle size A of the positive electrode active material is 5 μm ≦ A ≦ 25 μm, the thickness B of the coating layer is 1 nm ≦ B ≦ 100 nm, and the particle size A of the positive electrode active material It was found that when the ratio of the thickness B of the coating layer to 0.0008 ≦ B / A ≦ 0.02, an excellent cycle retention ratio was exhibited.

Claims (5)

A positive electrode active material exhibiting basicity;
Coating the surface of the positive electrode active material, and a coating layer comprising a compound represented by Formula 1 (R1 and R2 are hydrocarbons or oxygen, and n is 1 to 30);
A positive electrode active material for a lithium ion secondary battery.

The particle size indicated by D50 of the positive electrode active material is 5 μm or more and 25 μm or less,
The coating layer has a thickness of 1 nm or more and 100 nm or less,
2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the ratio of the thickness B of the coating layer to the particle size A of the positive electrode active material is 0.0008 ≦ B / A ≦ 0.02. Material material. The positive electrode active material has the general formula Li _x Ni _(1-yz) Co _y M _z O ₂ (M is Mg, Ca, Sr, Ba, Ti, Al, Cr, Mn, Fe, Ge, W, Cu , Zn, and represented by the following: 0.95 ≦ x ≦ 1.2, 0 <y ≦ 1.0, 0 ≦ z ≦ 0.5, 0 <y + z ≦ 1.0) The positive electrode active material for a lithium ion secondary battery according to claim 1, comprising a lithium transition metal oxide.   The positive electrode for lithium ion secondary batteries containing the positive electrode active material material for lithium ion secondary batteries of Claim 1 to 3.   A lithium ion secondary battery comprising: the positive electrode according to claim 4; a negative electrode having a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte.

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