JP2015015088A - Method for processing positive electrode active material for lithium ion secondary batteries, positive electrode active material for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for processing a positive electrode active material for lithium ion secondary batteries which enables the suppression of the reaction between a positive electrode active material and an electrolytic solution, and the improvement in high-temperature shelf life.SOLUTION: A method for processing a positive electrode active material for lithium ion secondary batteries comprises: the first step of mixing a mixed process liquid prepared by mixing a first process liquid including a first solvent and a fluoride salt dissolved in the first solvent, and a second process liquid including a second solvent and an erbium salt dissolved in the second solvent with a positive electrode active material including a lithium-containing oxide; and the second step of baking the positive electrode active material after the first step at a temperature of 300-600°C. In the first step, the mixed process liquid and the positive electrode active material are mixed under the condition that no erbium fluoride is precipitated. In the second step, a quality-modified surface layer portion including F and Er elements is formed on the surface of the positive electrode active material.

Description

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

In recent years, with the widespread use of mobile devices such as mobile phones and notebook computers, development of secondary batteries having high energy density, small size, light weight and high capacity is strongly desired. Currently, lithium ion secondary batteries using lithium cobalt oxide (LiCoO ₂ ) as a positive electrode material and a carbon-based material as a negative electrode material are commercialized as high capacity secondary batteries.

  Lithium ion secondary batteries have a problem in that the battery capacity decreases due to repeated charge and discharge and high-temperature storage in a charged state. As a cause of this, it is considered that oxidative decomposition of the electrolytic solution occurs in the vicinity of the positive electrode during charging, and metal components such as the positive electrode active material are eluted by acid generated by oxidative decomposition. When the metal component is eluted from the positive electrode active material, the capacity of the positive electrode decreases, and as a result, the cycle characteristics and the high temperature storage characteristics deteriorate. Also, the electrolytic solution decomposition product and metal component elution product generated by the oxidative decomposition of the electrolytic solution and the elution of the metal component move from the positive electrode side to the negative electrode side, and are reductively decomposed on the negative electrode surface. As a result, a decomposition product is deposited on the surface of the negative electrode active material, and the deposit inhibits lithium insertion into the negative electrode active material, resulting in deterioration of cycle characteristics and high-temperature storage characteristics.

  Various studies have been conducted to improve cycle characteristics and high-temperature storage characteristics.

  For example, in Patent Literature 1, the rare earth hydroxide or rare earth oxyhydroxide particles are adhered to the surface of the positive electrode active material, thereby suppressing the reaction between the positive electrode active material and the electrolytic solution, and the capacity after the high temperature storage test. It discloses that the maintenance ratio and the capacity maintenance ratio after the high-temperature continuous charge test can be improved.

  Patent Document 2 discloses that cycle characteristics can be improved by attaching a metal fluorine compound powder to the surface of the positive electrode active material.

  However, in the techniques described in Patent Documents 1 and 2, since predetermined particles are attached to the surface of the positive electrode active material, the coating layer made of these particles may increase the electrode resistance and decrease the battery capacity. There is.

JP 2010-165657 A Special table 2008-536285 gazette

  This invention is made | formed in view of such a situation, The process of the positive electrode active material for lithium ion secondary batteries which can improve a high temperature storage characteristic, without making a particle adhere to the surface of a positive electrode active material It aims to provide a method.

  As a result of intensive studies by the present inventors, it has been found that the high-temperature storage characteristics can be enhanced by modifying the surface of the positive electrode active material so that a specific element exists on the surface of the positive electrode active material.

  That is, the method for treating a positive electrode active material for a lithium ion secondary battery of the present invention comprises mixing a first treatment liquid in which a fluoride salt is dissolved in a first solvent and a second treatment liquid in which an erbium salt is dissolved in a second solvent. And a second step of firing the positive electrode active material after the first step at a temperature of 300 ° C. or higher and 600 ° C. or lower. In the first step, the mixed treatment liquid and the positive electrode active material are mixed under the condition that erbium fluoride does not precipitate. In the second step, the modified surface layer portion containing the F element and the Er element is formed on the surface of the positive electrode active material. It is characterized by forming.

  When the treatment method is performed, a modified surface layer portion containing F element and Er element can be formed on the surface of the positive electrode active material without depositing particles on the surface of the positive electrode active material. Although the reason is not clear, when the positive electrode active material subjected to this treatment method is used in a lithium ion secondary battery, the high-temperature storage characteristics of the lithium ion secondary battery can be improved.

  The lithium-containing oxide preferably contains manganese.

  The lithium-containing oxide preferably has a layered rock salt structure or a spinel structure.

Lithium-containing oxide represented by the general _{formula: Li a Co p Ni q Mn} r D s O x (D is, Al, Mg, Ti, Sn , Zn, W, Zr, Mo, at least one selected from Fe and Na Yes, p + q + r + s = 1, 0 ≦ p <1, 0 ≦ q <1, 0 <r ≦ 1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) A lithium-containing composite oxide having a layered rock salt structure represented by ≦ 0.2) is preferable.

Lithium-containing oxides are LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Mn _1.5 O ₄ and LiMn ₂ O ₄ are preferable.

  The positive electrode active material for a lithium ion secondary battery of the present invention is made of a lithium-containing oxide having a modified surface layer whose surface has been modified without precipitating particles, and the modified surface layer contains F element and Er element. It is characterized by including.

Lithium-containing oxides are LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Mn _1.5 O ₄ and LiMn ₂ O ₄ are preferable.

  Another positive electrode active material for a lithium ion secondary battery of the present invention is characterized by being treated by the above-described method for treating a positive electrode active material for a lithium ion secondary battery.

  Moreover, the lithium ion secondary battery of this invention has the said positive electrode active material for lithium ion secondary batteries, It is characterized by the above-mentioned.

  According to the method for treating a positive electrode active material for a lithium ion secondary battery of the present invention, a modified surface layer portion containing F element and Er element on the surface of the positive electrode active material without depositing particles on the surface of the positive electrode active material. Can be formed. When the positive electrode active material subjected to this treatment method is used in a lithium ion secondary battery, the high-temperature storage characteristics of the lithium ion secondary battery can be improved.

It is a schematic cross section explaining the positive electrode active material for lithium ion secondary batteries of this embodiment. It is the image observed with the scanning electron microscope (SEM: Scanning Electron Microscope) and the energy dispersive X ray spectroscopy (EDX: Energy Dispersive X-ray Spectroscopy) of the positive electrode active material of Example 1. FIG. It is the image which expanded the SEM image of FIG.

<Method of treating positive electrode active material for lithium ion secondary battery>
The processing method of the positive electrode active material for lithium ion secondary batteries of this invention has a 1st process and a 2nd process.

  In the first step, a positive electrode active comprising a mixed treatment liquid obtained by mixing a first treatment liquid in which a fluoride salt is dissolved in a first solvent and a second treatment liquid in which an erbium salt is dissolved in a second solvent, and a lithium-containing oxide. The substance is mixed.

  Examples of fluoride salts include ammonium fluoride, potassium fluoride, and sodium fluoride.

  Examples of erbium salts include erbium nitrate, erbium hydrochloride, erbium sulfate, and erbium oxalate.

  The first solvent and the second solvent may be different from each other, but the same is preferable. Examples of the solvent include water, ethanol, ether, and acetone.

  In the first step, the mixed treatment liquid and the positive electrode active material are mixed under the condition that erbium fluoride does not precipitate.

  Examples of conditions under which erbium fluoride does not precipitate include adjustment of the concentration of the mixed treatment liquid, adjustment of the mixing ratio of the mixed treatment liquid and the positive electrode active material, temperature during mixing, and mixing time.

  The concentration of the mixed treatment liquid is adjusted by adjusting the concentration of the fluoride salt in the first treatment liquid, the concentration of the erbium salt in the second treatment liquid, and the mixing ratio of the first treatment liquid and the second treatment liquid in the mixed treatment liquid. Can be done. The adjustment method of the density | concentration of a mixed process liquid can be selected suitably. For example, the first step can be performed under the following conditions.

  The concentration of the fluoride salt in the first treatment liquid is preferably 50 mmol / l or more and 200 mmol / l.

  The concentration of the erbium salt in the second treatment liquid is preferably 50 mmol / l or more and 200 mmol / l.

  The mixing ratio of the first treatment liquid and the second treatment liquid in the mixed treatment liquid is preferably first treatment liquid: second treatment liquid = 3: 7 to 7: 3 (volume ratio). When the mixing ratio is out of this range, a large amount of erbium salt or fluoride salt not involved in the reaction is present in the mixed solution, and the material is wasted.

  The mixing ratio of the mixed treatment liquid and the positive electrode active material is preferably positive electrode active material: mixed treatment liquid = 1: 1 to 1: 5 (mass ratio). If the amount of the positive electrode active material exceeds this range, the treatment becomes insufficient, and if the amount of the mixed treatment liquid exceeds this range, the treatment becomes excessive.

  The mixing time is preferably 0.5 hours or more and 10 hours or less. When the mixing time is shorter than 0.5 hours, the reaction is insufficient, and even longer than 10 hours hardly causes further reaction.

  The temperature at the time of mixing hardly affects the treatment and is not particularly limited.

  The modified surface layer portion is formed on the surface of the positive electrode active material by the method for treating a positive electrode active material for a lithium ion secondary battery of the present invention. The positive electrode active material is made of a lithium-containing oxide. In the modified surface layer portion, it is presumed that a part of oxygen in the positive electrode active material is substituted with fluorine, and the surface of the positive electrode active material is doped with erbium. The positive electrode active material is presumed that the crystal structure of the positive electrode active material is stabilized by having the modified surface layer portion on the surface of the positive electrode active material. Therefore, even if lithium enters and exits the positive electrode active material due to charging / discharging of the battery, it is presumed that other metal components are not easily eluted because the crystal structure is stable.

  The lithium-containing oxide preferably contains manganese. In the lithium-containing oxide containing manganese, manganese is easily eluted into the electrolytic solution. Therefore, the effect by the said processing method appears notably.

  The lithium-containing oxide preferably has a layered rock salt structure or a spinel structure. In the lithium-containing oxide having a layered rock salt structure or a spinel structure, an ion exchange reaction between lithium and erbium is likely to occur during the first step. Therefore, in the lithium-containing oxide having a layered rock salt structure or a spinel structure, a modified surface layer portion is easily formed.

Lithium-containing oxide represented by the general _{formula: Li a Co p Ni q Mn} r D s O x (D is, Al, Mg, Ti, Sn , Zn, W, Zr, Mo, at least one selected from Fe and Na Yes, p + q + r + s = 1, 0 ≦ p <1, 0 ≦ q <1, 0 <r ≦ 1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s) A lithium-containing composite oxide having a layered rock salt structure represented by ≦ 0.2) is preferable.

Lithium-containing oxides are LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Mn _1.5 O ₄ and LiMn ₂ O ₄ are preferable.

The positive electrode active material is preferably in the form of a powder, and the average particle diameter D50 is preferably 1 μm to 20 μm, and more preferably ₅ μm to 10 μm. The average particle diameter D ₅₀ of the positive electrode active material may be any size suitable for use as a positive electrode active material. Note do it by controlling the processing conditions according to the average particle diameter D ₅₀ of the positive electrode active material can be treated as a positive electrode active material having the average particle size D ₅₀ regardless of the size of the average particle diameter D _50. However, the average particle diameter D ₅₀ of 1μm smaller than a cathode active material of the positive electrode active material tends to agglomerate, it may become difficult to mix the cathode active material and mixing treatment liquid.

The average particle diameter D ₅₀ of the positive electrode active material can be measured by particle size distribution measurement method. The average particle diameter D ₅₀ is that the particle size cumulative value of the volume distribution in the particle size distribution measurement by laser diffraction method is equivalent to 50%. That is, the average particle diameter D ₅₀ means the median size measured by volume.

  The filtration step may be performed after the first step and before the second step. In the filtration step, the positive electrode active material may be separated from the mixed treatment liquid after the first step by filtration.

  In the second step, the positive electrode active material after the first step is fired at a temperature of 300 ° C. to 600 ° C. The second step may be performed for about 3 hours to 10 hours. When the positive electrode active material is fired at a temperature lower than 300 ° C., moisture is not sufficiently removed from the positive electrode active material, and when the positive electrode active material is fired at a temperature higher than 600 ° C., erbium diffuses into the positive electrode active material, The effect of surface protection is weakened.

  Further, a drying step may be further added before the second step. The drying step may be performed by putting the filtrate in a drying furnace at a temperature of about 120 ° C. and drying for 6 hours to 12 hours.

  In the second step, a modified surface layer portion containing F element and Er element is formed on the surface of the positive electrode active material. Although the details are unclear by performing the first step and the second step, F element and Er element are included on the surface of the positive electrode active material without precipitation of erbium fluoride particles on the surface of the positive electrode active material. A modified surface layer portion is formed.

  FIG. 1 is a schematic cross-sectional view illustrating the positive electrode active material for a lithium ion secondary battery according to this embodiment. As shown in FIG. 1, the modified surface layer portion 2 is disposed on the entire surface of the positive electrode active material 1.

  The thickness of the modified surface layer portion is preferably 1 nm or more and 100 nm or less. When the thickness of the modified surface layer portion is less than 1 nm, the effect of surface protection is small, and when the thickness of the modified surface layer portion is greater than 100 nm, the resistance of the battery increases.

  The thickness of the modified surface portion is determined by, for example, observing a cut surface obtained by cutting the positive electrode active material for a lithium ion secondary battery of the present invention with a transmission electron microscope (TEM), or a transmission electron microscope and a dispersion type. It can be confirmed by measuring with a TEM-EDX combined with an X-ray analyzer and analyzing the composition.

  If both the F element and the Er element are included in the modified surface layer portion of the surface of the positive electrode active material, the reason is not clear, but the surface of the positive electrode active material is highly resistant to hydrofluoric acid, and the surface of the positive electrode active material is The elution of the metal component is suppressed. In addition, a lithium ion secondary battery using the positive electrode active material has improved high-temperature storage characteristics.

  Here, since the erbium fluoride particles are not attached to the surface of the positive electrode active material, the electrode resistance is difficult to increase.

<Positive electrode active material for lithium ion secondary battery>
The positive electrode active material for a lithium ion secondary battery of the present invention is made of a lithium-containing oxide having a modified surface layer whose surface has been modified without precipitating particles, and the modified surface layer contains F element and Er element. It is characterized by including.

  The description of the lithium-containing oxide and the modified surface layer is the same as that described in the above processing method.

  The positive electrode active material for a lithium ion secondary battery of the present invention can be obtained by being treated by the above-described method for treating a positive electrode active material.

The positive electrode active material for a lithium ion secondary battery of the present invention preferably has a powder shape with an average particle diameter D50 of 1 μm to 20 μm, and more preferably ₅ μm to 10 μm. Reaction area of the specific surface area of an average particle diameter D ₅₀ of 1μm smaller than the positive electrode active material greatly becomes the positive electrode active material and the electrolyte increases. The average particle diameter D ₅₀ of the positive electrode active material becomes large 20μm greater than the resistance of the lithium ion secondary battery, there is a possibility that the output characteristics of the lithium ion secondary battery decreases.

<Lithium ion secondary battery>
The lithium ion secondary battery of this invention has the positive electrode active material for lithium ion secondary batteries mentioned above.

  The positive electrode is formed by adhering a positive electrode active material layer formed by binding the positive electrode active material for a lithium ion secondary battery with a binder to a current collector.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. Examples of materials that can be used for the current collector include metal materials such as stainless steel, titanium, nickel, aluminum, and copper, or conductive resins. The current collector can take the form of a foil, a sheet, a film, or the like. Therefore, metal foils, such as copper foil, nickel foil, aluminum foil, stainless steel foil, can be used suitably as a collector. The thickness of the current collector is preferably 10 μm to 100 μm.

  The positive electrode active material layer may further contain a conductive additive. The positive electrode is prepared by forming a positive electrode active material layer-forming composition containing a positive electrode active material and a binder and, if necessary, a conductive additive, and further adding a suitable solvent to the composition to make a paste. After applying to the surface of the current collector, it can be dried and compressed to increase the electrode density as necessary.

  As a method for applying the composition for forming a positive electrode active material layer, conventionally known methods such as a roll coating method, a dip coating method, a doctor blade method, a spray coating method, and a curtain coating method may be used.

  As a solvent for adjusting the viscosity, N-methyl-2-pyrrolidone (NMP), methanol, methyl isobutyl ketone (MIBK) and the like can be used.

  The binder serves to bind the positive electrode active material and the conductive additive to the current collector. For example, the binder includes a fluorine-containing resin such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, polypropylene, polyethylene and poly Thermoplastic resins such as vinyl acetate resins, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, and rubbers such as styrene butadiene rubber (SBR) can be used.

  The conductive assistant is added to increase the conductivity of the electrode. As the conductive assistant, for example, carbon black, graphite, acetylene black (AB), ketjen black (registered trademark) (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination of two or more. They can be added in combination. The amount of the conductive auxiliary agent used is not particularly limited, but can be, for example, about 1 part by mass to 30 parts by mass with respect to 100 parts by mass of the active material contained in the positive electrode.

(Other components)
The lithium ion secondary battery of this invention has a negative electrode, a separator, and electrolyte solution in addition to the above-mentioned positive electrode as a battery component.

  The negative electrode has a current collector and a negative electrode active material layer bound to the surface of the current collector. A negative electrode active material layer contains a negative electrode active material and a binder, and contains a conductive support agent as needed. The current collector, binder and conductive additive are the same as those described for the positive electrode.

  As the negative electrode active material, a carbon-based material that can occlude and release lithium, an element that can be alloyed with lithium, a compound that includes an element that can be alloyed with lithium, a polymer material, or the like can be used.

  Examples of the carbon-based material include non-graphitizable carbon, artificial graphite, coke, graphite, glassy carbon, organic polymer compound fired body, carbon fiber, activated carbon, or carbon black. Here, the organic polymer compound fired body refers to a material obtained by firing and carbonizing a polymer material such as phenols and furans at an appropriate temperature.

  Elements that can be alloyed with lithium include Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn , Pb, Sb and Bi. Among them, the element that can be alloyed with lithium is preferably silicon (Si) or tin (Sn).

Examples of the compound having an element that can be alloyed with lithium include ZnLiAl, AlSb, SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , and CaSi. _{2, CrSi 2, Cu 5 Si} , FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2, SiC, Si 3 N 4, Si 2 N 2 O, SiO v (0 <v ≦ 2), SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSiO or LiSnO can be used. As the compound having an element that can be alloyed with lithium, a silicon compound or a tin compound is preferable. As the silicon compound, SiO _x (0.5 ≦ x ≦ 1.5) is preferable. As the tin compound, for example, a tin alloy (Cu—Sn alloy, Co—Sn alloy, etc.) is preferable.

  As the polymer material, for example, polyacetylene or polypyrrole can be used.

The negative electrode active material is preferably in powder form. If the anode active material is in powder form, it is preferable that the average particle size _{D 50} of the negative electrode active material is 0.1μm or more 30μm or less, and more preferably 1μm or more 10μm or less. The average particle diameter D ₅₀ of the negative electrode active material 0.1μm smaller, the specific surface area of the powder of the negative electrode active material is increased, the contact area of the powder of the anode active material and the electrolyte solution is increased, the decomposition of the electrolyte solution Advances and the cycle characteristics deteriorate. Further, the average particle diameter D ₅₀ of the negative electrode active material is larger than 30 [mu] m, the conductivity of the whole electrode becomes uneven, charging and discharging characteristics are degraded. The average particle diameter D ₅₀ of the negative electrode active material can be measured by particle size distribution measurement method.

  The separator separates the positive electrode and the negative electrode and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. As the separator, for example, a porous film made of synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene, or a porous film made of ceramics can be used.

  The electrolytic solution includes a solvent and an electrolyte dissolved in the solvent.

  As the solvent, for example, cyclic esters, chain esters, and ethers can be used. Examples of cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, gamma butyrolactone, vinylene carbonate, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, methyl ethyl carbonate, propionic acid alkyl ester, malonic acid dialkyl ester, and acetic acid alkyl ester. Examples of ethers that can be used include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, and 1,2-dibutoxyethane.

Moreover, as an electrolyte dissolved in the electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ can be used.

As an electrolytic solution, for example, a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 is} added to a solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, dimethyl carbonate, and the like from 0.5 mol / l to 1.7 mol / l. A solution dissolved at a certain concentration can be used.

  The lithium ion secondary battery can be mounted on a vehicle. Since the lithium ion secondary battery has an excellent discharge capacity, a vehicle equipped with the lithium ion secondary battery has high performance in terms of output.

  The vehicle may be a vehicle that uses electric energy from a battery as a whole or a part of a power source. For example, an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, a hybrid railway vehicle, an electric forklift, an electric wheelchair, and an electric assist. Bicycles and electric motorcycles are examples.

  As mentioned above, although the processing method of the positive electrode active material for lithium ion secondary batteries of the present invention, the positive electrode active material for lithium ion secondary batteries, and the lithium ion secondary battery having the same have been described, the present invention has been described above. The form is not limited. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

  Hereinafter, the present invention will be described in more detail with reference to examples.

<Preparation for treatment of positive electrode active material>
NCM523 (LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) having an average particle diameter D ₅₀ of 10 μm was prepared as a positive electrode active material. As materials for the first treatment liquid and the second treatment liquid, pure water, NH ₄ F (manufactured by Kanto Chemical Co., Inc.), Er (NO ₃ ) ₃ / 5H ₂ O (manufactured by Kojundo Chemical Laboratory Co., Ltd.), , was prepared _{Al (NO 3) 3 · 9H} 2 O ( manufactured by Kojundo Chemical Laboratory Co., Ltd.).

Example 1
<Creation of the first treatment liquid>
NH ₄ F was dissolved in pure water at a concentration of 50 mmol / L to obtain a first treatment liquid.

<Creation of second treatment liquid>
Er (NO ₃ ) ₃ .5H ₂ O was dissolved in pure water at a concentration of 50 mmol / L to obtain a second treatment liquid.

<Creation of mixed processing solution>
The first treatment liquid and the second treatment liquid were mixed at a volume ratio of 1: 1 and stirred to obtain a mixed treatment liquid.

<Treatment of positive electrode active material>
30 g of NCM523 was placed in 100 ml of the mixed treatment solution and stirred at room temperature for 5 hours using a glass beaker. The mixed treatment liquid after stirring was subjected to suction filtration, and the slurry-like filtrate was dried at 120 ° C. for 6 hours. The dried filtrate that had become agglomerated was pulverized using a pestle and mortar, placed in a crucible, and baked at 400 ° C. for 5 hours. The average particle diameter D ₅₀ of the cathode active material was ground using a pestle and mortar so as to 10μm after firing, to obtain a positive electrode active material of Example 1.

(Example 2)
Implementation was performed in the same manner as in Example 1 except that the concentration of NH ₄ F in the first treatment liquid was 100 mmol / L and the concentration of Er (NO ₃ ) ₃ .5H ₂ O in the second treatment liquid was 100 mmol / L. The positive electrode active material of Example 2 was obtained.

Example 3
Implementation was performed in the same manner as in Example 1 except that the concentration of NH ₄ F in the first treatment liquid was ₂₀₀ mmol / L and the concentration of Er (NO ₃ ) ₃ .5H ₂ O in the second treatment liquid was ₂₀₀ mmol / L. The positive electrode active material of Example 3 was obtained.

(Comparative Example 1)
A positive electrode active material of Comparative Example 1 was obtained in the same manner as in Example 1 except that the first treatment liquid was used instead of the mixed treatment liquid.

(Comparative Example 2)
A positive electrode active material of Comparative Example 2 was obtained in the same manner as in Example 2 except that the first treatment liquid was used instead of the mixed treatment liquid.

(Comparative Example 3)
A positive electrode active material of Comparative Example 3 was obtained in the same manner as in Example 3 except that the first treatment liquid was used instead of the mixed treatment liquid.

(Comparative Example 4)
Untreated NCM523 was used as the positive electrode active material of Comparative Example 4.

(Comparative Example 5)
As the second treatment liquid, to obtain a positive electrode active material of _{Al (NO 3) 3 · 9H} 2 O , except that used was dissolved at a concentration of 50 mmol / L in the same manner as in Example 1 Comparative Example 5 in deionized water It was.

(Comparative Example 6)
As the second treatment liquid, to obtain a positive electrode active material of pure water _{Al (NO 3) 3 · 9H} 2 O , except that used was dissolved at a concentration of 100 mmol / L in the same manner as in Example 2 Comparative Example 6 It was.

(Comparative Example 7)
As the second treatment liquid, to obtain a positive electrode active material of pure water _{Al (NO 3) 3 · 9H} 2 O except for using a solution at a concentration of 200 mmol / L and in the same manner as in Example 3 Comparative Example 7 It was.

<SEM-EDX observation>
Surface observation of the positive electrode active material of Example 1 was performed with a SEM-EDX apparatus. The image by the SEM-EDX apparatus of the positive electrode active material of Example 1 is shown in FIG. 2A is an SEM image, FIG. 2B is an EDX image obtained by measuring the F element, and FIG. 2C is an EDX image obtained by measuring the Er element. 2A, 2B, and 2C, it was found that the F element and the Er element exist on the entire surface of the positive electrode active material.

  FIG. 3 shows an enlarged image of the SEM image of FIG. When the SEM image of FIG. 2A and the SEM image of FIG. 3 are viewed, the positive electrode active material of Example 1 has aggregated primary particles to form secondary particles. Further, as can be seen from the image of FIG. 3, it was found that no other particles were deposited on the surface of the primary particles of the positive electrode active material.

[Production of laminated lithium ion lithium ion secondary battery]
(Laminated lithium ion secondary battery of Example 1)
The laminated lithium ion secondary battery of Example 1 was produced as follows.

  First, the positive electrode active material of Example 1, acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder were mixed in a ratio of 94 parts by mass, 3 parts by mass, and 3 parts by mass, respectively. The mixture was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP) to prepare a slurry.

An aluminum foil having a thickness of 20 μm was prepared as a current collector. The slurry was applied to the surface of the current collector in the form of a film using a doctor blade and dried at 80 ° C. for 20 minutes to volatilize and remove NMP. Thereafter, the current collector and the coated material on the current collector were tightly bonded with a roll press. At this time, the electrode density was set to 3.2 g / cm ² . The bonded product was heated in a vacuum dryer at 120 ° C. for 6 hours. The bonded product after heating was cut into a predetermined shape (rectangular shape of 25 mm × 30 mm) to obtain a positive electrode. The thickness of the positive electrode active material layer was about 40 μm.

The negative electrode was produced as follows. As the negative electrode active material, SiO (manufactured by Aldrich) having an average particle diameter D ₅₀ of 4 μm and graphite (natural graphite (manufactured by Hitachi Chemical Co., Ltd.) having an average particle diameter D ₅₀ of 20 μm) were prepared. As a binder resin, an alkoxy group-containing silane-modified polyamideimide resin (Arakawa Chemical Industries, Ltd., trade name Composeran, product number H900-2) was prepared. KB (Ketjen Black) manufactured by Ketjen Black International Co., Ltd. was prepared as a conductive aid.

  The negative electrode active material, the conductive auxiliary agent, and the binder resin were mixed at a mass ratio of SiO: graphite: conductive auxiliary agent: binder resin = 22: 60: 3: 15. Here, when the total of the mass of graphite and the mass of SiO is 100 mass%, the mixing ratio of SiO is 27 mass%. An appropriate amount of NMP was added as a solvent to the above mixture to prepare a slurry, which was then slurried for the negative electrode active material layer.

A 20 μm copper foil was prepared as a current collector for the negative electrode, and the slurry for negative electrode active material layer was applied to the copper foil in a film form using a doctor blade. The copper foil coated with the negative electrode active material layer slurry was dried at 80 ° C. for 20 minutes to volatilize and remove NMP, and then pressed by a roll press to obtain a bonded product. At this time, the electrode density was set to 1.6 g / cm ² . The bonded product was heated with a vacuum dryer at 200 ° C. for 2 hours, and then cut into a predetermined shape (26 mm × 31 mm rectangular shape) to form a negative electrode having a negative electrode active material layer thickness of 20 μm.

A laminate type lithium ion secondary battery was manufactured using the positive electrode and the negative electrode. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then an electrolyte solution was injected into the bag-like laminated film. 1 mol / liter of LiPF ₆ was added to a solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as an electrolytic solution in EC: EMC: DMC = 3: 3: 4 (volume ratio). A solution dissolved so as to be 1 was used. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery. The laminated lithium ion secondary battery of Example 1 was produced through the above steps.

  In addition, conditioning treatment was performed on the manufactured laminated lithium ion secondary battery. In the conditioning process, the manufactured laminated lithium ion secondary battery was charged stepwise to 4.5V, finally charged to 4.5V at a 1C rate, and then CV charged for 5 hours. Then, after discharging to 2.5 V at a 0.33 C rate, CV discharging was performed at 2.5 V for 5 hours.

(Laminated lithium ion secondary battery of Example 2)
A laminated lithium ion secondary battery of Example 2 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Example 2 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Example 3)
A laminated lithium ion secondary battery of Example 3 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Example 3 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 1)
A laminated lithium ion secondary battery of Comparative Example 1 was prepared in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 1 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 2)
A laminated lithium ion secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 2 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 3)
A laminated lithium ion secondary battery of Comparative Example 3 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 3 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 4)
A laminated lithium ion secondary battery of Comparative Example 4 was prepared in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 4 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 5)
A laminated lithium ion secondary battery of Comparative Example 5 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 5 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 6)
A laminated lithium ion secondary battery of Comparative Example 6 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 6 in the laminated lithium ion secondary battery of Example 1. .

(Laminated lithium ion secondary battery of Comparative Example 7)
A laminated lithium ion secondary battery of Comparative Example 7 was produced in the same manner as in Example 1 except that the positive electrode active material was changed to the positive electrode active material of Comparative Example 7 in the laminated lithium ion secondary battery of Example 1. .

<Initial discharge capacity measurement>
The initial discharge capacity was measured using the laminated lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7.

  The initial discharge capacity was measured as follows. After performing CC charge (constant current charge) to 0.33C rate and voltage 4.5V at room temperature, CV charge (constant voltage charge) was performed at voltage 4.5V for 1.5 hours. Then, CC discharge (constant current discharge) was performed at a rate of 0.33 C up to a voltage of 2.5 V, and CV discharge was performed at a voltage of 2.5 V for 2 hours. Thereafter, the discharge capacity at 0.33 C was measured and used as the initial discharge capacity.

<60 ° C storage test>
About the laminated type lithium ion secondary battery of Examples 1-3 and Comparative Examples 1-7, the 60 degreeC storage test was done. In this test, a charge / discharge test was performed once on the laminated lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 under the following conditions, and the recharged battery was placed in a 60 ° C. constant temperature bath. Let stand for days. At the time of charging, CCCV charging (constant current constant voltage charging) was performed at a rate of 1 C at a voltage (4.3 V) when SOC (State of charge) 90% at 60 ° C. And it hold | maintained for 1 hour with the voltage after charge. During the subsequent discharge, CC discharge (constant current discharge) was performed at a rate of 2.5 V and 0.33 C.

  Here, since the charged state is maintained in the storage test, a side reaction is likely to occur between the electrolytic solution and the active material, and the laminated lithium ion secondary battery is easily self-discharged.

  After this storage test, the temperature was returned to room temperature, and the discharge capacity was measured under the same conditions as the measurement of the initial discharge capacity.

  The results are shown in Table 1. The capacity retention rate (%) was calculated by the formula: capacity retention rate (%) = (discharge capacity after storage test / initial capacity) × 100.

<Measurement of Mn content of negative electrode>
For the laminated lithium ion secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 4, the amount of Mn of the negative electrode after the 60 ° C. storage test was measured. Each laminated lithium ion secondary battery after the 60 ° C. storage test was disassembled, and each negative electrode was separated. The separated negative electrode was washed with dimethyl carbonate (DMC), and the amount of Mn of the negative electrode was measured with an inductively coupled plasma mass spectrometer (ICP-MS).

  The results are shown in Table 1.

  From the results in Table 1, the negative electrode Mn amount of the laminate type lithium ion secondary battery of Comparative Example 4 using the untreated positive electrode active material was 15 μg, whereas the laminate type lithium ions of Comparative Examples 1 to 3 were used. The amount of Mn in the negative electrode of the secondary battery was reduced to 8.8 μg to 9.5 μg. From this, it was found that the elution of Mn is suppressed when the fluorine (F) element is present on the surface of the positive electrode active material. Furthermore, the Mn content of the negative electrodes of the laminated lithium ion secondary batteries of Examples 1 to 3 was dramatically reduced to 0.9 μg to 1.3 μg. From this, it was found that when both the F element and the Er element exist on the surface of the positive electrode active material, the elution of Mn is dramatically suppressed, although the reason is not clear.

Comparing the capacity retention rate (%) of the high temperature storage test, the capacity retention rate (%) of the high temperature storage test of the laminate type lithium ion secondary batteries of Examples 1 to 3 is the laminate type lithium ion of Comparative Examples 1 to 7. The capacity retention rate (%) of the secondary battery high-temperature storage test was significantly higher. The capacity retention rate (%) in the high-temperature storage test of the laminated lithium ion secondary batteries of Comparative Examples 1 to 3 and the laminated lithium ion secondary batteries of Comparative Examples 5 to 7 is a comparative example using an untreated positive electrode active material. 4 was almost the same as the capacity retention rate (%) of the high temperature storage test of the laminate type lithium ion secondary battery. Here, observation of the surface of the positive electrode active material of Comparative Example 5 using _{Al (NO 3) 3 · 9H} 2 O to a second treatment liquid, there are Al element to the surface of the positive electrode active material of Comparative Example 5 I was able to confirm. As a result, it was found that the capacity retention rate (%) in the high-temperature storage test did not increase even when F element and Al element were present on the surface of the positive electrode active material.

  From the above, it was found that when F element and Er element exist on the surface of the positive electrode active material, the capacity retention rate (%) in the high temperature storage test of the laminated lithium ion secondary battery is greatly improved.

  1: Positive electrode active material, 2: Modified surface layer part.

Claims (9)

Mixing a mixed treatment liquid in which a first treatment liquid in which a fluoride salt is dissolved in a first solvent and a second treatment liquid in which an erbium salt is dissolved in a second solvent is mixed with a positive electrode active material made of a lithium-containing oxide. A first step of
A second step of firing the positive electrode active material after the first step at 300 ° C. or higher and 600 ° C. or lower;
Have
In the first step, the mixed treatment liquid and the positive electrode active material are mixed under the condition that erbium fluoride does not precipitate,
In the second step, a modified surface layer portion containing an F element and an Er element is formed on the surface of the positive electrode active material. A method for treating a positive electrode active material for a lithium ion secondary battery.   The method for treating a positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the lithium-containing oxide contains manganese.   The method for treating a positive electrode active material for a lithium ion secondary battery according to claim 2, wherein the lithium-containing oxide has a layered rock salt structure or a spinel structure. The lithium-containing oxide has the general formula: at least one _{Li a Co p Ni q Mn r} D s O x (D is the Al, Mg, Ti, Sn, Zn, W, Zr, Mo, selected from Fe and Na P + q + r + s = 1, 0 ≦ p <1, 0 ≦ q <1, 0 <r ≦ 1, 0 ≦ s <1, 0.8 ≦ a <2.0, −0.2 ≦ x− (a + p + q + r + s The method for treating a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the lithium-containing composite oxide has a layered rock salt structure represented by: ≤ 0.2). The lithium-containing oxides are LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O _{2, LiNi} 0.5 _Mn 1.5 _{O 4} and at least one processing method of the positive electrode active material for a lithium ion secondary battery according to claim 4 which is selected from LiMn ₂ O _4.   A positive electrode for a lithium ion secondary battery comprising a lithium-containing oxide having a modified surface layer portion whose surface is modified without precipitating particles, the modified surface layer portion including an F element and an Er element Active material. The lithium-containing oxides are LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O _{2. The} positive electrode active material for a lithium ion secondary battery according to claim 6, wherein the positive electrode active material is at least one selected from LiNi _0.5 Mn _1.5 O ₄ and LiMn ₂ O ₄ .   The positive electrode active material for lithium ion secondary batteries processed with the processing method of the positive electrode active material for lithium ion secondary batteries as described in any one of Claims 1-5.   The lithium ion secondary battery which has a positive electrode active material for lithium ion secondary batteries of Claims 6-8.