JP7302165B2 - Positive electrode for lithium ion secondary battery, coating solution for lithium ion secondary battery and positive electrode mixture - Google Patents

Description

TECHNICAL FIELD The present invention relates to a positive electrode for a lithium ion secondary battery , a lithium ion secondary battery and a coating liquid for a positive electrode mixture.

The market for lithium-ion secondary batteries is expanding for consumer use, automotive use, and infrastructure use. Desired.

Patent Document 1 discloses a positive electrode provided with a positive electrode mixture layer containing a positive electrode active material. Here, the positive electrode active material contains lithium vanadium phosphate and lithium nickel composite oxide in a mass ratio of 8:82 to 70:20. Also, the lithium vanadium phosphate particles have a carbon content of 0.5 mass % to 2.4 mass %.

However, when forming the positive electrode mixture layer, there is a problem that coating unevenness occurs and the output density of the lithium ion secondary battery decreases.

An object of one embodiment of the present invention is to provide a positive electrode capable of achieving both energy density and output density of a lithium ion secondary battery.

In one aspect of the present invention, the positive electrode has a positive electrode mixture containing lithium vanadium phosphate particles and lithium nickel composite oxide particles, and the lithium vanadium phosphate particles have a primary particle median diameter _D50 of 0. 0.8 μm or less, the carbon content is 2.5% by mass or more, and the mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles in the positive electrode mixture is 9% or less.

According to one embodiment of the present invention, it is possible to provide a positive electrode capable of achieving both the energy density and the output density of a lithium ion secondary battery.

1 is a schematic diagram showing the structure of lithium vanadium phosphate particles; FIG. It is a schematic diagram showing an example of a non-aqueous electric storage element of the present embodiment. 1 is a plan view showing a negative electrode of an example; FIG. It is a top view which shows the positive electrode of an Example. It is a figure which shows the electrode element of an Example. 4 is a graph showing the relationship between output density and energy density of a lithium ion secondary battery.

DETAILED DESCRIPTION OF THE INVENTION Embodiments for carrying out the present invention will be described below.

<Positive electrode>
The positive electrode of the present embodiment is not particularly limited as long as it has a positive electrode mixture containing lithium vanadium phosphate particles and lithium nickel composite oxide particles as a positive electrode active material, and is appropriately selected according to the purpose. Examples include a positive electrode having a positive electrode mixture on a positive electrode substrate.

The shape of the positive electrode is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a flat plate shape.

<<Positive electrode mixture>>
The positive electrode mixture contains lithium vanadium phosphate particles and lithium nickel composite oxide particles, and if necessary, further contains a conductive agent, a binder, a thickener, and the like.

The mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles in the positive electrode mixture is 9% or less, preferably 7% or less. When the mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles in the positive electrode mixture exceeds 9%, coating unevenness occurs when the positive electrode mixture is formed, and the output of the lithium ion secondary battery is reduced. Density decreases. The mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles in the positive electrode mixture is usually 1% or more.

－Lithium Vanadium Phosphate Particles－
FIG. 1 shows the structure of lithium vanadium phosphate particles.

The lithium vanadium phosphate particles 10 are aggregates of primary particles 11 , that is, secondary particles 12 . Here, the primary particles 11 are aggregates of crystallites 13, and a conductive carbon coating layer 14 exists on the surface.

The median diameter _D50 of the primary particles 11 is 0.8 μm or less, preferably 0.5 μm or less. When the median diameter _D50 of the primary particles 11 exceeds 0.5 μm, the power density of the lithium ion secondary battery is lowered. The median diameter _D50 of the primary particles 11 is usually 0.05 μm or more.

The content of carbon in the lithium vanadium phosphate particles 10 is 2.5% by mass or more, preferably 3% by mass or more. When the carbon content in the lithium vanadium phosphate particles 10 is less than 2.5% by mass, the power density of the lithium ion secondary battery is lowered. The content of carbon in the lithium vanadium phosphate particles 10 is usually 10% by mass or less.

The median diameter _D50 of the secondary particles 12 is preferably 5 μm or less, more preferably 3.5 μm or less. When the median diameter _D50 of the secondary particles 12 is 5 μm or less, the power density of the lithium ion secondary battery is improved. The median diameter _D50 of the secondary particles 12 is usually 0.5 μm or more.

In the present embodiment, lithium vanadium phosphate is Nasicon-type lithium vanadium phosphate, for example, Li _x V _{2-y My} (PO ₄ ) _z
(Wherein, M is one or more selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, Sr, and Zr, and the formula x-y+6=3z
meet. )
The compound represented by is used as a basic skeleton.

Lithium vanadium phosphate has the chemical formula Li ₃ V ₂ (PO ₄ ) ₃ in terms of the output density of a lithium ion secondary battery.
or a compound represented by the general formula Li ₃ V _2-x M _x (PO ₄ ) ₃
(In the formula, M is one or more selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Ti, Mg, Ca and Sr.)
It is preferable to use a compound represented by as a basic skeleton.

As the lithium vanadium phosphate, a similar compound in which the basic skeleton is doped with a different element can be used.

As a method for synthesizing lithium vanadium phosphate, a known synthesis method can be used (see, for example, Patent Document 1).

-Lithium Nickel Composite Oxide Particles-
In the present embodiment, the lithium- _nickel composite oxide is, for example, represented by the general _{formula LiNixMyO2}
(Wherein, M is one or more selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr, and the formula x + y = 1
meet. )
The compound represented by is used as a basic skeleton.

Lithium-nickel composite oxides have _the general formula _LiNixCoyMzO2 in terms of the energy density _of lithium-ion secondary batteries _.
(Wherein, M is one or more selected from the group consisting of Fe, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr, and the formula x + y + z = 1
meet. )
It is preferable to use a compound represented by as a basic skeleton.

As the lithium-nickel composite oxide, a similar compound in which the basic skeleton is doped with a different element can be used.

As a method for synthesizing the lithium-nickel composite oxide, a known synthesis method can be used (see, for example, Patent Document 1).

The median diameter _D50 of the lithium-nickel composite oxide particles is preferably 30 μm or less, more preferably 22 μm or less. When the median diameter _D50 of the lithium-nickel composite oxide particles is 30 μm or more, the power density of the lithium-ion secondary battery is improved. In addition, coating unevenness is less likely to occur when the positive electrode mixture is formed, and long-term life characteristics are improved. The median diameter _D50 of the lithium-nickel composite oxide particles is usually 0.5 μm or more.

-Binder-
The binder is not particularly limited as long as it is a material that is stable against the solvent or dispersion medium, non-aqueous electrolyte, and applied potential contained in the coating liquid used when manufacturing the positive electrode, and may be used depending on the purpose. It can be selected as appropriate, for example, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR)
, isoprene rubber, polyacrylic acid ester, and the like.

In addition, a binder may be used individually and may use 2 or more types together.

- Thickener -
Examples of thickeners include carboxymethylcellulose (CMC), methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein and the like.

In addition, a thickener may be used individually and may use 2 or more types together.

-Conductive agent-
Examples of conductive agents include carbonaceous materials such as carbon black and acetylene black.

In addition, a conductive agent may be used individually and may use 2 or more types together.

-Method of Forming Positive Electrode Mixture-
The positive electrode mixture is prepared by adding a binder, a thickener, a conductive agent, a dispersion medium, and the like to lithium vanadium phosphate particles and lithium nickel composite oxide particles, if necessary, and adding a binder, a thickener, a conductive agent, a dispersion medium, etc., to form a slurry coating liquid, which is applied to the positive electrode substrate. It can be formed by coating on top and then drying.

The dispersion medium is not particularly limited and can be appropriately selected depending on the intended purpose. Examples thereof include aqueous solvents and organic solvents.

Examples of aqueous solvents include water and alcohols.

Examples of organic solvents include N-methyl-2-pyrrolidone (NMP) and toluene.

<<Positive electrode substrate (current collector)>>
The material constituting the positive electrode substrate is not particularly limited as long as it is made of a conductive material and is stable with respect to the applied potential, and can be appropriately selected according to the purpose. aluminum, titanium, tantalum, and the like. Among these, aluminum is particularly preferable because it is lightweight, inexpensive, and highly resistant to oxidation.

The shape of the positive electrode substrate is not particularly limited, and can be appropriately selected according to the purpose.

The size of the positive electrode substrate is not particularly limited as long as it is a size that can be used in a non-aqueous electric storage device, and can be appropriately selected according to the purpose.

<<Use of positive electrode>>
The positive electrode of the present embodiment can be applied to, for example, non-aqueous storage devices such as non-aqueous secondary batteries and non-aqueous capacitors.

<Non-aqueous power storage element>
The non-aqueous electric storage element of the present embodiment is formed by assembling the positive electrode, the negative electrode, the non-aqueous electrolyte of the present embodiment, and the separator used as necessary into a predetermined shape.

The non-aqueous power storage element of this embodiment has the formula y>−47.115x+11310
(In the formula, x is the energy density [Wh/kg] and y is the power density [W/kg] when the charging depth is 50%.)
is preferably satisfied.

The non-aqueous electric storage element of the present embodiment may further have constituent members such as an outer can, an electrode lead-out wire, and the like, if necessary.

The method for assembling the positive electrode, the negative electrode, the non-aqueous electrolyte, and the optionally used separator is not particularly limited, and can be appropriately selected from known methods.

The shape of the non-aqueous electricity storage element of the present embodiment is not particularly limited, and can be appropriately selected from various commonly used shapes according to the application. A cylinder type with a spiral separator, a cylinder type with an inside-out structure combining a pellet electrode and a separator, a coin type with a pellet electrode and a separator laminated, a type using a laminated film exterior with a sheet electrode and a separator laminated, etc. be done.

<Negative Electrode>
The negative electrode is not particularly limited as long as it contains a negative electrode active material, and can be appropriately selected according to the purpose. mentioned.

The shape of the negative electrode is not particularly limited and can be appropriately selected depending on the intended purpose.

<<Negative electrode mixture>>
The negative electrode mixture contains a negative electrode active material and, if necessary, further contains a binder, a conductive agent, and the like.

-Negative electrode active material-
Examples of negative electrode active materials include lithium, lithium alloys, graphite (artificial graphite, natural graphite), graphitizable carbon, non-graphitizable carbon, thermal decomposition products of organic matter under various thermal decomposition conditions, lithium titanate, and the like. is mentioned.

-Binder-
The binder is not particularly limited as long as it is a solvent or dispersion medium, a non-aqueous electrolyte, or a material that is stable with respect to the applied potential, and can be appropriately selected according to the purpose. For example, fluorine-based binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE), ethylene-propylene-butadiene rubber (EPBR), styrene-butadiene rubber (SBR), isoprene rubber, carboxymethylcellulose (CMC) etc.

In addition, a binder may be used individually and may use 2 or more types together.

-Conductive agent-
Examples of conductive agents include carbonaceous materials such as carbon black and acetylene black.

In addition, a conductive agent may be used individually and may use 2 or more types together.

-Method of forming negative electrode mixture-
The negative electrode mixture can be formed by adding a binder, a conductive agent, a dispersion medium, and the like to the negative electrode active material, if necessary, to prepare a slurry-like coating liquid, applying the slurry onto the negative electrode substrate, and then drying it. can.

As the dispersion medium, the same dispersion medium as in the case of forming the positive electrode mixture can be used.

A composition obtained by adding a binder, a conductive agent, and the like to the negative electrode active material, if necessary, may be roll-formed into a sheet electrode, punched into a sheet electrode, or compression-formed into a pellet electrode. can also

A thin film of the negative electrode active material can also be formed on the negative electrode substrate by a method such as vapor deposition, sputtering, or plating.

<<Negative electrode substrate (current collector)>>
The material constituting the negative electrode substrate is not particularly limited as long as it is made of a conductive material and is stable with respect to the applied potential, and can be appropriately selected according to the purpose. Examples include stainless steel, nickel, aluminum, copper, and the like. Among these, stainless steel, copper and aluminum are particularly preferred.

The shape of the negative electrode substrate is not particularly limited and can be appropriately selected according to the purpose.

The size of the negative electrode substrate is not particularly limited as long as it is a size that can be used in a non-aqueous electric storage device, and can be appropriately selected according to the purpose.

<Non-aqueous electrolyte>
A solid electrolyte or a non-aqueous electrolyte can be used as the non-aqueous electrolyte.

Here, the non-aqueous electrolytic solution is an electrolytic solution in which an electrolyte salt (especially an electrolytic salt containing halogen atoms) is dissolved in a non-aqueous solvent.

<<Non-aqueous solvent>>
The non-aqueous solvent is not particularly limited and can be appropriately selected depending on the purpose, but an aprotic organic solvent is preferred.

As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates can be used. Among these, chain carbonates are preferred because they have high dissolving power for electrolyte salts.

Also, the aprotic organic solvent preferably has a low viscosity.

Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC) and the like.

The content of the chain carbonate in the non-aqueous solvent is not particularly limited and can be appropriately selected depending on the purpose, but the content of the chain carbonate in the non-aqueous solvent is preferably 50% by mass or more. When the amount is 50% by mass or more, the content of the cyclic substance is reduced even if the solvent other than the chain carbonate is a cyclic substance with a high dielectric constant (eg, cyclic carbonate, cyclic ester). Therefore, even if a non-aqueous electrolytic solution having a high concentration of 2 M or more is prepared, the viscosity of the non-aqueous electrolytic solution is lowered, and the penetration of the non-aqueous electrolytic solution into the electrode and the diffusion of ions are improved.

Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC) and the like.

As the non-aqueous solvent other than the carbonate-based organic solvent, ester-based organic solvents such as cyclic esters and chain esters, ether-based organic solvents such as cyclic ethers and chain ethers, and the like can be used, if necessary. .

Cyclic esters include, for example, γ-butyrolactone (γBL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, γ-valerolactone and the like.

Examples of chain esters include alkyl propionate, dialkyl malonate, alkyl acetate (methyl acetate (MA), ethyl acetate, etc.), alkyl formate (methyl formate (MF), ethyl formate, etc.), and the like. be done.

Cyclic ethers include, for example, tetrahydrofuran, alkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane and the like.

Examples of chain ethers include 1,2-dimethoxyethane (DME), diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol dialkyl ether and the like.

<<Electrolyte salt>>
The electrolyte salt is not particularly limited as long as it dissolves in a non-aqueous solvent and has high ionic conductivity, but it preferably contains a halogen atom.

Examples of cations constituting the electrolyte salt include lithium ions.

Anions constituting the electrolyte salt include, for example, BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , (C ₂ F ₅ SO ₂ ) ₂ N ⁻ etc.

_The lithium salt is _not particularly limited and can be appropriately selected _depending on the intended purpose. ), lithium trifluoromethosulfonate (LiCF ₃ SO ₃ ), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF ₃ SO ₂ ) ₂ ), lithium bis(perfluoroethylsulfonyl)imide (LiN(C ₂ F ₅ SO ₂ ) ₂ ) and the like. Among these, LiPF ₆ is preferable from the point of ionic conductivity, and LiBF ₄ is preferable from the point of stability.

In addition, electrolyte salt may be used individually and may use 2 or more types together.

The concentration of the electrolyte salt in the non-aqueous solvent can be appropriately selected depending on the purpose. In that case, it is preferably 2 mol/L to 4 mol/L.

<Separator>
A separator is optionally provided between the positive electrode and the negative electrode in order to prevent a short circuit between the positive electrode and the negative electrode.

Examples of the separator include paper such as kraft paper, vinylon mixed paper, synthetic pulp mixed paper, cellophane, polyethylene graft membrane, polyolefin nonwoven fabric such as polypropylene meltblown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, micropore membrane, and the like.

The size of the separator is not particularly limited as long as it can be used for a non-aqueous electric storage device, and can be appropriately selected according to the purpose.

The structure of the separator may be a single layer structure or a laminated structure.

In addition, when using a solid electrolyte as a nonaqueous electrolyte, a separator is unnecessary.

FIG. 2 shows an example of the non-aqueous storage element of this embodiment.

The non-aqueous storage element 20 has a positive electrode 21, a negative electrode 22, a separator 23 holding a non-aqueous electrolyte, an outer can 24, a lead wire 25 of the positive electrode 21, and a lead wire 26 of the negative electrode 22. .

<Application of non-aqueous storage device>
The use of the non-aqueous power storage device of the present embodiment is not particularly limited, and it can be used for various purposes. Copiers, portable printers, headphone stereos, video movies, liquid crystal televisions, handy cleaners, portable CDs, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, games Devices, clocks, strobes, cameras, etc. can be mentioned.

Examples of the present invention will be described below, but the present invention is not limited to these examples.

Using the positive electrode mixture coating liquid and the lithium ion secondary battery prepared by the method described later, the thixotropy index (TI) and coating unevenness of the positive electrode mixture coating liquid were evaluated by the following methods. A charge/discharge test was performed on the following battery.

[TI of coating liquid for positive electrode mixture]
B-type viscometer No. No. 4 rotor was mounted, and the viscosity of the positive electrode mixture coating solution at 6 rpm and 60 rpm was measured at 25°C. Then the formula (viscosity at 6 rpm)/(viscosity at 60 rpm)
TI of the coating liquid for the positive electrode mixture was calculated.

[Uneven coating of positive electrode mixture coating solution]
As will be described later, when the positive electrode mixture coating liquid was applied onto the current collector foil made of aluminum, coating unevenness was visually evaluated. Criteria for determining coating unevenness are as follows.

○: When coating unevenness cannot be visually confirmed ×: When coating unevenness can be visually confirmed [Charging and discharging test of lithium ion secondary battery]
Using a charge/discharge measuring device TOSCAT3001 (manufactured by Toyo System Co., Ltd.), a charge/discharge test was performed on the lithium ion secondary battery. Specifically, at room temperature (25° C.), the charge-discharge cycle includes constant-current constant-voltage charging at a maximum voltage of 4.2 V and a current rate of 0.7 C for 3 hours, followed by constant-current discharging to 2.5 V at a current rate of 1 C. was repeated 1000 times with a 10 minute rest interval.

Formula (Capacity at first discharge) x (Average discharge voltage) / (Battery mass)
The energy density was calculated by

Also, the formula (capacity at the 1000th discharge) / (capacity at the first discharge) x 100)
The capacity retention rate was calculated by

In addition, with the lithium ion secondary battery having a charge depth of 50%, the voltage and current correlation line after discharging for 10 seconds with a pulse at a current rate of 1C to 10C shows that the power reaches a cutoff voltage of 2.5V. was calculated, and the power density was calculated from the ratio to the mass of the lithium ion secondary battery.

[Synthesis of lithium vanadium phosphate particles]
A reaction precursor was obtained by putting phosphoric acid, a carbon source, vanadium pentoxide and lithium hydroxide into a beaker and heating. Here, the addition amount of the carbon source was adjusted so as to obtain a predetermined carbon content. The resulting reaction precursor was pulverized with a bead mill to a predetermined median diameter _D50 of the primary particles to obtain a dispersion. The resulting dispersion was spray-dried to obtain secondary particles in which primary particles were agglomerated. After firing the obtained secondary particles at 800 ° C. to 1100 ° C. in an inert gas atmosphere, they are pulverized with a jet mill until the median diameter of the secondary particles is D ₅₀ , thereby producing lithium vanadium phosphate. (Li ₃ V ₂ (PO ₄ ) ₃ ) particles (hereinafter referred to as LVP particles) were obtained.

LVP particles (1) had a primary particle median diameter _D50 of 0.53 μm, a secondary particle median diameter _D50 of 3.2 μm, and a carbon content of 5.3% by mass. .

The LVP particles (2) had a primary particle median diameter _D50 of 0.76 μm, a secondary particle median diameter _D50 of 3.2 μm, and a carbon content of 5.3% by mass. .

The LVP particles (3) had a primary particle median diameter _D50 of 0.41 μm, a secondary particle median diameter _D50 of 3.0 μm, and a carbon content of 5.3% by mass. .

The LVP particles (4) had a primary particle median diameter _D50 of 0.53 μm, a secondary particle median diameter _D50 of 3.2 μm, and a carbon content of 3.5% by mass. .

The LVP particles (5) had a primary particle median diameter _D50 of 0.53 μm, a secondary particle median diameter _D50 of 3.3 μm, and a carbon content of 7.2% by mass. .

Table 1 shows the properties of the LVP particles.

［ＬＶＰ粒子の１次粒子のメジアン径Ｄ_５０］
ＬＶＰ粒子を走査型電子顕微鏡（ＳＥＭ）で観察し、粒子をランダムに選んでカウントし、ＬＶＰ粒子の１次粒子のメジアン径Ｄ_５０を測定した。

[Median diameter D ₅₀ of primary particles of LVP particles]
The LVP particles were observed with a scanning electron microscope (SEM), the particles were randomly selected and counted, and the median diameter _D50 of the primary particles of the LVP particles was measured.

[Median diameter D ₅₀ of secondary particles of LVP particles]
The LVP particles were measured with a particle size distribution meter (manufactured by Malvarn) to measure the median diameter _D50 of the secondary particles of the LVP particles.

[Carbon content of LVP particles]
The carbon content of the LVP particles was measured using a TOC total organic carbon meter TOC-5000A (manufactured by Shimadzu Corporation).

[Lithium-nickel composite oxide particles]
NCA particles (manufactured by JFE Mineral) were used as the lithium-nickel composite oxide particles.

[Example 1]
97 parts by mass of graphite as a negative electrode active material, 1 part by mass of carboxymethyl cellulose (CMC) and 2 parts by mass of styrene-butadiene rubber (SBR) as a binder, and 100 parts by mass of water are added to prepare a negative electrode mixture coating solution. made.

After applying the negative electrode mixture coating liquid to both surfaces of a current collector foil made of copper, it was dried to form a negative electrode mixture. At this time, the coating liquid for the negative electrode mixture was applied so that the mass per unit area (area density) of the negative electrode mixture in the region (one side) where the negative electrode mixture was formed was 5 mg/cm ² . Next, the negative electrode 30 (see FIG. 3) was manufactured by punching into a predetermined size. At this time, the area on the negative electrode substrate 31 where the negative electrode mixture 32 was formed was 30 mm×50 mm, and the area on the negative electrode substrate 31 where the negative electrode mixture 32 was not formed was 10 mm×11 mm.

7.5 parts by mass of LVP particles (1) and 85 parts by mass of NCA particles as a positive electrode active material, 1 part by mass of Ketjenblack (manufactured by Lion) and 2 parts by mass of carbon fiber (manufactured by Showa Denko) as a conductive agent, As binders, 4 parts by mass of polyvinylidene fluoride (PVDF) and 100 parts by mass of N-methyl-2-pyrrolidone (NMP) were added to prepare a positive electrode mixture coating liquid.

The positive electrode mixture coating liquid had a viscosity of 27,900 mPa·s at 6 rpm, a viscosity of 6,500 mPa·s at 60 rpm, and a TI of 4.5.

The positive electrode mixture coating liquid was applied to both surfaces of the current collector foil made of aluminum, and then dried to form the positive electrode mixture 42 . At this time, the coating solution for the positive electrode mixture was applied so that the area density of the positive electrode mixture in the region (one side) where the positive electrode mixture was formed was 8.3 mg/cm ² . Next, the positive electrode 40 (see FIG. 4) was produced by punching into a predetermined size. At this time, the area on the positive electrode substrate 41 where the positive electrode mixture 42 was formed was 28 mm×48 mm, and the area on the positive electrode substrate 41 where the positive electrode mixture 42 was not formed was 10 mm×13 mm.

An electrode element 50 having a thickness of about 10 mm was produced by laminating the negative electrode 30 and the positive electrode 40 via a polypropylene (PP) film as a separator 51 (see FIG. 5). At this time, a tab 52 made of nickel is welded to a portion of the region on the negative electrode substrate 31 where the negative electrode mixture 32 is not formed, and a portion of the region on the positive electrode substrate 41 where the positive electrode mixture 42 is not formed is welded. A tab 53 made of aluminum was welded to. 5A and 5B are a plan view and a cross-sectional view, respectively.

After impregnating the electrode element 50 with the non-aqueous electrolyte, it was enclosed in an aluminum laminate film to produce a lithium ion secondary battery. At this time, as an electrolytic solution, a solution in which 1.5M LiPF ₆ was dissolved in a non-aqueous solvent was used. As the non-aqueous solvent, a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) mixed at a volume ratio of 1:1:1 was used.

The lithium ion secondary battery had an energy density of 160.5 Wh/kg, a capacity retention rate of 90%, and an output density of 4200 W/kg.

[Example 2]
In the same manner as in Example 1, except that the amounts of the LVP particles (1) and NCA particles added were changed to 4 parts by mass and 90 parts by mass, respectively, when preparing the coating liquid for the positive electrode mixture, two lithium ions were added. A following battery was produced.

The positive electrode mixture coating liquid had a viscosity of 14200 mPa·s at 6 rpm, a viscosity of 4300 mPa·s at 60 rpm, and a TI of 3.3.

The lithium ion secondary battery had an energy density of 160.9 Wh/kg, a capacity retention rate of 88%, and an output density of 3900 W/kg.

[Example 3]
In the same manner as in Example 1, except that the amounts of LVP particles (1) and NCA particles added were changed to 2 parts by mass and 92 parts by mass, respectively, when preparing the coating liquid for the positive electrode mixture, two lithium ions were added. A following battery was produced.

The positive electrode mixture coating liquid had a viscosity of 9200 mPa·s at 6 rpm, a viscosity of 3400 mPa·s at 60 rpm, and a TI of 2.7.

The lithium ion secondary battery had an energy density of 160.9 Wh/kg, a capacity retention rate of 88%, and an output density of 3720 W/kg.

[Example 4]
The area density of the negative electrode mixture in the region (one side) where the negative electrode mixture is formed is changed to 9 mg/cm ² , and the area density of the positive electrode mixture in the region (one side) where the positive electrode mixture is formed is changed to 15. A lithium ion secondary battery was produced in the same manner as in Example 1, except that the content was changed to 5 mg/cm ² .

The lithium ion secondary battery had an energy density of 191.2 Wh/kg, a capacity retention rate of 89%, and an output density of 2850 W/kg.

[Example 5]
The area density of the negative electrode mixture in the region (one side) where the negative electrode mixture is formed is changed to 9 mg/cm ² , and the area density of the positive electrode mixture in the region (one side) where the positive electrode mixture is formed is changed to 15. A lithium ion secondary battery was produced in the same manner as in Example 2, except that the content was changed to 5 mg/cm ² .

The lithium ion secondary battery had an energy density of 192.0 Wh/kg, a capacity retention rate of 90%, and an output density of 2650 W/kg.

[Example 6]
The area density of the negative electrode mixture in the region (one side) where the negative electrode mixture is formed is changed to 9 mg/cm ² , and the area density of the positive electrode mixture in the region (one side) where the positive electrode mixture is formed is changed to 15. A lithium ion secondary battery was produced in the same manner as in Example 3, except that the content was changed to 5 mg/cm ² .

The lithium ion secondary battery had an energy density of 192.3 Wh/kg, a capacity retention rate of 88%, and an output density of 2250 W/kg.

[Example 7]
A lithium ion secondary battery was produced in the same manner as in Example 6, except that the LVP particles (2) were used instead of the LVP particles (1).

The lithium ion secondary battery had an energy density of 190.9 Wh/kg, a capacity retention rate of 86%, and an output density of 2180 W/kg.

[Example 8]
A lithium ion secondary battery was produced in the same manner as in Example 6, except that the LVP particles (3) were used instead of the LVP particles (1).

The lithium ion secondary battery had an energy density of 191.8 Wh/kg, a capacity retention rate of 87%, and an output density of 2232 W/kg.

[Example 9]
A lithium ion secondary battery was produced in the same manner as in Example 6, except that the LVP particles (4) were used instead of the LVP particles (1).

The lithium ion secondary battery had an energy density of 194.1 Wh/kg, a capacity retention rate of 88%, and an output density of 2229 W/kg.

[Example 10]
A lithium ion secondary battery was produced in the same manner as in Example 6, except that the LVP particles (5) were used instead of the LVP particles (1).

The lithium ion secondary battery had an energy density of 189.7 Wh/kg, a capacity retention rate of 86%, and an output density of 2276 W/kg.

[Comparative Example 1]
In the same manner as in Example 1, except that the amounts of the LVP particles (1) and NCA particles added were changed to 0 parts by mass and 94 parts by mass, respectively, when preparing the coating liquid for the positive electrode mixture, two lithium ions were added. A following battery was produced.

The positive electrode mixture coating liquid had a viscosity of 5200 mPa·s at 6 rpm, a viscosity of 1700 mPa·s at 60 rpm, and a TI of 3.1.

The lithium ion secondary battery had an energy density of 161.3 Wh/kg, a capacity retention rate of 86%, and an output density of 2600 W/kg.

[Comparative Example 2]
The area density of the negative electrode mixture in the region (one side) where the negative electrode mixture is formed is changed to 9 mg/cm ² , and the area density of the positive electrode mixture in the region (one side) where the positive electrode mixture is formed is changed to 15. A lithium ion secondary battery was produced in the same manner as in Comparative Example 1, except that the content was changed to 5 mg/cm ² .

The lithium ion secondary battery had an energy density of 192.6 Wh/kg, a capacity retention rate of 84%, and an output density of 1750 W/kg.

[Comparative Example 3]
In the same manner as in Example 1, except that the amounts of LVP particles (1) and NCA particles added were changed to 30 parts by mass and 64 parts by mass, respectively, when preparing the coating liquid for positive electrode mixture, lithium ion two A following battery was produced.

The positive electrode mixture coating liquid had a viscosity of 77200 mPa·s at 6 rpm, a viscosity of 13200 mPa·s at 60 rpm, and a TI of 5.8.

The lithium ion secondary battery had an energy density of 186.5 Wh/kg, a capacity retention rate of 91%, and an output density of 3080 W/kg.

[Comparative Example 4]
In the same manner as in Example 1, except that the amounts of LVP particles (1) and NCA particles added were changed to 15 parts by mass and 79 parts by mass, respectively, when preparing the coating liquid for positive electrode mixture, lithium ion two A following battery was produced.

The positive electrode mixture coating liquid had a viscosity of 43700 mPa·s at 6 rpm, a viscosity of 8600 mPa·s at 60 rpm, and a TI of 5.1.

The lithium ion secondary battery had an energy density of 189.1 Wh/kg, a capacity retention rate of 89%, and an output density of 2980 W/kg.

Table 2 shows the evaluation results of the thixotropy index (TI) and coating unevenness of the positive electrode mixture coating liquid, and the results of the charge/discharge test of the lithium ion secondary battery.

表２から、実施例１～１０のリチウムイオン二次電池は、エネルギー密度と出力密度が高いことがわかる。

From Table 2, it can be seen that the lithium ion secondary batteries of Examples 1 to 10 have high energy densities and high power densities.

On the other hand, the lithium ion secondary batteries of Comparative Examples 1 and 2 have low output densities because the positive electrode mixture does not contain NVP particles.

In addition, in the lithium ion secondary batteries of Comparative Examples 3 and 4, the mass ratio of the NVP particles to the NCA particles in the positive electrode mixture was 46.9 and 19.0, so the TI of the positive electrode mixture coating liquid was large. As a result, coating unevenness occurs. As a result, the lithium ion secondary batteries of Comparative Examples 3 and 4 have low output densities.

FIG. 6 shows the relationship between the energy density and the output density of the lithium ion secondary battery.

REFERENCE SIGNS LIST 10 lithium vanadium phosphate particles 11 primary particles 12 secondary particles 13 crystallite 14 carbon coating layer 20 non-aqueous storage element 21 positive electrode 22 negative electrode 23 separator 24 outer can 25, 26 lead wire 30 negative electrode 31 negative electrode substrate 32 negative electrode mixture 40 Positive electrode 41 Positive electrode substrate 42 Positive electrode mixture 50 Electrode element 51 Separator 52, 53 Tab

JP 2012-256591 A

Claims (6)

Having a positive electrode mixture containing Nasicon-type lithium vanadium phosphate particles having a conductive carbon coating layer on the surface and lithium nickel composite oxide particles,
The lithium vanadium phosphate particles have a median diameter _D50 of primary particles of 0.8 μm or less and a carbon content of 2.5% by mass or more,
A positive electrode for a lithium ion secondary battery, wherein the positive electrode mixture has a mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles of 1% or more and 9% or less. The lithium vanadium phosphate particles have the chemical formula Li ₃ V ₂ (PO ₄ ) ₃
or a compound represented by the general formula Li ₃ V _2-x M _x (PO ₄ ) ₃
(In the formula, M is one or more selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Ti, Mg, Ca and Sr.)
2. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the compound represented by is used as a basic skeleton. The lithium- _{nickel composite} oxide particles have _the general formula _LiNixCoyMzO2
(Wherein, M is one or more selected from the group consisting of Fe, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr, and the formula x + y + z = 1
meet. )
3. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the compound represented by is used as a basic skeleton. A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3. Formula y>−47.115x+11310
(In the formula, x is the energy density [Wh/kg] and y is the power density [W/kg] when the charging depth is 50%.)
5. The lithium ion secondary battery according to claim 4, wherein: A positive electrode mixture for a lithium ion secondary battery containing Nasicon type lithium vanadium phosphate particles having a conductive carbon coating layer on the surface and lithium nickel composite oxide particles in a dispersion medium,
The lithium vanadium phosphate particles have a median diameter _D50 of primary particles of 0.8 μm or less and a carbon content of 2.5% by mass or more,
A coating liquid for a positive electrode mixture, wherein the mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles is 1% or more and 9% or less.

Images