JP2019164986A - Positive electrode, nonaqueous power storage element and coating liquid for positive electrode mixture material - Google Patents

Abstract

To provide a positive electrode which enables the achievement of both of an energy density and an output density of a lithium ion secondary battery.SOLUTION: A positive electrode 40 comprises: lithium vanadium phosphate particles; and a positive electrode mixture material 42 containing lithium nickel composite oxide particles. The lithium vanadium phosphate particles include primary particles having a median diameter Dof 0.8 μm or less, and have a carbon content of 2.5 mass% or more. As to the positive electrode mixture material 42, the mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles is 9% or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a positive electrode, a nonaqueous storage element, and a positive electrode mixture coating solution.

  Lithium ion secondary batteries are expanding in the consumer, automotive, and infrastructure markets, but they are used in a variety of devices in a variety of environments, which can improve energy density and output density. It is desired.

  Patent Document 1 discloses a positive electrode including a positive electrode mixture layer containing a positive electrode active material. Here, the positive electrode active material contains lithium vanadium phosphate and a lithium nickel composite oxide in a mass ratio of 8:82 to 70:20. 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 the energy density and the power density of a lithium ion secondary battery.

In one embodiment of the present invention, the positive electrode includes a positive electrode mixture containing lithium vanadium phosphate particles and lithium nickel composite oxide particles, and the lithium vanadium phosphate particles have a median diameter D _{50 of} primary particles of 0. 0.8 mass or less, the carbon content is 2.5 mass% or more, and the positive electrode mixture has a mass ratio of the lithium vanadium phosphate particles to 9% or less with respect to the lithium nickel composite oxide particles.

  According to one embodiment of the present invention, a positive electrode capable of achieving both the energy density and the power density of a lithium ion secondary battery can be provided.

It is a schematic diagram which shows the structure of a lithium vanadium phosphate particle. It is the schematic which shows an example of the non-aqueous electrical storage element of this embodiment. It is a top view which shows the negative electrode of an Example. 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. It is a graph which shows the relationship of the output density with respect to the energy density of a lithium ion secondary battery.

  Hereinafter, modes for carrying out the present invention will be described.

<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. For example, a positive electrode including a positive electrode mixture on a positive electrode substrate may be used.

  There is no restriction | limiting in particular as a shape of a positive electrode, Although it can select suitably according to the objective, For example, flat form etc. are mentioned.

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

  The mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles in the positive electrode composite material is 9% or less, and 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 Density decreases. In addition, 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 the conductive carbon coating layer 14 exists on the surface.

The median diameter D ₅₀ of the primary particles 11 is 0.8 μm or less, and preferably 0.5 μm or less. When the median diameter D ₅₀ of the primary particles 11 exceeds 0.5 μm, the output density of the lithium ion secondary battery decreases. The median diameter D ₅₀ 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, and preferably 3% by mass or more. When the content of carbon in the lithium vanadium phosphate particles 10 is less than 2.5% by mass, the output density of the lithium ion secondary battery decreases. The carbon content in the lithium vanadium phosphate particles 10 is usually 10% by mass or less.

The median diameter D ₅₀ of the secondary particles 12 is preferably 5 μm or less, and more preferably 3.5 μm or less. When the median diameter D ₅₀ of the secondary particles 12 is 5 μm or less, the output density of the lithium ion secondary battery is improved. Incidentally, the median diameter _{D 50} of the secondary particles 12 are typically, 0.5 [mu] m or more.

In the present embodiment, the lithium vanadium phosphate is a NASICON type lithium vanadium phosphate. For example, the general formula Li _x V _{2 -y My} (PO ₄ ) _z
(In the formula, M is at least one selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, Sr, Zr, xy + 6 = 3z
Meet. )
The basic skeleton is a compound represented by

Lithium vanadium phosphate has the chemical formula Li ₃ V ₂ (PO ₄ ) _{3 in} terms of the power density of the 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

  Note that as the vanadium lithium phosphate, a similar compound having a basic skeleton doped with a different element can be used.

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

-Lithium nickel composite oxide particles-
In the present embodiment, the lithium nickel composite oxide, for example, the general formula LiNi _x M _y O ₂
(In the formula, 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 basic skeleton is a compound represented by

Lithium nickel composite oxide, in terms of energy density of the lithium ion secondary battery, the general formula LiNi _x Co _y M _z O ₂
(In the formula, 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 the lithium nickel composite oxide, a similar compound having a basic skeleton 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 (for example, see Patent Document 1).

The median diameter D ₅₀ of the lithium nickel composite oxide particles is preferably 30 μm or less, and more preferably 22 μm or less. When the median diameter D _{50 of the} lithium nickel composite oxide particles is 30 μm or more, the output density of the lithium ion secondary battery is improved. Further, uneven coating is less likely to occur when the positive electrode mixture is formed, and long-term life characteristics are improved. Incidentally, the median diameter _{D 50} of the lithium nickel composite oxide particles is usually, 0.5 [mu] m or more.

-Binder-
The binder is not particularly limited as long as it is a solvent or dispersion medium contained in the coating liquid used for manufacturing the positive electrode, a non-aqueous electrolyte, and a material that is stable with respect to an applied potential. 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 independently and may use 2 or more types together.

-Thickener-
Examples of the thickener include carboxymethyl cellulose (CMC), methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

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

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

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

-Method for forming positive electrode mixture-
The positive electrode mixture is obtained by adding a coating solution in a slurry form by adding a binder, a thickener, a conductive agent, a dispersion medium, etc., to lithium vanadium phosphate particles and lithium nickel composite oxide particles as necessary. It can be formed by applying on the top and then drying.

  There is no restriction | limiting in particular as a dispersion medium, Although it can select suitably according to the objective, For example, an aqueous solvent, an organic solvent, etc. are mentioned.

  Examples of the aqueous solvent include water and alcohol.

  Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), toluene and the like.

<< Positive electrode substrate (current collector) >>
The material constituting the positive electrode substrate is not particularly limited as long as it is formed of a conductive material and is stable with respect to an applied potential, and can be appropriately selected according to the purpose. Aluminum, titanium, tantalum, etc. are mentioned. Among these, aluminum is particularly preferable because it is lightweight, inexpensive, and has high oxidation resistance.

  There is no restriction | limiting in particular as a shape of a positive electrode base | substrate, According to the objective, it can select suitably.

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

<< Application of positive electrode >>
The positive electrode of the present embodiment can be applied to nonaqueous storage elements such as nonaqueous secondary batteries and nonaqueous capacitors, for example.

<Non-aqueous storage element>
In the non-aqueous storage element of the present embodiment, the positive electrode, the negative electrode, and the non-aqueous electrolyte of the present embodiment, and a separator used as necessary are assembled in a predetermined shape.

The non-aqueous electricity storage device of this embodiment has the formula y> −47.115x + 11310.
(In the formula, x is energy density [Wh / kg], and y is output density [W / kg] when the charging depth is 50%.)
It is preferable to satisfy.

  The non-aqueous electricity storage device of this embodiment may further include components such as an outer can and an electrode lead-out line as necessary.

  There is no restriction | limiting in particular as a method of assembling a positive electrode, a negative electrode, a nonaqueous electrolyte, and the separator used as needed, It can select suitably from well-known methods.

  The shape of the non-aqueous storage element of the present embodiment is not particularly limited, and can be appropriately selected from various shapes that are generally employed according to the application. Examples include a cylinder type with a spiral separator, a cylinder type with an inside-out structure that combines a pellet electrode and a separator, a coin type that stacks a pellet electrode and a separator, a type that uses a laminate film exterior that has a sheet electrode and a separator stacked, etc. It is 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. For example, a negative electrode including a negative electrode mixture containing a negative electrode active material on a negative electrode substrate Can be mentioned.

  There is no restriction | limiting in particular as a shape of a negative electrode, Although it can select suitably according to the objective, For example, flat form etc. are mentioned.

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

-Negative electrode active material-
Examples of the negative electrode active material include lithium, lithium alloy, graphite (artificial graphite, natural graphite), graphitizable carbon, non-graphitizable carbon, pyrolyzate of organic matter under various pyrolysis conditions, lithium titanate, etc. Is mentioned.

-Binder-
The binder is not particularly limited as long as it is a solvent or dispersion medium used when producing the negative electrode, a non-aqueous electrolyte, and a material that is stable with respect to an 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 independently and may use 2 or more types together.

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

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

-Method for forming negative electrode mixture-
The negative electrode mixture may be formed by applying a slurry, a coating solution added to the negative electrode active material, if necessary, by adding a binder, a conductive agent, a dispersion medium, etc. 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.

  In addition, the composition which added a binder, the electrically conductive agent, etc. to the negative electrode active material as needed is roll-formed into a sheet electrode, punched into a sheet electrode, or compressed into a pellet electrode. You can also.

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

<< Negative Electrode Base (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, and copper. Among these, stainless steel, copper, and aluminum are particularly preferable.

  There is no restriction | limiting in particular as a shape of a negative electrode base | substrate, According to the objective, it can select suitably.

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

<Nonaqueous electrolyte>
As the non-aqueous electrolyte, a solid electrolyte or a non-aqueous electrolyte can be used.

  Here, the nonaqueous electrolytic solution is an electrolytic solution in which an electrolyte salt (particularly, an electrolyte salt containing a halogen atom) is dissolved in a nonaqueous solvent.

<< Non-aqueous solvent >>
There is no restriction | limiting in particular as a non-aqueous solvent, Although it can select suitably according to the objective, An aprotic organic solvent is preferable.

  As the aprotic organic solvent, carbonate-based organic solvents such as chain carbonates and cyclic carbonates can be used. Among these, a chain carbonate is preferable from the viewpoint that the electrolyte salt has a high dissolving power.

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

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

  The content of the chain carbonate in the non-aqueous solvent is not particularly limited and may be appropriately selected depending on the intended purpose. However, 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, even if the solvent other than the chain carbonate is a cyclic substance having a high dielectric constant (for example, cyclic carbonate or cyclic ester), the content of the cyclic substance is reduced. For this reason, even when a non-aqueous electrolyte solution having a high concentration of 2M or more is produced, the viscosity of the non-aqueous electrolyte solution is lowered, and the penetration of the non-aqueous electrolyte solution into the electrode and ion diffusion are improved.

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

  In addition, as the non-aqueous solvent other than the carbonate-based organic solvent, an ester-based organic solvent such as a cyclic ester or a chain ester, an ether-based organic solvent such as a cyclic ether or a chain ether, or the like can be used as necessary. .

  Examples of the cyclic ester include γ-butyrolactone (γBL), 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone.

  Examples of the chain ester include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester (methyl acetate (MA), ethyl acetate, etc.), formic acid alkyl ester (methyl formate (MF), ethyl formate, etc.) and the like. It is done.

  Examples of the cyclic ether include tetrahydrofuran, alkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane and the like.

  Examples of the chain ether 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 preferably contains a halogen atom.

  As a cation which comprises electrolyte salt, lithium ion etc. are mentioned, for example.

Examples of the anion constituting the electrolyte salt include BF ₄ ⁻ , PF ₆ ⁻ , AsF ₆ ⁻ , CF ₃ SO ₃ ⁻ , (CF ₃ SO ₂ ) ₂ N ⁻ , and (C ₂ F ₅ SO ₂ ) ₂ N ^−. Etc.

The lithium salt is not particularly limited and may be appropriately selected depending on the intended purpose. For example, lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium hexafluoride (LiAsF ₆₎ ), Lithium trifluorometasulfonate (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 viewpoint of ion conductivity, and LiBF ₄ is preferable from the viewpoint of stability.

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

  The concentration of the electrolyte salt in the non-aqueous solvent can be appropriately selected according to the purpose. However, in the case of a swing type energy storage device, it is preferably 1 mol / L to 2 mol / L. In this case, it is preferably 2 mol / L to 4 mol / L.

<Separator>
The separator is provided between the positive electrode and the negative electrode as necessary 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 and synthetic pulp mixed paper, cellophane, polyethylene graft membrane, polyolefin nonwoven fabric such as polypropylene melt blown nonwoven fabric, polyamide nonwoven fabric, glass fiber nonwoven fabric, and micropore membrane.

  If the magnitude | size of a separator is a magnitude | size which can be used for a non-aqueous electrical storage element, there will be no restriction | limiting in particular, According to the objective, it can select suitably.

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

  Note that when a solid electrolyte is used as the nonaqueous electrolyte, a separator is not necessary.

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

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

<Applications of non-aqueous energy storage devices>
The application of the non-aqueous storage element of the present embodiment is not particularly limited and can be used for various applications. For example, a notebook computer, a pen input personal computer, a mobile personal computer, an electronic book player, a mobile phone, a mobile fax machine, a mobile phone Copy, portable printer, headphone stereo, video movie, LCD TV, handy cleaner, portable CD, minidisc, walkie-talkie, electronic notebook, calculator, memory card, portable tape recorder, radio, backup power supply, motor, lighting equipment, toy, game Equipment, watches, strobes, cameras, etc.

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

  Using the coating solution for positive electrode mixture and lithium ion secondary battery produced by the method described later, the thixotropy index (TI) and coating unevenness of the coating solution for positive electrode mixture were evaluated by the following method. A secondary battery charge / discharge test was conducted.

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

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

○: When coating unevenness cannot be visually confirmed ×: When coating unevenness can be visually confirmed [Charge / discharge test of lithium ion secondary battery]
A charge / discharge test of the lithium ion secondary battery was performed using a charge / discharge measuring apparatus TOSCAT3001 (manufactured by Toyo System). Specifically, at room temperature (25 ° C.), a charge / discharge cycle in which a constant current and a constant voltage are charged for 3 hours at a maximum voltage of 4.2 V and a current rate of 0.7 C and then a constant current is discharged to 2.5 V at a current rate of 1 C Was repeated 1000 times with a 10 minute pause.

Formula (Capacity at the first discharge) x (Discharge average voltage) / (Battery mass)
Thus, the energy density was calculated.

Also, the formula (capacity at the time of the 1000th discharge) / (capacity at the first discharge) × 100)
Thus, the capacity maintenance rate was calculated.

  In addition, in a state where the charging depth of the lithium ion secondary battery is 50%, the electric power reaching the 2.5 V cut-off voltage from the correlation line between the voltage and the current after being discharged for 10 seconds by the pulse of the current rate 1C to 10C. The power density was calculated from the ratio to the mass of the lithium ion secondary battery.

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

The LVP particles (1) had a primary particle median diameter D ₅₀ of 0.53 μm, a secondary particle median diameter D ₅₀ of 3.2 μm, and a carbon content of 5.3 mass%. .

The LVP particles (2) had a primary particle median diameter D ₅₀ of 0.76 μm, a secondary particle median diameter D ₅₀ of 3.2 μm, and a carbon content of 5.3 mass%. .

The LVP particles (3) had a primary particle median diameter D ₅₀ of 0.41 μm, a secondary particle median diameter D ₅₀ of 3.0 μm, and a carbon content of 5.3 mass%. .

The LVP particles (4) had a primary particle median diameter D ₅₀ of 0.53 μm, a secondary particle median diameter D ₅₀ of 3.2 μm, and a carbon content of 3.5 mass%. .

The LVP particles (5) had a median diameter D _{50 of} primary particles of 0.53 μm, a median diameter D _{50 of} secondary particles of 3.3 μm, and a carbon content of 7.2 mass%. .

  Table 1 shows the characteristics 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 was observed with a scanning electron microscope (SEM), counting choose particles randomly were measured median diameter _{D 50} of the primary particles of the LVP particles.

[Median diameter D _{50 of} secondary particles of LVP particles]
The LVP particles measured by particle size distribution analyzer (manufactured by Malvarn), was measured median diameter _{D 50} of the secondary particles of the LVP particles.

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

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

[Example 1]
Add 97 parts by weight of graphite as a negative electrode active material, 1 part by weight of carboxymethyl cellulose (CMC) and 2 parts by weight of styrene-butadiene rubber (SBR) as binder, 100 parts by weight of water, and apply a coating solution for negative electrode mixture. Produced.

After apply | coating the coating liquid for negative electrode compound materials on both surfaces of copper current collection foil, it was made to dry and the negative electrode compound material was formed. At this time, the coating solution for negative electrode mixture was applied so that the mass per unit area (area density) of the negative electrode mixture in the region (one surface) where the negative electrode mixture was formed was 5 mg / cm ² . Next, the negative electrode 30 (refer FIG. 3) was produced by punching to a predetermined size. At this time, the region where the negative electrode mixture 32 was formed on the negative electrode substrate 31 was 30 mm × 50 mm, and the region where the negative electrode mixture 32 was not formed on the negative electrode substrate 31 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 Ketjen black (manufactured by Lion) and 2 parts by mass of carbon fiber (manufactured by Showa Denko) as a conductive agent, As a binder, 4 parts by mass of polyvinylidene fluoride (PVDF) and 100 parts by mass of N-methyl-2-pyrrolidone (NMP) were added to prepare a coating solution for positive electrode mixture.

  The coating liquid for positive electrode mixture had a viscosity at 6 rpm of 27900 mPa · s, a viscosity at 60 rpm of 6500 mPa · s, and a TI of 4.5.

A positive electrode mixture coating solution was applied to both surfaces of an aluminum current collector foil and then dried to form a positive electrode mixture 42. At this time, the coating solution for 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 (refer FIG. 4) was produced by punching into a predetermined size. At this time, the area where the positive electrode mixture 42 was formed on the positive electrode base 41 was 28 mm × 48 mm, and the area where the positive electrode mixture 42 was not formed on the positive electrode base 41 was 10 mm × 13 mm.

  The negative electrode 30 and the positive electrode 40 were laminated via a polypropylene (PP) film as the separator 51 to produce an electrode element 50 having a thickness of about 10 mm (see FIG. 5). At this time, a nickel tab 52 is welded to a part of the area where the negative electrode mixture 32 is not formed on the negative electrode base 31, and a part of the area where the positive electrode mixture 42 is not formed on the positive electrode base 41. The aluminum tab 53 was welded. 5A and 5B are a plan view and a cross-sectional view, respectively.

The electrode element 50 was impregnated with a nonaqueous electrolytic solution and then encapsulated in an aluminum laminate film to produce a lithium ion secondary battery. At this time, as the electrolytic solution, a solution in which 1.5 M LiPF ₆ was dissolved in a non-aqueous solvent was used. As the non-aqueous solvent, a mixed solvent in which ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were 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]
When preparing the coating solution for the positive electrode mixture, the amount of the LVP particles (1) and the NCA particles was changed to 4 parts by mass and 90 parts by mass, respectively, in the same manner as in Example 1 except that the lithium ion 2 A secondary battery was produced.

  The coating solution for positive electrode mixture had a viscosity at 6 rpm of 14200 mPa · s, a viscosity at 60 rpm of 4300 mPa · s, 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]
When preparing the coating solution for the positive electrode mixture, the amount of the LVP particles (1) and the NCA particles was changed to 2 parts by mass and 92 parts by mass, respectively. A secondary battery was produced.

  The coating liquid for positive electrode mixture had a viscosity at 6 rpm of 9200 mPa · s, a viscosity at 60 rpm of 3400 mPa · s, 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 15. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the concentration 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 15. A lithium ion secondary battery was produced in the same manner as in Example 2 except that the concentration 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 15. A lithium ion secondary battery was produced in the same manner as in Example 3 except that the concentration 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]
When preparing the coating liquid for the positive electrode mixture, the amount of the LVP particles (1) and the NCA particles was changed to 0 parts by mass and 94 parts by mass, respectively, in the same manner as in Example 1, except that the lithium ion 2 A secondary battery was produced.

  The coating liquid for positive electrode mixture had a viscosity at 6 rpm of 5200 mPa · s, a viscosity at 60 rpm of 1700 mPa · s, 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 15. A lithium ion secondary battery was produced in the same manner as in Comparative Example 1 except that the concentration 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]
When preparing the coating solution for the positive electrode mixture, the amount of the LVP particles (1) and the NCA particles was changed to 30 parts by mass and 64 parts by mass, respectively. A secondary battery was produced.

  The coating liquid for positive electrode mixture had a viscosity at 6 rpm of 77200 mPa · s, a viscosity at 60 rpm of 13200 mPa · s, 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]
When preparing the coating solution for the positive electrode mixture, the amount of LVP particles (1) and NCA particles was changed to 15 parts by mass and 79 parts by mass, respectively, in the same manner as in Example 1, except that A secondary battery was produced.

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

  In Table 2, the evaluation result of the thixotropy index (TI) and coating unevenness of the coating liquid for positive electrode mixture and the result of the charge / discharge test of the lithium ion secondary battery are shown.

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 density and output density.

  In contrast, the lithium ion secondary batteries of Comparative Examples 1 and 2 have a low output density because the positive electrode mixture does not contain NVP particles.

  Further, 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 is 46.9 and 19.0, so the TI of the coating solution for the positive electrode mixture is large. As a result, uneven coating occurs. As a result, the lithium ion secondary batteries of Comparative Examples 3 and 4 have a low output density.

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

DESCRIPTION OF SYMBOLS 10 Lithium vanadium phosphate particle 11 Primary particle 12 Secondary particle 13 Crystallite 14 Carbon coating layer 20 Nonaqueous storage element 21 Positive electrode 22 Negative electrode 23 Separator 24 Outer can 25, 26 Lead wire 30 Negative electrode 31 Negative electrode base body 32 Negative electrode compound material 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)

It has a positive electrode mixture containing lithium vanadium phosphate particles and lithium nickel composite oxide particles,
The lithium vanadium phosphate particles, the median diameter D ₅₀ of the primary particles is at 0.8μm or less, the content of carbon of 2.5 wt% or more,
The positive electrode mixture is characterized in that a mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles is 9% or less. The lithium vanadium phosphate has 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.)
The positive electrode according to claim 1, wherein the basic skeleton is a compound represented by the formula: The lithium nickel composite oxide has a general formula of LiNi _x Co _y M _z O _2.
(In the formula, 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. )
The positive electrode according to claim 1, wherein the compound represented by the formula is used as a basic skeleton.   A lithium ion secondary battery comprising the positive electrode according to any one of claims 1 to 3. Formula y> -47.115x + 11310
(In the formula, x is energy density [Wh / kg], and y is output density [W / kg] when the charging depth is 50%.)
The lithium ion secondary battery according to claim 4, wherein: Including lithium vanadium phosphate particles and lithium nickel composite oxide particles,
The lithium vanadium phosphate particles, the median diameter D ₅₀ of the primary particles is at 0.8μm or less, the content of carbon of 2.5 wt% or more,
The positive electrode mixture coating solution, wherein a mass ratio of the lithium vanadium phosphate particles to the lithium nickel composite oxide particles is 9% or less.

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