JP2018060618A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery superior in durability against lithium precipitation.SOLUTION: A lithium ion secondary battery comprises an electrolyte solution, a positive electrode 10, a separator 20, a lithium ion-containing zeolite, and a negative electrode 40. The positive electrode 10 includes a lithium metal composite oxide. The electrolyte solution contains a lithium bis(oxalate)borate. The separator 20 is disposed between the positive electrode 10 and the negative electrode 40. The negative electrode 40 includes a sodium ion-containing binder. The lithium ion-containing zeolite is disposed between the separator 20 and the negative electrode 40.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a lithium ion secondary battery.

  Japanese Patent Laying-Open No. 2006-058338 (Patent Document 1) impregnates an electrode group containing sodium (Na) ions with an electrolyte solution that does not contain lithium bis (oxalato) borate (LiBOB). Thus, it is disclosed that an electrode group is impregnated with an electrolytic solution containing LiBOB after Na ions are dispersed in the electrolytic solution.

JP 2006-058338 A

  An aqueous binder is used as a negative electrode binder for lithium ion secondary batteries. The water-based binder refers to a binder that is excellent in water dispersibility. Typical water-based binders include, for example, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and the like.

  The reason why the water-based binder is preferred is that water can be used as the solvent, so that the manufacturing cost can be kept low. Generally, the manufacturing process of an aqueous binder includes a neutralization treatment with sodium hydroxide (NaOH). The aqueous binder that has undergone the neutralization treatment contains Na ions.

  LiBOB is known as an electrolytic solution additive. LiBOB is dispersed and dissolved in the electrolytic solution. LiBOB is said to have an effect of improving the cycle life of the lithium ion secondary battery. According to Patent Literature 1, NaBOB is generated when an electrolytic solution including LiBOB comes into contact with a negative electrode including an aqueous binder. NaBOB precipitates without being dispersed or dissolved in the electrolytic solution. NaBOB deposited on the negative electrode hinders the charging reaction. That is, when NaBOB is deposited on the negative electrode, lithium (Li) is likely to be deposited during charging.

  Patent Document 1 suppresses the formation of NaBOB by lowering the Na ion concentration in the negative electrode. However, NaBOB is not the only substance that hinders the charging reaction. That is, it has also been confirmed that the metal eluted from the positive electrode active material contained in the positive electrode interferes with the charging reaction by precipitating on the negative electrode.

  Then, this indication aims at providing the lithium ion secondary battery excellent in Li precipitation tolerance.

  The lithium ion secondary battery of the present disclosure includes an electrolytic solution, a positive electrode, a separator, a lithium ion-containing zeolite, and a negative electrode. The positive electrode includes a lithium metal composite oxide. The electrolytic solution includes lithium bis (oxalato) borate. The separator is disposed between the positive electrode and the negative electrode. The negative electrode includes a sodium ion-containing binder. The lithium ion-containing zeolite is disposed between the separator and the negative electrode.

  In the lithium ion secondary battery of the present disclosure, a lithium (Li) ion-containing zeolite is disposed between the separator and the negative electrode. The Li ion-containing zeolite traps metal ions that have migrated from the positive electrode. This metal ion is derived from a lithium metal composite oxide (positive electrode active material). The Li ion-containing zeolite also traps Na ions eluted from the negative electrode. That is, the substance that hinders the charging reaction is suppressed from being deposited on the negative electrode. Therefore, it is thought that the lithium ion secondary battery of this indication is excellent in Li precipitation tolerance.

  In addition, when Li ion containing zeolite is arrange | positioned in the positive electrode, it is thought that Na ion of the negative electrode side cannot be efficiently trapped. The same applies when Li ion-containing zeolite is disposed between the separator and the positive electrode.

  Moreover, when Li ion containing zeolite is arrange | positioned in a negative electrode, it is thought that the metal ion which moves from a positive electrode cannot be trapped efficiently. Furthermore, zeolite is an insulator. Therefore, when a large amount of Li ion-containing zeolite is present in the negative electrode, the resistance of the negative electrode may be increased.

FIG. 1 is a schematic diagram illustrating an example of a configuration of a lithium ion secondary battery according to an embodiment of the present disclosure. FIG. 2 is a conceptual diagram showing a laminated configuration of the electrode group. FIG. 3 is a graph showing the relationship between the initial limiting current and the surface density of the Li ion-containing zeolite. FIG. 4 is a graph showing the relationship between the limit current after endurance and the surface density of the Li ion-containing zeolite.

  Hereinafter, an embodiment of the present disclosure (hereinafter referred to as “the present embodiment”) will be described. However, the following description does not limit the scope of the present disclosure. Hereinafter, a lithium ion secondary battery may be abbreviated as “battery”.

<Lithium ion secondary battery>
FIG. 1 is a schematic diagram illustrating an example of the configuration of the lithium ion secondary battery according to the present embodiment. The battery 100 includes a housing 90. The housing 90 in FIG. 1 has a square shape (flat rectangular parallelepiped). However, the casing of the present embodiment may be cylindrical. For example, a metal such as aluminum (Al) or an Al alloy constitutes the housing 90. However, as long as the housing 90 has a predetermined hermeticity, for example, a composite material of metal and resin may constitute the housing 90. Examples of the composite material of metal and resin include an aluminum laminate film. The housing 90 may include an external terminal, a liquid injection hole, a gas discharge valve, a current interruption mechanism (CID), and the like.

  An electrode group 50 and an electrolytic solution 60 are arranged in the housing 90. That is, the battery 100 includes the electrolytic solution 60. The electrolytic solution 60 is also held in the electrode group 50. The electrolytic solution 60 of the present embodiment includes LiBOB.

<Electrode group>
FIG. 2 is a conceptual diagram showing a laminated configuration of the electrode group. The electrode group 50 may be a stacked electrode group or a wound electrode group. The stacked electrode group is configured by alternately stacking the rectangular positive electrode 10 and the rectangular negative electrode 40 with the rectangular separator 20 interposed therebetween. The wound electrode group is configured by laminating the strip-shaped positive electrode 10 and the strip-shaped negative electrode 40 with the strip-shaped separator 20 therebetween, and further winding the strip-shaped positive electrode 10 and the strip-shaped negative electrode 40.

  The electrode group 50 includes a positive electrode 10, a separator 20, a filler layer 30, and a negative electrode 40. The separator 20 is disposed between the positive electrode 10 and the negative electrode 40. The filler layer 30 is disposed between the separator 20 and the negative electrode 40. The filler layer 30 includes a Li ion-containing zeolite. That is, battery 100 includes positive electrode 10, separator 20, Li ion-containing zeolite, and negative electrode 40. The Li ion-containing zeolite is disposed between the separator 20 and the negative electrode 40.

The positive electrode 10 includes a lithium metal composite oxide. The lithium metal composite oxide elutes metal ions (M ⁺ ) by reacting with HF, which is a decomposition product of LiPF ₆ , for example. The negative electrode 40 includes a Na ion-containing binder. The Na ion-containing binder releases Na ions (Na ⁺ ) into the electrolytic solution.

The filler layer 30 adjacent to the negative electrode 40 efficiently traps Na ions (Na ⁺ ) released from the Na ion-containing binder. This is because the filler layer 30 includes a Li ion-containing zeolite. Further, the filler layer 30 traps metal ions (M ⁺ ) moving from the positive electrode 10 in front of the negative electrode 40. Thereby, in the negative electrode 40, precipitation of both NaBOB and a metal is suppressed. Therefore, the battery 100 is considered to be excellent in Li deposition resistance.

<Electrolyte>
The electrolytic solution 60 includes a solvent and a supporting electrolyte salt. The solvent is aprotic. The solvent may be, for example, a mixture of cyclic carbonate and chain carbonate. The mixing ratio may be, for example, cyclic carbonate: chain carbonate = 1: 9 to 5: 5 (volume ratio). Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of the chain carbonate include ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). A cyclic carbonate and a chain carbonate may be used individually by 1 type, and 2 or more types may be used in combination. The supporting electrolyte salt may be, for example, LiPF ₆ , LiBF ₄ , Li [N (FSO ₂ ) ₂ ] or the like. In the electrolytic solution 60, the supporting electrolyte salt may have a concentration of 0.5 to 2.0 mol / l, for example. The supporting electrolyte salt may be used alone, or two or more supporting electrolyte salts may be used in combination.

  The electrolytic solution 60 further includes LiBOB. LiBOB is a compound represented by the following chemical formula (I).

  LiBOB is considered to form high quality SEI (Solid Electrolyte Interface) on the surface of the negative electrode 40. It is considered that the cycle life of the battery 100 is improved by forming a high-quality SEI. In the electrolytic solution 60, LiBOB may have a concentration of, for example, 0.01 to 0.20 mol / l (typically 0.01 to 0.10 mol / l).

《Positive electrode》
The positive electrode 10 is a belt-like or rectangular sheet. The positive electrode 10 includes, for example, a current collector 11 and a positive electrode mixture layer 12. The current collector 11 may be an Al foil, for example. The Al foil may be a pure Al foil or an Al alloy foil. For example, the current collector 11 may have a thickness of 5 to 30 μm. The positive electrode mixture layer 12 is applied to the surface of the current collector. The positive electrode mixture layer 12 may have a thickness of 10 to 150 μm, for example.

  The positive electrode mixture layer 12 includes a positive electrode active material, a conductive material, and a binder. For example, the positive electrode mixture layer 12 includes 80 to 98% by mass of a positive electrode active material, 1 to 15% by mass of a conductive material, and 1 to 5% by mass of a binder. The positive electrode active material is a particle that can occlude and release Li ions. The positive electrode active material may have an average particle diameter of 1 to 20 μm, for example. The average particle size in this specification indicates a particle size of 50% cumulative from the fine particle side in the volume-based particle size distribution measured by the laser diffraction scattering method.

The positive electrode active material is a lithium metal composite oxide. That is, the positive electrode 10 includes a lithium metal composite oxide. The lithium metal composite oxide refers to a composite oxide comprising lithium (Li), a metal (typically a transition metal), and oxygen (O). Examples of the lithium metal composite oxide include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNi _x Co _y Mn _z O ₂ (0 <x <1, 0 <y <1, 0 <z <1. , X + y + z = 1) and the like.

_{Examples of the} lithium metal composite oxide represented by LiNi _x Co _y Mn _z O ₂ include LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2. Examples thereof include Mn _0.3 O ₂ , LiNi _0.4 Co _0.2 Mn _0.4 O ₂ , LiNi _0.4 Co _0.4 Mn _0.2 O _{2 and the} like. In the present specification, a phosphate such as LiFePO ₄ is also regarded as a lithium metal composite oxide because it includes Li, metal (Fe), and oxygen (O). A lithium metal complex oxide may be used individually by 1 type, and may be used in combination of 2 or more type.

  The conductive material should not be particularly limited. Examples of the conductive material include carbon black such as acetylene black and thermal black, vapor grown carbon fiber (VGCF), graphite, and the like. A conductive material may be used individually by 1 type, and 2 or more types may be combined and used for it. The binder should not be particularly limited. Examples of the binder include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and the like. A binder may be used individually by 1 type and may be used in combination of 2 or more type.

<< Separator >>
The separator 20 is a band-shaped or rectangular porous film. The separator 20 is electrically insulating. The separator 20 is disposed between the positive electrode 10 and the negative electrode 40. For example, the separator 20 may have an average thickness of 5 to 30 μm. The average thickness is an average value of at least five thicknesses. The thickness is measured by, for example, a micrometer. For example, a polyethylene (PE) porous film, a polypropylene (PP) porous film, and the like constitute the separator 20. The separator 20 may have a multilayer structure. For example, the separator 20 can be configured by stacking a PP porous film, a PE porous film, and a PP porous film in this order.

<< Filler layer >>
The filler layer 30 is disposed between the separator 20 and the negative electrode 40. As long as the filler layer 30 is disposed between the separator 20 and the negative electrode 40, for example, the filler layer 30 may be disposed on the surface of the separator 20, or may be disposed on the surface of the negative electrode 40.

  The filler layer 30 includes a Li ion-containing zeolite. The zeolite that becomes the skeleton of the Li ion-containing zeolite may be a natural zeolite or a synthetic zeolite. Li ion-containing zeolite is produced by exchanging metal ions in the zeolite with Li ions. For example, when Na ion-containing A-type zeolite is immersed in an LiCl aqueous solution, Na ions are exchanged for Li ions. Thereby, Li ion containing zeolite is produced | generated. As long as at least part of the Na ions are exchanged for Li ions, it is considered to be a Li ion-containing zeolite. Of the metal ions in the zeolite, for example, 50 to 100 mol% is preferably exchanged for Li ions.

  Li ion-containing zeolite adsorbs metal ions that have migrated from the positive electrode and releases Li ions instead. The Li ion-containing zeolite adsorbs Na ions that have moved from the negative electrode, and releases Li ions instead. Li ion containing zeolite may have an average particle diameter of 0.1-10 micrometers (typically 0.5-2 micrometers), for example. The Li ion-containing zeolite may have an average pore diameter of, for example, 0.1 to 10 nm (typically 0.1 to 1 nm). The average pore diameter can be measured by a gas adsorption method. For example, nitrogen gas is used as the medium for the gas adsorption method.

  The filler layer 30 may include other substances as long as it includes the Li ion-containing zeolite. For example, the filler layer 30 may include 20 to 90 mass% Li ion-containing zeolite, 9 to 75 mass% inorganic filler, and 1 to 5 mass% binder. The inorganic filler should not be particularly limited. Examples of the inorganic filler include alumina, boehmite, titania, magnesia and the like. An inorganic filler may have an average particle diameter of 0.1-5 micrometers, for example. The binder should not be particularly limited. Examples of the binder include carboxymethyl cellulose (CMC), an acrylic polymer (for example, a copolymer of styrene and an acrylate ester), and the like. An inorganic filler and a binder may be used individually by 1 type, and 2 or more types may be used in combination.

In the filler layer 30, the Li ion-containing zeolite may have a surface density of, for example, 0.10 mg / cm ² or more and 1 mg / cm ² or less. From the viewpoint of efficiently trapping Na ions and metal ions derived from the positive electrode active material, in the filler layer 30, the Li ion-containing zeolite preferably has an area density of 0.15 mg / cm ² or more and 0.6 mg / cm ² or less. More preferably, it has a surface density of 0.3 mg / cm ² or more and 0.6 mg / cm ² or less.

<Negative electrode>
The negative electrode 40 is a belt-like or rectangular sheet. The negative electrode 40 includes, for example, a current collector 41 and a negative electrode mixture layer 42. The current collector 41 may be a copper (Cu) foil, for example. The Cu foil may be a pure Cu foil or a Cu alloy foil. The current collector 41 may have a thickness of 5 to 30 μm, for example. The negative electrode mixture layer 42 is applied to the surface of the current collector 41. The negative electrode mixture layer 42 may have a thickness of 10 to 150 μm, for example.

  The negative electrode mixture layer 42 includes a negative electrode active material and a binder. For example, the negative electrode mixture layer 42 includes 95 to 99% by mass of a negative electrode active material and 1 to 5% by mass of a binder. The negative electrode active material is a particle that can occlude and release Li ions. The negative electrode active material may have an average particle diameter of 1 to 20 μm, for example. Examples of the negative electrode active material include graphite, graphitizable carbon (soft carbon), non-graphitizable carbon (hard carbon), silicon, silicon oxide, tin, and tin oxide. A negative electrode active material may be used individually by 1 type, and 2 or more types may be used in combination.

  In the present embodiment, the binder of the negative electrode 40 is a Na ion-containing binder. That is, the negative electrode 40 includes a Na ion-containing binder. The Na ion-containing binder is not particularly limited as long as it contains Na ions. Examples of the Na ion-containing binder include CMC, SBR, PAA, polyacrylate ester, styrene and acrylate copolymer, and the like. In these binders, Na ions are taken into the binder in the form of COONa groups, for example. A Na ion containing binder may be used individually by 1 type, and 2 or more types may be used in combination. Whether or not the binder contains Na ions can be confirmed by ICP emission spectrometry.

<Applications of lithium ion secondary batteries>
As described above, the battery 100 is excellent in Li deposition resistance. Therefore, the battery 100 is particularly suitable as a power source for a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), an electric vehicle (EV), and the like. However, the use of the battery 100 should not be limited to such in-vehicle use. The battery 100 is applicable to all uses.

  Examples will be described below. However, the following examples do not limit the scope of the invention of the present disclosure.

<Manufacture of lithium ion secondary batteries>
Various lithium ion secondary batteries shown in Table 1 below were produced. In Table 1 below, examples marked with “*” correspond to examples. For example, “Example * 1” corresponds to Example 1. An example without “*” corresponds to a comparative example. For example, “Example 1” corresponds to Comparative Example 1.

<< Comparative Example 1 >>
1. Production of Positive Electrode As a positive electrode active material (lithium metal composite oxide), LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (hereinafter abbreviated as “NCM”) was prepared. 90 parts by mass of NCM, 8 parts by mass of conductive material and 2 parts by mass of PVdF were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture paste. Al foil was prepared as a current collector. The positive electrode mixture paste was applied to the surface (both front and back surfaces) of the Al foil and dried, whereby a positive electrode mixture layer was formed. This produced a positive electrode. The mass per unit area of the positive electrode mixture layer after drying was 6 mg / cm ^{2 on} one side (12 mg / cm ^{2 on} both sides). The positive electrode was rolled and cut into strips. Thereby, the positive electrode which is a strip | belt-shaped sheet | seat was manufactured.

2. Manufacture of negative electrode Graphite was prepared as a negative electrode active material. CMC and SBR were prepared as Na ion-containing binders. 98 parts by mass of graphite, 1 part by mass of CMC, and 1 part by mass of SBR were dispersed in water to prepare a negative electrode mixture paste. Cu foil was prepared as a current collector. The negative electrode mixture paste was coated on the surface (both front and back surfaces) of the Cu foil, and dried to form a negative electrode mixture layer. This produced a negative electrode. The mass per unit area of the negative electrode mixture layer after drying was 3 mg / cm ^{2 on} one side (6 mg / cm ^{2 on} both sides). The negative electrode was rolled and cut into strips. Thereby, the negative electrode which is a strip-shaped sheet was manufactured.

3. Preparation of separator A separator having an average thickness of 20 μm was prepared. The separator is a belt-like porous film. The separator includes a PP porous film, a PE porous film, and a PP porous film. In the separator, the PP porous film, the PE porous film, and the PP porous film are laminated in this order.

4). Formation of filler layer Boehmite was prepared as an inorganic filler. A paste was prepared by dispersing 95 parts by weight boehmite, 2.5 parts by weight CMC, and 2.5 parts by weight acrylic polymer in water. The paste was applied to the surface (one side) of the separator and dried. Thereby, the filler layer was formed. The mass per unit area of the filler layer after drying was set to 0.75 mg / cm ² .

5. Configuration of Electrode Group The electrode group was configured by laminating and further winding the positive electrode and the negative electrode with a separator having a filler layer formed on one side in between. The filler layer was disposed between the separator and the negative electrode. In the “Arrangement” column in Table 1 below, the fact that the filler layer is arranged between the separator and the negative electrode is described as “separator / negative electrode”, and the filler layer is arranged between the separator and the positive electrode. "Separator / positive electrode" is written.

6). Electrolyte impregnation A square casing was prepared. The electrode group was housed in a housing.
An electrolyte solution having the following components was prepared.

Supporting electrolyte salt: LiPF ₆ (1 mol / l)
Solvent: [EC: EMC: DMC = 3: 3: 4 (volume ratio)]

  Electrolytic solution was injected into the casing, and the electrode group was sufficiently impregnated. This produced a battery. The battery was initially charged. After the initial charging, the SOC (State Of Charge) of the battery was adjusted to 100%. The battery was left for 24 hours in an environment of 60 ° C. As described above, a battery according to Comparative Example 1 (Example 1) was manufactured.

<< Comparative Example 2 >>
A battery according to Comparative Example 2 (Example 2) was manufactured by the same procedure as Comparative Example 1 except that an electrolytic solution having the following components was used.

Supporting electrolyte salt: LiPF ₆ (1 mol / l)
Solvent: [EC: EMC: DMC = 3: 3: 4 (volume ratio)]
Additive: LiBOB (0.05 mol / l)

<< Comparative Example 3 >>
A Na ion-containing zeolite having an average pore diameter of 0.4 nm was prepared. This Na ion-containing zeolite is pulverized to have an average particle diameter of 1 μm.

A positive electrode mixture paste was prepared by dispersing 90 parts by mass of NCM, 8 parts by mass of a conductive material, 2 parts by mass of PVdF, and 5 parts by mass of a Na ion-containing zeolite in NMP. The positive electrode mixture paste was applied to the surface (both front and back surfaces) of the Al foil and dried, whereby a positive electrode mixture layer was formed. This produced a positive electrode. Mass per unit area of the positive-electrode mixture layer after drying was set to be 6.3 mg / cm ² on one side (in both 12.6mg / cm ^2). Except for these, a battery according to Comparative Example 3 (Example 3) was manufactured by the same procedure as Comparative Example 1.

<< Comparative Example 4 >>
A paste was prepared by dispersing 55 parts by weight boehmite, 40 parts by weight Na ion-containing zeolite, 2.5 parts by weight CMC, and 2.5 parts by weight acrylic polymer in water. The paste was applied to the surface (one side) of the separator and dried. Thereby, the filler layer was formed. The mass per unit area of the filler layer after drying was set to 0.75 mg / cm ² . A battery according to Comparative Example 4 (Example 4) was manufactured by the same procedure as Comparative Example 1 except for these.

<< Comparative Example 5 >>
98 parts by mass of graphite, 1 part by mass of CMC, 1 part by mass of SBR, and 10 parts by mass of Na ion-containing zeolite were dispersed in water to prepare a negative electrode mixture paste. The negative electrode mixture paste was coated on the surface (both front and back surfaces) of the Cu foil, and dried to form a negative electrode mixture layer. This produced a negative electrode. The mass per unit area of the negative electrode mixture layer after drying was 3.3 mg / cm ^{2 on} one side (6.6 mg / cm ^{2 on} both sides). Except for these, a battery according to Comparative Example 5 (Example 5) was manufactured in the same procedure as Comparative Example 1.

<< Comparative Example 6 >>
A battery according to Comparative Example 6 (Example 6) was manufactured by the same procedure as Comparative Example 3 except that an electrolytic solution including LiBOB (the one used in Comparative Example 2) was used.

<< Comparative Example 7 >>
A battery according to Comparative Example 7 (Example 7) was manufactured by the same procedure as Comparative Example 4 except that an electrolytic solution including LiBOB (the one used in Comparative Example 2) was used.

<< Comparative Example 8 >>
A battery according to Comparative Example 8 (Example 8) was manufactured by the same procedure as Comparative Example 5 except that an electrolytic solution including LiBOB (the one used in Comparative Example 2) was used.

<< Comparative Example 9 >>
By ion exchange, Na ions in the Na ion-containing zeolite were exchanged for Li ions. Thereby, Li ion containing zeolite was prepared. This Li ion-containing zeolite is obtained by replacing 90 mol% of Na ions with Li ions.

  A battery according to Comparative Example 9 (Example 9) was produced by the same procedure as Comparative Example 3 except that Li ion-containing zeolite was used instead of Na ion-containing zeolite.

<< Comparative Example 10 >>
A battery according to Comparative Example 10 (Example 10) was produced by the same procedure as Comparative Example 4 except that Li ion-containing zeolite was used instead of Na ion-containing zeolite.

<< Comparative Example 11 >>
A battery according to Comparative Example 11 (Example 11) was manufactured by the same procedure as Comparative Example 5 except that Li ion-containing zeolite was used instead of Na ion-containing zeolite.

<< Comparative Example 12 >>
A positive electrode mixture paste was prepared by dispersing 90 parts by mass of NCM, 8 parts by mass of a conductive material, 2 parts by mass of PVdF, and 2.5 parts by mass of a Li ion-containing zeolite in NMP. The positive electrode mixture paste was applied to the surface (both front and back surfaces) of the Al foil and dried, whereby a positive electrode mixture layer was formed. This produced a positive electrode. Mass per unit area of the positive-electrode mixture layer after drying was set to 6.15mg / cm ² on one side (in both 12.3mg / cm ^2). A battery according to Comparative Example 12 (Example 12) was manufactured by the same procedure as Comparative Example 6 except for these. The surface density of the Li ion-containing zeolite in the positive electrode mixture layer is calculated by the formula “Area density = 6.15 [mg / cm ² ] × 2.5 [parts by mass] ÷ (90 + 8 + 2 + 2.5) [parts by mass]”. 0.15 mg / cm ² .

<< Comparative Examples 13 and 14 >>
Comparative examples 13 and 14 (examples) were performed in the same procedure as in comparative example 12 except that the blending amount of the Li ion-containing zeolite in the positive electrode mixture paste was changed so as to have the areal density shown in Table 1 below. A battery according to 13 and 14) was produced.

<< Comparative Example 15 >>
A paste was prepared by dispersing 75 parts by weight of boehmite, 20 parts by weight of Li ion-containing zeolite, 2.5 parts by weight of CMC, and 2.5 parts by weight of an acrylic polymer. The paste was applied to the surface (one side) of the separator and dried. Thereby, the filler layer was formed. The mass per unit area of the filler layer after drying was set to 0.75 mg / cm ² . The surface density of the Li ion-containing zeolite in the filler layer is calculated according to the calculation formula “surface density = 0.75 [mg / cm ² ] × 20 [parts by mass] ÷ (75 + 20 + 2.5 + 2.5) [parts by mass]”. 15 mg / cm ² .

  A positive electrode and a negative electrode were laminated with a separator having a filler layer formed on one side in between, and further wound to form an electrode group. The filler layer was disposed between the separator and the positive electrode. Except for these, a battery according to Comparative Example 15 (Example 15) was manufactured by the same procedure as Comparative Example 7.

<< Comparative Examples 16 and 17 >>
Comparative Examples 16 and 17 (Examples 16 and 17) were carried out in the same procedure as Comparative Example 15 except that the blending amount of the Li ion-containing zeolite in the paste was changed so that the surface density shown in Table 1 was obtained. ) Was manufactured. Here, in the solid content of the paste, the blending amount of boehmite is reduced according to the increment of the blending amount of the Li ion-containing zeolite. The blending amounts of CMC and acrylic polymer are not changed.

<< Examples 1-3 >>
Batteries according to Examples 1 to 3 (Examples * 1 to * 3) were manufactured by the same procedure as Comparative Examples 15 to 17 except that the filler layer was disposed between the separator and the negative electrode.

<< Comparative Example 18 >>
98 parts by mass of graphite, 1 part by mass of CMC, 1 part by mass of SBR, and 5 parts by mass of Li ion-containing zeolite were dispersed in water to prepare a negative electrode mixture paste. The negative electrode mixture paste was coated on the surface (both front and back surfaces) of the Cu foil, and dried to form a negative electrode mixture layer. This produced a negative electrode. Mass per unit area of the negative electrode mixture layer after drying was set to 3.15mg / cm ² on one side (on both sides 6.3mg / cm ^2). The surface density of the Li ion-containing zeolite in the negative electrode mixture layer is 0.15 mg / kg according to the calculation formula “surface density = 3.15 [mg / cm ² ] × 5 [part by mass] ÷ (98 + 1 + 1 + 5) [part by mass]”. cm ² . Except for these, a battery according to Comparative Example 18 (Example 18) was manufactured by the same procedure as Comparative Example 8.

<< Comparative Examples 19 and 20 >>
Comparative examples 19 and 20 (examples) were performed in the same procedure as comparative example 18 except that the blending amount of the Li ion-containing zeolite in the negative electrode mixture paste was changed so as to have the areal density shown in Table 1 below. A battery according to 19 and 20) was produced.

<Evaluation>
1. Initial Limit Current Measurement The battery was charged at a predetermined current for 5 seconds in an environment of −10 ° C. After charging, the battery was left for 10 minutes. After standing, the battery was discharged at a predetermined current for 5 seconds. This one-round operation was defined as one cycle, and one cycle was repeated 1000 times. After the test, the battery was disassembled, and it was confirmed whether Li was deposited on the negative electrode. By repeating this test while changing the current each time, the largest current at which Li did not precipitate was identified. This current is the initial limiting current. The results are shown in the “Initial” column of Table 1 above. The value shown in the column of “Initial” in Table 1 is a percentage of the value obtained by dividing the initial limit current of each example by the initial limit current of Comparative Example 1 (Example 1). Here, the larger the value, the better the initial Li precipitation resistance.

2. Measurement of limit current after endurance The battery was stored in an environment of 75 ° C. for 60 days. Thereby, a battery after endurance was obtained. The limit current of the battery after endurance was determined by the same procedure as in “1. Measurement of initial limit current”. The results are shown in the column “After Durability” in Table 1 above. In Table 1 above, the value shown in the column “After Endurance” is the percentage of the value obtained by dividing the limit current after endurance of each example by the limit current after endurance of Comparative Example 1 (Example 1). Here, it shows that it is excellent in Li precipitation tolerance after durability, so that a value is large.

<Result>
From the results of Comparative Examples 1 and 2, it can be seen that the limit current after endurance is improved when the electrolytic solution includes LiBOB.

  From the results of Comparative Example 1, Comparative Examples 3 to 5, and Comparative Examples 9 to 11, the zeolite is arranged in the positive electrode or the zeolite is arranged between the separator and the negative electrode, so that the limit current is small. It has improved. This is probably because the metal ions eluted from the lithium metal composite oxide are trapped in the zeolite. However, in the example in which zeolite was disposed in the negative electrode, the limiting current was not improved. Since metal ions moving from the positive electrode are deposited on the surface of the negative electrode, it is considered that the effect cannot be obtained even if zeolite is arranged in the negative electrode.

  When the electrolyte solution did not include LiBOB, there was no difference in effect between the Li ion-containing zeolite and the Na ion-containing zeolite. This is probably because the BOB anion does not exist. However, when the electrolytic solution was provided with LiBOB, the limit current was lowered in the Na ion-containing zeolite, and the limit current was improved in the Li ion-containing zeolite. This is considered to be a result reflecting that the Li ion-containing zeolite has a NaBOB production inhibitory action and the Na ion-containing zeolite does not have the same action.

From the results of Comparative Examples 12 to 20 and Examples 1 to 3, it can be seen that the effect varies depending on the location of the Li ion-containing zeolite. FIG. 3 is a graph showing the relationship between the initial limiting current and the surface density of the Li ion-containing zeolite. FIG. 4 is a graph showing the relationship between the limit current after endurance and the surface density of the Li ion-containing zeolite. As shown in FIG. 3 and FIG. 4, in Examples 1 to 3 in which the Li ion-containing zeolite is disposed between the separator and the negative electrode, the Li ion-containing zeolite is compared with the comparative example that does not satisfy the same condition. The improvement width of the limit current with respect to the surface density is large. This tendency is particularly remarkable when the surface density is in the range of 0.3 mg / cm ² or more.

  In Comparative Examples 12 to 14, the margin of improvement in the limiting current with respect to the surface density of the Li ion-containing zeolite is small. In Comparative Examples 12 to 14, Li ion-containing zeolite is disposed in the positive electrode. Therefore, it is considered that the Li ion-containing zeolite can trap metal ions eluted from the positive electrode active material, but cannot efficiently trap Na ions in the negative electrode. The same can be said for Comparative Examples 15 to 17 in which Li ion-containing zeolite is disposed between the separator and the positive electrode.

  Comparative Examples 18 to 20 have a small improvement width of the limiting current with respect to the surface density of the Li ion-containing zeolite. In Comparative Examples 18 to 20, Li ion-containing zeolite is disposed in the negative electrode. Therefore, it is considered that Li ion-containing zeolite can trap Na ions in the negative electrode but cannot trap metal ions moving from the positive electrode. Moreover, when Li ion containing zeolite is arrange | positioned in a negative electrode, inconveniences, such as resistance increasing with the increase in the amount of Li ion containing zeolite, are also assumed.

  In Examples 1-3, the Li ion containing zeolite is arrange | positioned between the separator and the negative electrode. Therefore, it is considered that the metal ions from which the Li ion-containing zeolite moves from the positive electrode can be trapped before the negative electrode, and Na ions in the negative electrode can also be trapped. Thereby, it is thought that the improvement width of the limiting current with respect to the surface density of the Li ion-containing zeolite is remarkably increased.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present disclosure is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Positive electrode, 11, 41 Current collector, 12 Positive electrode mixture layer, 20 Separator, 30 Filler layer, 40 Negative electrode, 42 Negative electrode mixture layer, 50 Electrode group, 60 Electrolyte, 90 Housing, 100 Battery.

Claims (1)

Electrolyte,
Positive electrode,
Separator,
A lithium ion-containing zeolite and a negative electrode,
The positive electrode comprises a lithium metal composite oxide,
The electrolyte includes lithium bis (oxalato) borate,
The separator is disposed between the positive electrode and the negative electrode;
The negative electrode includes a sodium ion-containing binder,
The lithium ion-containing zeolite is disposed between the separator and the negative electrode.
Lithium ion secondary battery.