JP2008112722A - Lithium polymer battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance the characteristics of a lithium polymer battery, such as rate characteristics, cycle characteristics, prevention of swelling of a cell by a simple method when increasing the energy density of the lithium polymer battery. <P>SOLUTION: The lithium polymer battery comprises at least a positive electrode, a negative electrode, a separator, and a gel electrolyte, and the gel electrolyte contains a solvent, a crosslinkable polymer, a polymerization initiator, and a sulfonate. Graphite is used as a negative active material, and the active material has a density of 1.35-1.65 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a lithium polymer battery containing a sulfonate ester in a gel electrolyte.

  Lithium polymer batteries are attracting attention as power sources for mobile devices because they can be thinned, have a high degree of freedom in shape selection, and have a high level of safety by not using an electrolyte. Recently, with the increase in functions of mobile devices to be used, higher energy and accompanying improvements in battery characteristics have become the goals of technological development.

  Among these, important technical issues are: 1. Improvement of safety 2. improvement of cycle characteristics; For example, high energy density. Among these, in order to improve safety, a battery employing a manganese-based positive electrode having a high heat resistance material and a gel electrolyte that does not cause liquid leakage is used in various devices. Regarding the improvement of the cycle characteristics, the applicant has filed an application as Japanese Patent Application No. 2006-64049 by adding a sulfonic acid ester as an additive. Regarding the increase in energy density, Patent Document 1 proposes that in a lithium polymer battery using a physical gel, the capacity density is improved by appropriately defining the porosity of the gel electrolyte-active material composite electrode. . Thus, in a lithium polymer battery using a gel electrolyte, selection of not only the material of the gel electrolyte but also the electrode material, the cell shape, the cell preparation conditions, the electrolyte solution material, and the like is extremely important.

JP-A-11-307100

  However, in the lithium polymer battery using the above prior art, when increasing the electrode density in order to increase the energy density, when using a physical gel, the physical gel is mixed in the electrode sheet, and the electrolytic solution is absorbed into it. Therefore, it is difficult to increase the electrode density, and when using a chemical gel, the viscosity of the polymer precursor solution is higher than that of a normal electrolyte solution, so the permeability to the electrode is low and the characteristics deteriorate. There is.

  The present invention has been made in view of the above problems. An object of the present invention is to improve the characteristics of a lithium polymer battery by a simple method for improving rate characteristics, cycle characteristics, prevention of cell swelling, and the like when increasing the energy density of a lithium polymer battery.

In order to solve the above problems, the lithium polymer battery of the present invention is a lithium polymer battery composed of at least a positive electrode, a negative electrode, a separator, and a gel electrolyte, and the gel electrolyte contains a solvent, a crosslinkable polymer, and a sulfonate ester. and contains the active material is a main component of graphite material in the negative electrode, the electrode density of the layer containing the active material in the negative electrode 1.35 g / cm ³ or more and 1.65 g / cm ³ or less. When the active material in the negative electrode is mainly an amorphous carbon material, the electrode density of the layer containing the active material in the negative electrode is 0.80 g / cm ³ or more and 1.35 g / cm ³ or less, When the active material in the negative electrode is based on Si or a Si compound material, the electrode density of the layer containing the active material in the negative electrode is 0.70 g / cm ³ or more and 1.30 g / cm ³ or less.

  The cross-linked polymer is preferably an acrylic polymer, and is preferably polymerized using a peroxide as a polymerization initiator, and the solvent preferably contains at least a chain carbonate and a cyclic carbonate. The ester is preferably composed of at least one of cyclic sulfonic acid ester, cyclic disulfonic acid ester or chain disulfonic acid ester, and the positive electrode preferably contains lithium manganate or lithium cobaltate as an active material.

  In a lithium polymer battery containing a gel electrolyte, an acrylic polymer having a different number of functional groups, a polymerization initiator, and a sulfonate ester are added to improve the rate characteristics and cycle characteristics in the pregel solution that is a precursor of the gel electrolyte. By containing, the gas generation at the initial charging can be suppressed, and the synergistic effect between the gel electrolyte and the positive electrode, the negative electrode, and the separator facilitates the delivery of lithium to the positive electrode and the negative electrode, and is equivalent to the electrolytic solution. Rate characteristics and cycle characteristics can be provided. The synergistic effect here refers to the following. That is, the organic sulfur compound reacts by the initial charge, and a film generally called a SEI (Solid Electrolyte Interface) film is formed on the negative electrode surface. By forming the film, the transfer between the negative electrode active material and the electrons becomes smooth. Also, the adhesion between the separator and each electrode is improved by mixing acrylic polymers with various functional groups (specifically, those with short chains, those with long chains, those with many polymer groups but short chains). To do. Specifically, impregnation is improved by the presence of short chain pores in the separator, and gelation ability is improved by the presence of a polymer having a large number of polymer groups, and the polymer in the separator pores. The adhesion of the member is improved by reacting with. The above elements are synergistic and the characteristics are improved. In order to increase the energy density, it is effective to increase the electrode density of the layer containing the active material. However, in the negative electrode, if the density is excessively increased, the lithium accepting property is lowered, and the polymer precursor solution electrode. Due to the decrease in permeability, the properties deteriorate. Conversely, when the density is lowered, the above-mentioned problems do not occur, but the energy density is lowered and the rate characteristics are lowered due to poor electrical contact between the active materials.

According to the present invention, in the lithium polymer battery, when the sulfonic acid ester is included as the gel electrolyte component and the negative electrode active material is based on the graphite material, the electrode density of the layer containing the active material in the negative electrode is 1.35 g / cm ³ or more, 1.65 g / cm ³ or less, also the case where the active material in the negative electrode has a main agent amorphous carbon material, the electrode density of the layer containing the active material in the negative electrode 0.80 g / cm ³ or more and 1.35 g / cm ³ or less, and when the active material in the negative electrode is based on Si or Si compound material, the electrode density of the layer containing the active material in the negative electrode is 0.70 g / cm ³ or more , 1.30 g / cm ³ or less can improve cycle characteristics and suppress cell swelling.

The positive electrode used in the lithium polymer battery of the present invention is obtained by applying a positive electrode active material layer to a current collector made of a metal such as an aluminum foil, and compressing and molding the dried material. The negative electrode is made of a copper foil or the like. A metal current collector is coated with a layer containing a negative electrode active material, dried, and then compressed and molded. Density of the electrode layer containing an active material of the negative electrode (hereinafter, described as negative electrode density) when using the graphite material as the negative electrode active material 1.35 g / cm ³ or more, preferably 1.65 g / cm ³ or less, further Preferably it is 1.40-1.60 g / cm < ³ >. When it is larger than 1.65 g / cm ³ , the cell swelling after the cycle is large and the cycle characteristics are also deteriorated. If it is less than 1.35 g / cm ^3, the contact between the active materials is insufficient, the rate characteristics are lowered, and it is difficult to increase the energy density. Similarly, the negative electrode density when an amorphous carbon material is used as the negative electrode active material is preferably 0.80 g / cm ³ or more and 1.35 g / cm ³ or less, more preferably 0.90 to 1.30 g / cm. ³ . Moreover, when using Si or Si compound material as a negative electrode active material, 0.70 g / cm < ³ > or more and 1.30 g / cm < ³ > or less are preferable, More preferably, it is 0.80-1.20 g / cm < ³ >. A separator will not be specifically limited if it is generally used with lithium polymer batteries, such as a nonwoven fabric and a polyolefin microporous film. A positive electrode and a negative electrode are stacked via a separator to produce a laminate, or a positive electrode and a negative electrode are wound flatly via a separator to form a wound body, and the laminate or the wound body is laminated material, etc. A lithium polymer battery is prepared by injecting and treating the gel electrolyte after being put in the outer packaging material.

  As the gelling component contained in the gel electrolyte, for example, a monomer having two or more polymerizable groups capable of thermal polymerization per molecule, an oligomer, a copolymerized oligomer, or the like can be given. As this gelling component, ethylene glycol diacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, propylene diacrylate, dipropylene diacrylate, tripropylene diacrylate, which forms an acrylic polymer, Bifunctional acrylates such as 1,3-butanediol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, and trifunctional acrylates such as trimethylolpropane triacrylate and pentaerythritol triacrylate, In addition, tetrafunctional acrylates such as ditrimethylolpropane tetraacrylate and pentaerythritol tetraacrylate, and the above-mentioned methacrylate. Tomonoma and the like. In addition to these, monomers such as urethane acrylate and urethane methacrylate, copolymer oligomers thereof, and copolymer oligomers with acrylonitrile are exemplified, but not limited thereto.

  In addition, polymers that can be dissolved in a plasticizer and gelled, such as polyvinylidene fluoride, polyethylene oxide, and polyacrylonitrile can also be used.

  The gel component is not limited to the above-described monomer, oligomer, or polymer, and any gel component that can be gelled can be used. Further, the gelation is not limited to one kind of monomer, oligomer or polymer, and it can be used by mixing 2 to several kinds of gel components as required.

  As a solvent contained in the gel electrolyte, cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), Chain carbonates such as ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, Chain ethers such as 2-ethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetami Dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl A mixture of one or more aprotic organic solvents such as 2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, fluorinated carboxylate, etc. However, the present invention is not limited to these.

  As the sulfonic acid ester contained in the gel electrolyte, a cyclic monosulfonic acid ester, a cyclic disulfonic acid ester, a chain sulfonic acid ester, and the like can be appropriately used. Examples of cyclic monosulfonic acid esters include 1,3-propane sultone (1,3-PS), α-trifluoromethyl-γ-sultone, β-trifluoromethyl-γ-sultone, and γ-trifluoromethyl-γ-sultone. , Α-methyl-γ-sultone, α, β-di (trifluoromethyl) -γ-sultone, α, α-di (trifluoromethyl) -γ-sultone, α-undecafluoropentyl-γ-sultone, Examples include α-heptafluoropropyl-γ-sultone and 1,4-butane sultone (1,4-BS). Examples of the cyclic disulfonate include methylene methane disulfonate (MMDS), ethylene methane disulfonate (EMDS), and propylene methane disulfonate (PMDS). Examples of chain sulfonic acid esters include methanesulfonic acid methyl ester, methanesulfonic acid ethyl ester, busulfan, and dimethyl-methane disulfonate.

  Among these sulfonic acid esters, it is particularly preferable to use 1,3-PS or MMDS. 1,3-PS and MMDS are considered to form a decomposition film on the electrode of the lithium ion secondary battery. For example, the lowest unoccupied orbital energy (LUMO) of 1,3-PS is 0.07 eV, and from EC (LUMO: 1.18 eV) and DEC (LUMO: 1.26 eV) where 1,3-PS is a solvent molecule. It is conceivable that the film is first decomposed to form a film. As a result, the decomposition of the solvent molecules is suppressed, and the suppression of battery swelling due to gas generation and the improvement of the rate characteristics can be expected. In addition, for example, when lithium manganate is included in the positive electrode, Mn eluted in the gel by adding 1,3-PS is prevented from adsorbing on the negative electrode surface, and as a result, the reduction in rate characteristics due to increase in resistance It is considered effective for improving cycle characteristics.

  The concentration of the sulfonic acid ester contained in these gel electrolytes is not particularly limited, but in the case of a secondary battery using a positive electrode containing lithium manganate as the positive electrode active material, 0.1% by mass The content is preferably 3.0% by mass or less, more preferably 0.5% by mass or more and 1.0% by mass or less. If it is less than 0.1% by mass, a sufficient film is not formed on the electrode surface, and the effect of improving the cycle characteristics and rate characteristics is small. If it exceeds 3.0% by mass, the resistance increases and the rate characteristics deteriorate.

  In the present invention, it is also effective to appropriately contain vinylene carbonate in the gel electrolyte. Vinylene carbonate is particularly effective when lithium cobaltate is used for the positive electrode, and the concentration of vinylene carbonate contained is preferably 0.1% by mass or more and 3.0% by mass or less, particularly preferably 0.1% by mass. The content is 1.0% by mass or less.

  When lithium cobaltate is used as the positive electrode active material, the concentration of the sulfonate ester contained in the gel electrolyte is not particularly limited, but is preferably 0.5% by mass or more and 5.0% by mass or less. If it is less than 0.5% by mass, a sufficient film is not formed on the electrode surface, and the effect of improving cycle characteristics and rate characteristics is small. If it exceeds 5.0% by mass, the resistance increases and the rate characteristics deteriorate.

The supporting salt contained in the gel electrolyte is not particularly limited, but electrolytes generally used for lithium polymer batteries such as LiPF ₆ , LiBF ₄ , LiAsPF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ O ₂ ) ₂ can be used. .

  In the present invention, benzoins, peroxides and the like can be used as thermal polymerization initiators as necessary, but are not limited thereto.

Also, as the positive electrode active material, for _{example, LiCoO 2, LiNiO 2, LiNi1} -xCoxO 2, LiNixMn 2-x O 4 (0 <x <1), LiNi 1/3 Co 1/3 Mn 1/3 O 2, LiMn Examples include Li composite oxide positive electrode materials such as ₂ O ₄ and LiFePO ₄ , transition metal portions of these Li-containing composite oxides may be substituted with other elements, and mixtures thereof may be used. It is not limited to these.

  The Si or Si compound material as the negative electrode active material is a Si-based material such as crystalline Si, amorphous Si, or a compound of Si and Fe, Co, Ni, Cu, or the like. Examples thereof include, but are not limited to, a Si-carbon composite material obtained by coating a compound with a carbon material or the like.

  As the separator, polyolefin such as polypropylene and polyethylene, and a porous film such as fluororesin can be used, but the separator is not limited thereto.

  The present invention will be described in detail by way of examples with reference to the drawings, but the present invention is not limited to these examples.

  FIG. 1 is a diagram illustrating the configuration of the positive electrode of the lithium polymer battery of the present invention, FIG. 2 is a diagram illustrating the configuration of the negative electrode of the lithium polymer battery of the present invention, and FIG. 3 is a diagram of the lithium polymer battery of the present invention. It is a figure explaining the structure of the battery element after winding.

(Example 1)
First, the production of the positive electrode will be described with reference to FIG. A mixture of 85% by mass of LiMn ₂ O ₄ , 7% by mass of acetylene black as a conductive auxiliary and 8% by mass of polyvinylidene fluoride as a binder is added to N-methylpyrrolidone and further mixed to prepare a positive electrode slurry. did. This was applied to both surfaces of a 20 μm thick Al foil 2 serving as a current collector by a doctor blade method so that the thickness after the roll press treatment was 160 μm, thereby forming a positive electrode active material coating portion 3. In addition, the positive electrode active material non-applied part 4 in which the positive electrode active material is not applied to either surface is provided at both ends, and the positive electrode conductive tab 6 is provided in one of the positive electrode active material non-applied parts 4 so that only one side is applied. The positive electrode active material single-sided coating portion 5 was provided as the positive electrode 1.

Next, the production of the negative electrode will be described with reference to FIG. 90% by mass of graphite and 10% by mass of polyvinylidene fluoride as a binder were mixed, and N-methylpyrrolidone was added and further mixed to prepare a negative electrode slurry. This was applied to both surfaces of a 10 μm thick Cu foil 8 serving as a current collector so that the thickness after the roll press treatment was 120 μm and the electrode density was 1.50 g / cm ³ , thereby forming a negative electrode active material coating portion 9. did. In addition, the negative electrode active material single-side application part 10 which applied only one side and the negative electrode active material non-application part 11 which is not apply | coated the negative electrode active material were provided in one end surface of both ends, the negative electrode conductive tab 12 was attached, and it was set as the negative electrode 7 .

  The production of the battery element will be described with reference to FIG. A portion obtained by welding and cutting two separators 13 made of polyethylene having a film thickness of 12 μm and a porosity of 35% is fixed to a winding core of a winding device, wound up, and positive electrode 1 (FIG. 1) and negative electrode 7 (FIG. 2) is introduced. The positive electrode 1 is disposed on the opposite side of the connecting portion of the positive electrode conductive tab 6, the negative electrode 7 is disposed on the connecting portion side of the negative electrode conductive tab 12, the negative electrode is disposed between the two separators, and the positive electrode is disposed on the upper surface of the separator. Then, the winding core was rotated and wound to form a battery element (hereinafter referred to as jelly roll (J / R)).

  The J / R was housed in an embossed laminate outer package, the positive electrode conductive tab 6 and the negative electrode conductive tab 12 were pulled out, the sides of the laminate outer package were folded back, and heat fusion was performed leaving a portion for injecting the pregel solution. .

The pregel solution is composed of 30% by mass of ethylene carbonate (EC) and 58% by mass of diethyl carbonate (DEC), and 1% by mass of 1,3-PS with respect to an electrolyte solution comprising 12% by mass of LiPF ₆ as a lithium salt. After adding 3.8 mass% and 1.0 mass% of tripropylene glycol diacrylate and trimethylol propane triacrylate, respectively, as mixing agents and mixing them well, t-butyl peroxypivalate as a polymerization initiator was added in an amount of 0.0. It was prepared by mixing 5% by mass.

  Next, the pregel solution was injected from the injection portion and vacuum impregnation was performed to obtain a lithium polymer battery.

  The obtained lithium polymer battery was charged to a battery voltage of 4.2 V (charging conditions: current 0.2 C, time 6.5 hours, temperature 20 ° C.), and discharged to battery voltage 3.0 V at 0.2 C. The discharge capacity at that time was defined as the initial capacity.

  The rate characteristics of the obtained lithium polymer battery are as follows: a battery charged to a battery voltage of 4.2 V is discharged at a discharge rate (0.2 C) to a battery voltage of 3.0 V, and the discharge capacity is 100. Table 1 shows the ratio with the discharge capacity obtained by discharging at 1.0 C).

  The cell volume change rate after cycling of the obtained lithium polymer battery is shown in Table 1 as a ratio with the cell volume after cycling, with the cell volume after initial charging being 1.0. The cycle conditions were: charging: upper limit voltage 4.2V, current 1.0C, time 2.5 hours, discharge: lower limit voltage 3.0V, current 1.0C, all at 20 ° C. The capacity retention rate was expressed as the ratio of the discharge capacity (1.0 C) at the 100th cycle to the discharge capacity (1.0 C) at the first cycle.

(Example 2)
A cell was prepared and evaluated in the same manner as in Example 1 except that the negative electrode density was 1.65 g / cm ³ .

(Example 3)
A cell was prepared and evaluated in the same manner as in Example 1 except that the negative electrode density was 1.60 g / cm ³ .

Example 4
A cell was prepared and evaluated in the same manner as in Example 1 except that the negative electrode density was 1.40 g / cm ³ .

(Example 5)
A cell was prepared and evaluated in the same manner as in Example 1 except that the negative electrode density was 1.35 g / cm ³ .

(Comparative Example 1)
A cell was prepared and evaluated in the same manner as in Example 1 except that the negative electrode density was 1.70 g / cm ³ .

(Comparative Example 2)
A cell was prepared and evaluated in the same manner as in Example 1 except that the negative electrode density was 1.30 g / cm ³ .

  Table 1 shows the rate characteristics, capacity retention rate, and cell volume change rate for Examples 1 to 5 and Comparative Examples 1 and 2.

In the lithium polymer battery of the present invention, as shown in Examples 1-5 of Table 1, the negative electrode density 1.35 g / cm ³ or more, in the case of 1.65 g / cm ³ or less, the rate characteristics and the like, more It was found that the characteristics were clearly better than those of Comparative Example 1 with an electrode density of.

(Example 6)
A cell was prepared and evaluated in the same manner as in Example 1 except that MMDS was used instead of 1,3-PS.

(Example 7)
A cell was prepared and evaluated in the same manner as in Example 2 except that MMDS was used instead of 1,3-PS.

(Example 8)
A cell was prepared and evaluated in the same manner as in Example 3 except that MMDS was used instead of 1,3-PS.

Example 9
A cell was prepared and evaluated in the same manner as in Example 4 except that MMDS was used instead of 1,3-PS.

(Example 10)
A cell was prepared and evaluated in the same manner as in Example 5 except that MMDS was used instead of 1,3-PS.

(Comparative Example 3)
A cell was prepared and evaluated in the same manner as in Comparative Example 1 except that MMDS was used instead of 1,3-PS.

(Comparative Example 4)
A cell was prepared and evaluated in the same manner as in Comparative Example 2 except that MMDS was used instead of 1,3-PS.

  Table 2 shows the rate characteristics, capacity retention ratio, and cell volume change rate for Examples 6 to 10 and Comparative Examples 3 and 4.

In the lithium polymer battery of the present invention, as shown in Examples 6 to 10 in Table 2, when the negative electrode active material is graphite, the negative electrode density 1.35 g / cm ³ or more, 1.65 g / cm ³ or less In this case, it was found that the characteristics were clearly better than Comparative Example 3 in which the electrode density was higher than that in the rate characteristics.

(Example 11)
The positive electrode in the present Example using positive electrode lithium cobaltate was produced as follows. N-methylpyrrolidone was added to and mixed with 87% by mass of LiCoO ₂ , 5% by mass of acetylene black as a conductive auxiliary material, and 8% by mass of polyvinylidene fluoride as a binder to prepare a positive electrode slurry. Other than that, a positive electrode and a negative electrode were produced in the same manner as in Example 1 to produce a cell. Moreover, the pregel solution produced and evaluated the cell similarly to Example 1 except having set it as VC: 0.5 mass% and 1,3-PS: 1.0 mass%.

(Example 12)
A cell was prepared and evaluated in the same manner as in Example 11 except that the negative electrode density was 1.65 g / cm ³ .

(Example 13)
A cell was prepared and evaluated in the same manner as in Example 11 except that the negative electrode density was 1.60 g / cm ³ .

(Example 14)
A cell was prepared and evaluated in the same manner as in Example 11 except that the negative electrode density was 1.40 g / cm ³ .

(Example 15)
A cell was prepared and evaluated in the same manner as in Example 11 except that the negative electrode density was 1.35 g / cm ³ .

(Comparative Example 5)
A cell was prepared and evaluated in the same manner as in Example 11 except that the negative electrode density was 1.70 g / cm ³ .

(Comparative Example 6)
A cell was prepared and evaluated in the same manner as in Example 11 except that the negative electrode density was 1.30 g / cm ³ .

  Table 3 shows the rate characteristics, capacity retention ratio, and cell volume change rate for Examples 11 to 15 and Comparative Example 3.

In the lithium polymer battery of the present invention, as shown in Examples 11 to 15 in Table 3, when the negative electrode active material is graphite, the negative electrode density 1.35 g / cm ³ or more, 1.65 g / cm ³ or less In this case, it was found that the characteristics were clearly better than Comparative Example 5 in which the electrode density was higher than that in the rate characteristics and the like.

(Example 16)
The negative electrode in this example using amorphous carbon as the negative electrode active material was prepared as follows. A negative electrode slurry was prepared by adding N-methylpyrrolidone to 85% by mass of amorphous carbon, 5% by mass of acetylene black as a conductive auxiliary material, and 10% by mass of polyvinylidene fluoride as a binder, and then mixing them. . Moreover, the negative electrode density was set to 1.00 g / cm ^3, and a positive electrode and a negative electrode were produced in the same manner as in Example 1 except that the lithium polymer battery was obtained.

  The obtained lithium polymer battery was charged to a battery voltage of 4.3 V (charging conditions: current 0.2 C, time 6.5 hours, temperature 20 ° C.), and discharged to battery voltage 2.5 V at 0.2 C. The discharge capacity at that time was defined as the initial capacity.

  The cell volume change rate after cycling of the obtained lithium polymer battery is shown in Table 4 in terms of the ratio of the cell volume after initial charging to 1.0 and the cell volume after 500 cycles. The cycle conditions were: charging: upper limit voltage 4.3V, current 1.0C, time 2.5 hours, discharge: lower limit voltage 2.5V, current 1.0C, all at 20 ° C. The capacity retention rate is shown in Table 4 as a ratio of the discharge capacity (1.0 C) at the 500th cycle to the discharge capacity (1.0 C) at the first cycle.

(Example 17)
A cell was prepared and evaluated in the same manner as in Example 16 except that the negative electrode density was 1.35 g / cm ³ .

(Example 18)
A cell was prepared and evaluated in the same manner as in Example 16 except that the negative electrode density was 1.30 g / cm ³ .

(Example 19)
A cell was prepared and evaluated in the same manner as in Example 16 except that the negative electrode density was 0.90 g / cm ³ .

(Example 20)
A cell was prepared and evaluated in the same manner as in Example 16 except that the negative electrode density was 0.80 g / cm ³ .

(Comparative Example 7)
A cell was prepared and evaluated in the same manner as in Example 16 except that the negative electrode density was 1.40 g / cm ³ .

(Comparative Example 8)
A cell was prepared and evaluated in the same manner as in Example 16 except that the negative electrode density was changed to 0.70 g / cm ³ .

  Table 4 shows the capacity retention rate and cell volume change rate for Examples 16 to 20 and Comparative Examples 7 and 8.

In the lithium polymer battery of the present invention, as shown in Example 16 to Example 20 of Table 4, when the negative electrode active material is amorphous carbon, the negative electrode density is 0.80 g / cm ³ or more and 1.35 g / In the case of cm ³ or less, it was found that the characteristics were clearly better than Comparative Example 7 in which the electrode density was higher than that in the capacity retention ratio and the like.

(Example 21)
The negative electrode in this example using amorphous Si as the negative electrode active material was produced as follows. A negative electrode slurry was prepared by adding N-methylpyrrolidone to 85% by mass of amorphous Si, 5% by mass of acetylene black as a conductive auxiliary, and 10% by mass of polyvinylidene fluoride as a binder, and then mixing them. . Moreover, the negative electrode density was set to 1.00 g / cm ^3, and a positive electrode and a negative electrode were produced in the same manner as in Example 1 except that the lithium polymer battery was obtained.

  The obtained lithium polymer battery was charged to a battery voltage of 4.2 V (charging conditions: current 0.2 C, time 6.5 hours, temperature 20 ° C.), and discharged to a battery voltage 2.5 V at 0.2 C. The discharge capacity at that time was defined as the initial capacity.

  The cell volume change rate after cycling of the obtained lithium polymer battery is shown in Table 5 as a ratio with the cell volume after 100 cycles, with the cell volume after initial charging being 1.0. The cycle conditions were: charging: upper limit voltage 4.2V, current 1.0C, time 2.5 hours, discharge: lower limit voltage 2.5V, current 1.0C, all at 20 ° C. The capacity retention rate is shown in Table 5 as the ratio of the discharge capacity (1.0 C) at the 100th cycle to the discharge capacity (1.0 C) at the first cycle.

(Example 22)
A cell was prepared and evaluated in the same manner as in Example 21 except that the negative electrode density was 1.30 g / cm ³ .

(Example 23)
A cell was prepared and evaluated in the same manner as in Example 21 except that the negative electrode density was 1.20 g / cm ³ .

(Example 24)
A cell was prepared and evaluated in the same manner as in Example 21 except that the negative electrode density was 0.80 g / cm ³ .

(Example 25)
A cell was prepared and evaluated in the same manner as in Example 21 except that the negative electrode density was 0.70 g / cm ³ .

(Comparative Example 9)
A cell was prepared and evaluated in the same manner as in Example 21 except that the negative electrode density was 1.40 g / cm ³ .

(Comparative Example 10)
A cell was prepared and evaluated in the same manner as in Example 21 except that the negative electrode density was 0.60 g / cm ³ .

Table 5 shows capacity retention ratios and cell volume change ratios for Examples 21 to 25 and Comparative Examples 9 and 10.

In the lithium polymer battery of the present invention, as shown in Example 21 to Example 25 of Table 5, when the negative electrode active material is amorphous Si, the negative electrode density is 0.70 g / cm ³ or more and 1.30 g / In the case of cm ³ or less, it was found that the characteristics were clearly better than Comparative Example 9 in which the electrode density was higher than that in the capacity retention rate and the like.

The figure explaining the structure of the positive electrode of the lithium polymer battery of this invention. The figure explaining the structure of the negative electrode of the lithium polymer battery of this invention. The figure explaining the structure of the battery element after winding of the lithium polymer battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Al foil 3 Positive electrode active material application part 4 Positive electrode active material non-application part 5 Positive electrode active material single side application part 6 Positive electrode conductive tab 7 Negative electrode 8 Cu foil 9 Negative electrode active material application part 10 Negative electrode active material single side application part 11 Negative electrode active Substance non-applied part 12 Negative electrode conductive tab 13 Separator

Claims (12)

In a lithium polymer battery comprising a positive electrode, a separator, a negative electrode, and including a gel electrolyte, the gel electrolyte includes a solvent, a cross-linked polymer, and a sulfonate ester, and the active material in the negative electrode includes a graphite material as a main component, density of the electrode layer containing an active material in the negative electrode is 1.35 g / cm ³ or more, a lithium polymer battery, characterized in that it is 1.65 g / cm ³ or less. In a lithium polymer battery including a positive electrode, a separator, and a negative electrode, and including a gel electrolyte, the gel electrolyte includes a solvent, a cross-linked polymer, and a sulfonate ester, and the active material in the negative electrode is an amorphous carbon material. And the electrode density of the layer containing the active material in the negative electrode is 0.80 g / cm ³ or more and 1.35 g / cm ³ or less. In a lithium polymer battery including a positive electrode, a separator, and a negative electrode, and including a gel electrolyte, the gel electrolyte includes a solvent, a cross-linked polymer, and a sulfonate ester, and the active material in the negative electrode is mainly composed of Si or a Si compound material. The lithium polymer battery is characterized in that the electrode density of the layer containing the active material in the negative electrode is 0.70 g / cm ³ or more and 1.30 g / cm ³ or less.   The lithium polymer battery according to any one of claims 1 to 3, wherein the gel electrolyte contains a solvent, a crosslinked polymer, and 0.1 to 3.0% by mass of a sulfonic acid ester.   The lithium polymer battery according to any one of claims 1 to 4, wherein the cross-linked polymer is composed of an acrylic polymer.   The lithium polymer battery according to claim 1, wherein the cross-linked polymer is polymerized using a peroxide as a polymerization initiator.   The lithium polymer battery according to any one of claims 1 to 6, wherein the solvent contains at least a chain carbonate or a cyclic carbonate.   The lithium polymer battery according to any one of claims 1 to 7, wherein the sulfonic acid ester is composed of at least one of a cyclic sulfonic acid ester, a cyclic disulfonic acid ester, and a chain disulfonic acid ester.   The lithium polymer battery according to claim 8, wherein the cyclic sulfonate ester is composed of at least one of 1,3-propane sultone and 1,4-butane sultone.   The lithium polymer battery according to claim 8, wherein the cyclic disulfonate is at least one selected from methylene methane disulfonate, ethylene methane disulfonate, and propylene methane disulfonate.   The lithium polymer battery according to any one of claims 1 to 10, wherein the positive electrode contains lithium manganate or lithium cobaltate as an active material.   The positive electrode contains lithium cobaltate, and the gel electrolyte contains a solvent containing vinylene carbonate, a crosslinked polymer, a polymerization initiator, and 0.1 to 3.0% by mass of a sulfonic acid ester. The lithium polymer battery described in 1.

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