Low-temperature electrolyte for laminated soft-package lithium ion battery, lithium ion battery and preparation method of lithium ion battery

Abstract

The invention discloses a low-temperature electrolyte for a laminated soft-package lithium ion battery, the lithium ion battery and a preparation method of the lithium ion battery. Comprising the following components: 4%-6% of propylene carbonate, 9%-11% of diethyl carbonate, 30%-32% of methyl ethyl carbonate, 24%-26% of ethylene carbonate, 9%-11% of ethyl propionate, 14%-16% of electrolyte salt and 3.6%-4.0% of an additive, according to the low-temperature electrolyte and the lithium ion battery, the solvent and the additive of the electrolyte are optimally combined, so that the obtained electrolyte has the characteristics of high conductivity and low impedance at low temperature, the low-temperature charge-discharge performance of the lithium ion battery can be remarkably improved, in addition, the obtained low-temperature electrolyte and the lithium ion battery have wide application prospects, and the application prospect is wide. And the method is especially suitable for the field with high low-temperature performance requirements.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery electrolytes, and in particular relates to a low-temperature electrolyte for laminated soft-pack lithium-ion batteries, a lithium-ion battery and a preparation method thereof. Background Art

[0002] With the widespread application of lithium-ion batteries in aerospace, military equipment, electric vehicles and other fields, higher requirements are placed on the low-temperature performance of lithium-ion batteries. Existing lithium-ion batteries have problems such as decreased conductivity and severe capacity decay under low-temperature conditions, which seriously affect their use in low-temperature environments. Most of the electrolyte formulas currently on the market are difficult to meet the high-performance requirements under low-temperature conditions. Summary of the invention

[0003] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a low-temperature electrolyte for laminated soft-pack lithium-ion batteries, which solves the problem that most of the electrolyte formulations on the market are difficult to meet the high performance requirements under low temperature conditions.

[0004] The present invention also aims to provide a lithium ion battery using the above-mentioned low-temperature electrolyte.

[0005] The present invention also aims to provide a method for preparing the above-mentioned lithium-ion battery.

[0006] In order to achieve the above object, the first technical solution of the present invention is implemented as follows: a low-temperature electrolyte for laminated soft-pack lithium-ion batteries, characterized in that it includes the following components by volume percentage:

[0007] Propylene carbonate 4%-6%, diethyl carbonate 9%-11%, ethyl methyl carbonate 30%-32%, ethylene carbonate 24%-26%, ethyl propionate 9%-11%, electrolyte salt 14%-16%, additives 3.6%-4.0%.

[0008] Preferably, the following components are included by volume percentage: 4%-6% propylene carbonate, 9%-11% diethyl carbonate, 30%-32% ethyl methyl carbonate, 24%-26% ethylene carbonate, 3%-7% methyl acetate, 9%-11% ethyl propionate, 14%-16% electrolyte salt, and 3.6%-4.0% additives.

[0009] Preferably, the following components are included by volume percentage: 5% propylene carbonate, 10% diethyl carbonate, 31.2% ethyl methyl carbonate, 25% ethylene carbonate, 5% methyl acetate, 10% ethyl propionate, 12% electrolyte salt, and 3.8% additives.

[0010] Preferably, the additive comprises the following components by volume percentage: 1.0% vinylene carbonate, 2.0% propylene sulfite and 0.8% LiPO2F2.

[0011] Preferably, the additive further comprises 0.5% of fluoroethylene carbonate by volume.

[0012] Preferably, the electrolyte salt is selected from lithium hexafluorophosphate.

[0013] Another technical solution of the present invention is achieved as follows: a laminated soft-pack lithium-ion battery comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1-6.

[0014] Preferably, the positive electrode active material used in the positive electrode is selected from at least one of LiCoO2 positive electrode material, LiFePO4 positive electrode material, and LiMn2O4 positive electrode material; the negative electrode active material used in the negative electrode is selected from at least one of artificial graphite, natural graphite, and soft carbon.

[0015] Preferably, the diaphragm is made of at least one of polyethylene and polypropylene.

[0016] The third technical solution of the present invention is achieved as follows: the preparation method of the above-mentioned laminated soft-pack lithium-ion battery specifically comprises the following steps:

[0017] S1, mixing the positive electrode active material, the conductive agent and the binder and coating them evenly on the positive electrode current collector to obtain a positive electrode;

[0018] S2, mixing the negative electrode active material, the conductive agent, the thickener and the binder and coating them uniformly on the negative electrode current collector to obtain a negative electrode;

[0019] S3. Form a battery core assembly by stacking the positive electrode, the separator and the negative electrode, and load it into a soft-pack battery shell; then inject the electrolyte described in any one of claims 1 to 4 into the battery shell, and obtain a laminated soft-pack lithium-ion battery after sealing.

[0020] Compared with the prior art, the present invention optimizes the combination of electrolyte solvents and additives so that the obtained electrolyte has the characteristics of high conductivity and low impedance at low temperatures, which can significantly improve the low-temperature charge and discharge performance of lithium-ion batteries. In addition, the low-temperature electrolyte and lithium-ion battery obtained by the present invention have broad application prospects and are particularly suitable for fields with high requirements for low-temperature performance. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] A low-temperature electrolyte for a laminated soft-pack lithium-ion battery provided in an embodiment of the present invention comprises the following components by volume percentage:

[0023] Propylene carbonate 4%-6%, diethyl carbonate 9%-11%, ethyl methyl carbonate 30%-32%, ethylene carbonate 24%-26%, ethyl propionate 9%-11%, electrolyte salt 14%-16%, additives 3.6%-4.0%.

[0024] In the specific implementation process of this embodiment, the following components are included by volume percentage: propylene carbonate 4% to 6%, diethyl carbonate 9% to 11%, ethyl methyl carbonate 30% to 32%, ethylene carbonate 24% to 26%, methyl acetate 3 to 7%, ethyl propionate 9% to 11%, electrolyte salt 14% to 16%, additives 3.6% to 4.0%;

[0025] In the specific implementation process of this embodiment, the following components are included by volume percentage: 5% propylene carbonate, 10% diethyl carbonate, 31.2% ethyl methyl carbonate, 25% ethylene carbonate, 5% methyl acetate, 10% ethyl propionate, 12% electrolyte salt, and 3.8% additives.

[0026] In the specific implementation process of this embodiment, the additives include 1.0% vinylene carbonate, 2.0% propylene sulfite and 0.8% LiPO2F2.

[0027] In the specific implementation process of this embodiment, 0.5% of fluoroethylene carbonate is further included.

[0028] In the specific implementation process of this embodiment, the electrolyte salt is selected from lithium hexafluorophosphate.

[0029] An embodiment of the present invention further provides a laminated soft-pack lithium-ion battery, comprising a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte.

[0030] In the specific implementation process of this embodiment, the positive electrode active material used in the positive electrode is selected from at least one of LiCoO2 positive electrode material, LiFePO4 positive electrode material, and LiMn2O4 positive electrode material.

[0031] In the specific implementation process of this embodiment, the negative electrode active material used in the negative electrode is selected from at least one of artificial graphite, natural graphite, and soft carbon.

[0032] In the specific implementation process of this embodiment, the diaphragm is selected from at least one of polyethylene and polypropylene.

[0033] The following are specific embodiments:

[0034] Example 1

[0035] The low-temperature electrolyte for laminated soft-pack lithium-ion batteries provided in Example 1 includes the following components by volume percentage:

[0036] Propylene carbonate 5%, diethyl carbonate 10%, ethyl methyl carbonate 31.2%, ethylene carbonate 25%, ethyl propionate 10%, lithium hexafluorophosphate 15%, vinylene carbonate 1%, propylene sulfite 2%, LiPO2F2 0.8%.

[0037] The low-temperature electrolyte for the laminated soft-pack lithium-ion battery provided in Example 1 is obtained by the following method:

[0038] Under a protective atmosphere, the components are mixed in proportion and stirred thoroughly to obtain the low-temperature electrolyte.

[0039] Example 2

[0040] The low-temperature electrolyte for laminated soft-pack lithium-ion batteries provided in Example 2 adjusts the proportion of additives while keeping the proportion of the main solvent and electrolyte salt unchanged, and introduces a new additive to further optimize the low-temperature performance. The specific formulation is as follows (by volume percentage):

[0041] Propylene carbonate 5%, diethyl carbonate 10%, ethyl methyl carbonate 31.2%, ethylene carbonate 25%, ethyl propionate: 10%, electrolyte salt: lithium hexafluorophosphate 15%, vinylene carbonate 0.8%, propylene sulfite 1.5%, LiPO2F2 0.8%, fluoroethylene carbonate (FEC) 0.5% (a newly introduced additive to further enhance the stability of the SEI film).

[0042] The new additive fluoroethylene carbonate is introduced to further enhance the stability of the SEI film.

[0043] The method for preparing the low-temperature electrolyte for laminated soft-pack lithium-ion batteries provided in this Example 2 is as described in Example 1.

[0044] Example 3

[0045] The low-temperature electrolyte for laminated soft-pack lithium-ion batteries provided in Example 3, while maintaining the ratio of the basic solvent to the electrolyte salt, tried a new auxiliary solvent (methyl acetate) to explore its effect on the performance of the electrolyte. The specific preparation is as follows (by volume percentage):

[0046] Diethyl carbonate 10%, ethyl methyl carbonate 30%, ethylene carbonate 25%, methyl acetate 5%, ethyl propionate 10%, lithium hexafluorophosphate 15%, vinylene carbonate 1%, propylene sulfite 2%, LiPO2F2 0.7%.

[0047] A new auxiliary solvent, methyl acetate, was introduced to further reduce the viscosity of the electrolyte.

[0048] The method for preparing the low-temperature electrolyte for laminated soft-pack lithium-ion batteries provided in this Example 2 is as described in Example 1.

[0049] Example 4

[0050] The laminated soft-pack lithium-ion battery provided in this embodiment 4 includes a positive electrode, a negative electrode, a separator and the above-mentioned electrolyte; wherein the positive electrode active material used in the positive electrode is selected from LiCoO2 positive electrode material; the negative electrode active material used in the negative electrode is selected from artificial graphite; and the separator is selected from polyethylene.

[0051] The laminated soft-pack lithium-ion battery provided in this embodiment 1 is obtained by the following method:

[0052] S1, mixing the positive electrode active material, the conductive agent and the binder and coating them evenly on the positive electrode current collector to obtain a positive electrode;

[0053] S2, mixing the negative electrode active material, the conductive agent, the thickener and the binder and coating them uniformly on the negative electrode current collector to obtain a negative electrode;

[0054] S3. Form a battery cell assembly by stacking the positive electrode, the separator and the negative electrode, and load it into a soft-pack battery shell; then inject the electrolyte described in any one of Examples 1-3 into the battery shell, and obtain a laminated soft-pack lithium-ion battery after sealing.

[0055] In order to verify the specific performance of the electrolyte obtained in the embodiment of the present invention, three laminated soft-pack lithium-ion batteries are made for the electrolyte obtained in Example 1, Example 2 or Example 3, 2 of each type are made, and the batteries are marked as: lithium-ion battery 1-1, lithium-ion battery 1-2, lithium-ion battery 2-1, lithium-ion battery 2-2, lithium-ion battery 3-1, lithium-ion battery 3-2; at the same time, the performance of the three batteries is tested at -40°C and 55°C, and during the test, the shelf time is 6h and the discharge current is 600mA. The specific test results are shown in Tables 1 and 2 below:

[0056] Table 1-40℃ test results of three laminated soft-pack lithium-ion batteries

[0057]

[0058]

[0059] Table 2 Test results of three laminated soft-pack lithium-ion batteries at 55°C

[0060]

[0061] By analyzing the contents in Table 1 and Table 2, we can know that:

[0062] After testing the performance of laminated soft-pack lithium-ion batteries (battery numbers are lithium-ion battery 1-1 and lithium-ion battery 1-2) obtained using the electrolyte in Example 1 at low temperatures of -40°C and high temperatures of 55°C, the test results show that the batteries obtained using the electrolyte described in Example 1 of the present invention have a high charge and discharge capacity retention rate and good cycle stability at low temperatures.

[0063] After testing the performance of the laminated soft-pack lithium-ion batteries (batteries numbered lithium-ion battery 2-1 and lithium-ion battery 2-2) obtained using the electrolyte of Example 2 at low temperature of -40°C and high temperature of 55°C, the test results showed that the use of the electrolyte described in Example 2 of the present invention to make batteries can further effectively improve the low-temperature charge and discharge efficiency and cycle stability of the battery, especially under high-rate charge and discharge conditions.

[0064] After testing the performance of the laminated soft-pack lithium-ion batteries (battery numbers are lithium-ion battery 3-1 and lithium-ion battery 3-2) obtained using the electrolyte of Example 3 at low temperature of -40°C and high temperature of 55°C, the test results show that the battery obtained using the electrolyte described in Example 3 of the present invention exhibits good low-temperature charge and discharge capacity retention and cycle stability in the low-temperature performance test. In particular, the introduction of methyl acetate may help to further reduce the viscosity of the electrolyte, thereby improving the ion migration rate and electrochemical performance at low temperatures.

[0065] In summary, the present invention optimizes the combination of electrolyte solvents and additives so that the obtained electrolyte has the characteristics of high conductivity and low impedance at low temperatures, which can significantly improve the low-temperature charge and discharge performance of lithium-ion batteries. In addition, the low-temperature electrolyte and lithium-ion battery obtained by the present invention have broad application prospects and are particularly suitable for fields with high requirements for low-temperature performance.

[0066] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A low-temperature electrolyte for laminated soft-pack lithium-ion batteries, characterized in that: Calculated by volume percentage, it includes the following components: Propylene carbonate 4%-6%, diethyl carbonate 9%-11%, ethyl methyl carbonate 30%-32%, ethylene carbonate 24%-26%, ethyl propionate 9%-11%, electrolyte salt 14%-16%, additives 3.6%-4.0%.

2. A low-temperature electrolyte for laminated soft-pack lithium-ion batteries according to claim 1, characterized in that: Calculated by volume percentage, it includes the following components: 4%-6% of propylene carbonate, 9%-11% of diethyl carbonate, 30%-32% of ethyl methyl carbonate, 24%-26% of ethylene carbonate, 3%-7% of methyl acetate, 9%-11% of ethyl propionate, 14%-16% of electrolyte salt, and 3.6%-4.0% of additives.

3. A low-temperature electrolyte for laminated soft-pack lithium-ion batteries according to claim 2, characterized in that: Calculated by volume percentage, the composition includes: 5% propylene carbonate, 10% diethyl carbonate, 31.2% ethyl methyl carbonate, 25% ethylene carbonate, 5% methyl acetate, 10% ethyl propionate, 12% electrolyte salt and 3.8% additives.

4. A low-temperature electrolyte for laminated soft-pack lithium-ion batteries according to any one of claims 1 to 3, characterized in that: The additive comprises the following components by volume percentage: 1.0% vinylene carbonate, 2.0% propylene sulfite and 0.8% LiPO2F2.

5. A low-temperature electrolyte for laminated soft-pack lithium-ion batteries according to claim 4, characterized in that: The additive further comprises 0.5% of fluoroethylene carbonate by volume.

6. A low-temperature electrolyte for laminated soft-pack lithium-ion batteries according to any one of claims 1 to 3, characterized in that: The electrolyte salt is selected from lithium hexafluorophosphate.

7. A laminated soft-pack lithium-ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 6.

8. The laminated soft-pack lithium-ion battery according to claim 7, characterized in that: The positive electrode active material used in the positive electrode is selected from at least one of LiCoO2 positive electrode material, LiFePO4 positive electrode material, and LiMn2O4 positive electrode material; the negative electrode active material used in the negative electrode is selected from at least one of artificial graphite, natural graphite, and soft carbon.

9. The laminated soft-pack lithium-ion battery according to claim 7, characterized in that: The diaphragm is selected from at least one of polyethylene and polypropylene.

10. The method for preparing a laminated soft-pack lithium-ion battery according to any one of claims 7 to 9, characterized in that: The specific steps include: S1, mixing the positive electrode active material, the conductive agent and the binder and coating them evenly on the positive electrode current collector to obtain a positive electrode; S2, mixing the negative electrode active material, the conductive agent, the thickener and the binder and coating them uniformly on the negative electrode current collector to obtain a negative electrode; S3. Form a battery core assembly by stacking the positive electrode, the separator and the negative electrode, and load it into a soft-pack battery shell; then inject the electrolyte described in any one of claims 1 to 4 into the battery shell, and obtain a laminated soft-pack lithium-ion battery after sealing.

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