A low-temperature lithium-ion battery formation method and lithium-ion battery

Abstract

The present invention discloses a low-temperature lithium-ion battery formation method and a lithium-ion battery. The low-temperature lithium-ion formation method comprises the following steps: cyclically charging and discharging the assembled lithium-ion battery, wherein the charging temperature during the charging and discharging process is ‑80°C to 10°C; and the electrolyte of the lithium-ion battery contains lithium hexafluorophosphate. The present invention forms a battery containing a lithium hexafluorophosphate electrolyte under a low-temperature environment, which can significantly improve the overall performance of the battery, showing low impedance, high and low temperature resistance, high voltage resistance, high rate and excellent cycle stability.

Description

Technical Field

[0001] The invention relates to the field of battery formation methods, and in particular to a low-temperature lithium ion battery formation method and a lithium ion battery. Background Art

[0002] Rechargeable batteries are considered to be the best large-scale energy storage system due to their long life, high energy efficiency and simple process. Driven by energy security and green transportation, electric vehicles have developed rapidly in recent years. Lithium-ion batteries have become the main power source for electric vehicles due to their high energy density, high power density and long cycle life, and have formed a large new energy industry. However, they still face major challenges under harsh conditions such as fast charging (<15 minutes) and low temperature. An important challenge facing the application of lithium-ion batteries is the increased capacity loss at low temperatures. The performance of the battery depends largely on the Li + Diffusion of Li, which is related to several processes: diffusion in the electrode, transport in the electrolyte, and motion at the electrode electrolyte interface. + The diffusion coefficient in the electrode electrolyte is 4-5 orders of magnitude lower than that in other interfaces. Improving the ion conductivity of the electrode electrolyte interface is a key factor in improving the low-temperature fast charging performance of lithium batteries.

[0003] The conventional cathode electrolyte interface (CEI) consists of Li 2 CO 3 , LiF, Li 2 O and alkyl lithium carbonate, among which Li 2 CO 3 Mainly, it has a high surface lithium ion diffusion barrier. At present, many studies are to add fluorine-containing additives (such as salts or solvents) to change and alleviate the deterioration of the interface. The additives have a lower oxidation potential than carbonate electrolytes and can form a uniform and stable CEI on the electrode before the carbonate electrolyte is electrolyzed, thereby improving the overall electrochemical performance.

[0004] However, the use of additives not only increases costs, but also leads to side reactions, which have a certain impact on battery performance. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a low-temperature lithium-ion battery formation method. It is found that lithium hexafluorophosphate formation under low-temperature conditions will decompose to produce a large amount of LiF substances, which have lower surface diffusion energy than lithium carbonate; the battery formed by low-temperature charging not only shows lower impedance, but also shows excellent performance in rate performance and cycle stability. In addition, the battery can still maintain excellent rate performance and cycle stability under extreme conditions of high temperature and high pressure.

[0006] The first aspect of the present invention is to provide a low-temperature lithium-ion battery formation method, which specifically comprises the following steps:

[0007] The assembled lithium-ion battery is subjected to cyclic charge and discharge, wherein the charging temperature during the charge and discharge process is between -80°C and 10°C; the electrolyte of the lithium-ion battery contains lithium hexafluorophosphate.

[0008] Furthermore, the battery charging temperature is -80°C, -70°C, -60°C, -50°C, -40°C, -30°C, -20°C, -10°C, 0°C and 10°C, including but not limited to the temperatures listed above; preferably -30°C to 10°C.

[0009] Furthermore, the concentration of lithium hexafluorophosphate in the electrolyte is 0.5-2 mol / L; including but not limited to 0.5 mol / L, 1 mol / L, 1.5 mol / L and 2 mol / L, etc.; preferably 1-1.5 mol / L; more preferably 1 mol / L.

[0010] Further, the solvent of the electrolyte is selected from one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene glycol propyl ether, propylene carbonate, dimethyl carbonate, acetonitrile, tetrahydrofuran, 2-methyl-tetrahydrofuran, butylene carbonate, ethyl acetate, methyl formate, dimethoxymethane, 1,2-dimethoxyethane, vinyl ethylene carbonate, 1,3-propane sultone, difluoroethylene carbonate, methyl methacrylate, ethylene glycol dimethyl ether, dioxolane ether ring, methyl propionate, methyl acetate or fluorobenzene.

[0011] Preferably, the electrolyte solvent is selected from one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propylene carbonate, methyl methacrylate, methyl propionate, methyl carbonate, and fluorobenzene. More preferably, it is one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl carbonate, and fluorobenzene.

[0012] Furthermore, the charging method includes but is not limited to constant current-constant voltage charging or constant current charging.

[0013] Furthermore, the constant current-constant voltage charging method is: the battery is left to stand, the constant current I is charged to the rated voltage U, the rated voltage is maintained and the charging is continued until the current value is I / 2, and after the charging is completed, the constant current I is continued to be discharged to 3-3.5V; the standing time is 1-24h; the constant current I is 0.01-0.5C; the rated voltage U is 4.0-4.9V.

[0014] Furthermore, the constant current charging method is: the battery is left to stand, and the constant current I1 is charged to the rated voltage U1, and then the constant current I1 is discharged to 3-3.5V after the charging is completed; the standing time is 1-24h; the constant current I1 is 0.01-0.5C; the rated voltage U1 is 4.0-4.9V.

[0015] Furthermore, the diaphragm is selected from a polyethylene diaphragm or a polypropylene diaphragm.

[0016] Furthermore, the positive electrode material includes, but is not limited to, one or more of a layered structure material, a spinel structure material, an olivine structure material, a polyanionic structure material, an organic electrode material and a carbon material.

[0017] Preferably, the positive electrode material is one or more of lithium iron phosphate material, lithium nickel cobalt aluminum oxide material, lithium manganese oxide material, lithium cobalt oxide material, lithium nickel oxide material, lithium manganese-rich based material, ternary material, lithium nickel manganese oxide material, lithium titanate material or sulfided polyacrylonitrile.

[0018] Furthermore, the negative electrode material includes but is not limited to one or more of lithium titanate, lithium metal, graphite, tin-based materials, hard carbon, soft carbon, carbon black, graphene, carbon nanotubes, metal oxides, metal sulfides, metal nitrides, silicon and organic materials.

[0019] Furthermore, the lithium-ion battery is assembled from a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

[0020] The second aspect of the present invention is to provide a battery prepared by the method described in the first aspect.

[0021] Further, the battery is used at a temperature of 80°C to -130°C, such as 80°C, 70°C, 60°C, 50°C, 40°C, 30°C, 20°C, 10°C, 0°C, -10°C, -20°C, -40°C, -60°C, -80°C, -100°C, -120°C, -130°C, etc., including but not limited to the temperatures listed above. Preferably, it is 60°C to -40°C.

[0022] Furthermore, the voltage range of the positive electrode material of the battery relative to lithium metal is 3-4.9 V. Working under high voltage can increase the potential difference of the battery, thereby increasing the energy density of the battery.

[0023] Furthermore, the battery uses a voltage range of 1-4.9V.

[0024] Beneficial effects of the present invention:

[0025] 1. The present invention finds that lithium hexafluorophosphate can form a large amount of lithium fluoride in the electrode electrolyte layer under a low-temperature charging environment, which significantly enhances the migration rate of lithium ions at the interface between the electrode and the electrolyte, thereby improving the rate performance of the battery. In addition, the low-temperature charging formation method has significant advantages over the traditional normal temperature formation method. Specifically, the low-temperature formed battery exhibits lower impedance and cycle stability; and when the battery operates under a high-voltage environment, the battery can not only achieve a higher energy density but also has better performance in cycle performance. In addition, the battery prepared by the formation method of the present invention can work stably in extreme high and low temperature environments (80°C to -30°C), which greatly broadens the application range of the battery.

[0026] 2. The present invention proposes an innovative battery formation method, which avoids the side reactions caused by adding additives to the electrolyte and reduces the economic cost of battery manufacturing. In addition, the formation method of the present invention is simple and can significantly improve the overall performance of the battery by only charging in a low temperature environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a comparison of XPS characterization of CEI of the battery after formation of Example 4 of the present invention and Comparative Example 4;

[0028] Figure 2 It is a comparison of XPS characterization of CEI of the battery after formation of Comparative Example 6 and Comparative Example 9 of the present invention;

[0029] Figure 3 It is a comparison of XPS characterization of CEI of the battery after formation between Example 8 of the present invention and Comparative Example 13;

[0030] Figure 4 It is the time-of-flight secondary ion mass spectrometry of the battery CEI after formation of Example 4 of the present invention and Comparative Example 4;

[0031] Figure 5 It is a comparison of the rate performance of the batteries formed in Example 1 of the present invention and Comparative Example 1 at -20°C;

[0032] Figure 6 It is a comparison of the rate performance of the batteries formed in Example 2 of the present invention and Comparative Example 2 at -20°C;

[0033] Figure 7 It is a comparison of the rate performance of the batteries formed in Example 3 of the present invention and Comparative Example 3 tested at 25°C;

[0034] Figure 8 It is a comparison of the rate performance of the batteries formed in Example 4 of the present invention and Comparative Example 4 at -20°C;

[0035] Fig. 9It is a comparison of the rate performance of the batteries formed in Example 5 of the present invention and Comparative Example 4 at 25°C;

[0036] Fig.10 It is a comparison of the rate performance of the batteries formed in Comparative Examples 5 and 8 of the present invention at 25°C;

[0037] Fig.11 It is a comparison of the rate performance of the batteries formed in Comparative Examples 6 and 9 of the present invention at -20°C;

[0038] Fig.12 It is a comparison of the rate performance of the batteries formed in Comparative Examples 7 and 10 of the present invention at 25°C;

[0039] Fig.13 It is a comparison of the rate performance of Example 4, Example 7, Comparative Example 4 and Comparative Example 12 tested at 25°C;

[0040] Fig.14 The comparison of the cycle stability of the batteries formed in Example 6 of the present invention and Comparative Example 11 at 25°C and 1C rate;

[0041] Fig.15 It is a scanning electron microscope (SEM) image of the positive electrode material of the battery formed in Example 5 of the present invention and Comparative Example 11 after 200 cycles;

[0042] Fig.16 The cycle performance test of the batteries formed in Example 4 of the present invention and Comparative Example 4 at 25° C. at a 1C rate;

[0043] Fig.17 The comparison of cycle stability and coulombic efficiency of the batteries formed in Example 4 of the present invention and Comparative Example 4 at 60°C 1C rate;

[0044] Fig.18 1 is a comparison diagram of cyclic voltammetry and impedance of the batteries formed in Example 4 of the present invention and Comparative Example 4;

[0045] Fig.19 The activation energy of the battery after formation of Example 4 of the present invention and Comparative Example 4 is compared;

[0046] Fig. 20 It is a comparison of the discharge specific capacity of the batteries formed in Example 9 of the present invention and in Comparative Example 14 tested at -40°C. DETAILED DESCRIPTION

[0047] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0048] Example 1 The lithium salt in the electrolyte is LiPF 6 Low temperature 0℃ constant current-constant voltage formation

[0049] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0050] (1) Ethylene carbonate and dimethyl carbonate were mixed in a volume ratio of 1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0051] (2) Assemble lithium nickel manganese oxide, lithium sheets, PP / PE / PP composite diaphragm and the electrolyte obtained in step (1) to form a battery.

[0052] (3) The lithium-ion battery was placed in a 10°C low-temperature box, left to stand for 10 hours, and then charged to 4.9V with a current of 0.01C, and kept at a constant voltage of 4.9V until the current dropped to 0.05C, and then discharged to 3V with a constant current of 0.1C for pretreatment. A stable CEI electrolyte interface was formed, and a lithium-ion battery with excellent performance was obtained.

[0053] Example 2 The lithium salt in the electrolyte is LiPF 6 Low temperature 10℃ constant current-constant voltage formation

[0054] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0055] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0056] (2) Assemble lithium nickel cobalt aluminum oxide (NCA), lithium sheets, PP / PE / PP composite separator and the electrolyte obtained in step (1) to form a battery.

[0057] (3) The lithium-ion battery was placed in a low-temperature box at 0°C, left to stand for 10 hours, and then charged to 4.3V with a current of 0.5C, and kept at a constant voltage of 4.3V until the current dropped to 0.2C, and then discharged to 3V with a constant current of 0.1C for pretreatment. After forming a stable CEI electrolyte interface, a lithium-ion battery with excellent performance was obtained.

[0058] Example 3 The lithium salt in the electrolyte is LiPF 6 Low temperature -5℃ constant current-constant voltage formation

[0059] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0060] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0061] (2) Lithium titanate, PP / PE / PP composite diaphragm, NMC111 and the electrolyte obtained in step (1) are used to obtain a lithium ion battery.

[0062] (3) After the lithium-ion battery was placed in a -5°C low-temperature box and left to stand for 10 hours, it was charged to 4.2V with a current of 0.1C, and kept at a constant voltage of 4.2V until the current dropped to 0.05C, and then discharged to 3V with a constant current of 0.1C for pretreatment. After a stable solid electrolyte interface was formed, a lithium-ion battery with excellent performance was obtained.

[0063] Example 4 The lithium salt in the electrolyte is LiPF 6 Low temperature -5℃ constant current-constant voltage formation

[0064] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0065] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0066] (2) A lithium sheet, a PP / PE / PP composite separator, NMC111 and the electrolyte obtained in step (1) are combined to obtain a lithium-ion battery.

[0067] (3) After the lithium-ion battery was placed in a -5°C low-temperature box and left to stand for 10 hours, it was charged to 4.2V with a current of 0.1C, and the constant voltage of 4.2V was maintained until the current dropped to 0.05C, and then discharged to 3V with a constant current of 0.1C for pretreatment. After a stable solid electrolyte interface was formed, a lithium-ion battery with excellent performance was obtained.

[0068] Example 5 The lithium salt in the electrolyte is LiPF 6 Low temperature -5℃ constant current formation

[0069] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0070] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0071] (2) A lithium sheet, a PP / PE / PP composite separator, NMC111 and the electrolyte obtained in step (1) are combined to obtain a lithium-ion battery.

[0072] (3) After the lithium-ion battery was placed in a -5°C low-temperature box and left to stand for 10 hours, it was charged to 4.2 V with a current of 0.1 C, and then discharged to 3 V with a constant current of 0.1 C for pretreatment. After a stable solid electrolyte interface was formed, a lithium-ion battery with excellent performance was obtained.

[0073] Example 6 The lithium salt in the electrolyte is LiPF 6 Low temperature -5℃ under high pressure

[0074] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0075] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0076] (2) Assemble the lithium sheet, PP / PE / PP composite diaphragm, NMC811 and the electrolyte obtained in step (1) to obtain a lithium-ion battery.

[0077] (3) After the lithium-ion battery was placed in a -5°C low-temperature box and left to stand for 10 hours, it was charged to 4.5V with a current of 0.1C, and kept at a constant voltage of 4.5V until the current dropped to 0.05C, and then discharged to 3V with a constant current of 0.1C for pretreatment. After a stable solid electrolyte interface was formed, a lithium-ion battery with excellent performance was obtained.

[0078] Example 7 Low temperature charging and normal temperature discharging

[0079] This embodiment relates to a formation method of a low-temperature lithium-ion battery, which specifically includes the following steps:

[0080] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0081] (2) Assemble the lithium sheet, PP / PE / PP composite diaphragm, NMC111 and the electrolyte obtained in step (1) into a lithium ion battery.

[0082] (3) Place the lithium-ion battery in a -5°C low-temperature box and let it stand for 10 hours. Then charge it to 4.2V at 0.1C at -5°C and maintain the voltage at 4.2V until the current drops to 0.05C. Then, place the battery at 25°C for 2 hours and discharge it to 3V at 0.1C constant current. Next, place the battery back in a -5°C low-temperature box and let it stand for 2 hours. Then, charge it using the same operation as above. After charging, place the battery at 25°C and discharge it. After a stable solid electrolyte interface is formed, the battery formation process is completed.

[0083] Example 8 The lithium salt in the electrolyte is LiPF 6 Low temperature -5℃ constant current-constant voltage formation

[0084] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0085] (1) Ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate were mixed in a volume ratio of 1:1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0086] (2) A lithium sheet, a PP / PE / PP composite separator, NMC111 and the electrolyte obtained in step (1) are combined to obtain a lithium-ion battery.

[0087] (3) After the lithium-ion battery was placed in a -5°C low-temperature box and left to stand for 10 hours, it was charged to 4.2V with a current of 0.01C, and the constant voltage of 4.2V was maintained until the current dropped to 0.005C, and then discharged to 3V with a constant current of 0.01C for pretreatment. After a stable solid electrolyte interface was formed, a lithium-ion battery with excellent performance was obtained.

[0088] Example 9 The lithium salt in the electrolyte is LiPF 6 Low temperature -30℃ constant current-constant voltage formation

[0089] This embodiment relates to a low-temperature lithium-ion battery formation method, the method comprising:

[0090] (1) Methyl carbonate and fluorobenzene were mixed in a volume ratio of 1:1, and then LiPF 6 After mixing evenly, an electrolyte is obtained; the electrolyte contains LiPF 6 The concentration is 1 mol / L.

[0091] (2) A lithium sheet, a PP / PE / PP composite diaphragm, a sulfide polyacrylonitrile SPAN and the electrolyte obtained in step (1) are combined to obtain a lithium ion battery.

[0092] (3) After the lithium-ion battery was placed in a -30°C low-temperature box and left to stand for 10 hours, it was charged to 4.2V with a current of 0.01C, and the constant voltage of 4.2V was maintained until the current dropped to 0.005C, and then discharged to 3V with a constant current of 0.01C for pretreatment. After a stable solid electrolyte interface was formed, a lithium-ion battery with excellent performance was obtained.

[0093] Comparative Example 1: The lithium salt in the electrolyte is LiPF 6 Formed at room temperature

[0094] The difference between this comparative example and Example 1 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0095] Comparative Example 2: The lithium salt in the electrolyte is LiPF 6 Formed at room temperature

[0096] The difference between this comparative example and Example 2 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0097] Comparative Example 3: The lithium salt in the electrolyte is LiPF 6 Formed at room temperature

[0098] The difference between this comparative example and Example 3 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0099] Comparative Example 4: The lithium salt in the electrolyte is LiPF 6 Formed at room temperature

[0100] The difference between this comparative example and Example 4 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0101] Comparative Example 5: The lithium salt in the electrolyte is LiClO 4 Low temperature

[0102] This comparative example relates to a low-temperature lithium-ion battery formation method. The difference between this comparative example and Example 4 is that the LiPF 6 Replace with LiClO with an equimolar concentration 4 .

[0103] Comparative Example 6: The lithium salt in the electrolyte is LiTFSI formed at low temperature

[0104] This comparative example relates to a low-temperature lithium-ion battery formation method. The difference between this comparative example and Example 4 is that the LiPF 6 Replace with LiTFSI at an equimolar concentration.

[0105] Comparative Example 7 The lithium salt in the electrolyte is LiFSI formed at low temperature

[0106] This comparative example relates to a low-temperature lithium-ion battery formation method. The difference between this comparative example and Example 4 is that the LiPF 6 Replace with LiFSI at an equal molar concentration.

[0107] Comparative Example 8 The lithium salt in the electrolyte is LiClO 4 Formed at room temperature

[0108] This comparative example relates to a lithium ion battery formation method. The difference between this comparative example and comparative example 5 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0109] Comparative Example 9 The lithium salt in the electrolyte is LiTFSI formed at room temperature

[0110] This comparative example relates to a lithium ion battery formation method. The difference between this comparative example and comparative example 6 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0111] Comparative Example 10 The lithium salt in the electrolyte is LiFSI formed at room temperature

[0112] This comparative example relates to a lithium ion battery formation method. The difference between this comparative example and comparative example 7 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is carried out at room temperature.

[0113] Comparative Example 11 High Pressure Normal Temperature Formation

[0114] The only difference between this comparative example and Example 6 is that the temperature of the low temperature box in step (3) is adjusted to 25° C., that is, the formation is completed at room temperature.

[0115] Comparative Example 12: Charging at room temperature and discharging at low temperature

[0116] The difference between this comparative example and Example 4 is only that step (3) is replaced by the following steps:

[0117] (3) Place the lithium-ion battery in a 25°C low-temperature box and let it stand for 10 hours. Charge it to 4.2V at 0.1C at 25°C and keep the voltage at 4.2V until the current drops to 0.05C. Then, keep the battery at -5°C for 2 hours and discharge it to 3V at a constant current of 0.1C. Next, place the battery back in a 25°C low-temperature box and let it stand for 2 hours, then repeat the above charge and discharge steps. After 8 cycles, a stable solid electrolyte interface is formed, and the battery formation process is completed.

[0118] Comparative Example 13: The lithium salt in the electrolyte is LiPF 6 Formed at room temperature

[0119] The difference between this comparative example and Example 8 is that the temperature of the low temperature box in step (3) is adjusted to 25°C, that is, the formation is carried out at room temperature.

[0120] Comparative Example 14: The lithium salt in the electrolyte is LiPF 6 Formed at room temperature

[0121] The difference between this comparative example and Example 9 is that the temperature of the low temperature box in step (3) is adjusted to 25°C, that is, the formation is carried out at room temperature.

[0122] Performance Testing and Characterization

[0123] 1. Characterization

[0124] like Figure 1 The XPS characterization of the CEI films prepared in Example 4 and Comparative Example 4 shows that the content of LiF increases during the low-temperature formation process, and the content of Li 2 CO 3 The surface diffusion energy of lithium fluoride is lower than that of Li 2 CO 3 Increasing the content of LiF helps to improve the diffusion of lithium ions and form a low-temperature lithium-ion battery with high rate performance. Figure 3 The XPS results also confirmed that LiPF 6 During low temperature formation, LiF is decomposed. 6 When changing to other LiTFSI lithium salts ( Figure 2 ), whether at room temperature or low temperature, XPS shows that the content of lithium fluoride is very low. The CEI prepared in Example 4 and Comparative Example 4 was tested by time-of-flight secondary ion mass spectrometry. The instrument used for the test was PHInanoTOF II Time-of-Flight SIMS. The results are as follows: Figure 4 As shown, it is proved that the content of LiF in CEI increases at low temperature, which is consistent with the results of XPS.

[0125] 2. Performance Testing

[0126] like Figure 5-8 As shown in the figure, when lithium hexafluorophosphate is formed at low temperature, the battery shows better rate performance; this shows that the formation temperature has an important influence on the rate performance of the battery. However, when lithium hexafluorophosphate is replaced with other lithium salts, the performance response in low temperature environment is worse ( Figure 10-12 This is because lithium hexafluorophosphate will produce LiF in CEI during low-temperature formation, thereby improving the performance of the battery, which is consistent with the XPS results. In order to explore the effect of the formation process on battery performance at low temperatures in more detail, the inventors replaced the constant current-constant voltage charging method with a constant current ( Fig. 9 ), it was found that the rate performance of the battery can also be improved, indicating that the present invention is not limited to the formation charge and discharge method.

[0127] In order to explore in more detail the effect of low temperature formation on battery performance, Example 4, Example 7, Comparative Example 4, and Comparative Example 12 are set to represent the low temperature charge and discharge group, the low temperature charge and normal temperature discharge group, the normal temperature charge and discharge group, and the normal temperature charge and low temperature discharge group, respectively. Fig.13 ); It was found that the battery would show excellent performance as long as it was charged at low temperature during formation.

[0128] The battery after low-temperature charging and formation not only exhibits excellent rate performance, but also exhibits excellent cycle stability and impedance performance under high temperature and high pressure environments.

[0129] The batteries prepared after the formation of Example 6 and Comparative Example 11 were subjected to cycle stability tests at 1C rate at 3V-4.5V. The results are as follows: Fig.14 As shown, the capacity retention rate after 200 cycles is 63.98%, which is better than the 36.9% stability data of Comparative Example 11 under high pressure.

[0130] The batteries prepared in Example 5 and the comparative example were subjected to cycle tests in a 3V-4.5V high voltage environment. The batteries were disassembled after 200 cycles. The scanning electron microscope images of the test materials showed that ( Fig.15 ), the results show that the structure of the positive electrode material of Example 5 does not change significantly after low-temperature formation, but cracks appear in the positive electrode particles of Comparative Example 11 formed at room temperature, indicating that the formed CEI is not stable enough, which leads to poor battery cycle stability.

[0131] The batteries of Example 4 and Comparative Example 4 were placed at 1C rate and 25°C to test the stability data. The results showed that ( Fig.16 ), the battery has excellent cycle stability at high rates. In addition, the battery prepared by the low-temperature formation method not only shows good cycle performance at room temperature, but also shows excellent cycle stability at a high temperature of 60°C ( Fig.17). The cyclic voltammetry test results at a scan rate of 0.1mV / s show that ( Fig.18 In a), the redox peak potential difference of the battery after low-temperature formation is small, indicating good electrochemical reversibility. Fig.18 Figure b shows that the impedance value of the battery formed in a low temperature environment is smaller at 25°C, which is more conducive to the rapid transmission of lithium ions in the battery. The activation energy of the battery is calculated by testing the impedance of the battery at different temperatures. The results are as follows Fig.19 As shown in Figure 2, the activation energy of the battery formed at -5°C is 49.60 kJ mol -1 , compared to 53.92 kJ mol at room temperature 25°C -1 The activation energy is lower.

[0132] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A formation method for a low-temperature lithium-ion battery, characterized in that: The following steps are involved: The assembled lithium-ion battery is subjected to cyclic charge and discharge, wherein the charging temperature during the charge and discharge process is between -80°C and 10°C; The charging method is constant current-constant voltage charging, specifically: the battery is left to stand, constant current I is charged to the rated voltage U, the rated voltage is maintained and the charging is continued until the current value is I / 2, and after the charging is completed, the constant current I is continued to be discharged to 3-3.5V; the standing time is 1-24h; the constant current I is 0.01-0.5C; the rated voltage U is 4.0-4.9V; The electrolyte of the lithium ion battery is a mixture of a solvent and lithium hexafluorophosphate, wherein the concentration of the lithium hexafluorophosphate is 0.5-2 mol / L.

2. The chemical formation method according to claim 1, characterized in that The charging temperature is -30℃ to 10℃.

3. The chemical formation method according to claim 1, characterized in that: The lithium-ion battery is assembled from a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator.

4. The chemical formation method according to claim 3, characterized in that: The material of the positive electrode plate includes one or more of a layered structure material, a spinel structure material, an olivine structure material, a polyanion structure material, an organic electrode material and a carbon material.

5. A lithium ion battery, characterized in that: The battery is formed by the formation method according to any one of claims 1 to 4.

6. The battery according to claim 5, characterized in that The battery is used in a temperature range of 80°C to -130°C.

7. The battery according to claim 5, characterized in that The battery uses a voltage range of 1-4.9V.

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