Lithium ion battery

Abstract

Provided is a lithium ion battery, used for solving the problems in the prior art of a battery being prone to be short circuited and the electrical performance of the battery being affected by the excessively low electrical conductivity when the electrical conductivity of a lithium ion battery is increased. The lithium ion battery comprises a positive electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode current collector, a primer coating, and a positive electrode material layer; the primer coating is located on the surface of the positive electrode current collector; the positive electrode material layer is located on the surface of the primer coating away from the positive electrode current collector; and the electrical conductivity of the electrolyte, the electrical conductivity of the primer coating, and the electrical conductivity of the positive electrode material layer meet the following conditions: (I), wherein σe is the electrical conductivity of the electrolyte, and has a unit of mS / cm, σa is the electrical conductivity of the primer coating, and has a unit of mS / cm, σc is the electrical conductivity of the positive electrode material layer, and has a unit of mS / cm, the electrical conductivity σe of the electrolyte is 6.5-8.5 mS / cm, the electrical conductivity σa of the primer coating is 1-6 mS / cm, and the electrical conductivity σc of the positive electrode material layer is 1.6-12.5 mS / cm. According to the lithium ion battery provided by the present invention, the short circuit of the lithium ion battery can be reduced, the cycle performance of the battery is improved, high-temperature combustion or explosion of the battery is avoided, and the pass rate of the battery in the nail penetration test is improved.

Description

A lithium-ion battery

[0001] This application is based on the Chinese invention application with application number 202410081615.5 filed on January 19, 2024, entitled “A lithium-ion battery”, and claims priority. Technical Field

[0002] The present application belongs to the technical field of lithium-ion batteries, and specifically relates to a lithium-ion battery. Background Art

[0003] As lithium-ion batteries are increasingly used in production and life, the safety performance of lithium-ion batteries during use needs to be highly valued. There are four short-circuit modes that occur when lithium-ion batteries fail safely, namely, positive current collector-negative active layer, positive current collector-negative current collector, positive active layer-negative current collector, and positive active layer-negative active layer. Among them, the short circuit between the positive current collector and the negative active layer is the most dangerous short-circuit mode because it has the highest heat generation power.

[0004] To improve the safety of lithium-ion batteries, a safety coating is applied to the surface of the positive current collector. This prevents short circuits between the positive current collector and the negative active material layer, while also shifting the short circuit pattern from safety coating to negative current collector and vice versa. The conductivity of the safety coating affects the current magnitude and heat generation during short circuits. A safety coating with high conductivity generates heat faster, impacting battery safety. A safety coating with low conductivity offers high safety but significantly hinders electron conduction between the positive active layer and the positive current collector, affecting the battery's charge, discharge, and cycling performance. The conductivity of the positive active layer, due to its short circuit pattern with the negative active layer and the negative current collector, also affects the battery's safety, charge, discharge, and cycling performance. High conductivity facilitates lithium ion migration and electron conduction during charge and discharge, but increases short-circuit current and heat generation during short circuits, hindering safety. Low conductivity in the positive electrode active layer helps reduce short-circuit current and heat generation, but it also affects lithium ion migration and electron transfer, impacting the charge, discharge, and cycling performance of lithium-ion batteries. Furthermore, electrolyte conductivity also impacts the safety, charge, discharge, and cycling performance of lithium-ion batteries. While improving safety, high electrical performance requirements must also be met. Increasing electrolyte conductivity reduces the battery's internal resistance, increasing the risk of thermal failure caused by a short circuit during a needle penetration test. However, excessively low electrolyte conductivity can negatively impact the battery's electrical performance. Summary of the Invention

[0005] To solve the problems in the prior art that when the conductivity of lithium ion batteries increases, the batteries are prone to short circuits, and that too low conductivity affects the electrical performance of the batteries, a lithium ion battery is provided.

[0006] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0007] The present invention provides a lithium-ion battery, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector, an undercoat layer, and a positive electrode material layer, wherein the undercoat layer is located on the surface of the positive electrode current collector, and the positive electrode material layer is located on the surface of the undercoat layer facing away from the positive electrode current collector, wherein the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer satisfy the following conditions:

[0008] Wherein, σe is the conductivity of the electrolyte, in mS / cm;

[0009] σa is the conductivity of the base coating, in mS / cm;

[0010] σc is the conductivity of the positive electrode material layer, in mS / cm;

[0011] The electrolyte conductivity σe is 6.5 to 8.5 mS / cm;

[0012] The conductivity σa of the base coating is 1 to 6 mS / cm;

[0013] The electrical conductivity σc of the positive electrode material layer is 1.6 to 12.5 mS / cm.

[0014] Optionally, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0015] Optionally, the electrolyte conductivity is 7.14-8.05 mS / cm.

[0016] Optionally, the conductivity of the primer layer is 1.2 to 5.5 mS / cm.

[0017] Optionally, the conductivity of the positive electrode material layer is 2.2 to 6.5 mS / cm.

[0018] Optionally, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0019] The electrolyte conductivity σe is 7.14 to 8.05 mS / cm;

[0020] The conductivity σa of the primer layer is 1.2 to 2.3 mS / cm;

[0021] The electrical conductivity σc of the positive electrode material layer is 3.04-4.5 mS / cm.

[0022] Optionally, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0023] The electrolyte conductivity σe is 7.14 to 8.05 mS / cm;

[0024] The conductivity σa of the primer layer is 1.6 to 5.5 mS / cm;

[0025] The electrical conductivity σc of the positive electrode material layer is 2.2 to 6.5 mS / cm.

[0026] Optionally, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0027] The electrolyte conductivity σe is 7.14 to 8.05 mS / cm;

[0028] The conductivity σa of the primer layer is 2.2 to 2.4 mS / cm;

[0029] The electrical conductivity σc of the positive electrode material layer is 3.04-4.5 mS / cm.

[0030] Optionally, the undercoat layer includes a first active material and an inorganic filler, and the positive electrode material layer includes a second active material. The mass of the first active material in the undercoat layer is 0% to 98%, the inorganic filler in the undercoat layer is 0% to 98%, and the mass of the second active material in the positive electrode material layer is 95% to 98.5%.

[0031] Optionally, the inorganic filler includes one or more of aluminum oxide, magnesium oxide and calcium carbonate.

[0032] The lithium-ion battery provided by the present invention has the following characteristics: when the conductivity of the electrolyte is 6.5 to 8.5 mS / cm, the conductivity of the undercoat layer is 1 to 6 mS / cm, and the conductivity of the positive electrode material layer is 1.6 to 12.5 mS / cm, and the conductivity of the three all satisfy the relationship When the positive electrode collector is in direct contact with the negative electrode active material layer, the occurrence of short circuit of the lithium ion battery can be effectively reduced while improving the battery cycle performance; since the short circuit heat generation rate of the positive electrode current collector in direct contact with the negative electrode active material layer is the highest, which seriously affects the safety performance of the lithium ion battery, the primer layer and the positive electrode material layer are arranged on the positive electrode sheet, and the conductivity of the two both satisfy the specific value range of the above relationship, thereby improving the battery short circuit caused by the excessively fast heat generation rate under high conductivity and the adverse effect of too low conductivity on the battery cycle performance; since the conductivity of the electrolyte also affects the battery safety and cyclability, the inventors have improved the battery short circuit caused by the excessively fast heat generation rate under high conductivity and the adverse effect of too low conductivity on the battery cycle performance. A large number of tests on the conductivity of the electrolyte found that when the conductivity of the electrolyte is in the range of 6.5 to 8.5 mS / cm and also satisfies the above relationship, the short circuit of the corresponding lithium-ion battery is alleviated and the cycle performance is effectively improved; in summary, when the conductivity of the electrolyte, the conductivity of the undercoat layer and the conductivity of the positive electrode material layer of the present application satisfy the above relationship, the probability of short circuit inside the lithium-ion battery can be effectively reduced, thereby reducing the heat generation of the battery, avoiding high-temperature combustion or explosion of the lithium-ion battery, improving the battery cycle performance, and also helping to improve the pass rate of the lithium-ion battery in the needle penetration test. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] The present invention provides a lithium-ion battery, comprising a positive electrode sheet and an electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector, an undercoat layer, and a positive electrode material layer, wherein the undercoat layer is located on the surface of the positive electrode current collector, and the positive electrode material layer is located on the surface of the undercoat layer facing away from the positive electrode current collector, wherein the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer satisfy the following conditions:

[0035] Wherein, σe is the conductivity of the electrolyte, in mS / cm;

[0036] σa is the conductivity of the base coating, in mS / cm;

[0037] σc is the conductivity of the positive electrode material layer, in mS / cm;

[0038] The electrolyte conductivity σe is 6.5 to 8.5 mS / cm;

[0039] The conductivity σa of the base coating is 1 to 6 mS / cm;

[0040] The electrical conductivity σc of the positive electrode material layer is 1.6 to 12.5 mS / cm.

[0041] Specifically, in the lithium-ion battery provided by the present invention, when the conductivity of the electrolyte is 6.5 to 8.5 mS / cm, the conductivity of the undercoat layer is 1 to 6 mS / cm, and the conductivity of the positive electrode material layer is 1.6 to 12.5 mS / cm, and the conductivity of the three all satisfy the relationship When the positive electrode collector is in direct contact with the negative electrode active material layer, the occurrence of short circuit of the lithium ion battery can be effectively reduced while improving the battery cycle performance; since the short circuit heat generation rate of the positive electrode current collector in direct contact with the negative electrode active material layer is the highest, which seriously affects the safety performance of the lithium ion battery, the primer layer and the positive electrode material layer are arranged on the positive electrode sheet, and the conductivity of the two both satisfy the specific value range of the above relationship, thereby improving the battery short circuit caused by the excessively fast heat generation rate under high conductivity and the adverse effect of too low conductivity on the battery cycle performance; since the conductivity of the electrolyte also affects the battery safety and cyclability, the inventors have improved the battery short circuit caused by the excessively fast heat generation rate under high conductivity and the adverse effect of too low conductivity on the battery cycle performance. A large number of tests on the conductivity of the electrolyte found that when the conductivity of the electrolyte is in the range of 6.5 to 8.5 mS / cm and also satisfies the above relationship, the short circuit of the corresponding lithium-ion battery is alleviated and the cycle performance is effectively improved; in summary, when the conductivity of the electrolyte, the conductivity of the undercoat layer and the conductivity of the positive electrode material layer of the present application satisfy the above relationship, the probability of short circuit inside the lithium-ion battery can be effectively reduced, thereby reducing the heat generation of the battery, avoiding high-temperature combustion or explosion of the lithium-ion battery, improving the battery cycle performance, and also helping to improve the pass rate of the lithium-ion battery in the needle penetration test.

[0042] In some embodiments, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0043] By further limiting the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer to meet the above conditions, the probability of short circuit inside the lithium-ion battery can be effectively reduced, the battery cycle performance can be improved, and it is also beneficial to increase the pass rate of the lithium-ion battery in the needle penetration test.

[0044] In specific embodiments, the electrolyte conductivity can be 6.5 mS / cm, 7.0 mS / cm, 7.14 mS / cm, 7.2 mS / cm, 7.4 mS / cm, 7.6 mS / cm, 7.8 mS / cm, 7.9 mS / cm, 8.0 mS / cm, 8.02 mS / cm, 8.03 mS / cm, 8.05 mS / cm, 8.07 mS / cm or 8.5 mS / cm.

[0045] In a preferred embodiment, the electrolyte conductivity is 7.14-8.05 mS / cm.

[0046] In specific embodiments, the conductivity of the primer layer can be 1.0 mS / cm, 1.2 mS / cm, 1.4 mS / cm, 1.6 mS / cm, 1.8 mS / cm, 2.0 mS / cm, 2.3 mS / cm, 2.5 mS / cm, 2.7 mS / cm, 3.0 mS / cm, 3.2 mS / cm, 3.4 mS / cm, 3.6 mS / cm, 3.8 mS / cm, 4.2 mS / cm, 4.4 mS / cm, 4.6 mS / cm, 5.0 mS / cm, 5.2 mS / cm, 5.5 mS / cm or 6.0 mS / cm.

[0047] In a preferred embodiment, the conductivity of the primer layer is 1.2-5.5 mS / cm.

[0048] Applying a coating on the surface of the positive electrode current collector can prevent short circuits between the positive electrode current collector and the negative electrode active material layer. The conductivity of the coating also affects the safety, charge and discharge, and cycle performance of the lithium-ion battery. A coating with high conductivity generates heat at a faster rate, affecting the safety of the battery. A coating with low conductivity has high safety, but seriously hinders the electron conduction between the positive electrode active layer and the positive electrode current collector, affecting the charge and discharge and cycle performance of the lithium-ion battery.

[0049] In a specific embodiment, the conductivity of the positive electrode material layer can be 2.0mS / cm, 2.2mS / cm, 2.3mS / cm, 2.6mS / cm, 3.1mS / cm, 3.5mS / cm, 4.0mS / cm, 4.6mS / cm, 5.0mS / cm, 5.5mS / cm, 6.0mS / cm, 6.5mS / cm or 7.0mS / cm in a preferred embodiment.

[0050] In a preferred embodiment, the conductivity of the positive electrode material layer is 2.2-6.5 mS / cm.

[0051] In some embodiments, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0052] The electrolyte conductivity σe is 7.14 to 8.05 mS / cm;

[0053] The conductivity σa of the primer layer is 1.2 to 2.3 mS / cm;

[0054] The electrical conductivity σc of the positive electrode material layer is 3.04-4.5 mS / cm.

[0055] It should be noted that the inventors have shown through experimental verification that when the lithium-ion battery meets the above-mentioned restrictions and setting parameters at the same time, the probability of short circuit inside the lithium-ion battery can be effectively reduced, the heat generated by the battery can be reduced, and high-temperature combustion or explosion of the lithium-ion battery can be avoided, thereby improving the performance of the lithium-ion battery in the needle penetration test.

[0056] In some embodiments, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0057] The electrolyte conductivity σe is 7.14 to 8.05 mS / cm;

[0058] The conductivity σa of the primer layer is 1.6 to 5.5 mS / cm;

[0059] The electrical conductivity σc of the positive electrode material layer is 2.2 to 6.5 mS / cm.

[0060] It should be noted that lower or higher conductivity of the undercoat layer and the positive electrode material layer is not conducive to improving battery safety and cycle performance. The inventors have previously demonstrated through a large number of experimental studies that when the values ​​of the conductivity of the lithium-ion battery electrolyte, the conductivity of the undercoat layer and the conductivity of the positive electrode material layer are within the above range, the cycle retention rate of the corresponding lithium-ion battery is effectively improved, that is, the cycle performance of the lithium-ion battery under the above-mentioned restrictions and parameter settings is excellent.

[0061] In some embodiments, the conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer meet the following conditions:

[0062] The electrolyte conductivity σe is 7.14 to 8.05 mS / cm;

[0063] The conductivity σa of the primer layer is 2.2 to 2.4 mS / cm;

[0064] The electrical conductivity σc of the positive electrode material layer is 3.04-4.5 mS / cm.

[0065] It should be noted that, in a large number of early experimental verifications, when the values ​​of the electrolyte conductivity, the bottom coating conductivity and the positive electrode material layer conductivity of the lithium-ion battery are within the above ranges, the corresponding lithium-ion battery's needle penetration pass rate and cycle retention rate are improved, that is, when the various parameter settings of the lithium-ion battery simultaneously meet the above-mentioned restrictive conditions and relationship formulas of this application, the needle penetration test pass rate and cycle performance of the lithium-ion battery are both improved at the same time.

[0066] In some embodiments, the primer layer has a thickness of 3 to 8 μm.

[0067] It should be noted that the thickness of the primer layer affects the transmission distance of electrons within the coating. A thin primer layer has a shorter electron transmission distance, thereby improving conductivity. However, when the coating thickness is too thick, it is difficult for current to penetrate the coating, resulting in a decrease in conductivity.

[0068] Through a large number of early experimental tests, the inventors concluded that when the thickness of the primer layer is between 3 and 8 μm, the conductivity of the positive electrode material layer satisfies the relationship.

[0069] In some embodiments, the undercoat layer includes a first active material and an inorganic filler, the positive electrode material layer includes a second active material, the mass of the first active material in the undercoat layer accounts for 0% to 98%, the inorganic filler in the undercoat layer accounts for 0% to 98%, and the mass of the second active material in the positive electrode material layer accounts for 95% to 98.5%.

[0070] In some embodiments, the conductivity of the undercoat layer (σa) is less than the conductivity of the positive electrode material layer (σc), that is, σa<σc.

[0071] It should be noted that the base coating layer includes the inorganic filler. In theory, the conductivity of the base coating layer is lower than the conductivity of the positive electrode material layer. Since the high-conductivity base coating layer generates heat at a fast rate, which affects the safety of the battery, the addition of inorganic fillers to the base coating layer in this application is beneficial to improving the safety of lithium-ion batteries.

[0072] This point should also be recognized from the description of the "safety coating" and the specific embodiments provided in the disclosure. This point is the difference between the primer layer and the positive electrode material layer. By limiting this point, the difference between the primer layer and the conventional positive electrode material layer can be distinguished.

[0073] In some embodiments, the first active material and the second active material include one or more of lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, and nickel cobalt lithium manganese oxide ternary materials.

[0074] In some embodiments, the inorganic filler includes one or more of aluminum oxide, magnesium oxide, and calcium carbonate.

[0075] It should be noted that the undercoat layer and the positive electrode material layer also include a positive electrode binder and a positive electrode conductor. The positive electrode binder, positive electrode conductor and first active material are blended to obtain the undercoat layer, and the positive electrode binder, positive electrode conductor and second active material are blended to obtain the positive electrode material layer.

[0076] The positive electrode binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, and styrene butadiene rubber.

[0077] The positive electrode conductive agent includes at least one of conductive carbon black, conductive graphite, conductive carbon fiber, carbon nanotube, graphene and reduced graphene oxide.

[0078] In some embodiments, the positive electrode sheet further includes a positive electrode current collector, and the positive electrode current collector is aluminum foil.

[0079] In some embodiments, the lithium-ion battery further includes a separator and a negative electrode sheet, and the separator is placed between the positive electrode sheet and the negative electrode sheet to form the lithium-ion battery.

[0080] The negative electrode sheet further includes a negative electrode coating, wherein the negative electrode coating includes a negative electrode active material, and the negative electrode active material includes one or more of a carbon-based negative electrode, a silicon-based negative electrode, and a lithium negative electrode.

[0081] The carbon-based negative electrode is selected from at least one of graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres; the silicon-based negative electrode is selected from at least one of silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials; the lithium negative electrode is specifically selected from metallic lithium or lithium alloys.

[0082] Specifically, when the lithium-ion battery formed by the positive electrode sheet, the negative electrode sheet and the separator satisfies the relationship described in the present application, the probability of a short circuit inside the lithium-ion battery can be effectively reduced, thereby reducing the heat generated by the battery, avoiding high-temperature combustion or explosion of the lithium-ion battery, improving the battery cycle, and also helping to improve the pass rate of the lithium-ion battery in the needle penetration and screw extrusion tests.

[0083] The present invention is further described below with reference to the following examples.

[0084] Table 1

[0085] Example 1

[0086] This embodiment is used to illustrate a lithium ion battery and a preparation method disclosed in the present invention, including the following steps:

[0087] Preparation of positive electrode

[0088] In NMP solvent, a preset weight of binder PVDF, conductive agent Super P, CNT and lithium iron phosphate were added and stirred thoroughly to obtain a primer slurry. The conductivity of the primer was 2.3 mS / cm.

[0089] In NMP solvent, a preset weight of binder PVDF, conductive agent Super P, CNT and lithium cobalt oxide were added and stirred thoroughly to obtain a positive electrode material layer slurry. The positive electrode material layer had an electrical conductivity of 3.04 mS / cm.

[0090] The primer slurry is evenly coated on the positive electrode current collector, and then the positive electrode material layer slurry is coated on the surface of the first coating slurry, and the positive electrode sheet is obtained by drying, rolling and stripping.

[0091] Preparation of negative electrode sheet

[0092] Take (mass ratio) graphite, conductive carbon, sodium carboxymethyl cellulose and styrene-butadiene rubber, first add sodium carboxymethyl cellulose to pure water, stir thoroughly, then add conductive carbon, stir thoroughly, continue to add graphite, stir thoroughly, and obtain the required negative electrode slurry;

[0093] The prepared negative electrode slurry is evenly coated on the negative electrode current collector, dried, rolled and sliced ​​to obtain negative electrode sheets.

[0094] Preparation of electrolyte

[0095] Ethylene carbonate, diethyl carbonate and ethyl methyl carbonate are mixed to obtain an organic solvent, lithium salt is dissolved in the organic solvent, and the mixture is uniformly mixed to obtain an electrolyte solution, wherein the electrolyte solution has an electrical conductivity of 8.05 mS / cm.

[0096] Preparation of lithium-ion batteries

[0097] The diaphragm is placed between the positive electrode sheet and the negative electrode sheet, and the tabs are welded at the positive and negative electrode positions respectively. The bare cell is prepared by winding or lamination process, and the bare cell is placed in the battery shell, injected with the above-mentioned electrolyte and packaged. After static, hot pressing and formation processes, a lithium-ion battery is obtained.

[0098] Examples 2 to 8

[0099] Examples 2 to 8 are used to illustrate a lithium ion battery and a preparation method disclosed in the present invention, and include most of the operations of Example 1, except that:

[0100] The values ​​of the electrolyte conductivity, the bottom coating conductivity, the positive electrode material layer conductivity and the relationship in Examples 2 to 8 are based on the parameters set in Examples 2 to 8 in Table 1.

[0101] Comparative Examples 1 to 14

[0102] Comparative Examples 1 to 14 are used to illustrate a lithium ion battery and a preparation method disclosed in the present invention, and include most of the operations of Example 1, except that:

[0103] The conductivity of the electrolyte, the conductivity of the undercoat layer, and the conductivity of the positive electrode material layer in Comparative Examples 1 to 14 are based on the conductivity values ​​described in Comparative Examples 1 to 14 in Table 1.

[0104] Performance Testing

[0105] The following performance tests were performed on Examples 1 to 8 and Comparative Examples 1 to 14 prepared above:

[0106] Conductivity test method:

[0107] Cut the electrode into a 6cm×10cm rectangle and place it flatly in the fixture. Place the fixture in the IEST BER1300 electrode resistance meter and test it under a pressure of 25MPa, holding time of 15s, temperature: 25℃, humidity (%RH): 70

[0108] Lithium-ion battery puncture test method:

[0109] Use the BE9002CY battery puncture tester to place a fully charged battery into the instrument. A 3mm diameter steel needle is inserted into the geometric center of the cell plane at a speed of 15mm / s until it penetrates the entire battery. After puncture, the steel needle remains in the battery for 30 seconds before being removed.

[0110] Normal temperature cycle performance test

[0111] The formed sodium ion battery was placed at room temperature (25℃±3℃), charged at a constant current of 1C to 3.9V, then charged at a constant voltage of 3.9V, with a cut-off current of 0.05C, and discharged at a constant current of 1C to 1.5V, and this cycle was repeated for 1000 cycles;

[0112] The capacity retention rate after 1000 cycles at 25°C is calculated using the following formula:

[0113] Capacity retention after 1000 cycles at 25°C (%) = discharge capacity at the 1000th cycle / discharge capacity at the first cycle × 100%.

[0114] Fill in the test results in Table 2.

[0115] Table 2

[0116] From the test results in Table 2, it can be seen that the sodium ion batteries prepared by using the parameters set in Examples 1 to 8 have better needle penetration rates and room temperature cycle capacity retention rates than comparative examples 1 to 14 as a whole; from the test results of Examples 1 to 8 and comparative examples 1 to 14, it can be seen that when the conductivity of the electrolyte, the conductivity of the undercoat layer and the conductivity of the positive electrode material layer meet the conditions When the electrolyte conductivity σe is 6.5-8.5 mS / cm, the bottom coating conductivity σa is 1-6 mS / cm, and the positive electrode material layer conductivity σc is 1.6-12.5 mS / cm, it is beneficial to improve the battery short circuit and the adverse effect of too low conductivity on the battery cycle performance, and the corresponding lithium ion battery short circuit situation is alleviated, and the cycle performance is effectively improved; in addition, in Example 7, the bottom coating conductivity and the positive electrode material layer conductivity are lower than those of other embodiments as a whole. In Example 8, the bottom coating conductivity and the positive electrode material layer conductivity are larger. The lower or higher conductivity of the bottom coating and the positive electrode material layer is not conducive to improving the battery safety and cycle performance. Therefore, the overall test results of Examples 7 and 8 are slightly worse than those of other embodiments.

[0117] Comparing the test results of Examples 1 to 8 and Comparative Examples 1 to 14, it can be seen that in Comparative Examples 1 to 3, the conductivity of the primer layer and The range is not satisfied. Comparative Examples 4 to 13 also have electrolyte conductivity, bottom coating conductivity, positive electrode material layer conductivity and If one or more of the factors do not meet the range limit, this condition is not conducive to the improvement of battery cycle performance and the improvement of short circuit conditions; in summary, when the electrolyte conductivity, the bottom coating conductivity and the positive electrode material layer conductivity simultaneously meet the range values ​​and relationship formula specified in this application, the probability of short circuit inside the lithium-ion battery can be effectively reduced, the heat generation of the battery can be reduced, the high-temperature combustion or explosion of the lithium-ion battery can be avoided, and the battery cycle performance can be improved.

[0118] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode sheet and an electrolyte. The positive electrode sheet includes a positive electrode current collector, a bottom coating layer, and a positive electrode material layer. The bottom coating layer is located on the surface of the positive electrode current collector, and the positive electrode material layer is located on the surface of the bottom coating layer facing away from the positive electrode current collector. The conductivity of the electrolyte, the conductivity of the bottom coating layer, and the conductivity of the positive electrode material layer satisfy the following conditions: Among them, σe is the electrolyte conductivity, with the unit of mS / cm; σa is the bottom coating conductivity, with the unit of mS / cm; σc is the positive electrode material layer conductivity, with the unit of mS / cm; The electrolyte conductivity σe is 6.5 - 8.5 mS / cm; The bottom coating conductivity σa is 1 - 6 mS / cm; The positive electrode material layer conductivity σc is 1.6 - 12.5 mS / cm.

2. The lithium-ion battery according to claim 1, characterized in that, The electrolyte conductivity, the bottom coating conductivity, and the positive electrode material layer conductivity satisfy the following conditions:

3. A lithium-ion battery according to claim 1, characterized in that, The electrolyte conductivity is 7.14 - 8.05 mS / cm.

4. A lithium-ion battery according to claim 1, characterized in that, The bottom coating conductivity is 1.2 - 5.5 mS / cm.

5. A lithium-ion battery according to claim 1, characterized in that, The positive electrode material layer conductivity is 2.2 - 6.5 mS / cm.

6. A lithium-ion battery according to claim 1, characterized in that, The electrolyte conductivity, the bottom coating conductivity, and the positive electrode material layer conductivity satisfy the following conditions: The electrolyte conductivity σe is 7.14 - 8.05 mS / cm; The bottom coating conductivity σa is 1.2 - 2.3 mS / cm; The positive electrode material layer conductivity σc is 3.04 - 4.5 mS / cm.

7. A lithium-ion battery according to claim 1, characterized in that, The electrolyte conductivity, the bottom coating conductivity, and the positive electrode material layer conductivity satisfy the following conditions: The electrolyte conductivity σe is 7.14 - 8.05 mS / cm; The bottom coating conductivity σa is 1.6 - 5.5 mS / cm; The positive electrode material layer conductivity σc is 2.2 - 6.5 mS / cm.

8. A lithium-ion battery according to claim 1, characterized in that, The electrolyte conductivity, the bottom coating conductivity, and the positive electrode material layer conductivity satisfy the following conditions: The electrolyte conductivity σe is 7.14 - 8.05 mS / cm; The bottom coating conductivity σa is 2.2 - 2.4 mS / cm; The positive electrode material layer conductivity σc is 3.04 - 4.5 mS / cm.

9. A lithium-ion battery according to claim 1, characterized in that, The bottom coating includes a first active material and an inorganic filler, the positive electrode material layer includes a second active material, the mass ratio of the first active material in the bottom coating is 0% - 98%, the mass ratio of the inorganic filler in the bottom coating is 0% - 98%, and the mass ratio of the second active material in the positive electrode material layer is 95% - 98.5%.

10. A lithium-ion battery according to claim 9, characterized in that, The inorganic filler includes one or more of alumina, magnesia, and calcium carbonate.

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