A lithium-ion battery

Abstract

The application provides a lithium ion battery. The lithium ion battery of the application comprises a negative electrode sheet, and the negative electrode sheet comprises a negative electrode current collector, and the elongation of the negative electrode current collector is greater than 7%. By limiting the elongation of the negative electrode current collector, the current collector has good toughness, and after tensile deformation, the current collector is not easy to break, so that the safety performance of the lithium ion battery can be ensured.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and relates to a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have been widely applied in smart phones, notebook computers, Bluetooth earphones and wearable devices due to their high platform voltage, large energy density, no memory effect and long service life.

[0003] Existing lithium ion batteries are usually packaged by aluminum plastic films, which have the advantages of light weight, thin thickness and flexible design, and have obvious advantages in specific capacity and internal resistance compared with traditional lithium battery packaging materials such as aluminum shell and steel shell. However, the strength of the aluminum plastic film is low, and the ability to resist impact force is weak. When a heavy object impacts, the battery is very easy to break, causing a serious internal short circuit and a thermal runaway phenomenon. SUMMARY

[0004] The present application provides a lithium ion battery, which has good safety performance by controlling the elongation of the negative current collector.

[0005] The present application provides a lithium ion battery, which includes a negative electrode sheet, and the negative electrode sheet includes a negative current collector, and the elongation of the negative current collector is greater than 7%.

[0006] The lithium ion battery as described above, wherein the elongation of the negative current collector is 10% to 20%.

[0007] The lithium ion battery as described above, wherein the elongation of the negative electrode sheet is greater than 7%.

[0008] The lithium ion battery as described above, wherein the elongation of the negative electrode sheet is 10% to 20%.

[0009] The lithium ion battery as described above, wherein the compressive strength of the negative electrode sheet is greater than 10 MPa.

[0010] The lithium ion battery as described above, wherein the compressive strength of the negative electrode sheet is 15 to 50 MPa.

[0011] The lithium ion battery as described above, wherein the elongation of the negative current collector is δ%, the thickness of the negative current collector is D, and D / δ is less than 1.

[0012] The lithium ion battery as described above, wherein D / δ is less than 1.

[0013] The lithium ion battery as described above, wherein the thickness of the negative current collector is 6 to 14 μm.

[0014] The lithium ion battery as described above, wherein the lithium ion battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector and a safety coating layer arranged on at least one functional surface of the positive electrode current collector; the safety coating layer comprises 62% to 96% of a filler, 0.1% to 8% of a conductive agent and 3% to 30% of a binder in terms of mass percentage.

[0015] The lithium ion battery of the present application can ensure the safety performance of the lithium ion battery by limiting the elongation of the negative electrode current collector to be greater than 7%, so that the current collector has good toughness and is not prone to breakage after tensile deformation when heavy impact or mechanical abuse occurs, thereby avoiding the situation that the positive electrode sheet pierces the separator after breakage, leading to short circuit of the battery. DETAILED DESCRIPTION

[0016] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described below in detail with reference to the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0017] The present application provides a lithium ion battery, comprising a negative electrode sheet, the negative electrode sheet comprises a negative electrode current collector and the elongation of the negative electrode current collector is greater than 7%.

[0018] The present application limits the elongation of the current collector in the negative electrode sheet to be greater than 7%, so that the current collector has good toughness and is not prone to breakage after tensile deformation when heavy impact or mechanical abuse occurs, thereby avoiding the situation that the positive electrode sheet pierces the separator after breakage, leading to short circuit of the battery, and ensuring the safety performance of the lithium ion battery.

[0019] It can be understood that the greater the elongation of the negative electrode current collector, the higher the safety performance of the battery, but the greater the elongation, the greater the thickness of the negative electrode current collector, which will cause loss of the energy density of the battery. In order to have both good safety performance and energy density of the battery, a negative electrode current collector with an elongation of 10% to 20% can be selected for use in the negative electrode sheet.

[0020] At the same time that the negative electrode current collector has high elongation, the elongation of the negative electrode sheet is controlled to be greater than 7%, and further controlled to be 10% to 20%, which can further ensure that the positive electrode sheet is not prone to breakage when heavy impact occurs, and improve the safety performance of the battery. Under normal circumstances, the elongation of the negative electrode sheet is affected by both the negative electrode current collector and the negative electrode active material layer. When the negative electrode active material layer remains unchanged, the higher the elongation of the negative electrode current collector, the higher the elongation of the negative electrode sheet. At the same time, the adhesion effect of the negative electrode active material and the negative electrode current collector also affects the elongation of the negative electrode sheet to some extent. Therefore, the elongation of the negative electrode sheet can be adjusted by adjusting the elongation of the negative electrode current collector and the negative electrode active layer to meet the above range.

[0021] The elongation of the negative current collector and the negative sheet in the present application is tested by the following test method:

[0022] The elongation of the negative current collector: the negative current collector is cut into a sample with a width of 15 mm, and then placed on a tensile testing machine, the initial length of the sample is 50 mm, and the sample is stretched at a speed of 100 mm / s until the sample is broken. Its elongation δ% = (breaking length-initial length) / initial length.

[0023] The elongation of the negative sheet: the negative sheet is cut into a sample with a width of 15 mm, and then placed on a tensile testing machine, the initial length of the sample is 50 mm, and the sample is stretched at a speed of 100 mm / min until the sample is broken. Its elongation δ% = (breaking length-initial length) / initial length.

[0024] By selecting a negative current collector and a negative sheet with high elongation, the negative sheet can have high compressive strength. The inventors found in research that when the compressive strength of the negative sheet is >10 MPa, further in the range of 15-50 MPa, it is more conducive to the excellent safety performance of the battery under heavy impact.

[0025] As the thickness of the negative current collector increases, the safety performance of the lithium ion battery can also be improved accordingly, but at the same time it will also cause the corresponding decrease of the volume energy density of the battery. In order to have both the safety performance and the energy density of the lithium ion battery, the thickness of the negative current collector can be set to 6-14 μm.

[0026] Further, the thickness of the negative current collector is D, the elongation of the negative current collector is δ%, when the thickness D of the negative current collector is 6-14 μm, D / δ<1, further D / δ<0.8, while ensuring good safety performance of the battery, it can further avoid the loss of energy density.

[0027] The negative sheet of the present application further includes an active material layer provided on at least one functional surface of the negative current collector. The types of the negative current collector and the active material layer of the present application can be selected from the commonly used negative current collector or active material layer in the art. The functional surface of the negative current collector refers to the two largest surfaces on the negative current collector, which are used for the coating of the active material layer.

[0028] The lithium ion battery of the present application further includes a positive sheet, which includes a positive current collector and a safety coating on at least one functional surface of the positive current collector, wherein the safety coating includes 62%-96% of a filler, 0.1%-8% of a conductive agent, and 3%-30% of a binder by mass percentage.

[0029] The positive electrode current collector can be selected from the positive electrode current collectors commonly used in the art, such as aluminum foil. The functional surface of the positive electrode current collector refers to the two largest surfaces of the positive electrode current collector, which are used for the coating of the functional layer. The functional layer can be either a safety coating or a positive electrode active material layer.

[0030] The positive electrode current collector comprises a first functional surface and a second functional surface. In one alternative embodiment, the positive electrode current collector is provided with a safety coating on the first functional surface, and a first positive electrode active material layer is further provided on the surface of the safety coating away from the positive electrode current collector. The positive electrode current collector is provided with a second positive electrode active material layer on the second functional surface. In another alternative embodiment, the positive electrode current collector is provided with a first safety coating on the first functional surface and a second safety coating on the second functional surface. The surface of the first safety coating away from the positive electrode current collector is provided with a first positive electrode active material layer, and the surface of the second safety coating away from the positive electrode current collector is provided with a second positive electrode active material layer. The compositions of the first positive electrode active material layer and the second positive electrode active material layer can be the same or different, and can be referred to the compositions of the positive electrode active material layers commonly used in the art.

[0031] The filler in the safety coating of the present application is selected from one or more of positive electrode active materials, oxides, carbides, and nitrides.

[0032] Specifically, the positive electrode active material includes but is not limited to at least one of lithium cobaltate, lithium nickel cobalt manganese phosphate, lithium iron phosphate, lithium manganese phosphate, lithium nickel cobalt aluminum phosphate, and lithium nickel cobalt manganese aluminum phosphate. When the filler is selected from the positive electrode active material, the average particle size of the positive electrode active material present in the safety coating is smaller than the average particle size of the positive electrode active material present in the positive electrode active material layer. The smaller the particle size, the more conducive to achieving a thin coating of the safety coating on the positive electrode current collector and a more dense coating. A thin coating can enable the lithium ion battery to have a higher energy density, and a dense safety coating can avoid the direct contact between the positive electrode current collector and the negative electrode active material during mechanical abuse, thereby preventing the occurrence of battery short circuit.

[0033] The oxide includes but is not limited to at least one of aluminum oxide, titanium oxide, magnesium oxide, zirconium oxide, antimony sulfide oxide, barium oxide, manganese oxide, silicon oxide, iron oxide, and triiron tetroxide.

[0034] The carbide is selected from metal carbide and / or non-metal carbide. The metal carbide includes but is not limited to at least one of titanium carbide, calcium carbide, chromium carbide, tantalum carbide, vanadium carbide, zirconium carbide, and tungsten carbide. The non-metal carbide includes but is not limited to at least one of boron carbide and silicon carbide.

[0035] The nitride is selected from metal nitride and / or non-metal nitride. The metal nitride includes at least one of lithium nitride, magnesium nitride, aluminum nitride, titanium nitride, and tantalum nitride.

[0036] In order to ensure that the lithium ion battery has good conductive performance in normal use, a conductive agent can be added in the safety coating, wherein the conductive agent is selected from one or more of conductive carbon black, acetylene black, graphite, graphene, carbon nanotube, and carbon nanofiber.

[0037] In addition, in order to enable the safety coating to be firmly connected with the positive current collector, the safety coating further comprises a bonding agent, wherein the bonding agent is selected from one or more of polyvinylidene fluoride, acrylic modified polyvinylidene fluoride, acrylate polymer, polyimide, butadiene styrene rubber, and benzene propyl rubber.

[0038] The above positive electrode sheet can be prepared by using conventional technical means in the art. Specifically, first, the raw materials for forming the safety coating are uniformly dispersed in a solvent to obtain a safety coating slurry, and the raw materials for forming the positive active layer are uniformly dispersed in a solvent to obtain a positive active layer slurry. Then, the safety coating slurry is coated on the surface of the positive current collector, and after drying, the safety coating is obtained. Then, the positive active layer slurry is coated on the safety coating, and after drying, the positive electrode sheet of the present application is obtained.

[0039] The present application does not make specific limitations on the coating method, and any one of gravure coating, extrusion coating, spraying, screen printing, etc. can be used to realize the coating of the safety coating slurry and the positive active layer slurry.

[0040] The present application does not make specific limitations on the solvent used in the preparation of the safety coating slurry and the positive active layer slurry, which can be, for example, N-methyl pyrrolidone.

[0041] The lithium ion battery of the present application further comprises a separator in addition to the positive electrode sheet and the negative electrode sheet, and the separator can be selected from conventional separators used in the art, such as PP film and PE film.

[0042] The lithium ion battery of the present application can be prepared by using conventional methods in the art. Specifically, the positive electrode sheet, the separator, and the negative electrode sheet are sequentially stacked, and then an electric core is obtained by lamination or winding process. Then, the above lithium ion battery can be obtained by going through processes such as baking, liquid injection, formation, and packaging.

[0043] In the following, the lithium ion battery provided by the present application will be described in detail through specific examples.

[0044] Unless otherwise specified, the reagents, materials, and instruments used in the following examples are conventional reagents, conventional materials, and conventional instruments in the art, which can be obtained by commercial purchase, and the reagents involved can also be synthesized by conventional methods in the art.

[0045] Example 1

[0046] The preparation of the lithium ion battery of the present embodiment comprises the following steps:

[0047] 1. Preparation of a positive electrode sheet

[0048] 1) Lithium iron phosphate, carbon black, and PVDF are mixed in a mass ratio of 90:3:7 to obtain a mixture, NMP is added to the mixture in a mass ratio of 4:6, and stirring is performed to obtain a safety coating slurry;

[0049] 2) Lithium cobaltate, carbon black, carbon nanotubes, and PVDF are mixed in a mass ratio of 96:1:1:2 to obtain a mixture, NMP is added to the mixture in a mass ratio of 3:7, and stirring is performed to obtain a positive active material layer slurry;

[0050] 3) The safety coating slurry is coated on both functional surfaces of the positive current collector aluminum foil, and drying is performed to obtain a safety coating, and then the positive active material layer slurry is coated on the surface of the safety coating, and drying is performed to obtain a positive electrode sheet;

[0051] The thickness of the positive current collector is 9 μm, the single-sided thickness of the safety coating is 4 μm, and the single-sided thickness of the positive active material layer is 45 μm.

[0052] 2. Preparation of a negative electrode sheet

[0053] 1) Artificial graphite, carbon black, butadiene rubber, and sodium carboxymethyl cellulose are mixed in a mass ratio of 96:1:1.5:1.5 to obtain a mixture, deionized water is added to the mixture in a mass ratio of 4:6, and stirring is performed to obtain a negative active material layer slurry;

[0054] 2) The negative active material layer slurry is coated on both functional surfaces of the negative current collector copper foil with an elongation of 12% by an extrusion coating process to obtain a negative electrode sheet;

[0055] The thickness of the negative current collector is 10 μm, and the single-sided thickness of the negative active material layer is 52 μm.

[0056] 3. Assembly of a lithium ion battery

[0057] 1) The above positive electrode sheet and the above negative electrode sheet are respectively subjected to rolling and slitting by using a rolling machine and a slitting machine, and then the positive electrode sheet and the negative electrode sheet are both welded with tabs and pasted with protective adhesive tape;

[0058] 2) A PE separator is placed between the positive electrode sheet and the negative electrode sheet for winding to obtain a winding core;

[0059] 3) An aluminum plastic film is punched using a punching mold, and then the winding core is packaged using the punched aluminum plastic film to obtain a battery core, which is baked to pass the moisture test and then injected with electrolyte;

[0060] 4) using lithium ion battery formation equipment, the battery is charged and discharged, the battery is hardened, and the capacity of the battery is sorted out;

[0061] 5) the battery is sealed and the edge is folded, and the lithium ion battery of the embodiment is obtained.

[0062] Example 2

[0063] The preparation of the lithium ion battery of the embodiment includes the following steps:

[0064] 1. Preparation of the positive electrode sheet

[0065] The preparation steps of the positive electrode sheet are consistent with those of Example 1.

[0066] 2. Preparation of the negative electrode sheet

[0067] 1) The artificial graphite, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 95:1:2.5:1.5 to obtain a mixture, deionized water is added to the mixture in a mass ratio of 4:6, and the negative electrode active material layer slurry is obtained by stirring;

[0068] 2) The negative electrode active material layer slurry is coated on the two functional surfaces of the negative electrode current collector copper foil with an elongation of 10% by extrusion coating to obtain the negative electrode sheet;

[0069] The thickness of the negative electrode current collector is 8 μm, and the single-sided thickness of the negative electrode active material layer is 52 μm.

[0070] 3. Assembly of the lithium ion battery

[0071] The assembly steps of the lithium ion battery are consistent with those of Example 1.

[0072] Example 3

[0073] The preparation of the lithium ion battery of the embodiment includes the following steps:

[0074] 1. Preparation of the positive electrode sheet

[0075] The preparation steps of the positive electrode sheet are consistent with those of Example 1.

[0076] 2. Preparation of the negative electrode sheet

[0077] 1) The artificial graphite, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed in a mass ratio of 95.5:1:2:1.5 to obtain a mixture, deionized water is added to the mixture in a mass ratio of 4:6, and the negative electrode active material layer slurry is obtained by stirring;

[0078] 2) The negative active material layer slurry is coated on both functional surfaces of the negative current collector copper foil with an elongation of 12% by the process of extrusion coating to obtain a negative electrode sheet;

[0079] The thickness of the negative current collector is 8 μm, and the single-sided thickness of the negative active material layer is 52 μm.

[0080] 3. Assembly of the lithium ion battery

[0081] The assembly steps of the lithium ion battery are consistent with those of Example 1.

[0082] Example 4

[0083] The preparation of the lithium ion battery of the present example includes the following steps:

[0084] 1. Preparation of the positive electrode sheet

[0085] The preparation steps of the positive electrode sheet are consistent with those of Example 1.

[0086] 2. Preparation of the negative electrode sheet

[0087] 1) The artificial graphite, carbon black, butadiene styrene rubber and sodium carboxymethyl cellulose are mixed according to the mass ratio of 96:1:1.5:1.5 to obtain a mixture, deionized water is added to the mixture at a mass ratio of 4:6, and the negative active material layer slurry is obtained by stirring;

[0088] 2) The negative active material layer slurry is coated on both functional surfaces of the negative current collector copper foil with an elongation of 15% by the process of extrusion coating to obtain a negative electrode sheet;

[0089] The thickness of the negative current collector is 12 μm, and the single-sided thickness of the negative active material layer is 52 μm.

[0090] 3. Assembly of the lithium ion battery

[0091] The assembly steps of the lithium ion battery are consistent with those of Example 1.

[0092] Example 5

[0093] The preparation of the lithium ion battery of the present example includes the following steps:

[0094] 1. Preparation of the positive electrode sheet

[0095] The preparation steps of the positive electrode sheet are consistent with those of Example 1.

[0096] 2. Preparation of the negative electrode sheet

[0097] 1) The artificial graphite, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed according to the mass ratio of 96:1:1.5:1.5 to obtain a mixture, deionized water is added to the mixture at a mass ratio of the mixture to deionized water of 4:6, and the negative electrode active material layer slurry is obtained by stirring;

[0098] 2) The negative electrode active material layer slurry is coated on the two functional surfaces of the negative electrode current collector copper foil with an elongation of 7.5% by the process of extrusion coating to obtain a negative electrode sheet;

[0099] The thickness of the negative electrode current collector is 6 μm, and the single-sided thickness of the negative electrode active material layer is 52 μm.

[0100] 3. Assembly of the lithium ion battery

[0101] The assembly steps of the lithium ion battery are consistent with those of Example 1.

[0102] Example 6

[0103] The preparation of the lithium ion battery of the present example comprises the following steps:

[0104] 1. Preparation of a positive electrode sheet

[0105] The preparation steps of the positive electrode sheet are consistent with those of Example 1.

[0106] 2. Preparation of a negative electrode sheet

[0107] 1) The artificial graphite, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose are mixed according to the mass ratio of 96:1:1.5:1.5 to obtain a mixture, deionized water is added to the mixture at a mass ratio of the mixture to deionized water of 4:6, and the negative electrode active material layer slurry is obtained by stirring;

[0108] 2) The negative electrode active material layer slurry is coated on the two functional surfaces of the negative electrode current collector copper foil with an elongation of 12% by the process of extrusion coating to obtain a negative electrode sheet;

[0109] The thickness of the negative electrode current collector is 14 μm, and the single-sided thickness of the negative electrode active material layer is 52 μm.

[0110] 3. Assembly of the lithium ion battery

[0111] The assembly steps of the lithium ion battery are consistent with those of Example 1.

[0112] Example 7

[0113] 1. Preparation of a positive electrode sheet

[0114] 1) The lithium cobaltate, carbon black, carbon nanotube and PVDF are mixed according to the mass ratio of 96:1:1:2 to obtain a mixture, NMP is added to the mixture at a mass ratio of the mixture to NMP of 3:7, and the positive electrode active material layer slurry is obtained by stirring;

[0115] 2) coating the positive electrode active material layer slurry on both functional surfaces of the positive electrode current collector aluminum foil, and drying to obtain a positive electrode sheet;

[0116] The thickness of the positive electrode current collector is 9 pm, and the single-sided thickness of the positive electrode active material layer is 45 pm.

[0117] 2. Preparation of a negative electrode sheet

[0118] 1) mixing artificial graphite, carbon black, butadiene styrene rubber and sodium carboxymethyl cellulose according to a mass ratio of 96:1:1.5:1.5 to obtain a mixture, adding deionized water to the mixture at a mass ratio of 4:6 of the mixture to deionized water, and obtaining a negative electrode active material layer slurry by stirring;

[0119] 2) coating the negative electrode active material layer slurry on both functional surfaces of the negative electrode current collector copper foil with an elongation of 10% by the process of extrusion coating to obtain a negative electrode sheet;

[0120] The thickness of the negative electrode current collector is 10 pm, and the single-sided thickness of the negative electrode active material layer is 52 pm.

[0121] 3. Assembly of a lithium ion battery

[0122] The assembly steps of the lithium ion battery are consistent with those of Example 1.

[0123] Comparative Example 1

[0124] The preparation of the lithium ion battery of the present example includes the following steps:

[0125] 1. Preparation of a positive electrode sheet

[0126] The preparation steps of the positive electrode sheet are consistent with those of Example 1.

[0127] 2. Preparation of a negative electrode sheet

[0128] 1) mixing artificial graphite, carbon black, butadiene styrene rubber and sodium carboxymethyl cellulose according to a mass ratio of 96:1:1.5:1.5 to obtain a mixture, adding deionized water to the mixture at a mass ratio of 4:6 of the mixture to deionized water, and obtaining a negative electrode active material layer slurry by stirring;

[0129] 2) coating the negative electrode active material layer slurry on both functional surfaces of the negative electrode current collector copper foil with an elongation of 4% by the process of extrusion coating to obtain a negative electrode sheet;

[0130] The thickness of the negative electrode current collector is 6 pm, and the single-sided thickness of the negative electrode active material layer is 52 pm.

[0131] 3. Assembly of a lithium ion battery

[0132] The assembling procedure of the lithium ion battery was consistent with that of Example 1.

[0133] Comparative Example 2

[0134] The preparation of the lithium ion battery of the present example included the following steps:

[0135] 1. Preparation of the positive electrode sheet

[0136] The preparation procedure of the positive electrode sheet was consistent with that of Example 1.

[0137] 2. Preparation of the negative electrode sheet

[0138] 1) The artificial graphite, carbon black, styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed according to the mass ratio of 96:1:1.5:1.5 to obtain a mixture, deionized water was added to the mixture at a mass ratio of 4:6 of the mixture to deionized water, and the negative electrode active material layer slurry was obtained by stirring;

[0139] 2) The negative electrode active material layer slurry was coated on the two functional surfaces of the negative electrode current collector copper foil with an elongation of 5% by the process of extrusion coating to obtain the negative electrode sheet;

[0140] The thickness of the negative electrode current collector was 6 μm, and the single-sided thickness of the negative electrode active material layer was 52 μm.

[0141] 3. Assembling of the lithium ion battery

[0142] The assembling procedure of the lithium ion battery was consistent with that of Example 1.

[0143] Test Example

[0144] The negative electrode sheet of the above examples and comparative examples was tested for the negative electrode sheet elongation and the negative electrode sheet compression strength, and the lithium ion battery of the above examples and comparative examples was tested for the energy density and the heavy object impact passing rate, and the test methods were as follows:

[0145] 1. Negative electrode sheet elongation

[0146] Test method: The negative electrode sheet was cut into a sample with a width of 15 mm, and then placed on a tensile testing machine. The initial length of the sample was 50 mm, and the sample was stretched at a speed of 100 mm / min until the sample was broken. The elongation δ = (broken length-initial length) / initial length.

[0147] 2. Negative electrode sheet compression strength

[0148] Test method: cut the negative electrode sheet into a 10mm diameter disc, the area is S, then stack 20 small discs together, use a pressure tester to apply pressure to the disc, record the pressure value change of the instrument, the maximum pressure value is the limit pressure F0 of the negative electrode sheet, then the compression strength M of the negative electrode sheet is F0 / S.

[0149] 3. Energy density

[0150] Test method: charge the lithium ion battery to the designed upper limit voltage 4.45V, then discharge at 0.2C to the lower limit voltage 3.0V, the discharge energy is recorded as E.

[0151] Energy density ED = E / (length x width x height of lithium ion battery)

[0152] 4. Heavy impact pass rate

[0153] Test method: fully charge the lithium ion battery, then place it on the test table of the heavy impact test equipment, place a 15.8mm diameter impact piece (rod, total weight 9.1kg) on the surface of the battery, drop the impact piece to hit the lithium ion battery at a vertical distance of 61cm from the lithium ion battery, the battery is not on fire, not explosion is considered to pass the test. Each group of test 20pcs battery.

[0154] Table 1

[0155]

[0156] From the data in Table 1, it can be seen that by the elongation of the negative electrode current collector >7%, the pass rate of the battery under heavy impact can be significantly improved, and the safety performance of the battery can be improved.

[0157] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A lithium-ion battery, characterized by, The negative electrode sheet comprises a negative electrode current collector, and the elongation of the negative electrode current collector is greater than 7%; The lithium ion battery further comprises a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, a safety coating layer arranged on at least one functional surface of the positive electrode current collector, and a positive electrode active material layer arranged on the surface of the safety coating layer away from the positive electrode current collector; the safety coating layer comprises 62% to 96% of a filler, 0.1% to 8% of a conductive agent, and 3% to 30% of a binder in terms of mass percentage; wherein the filler in the safety coating layer is selected from one or more of a positive electrode active material, an oxide, a carbide, and a nitride; when the filler is selected from the positive electrode active material, the average particle size of the positive electrode active material in the safety coating layer is smaller than the average particle size of the positive electrode active material in the positive electrode active material layer; The compressive strength of the negative electrode sheet is greater than 10 MPa. The thickness of the negative electrode current collector is 6 to 14 μm; the elongation of the negative electrode current collector is δ%, the thickness of the negative electrode current collector is D, and D / δ is less than 1.

2. The lithium-ion battery of claim 1, wherein, The elongation of the negative electrode current collector is 10% to 20%.

3. The lithium-ion battery according to claim 1 or 2, characterized in that The elongation of the negative electrode sheet is greater than 7%.

4. The lithium-ion battery of claim 3, wherein, The elongation of the negative electrode sheet is 10% to 20%.

5. The lithium-ion battery of claim 1, wherein, The compressive strength of the negative electrode sheet is 15 to 50 MPa.

6. The lithium-ion battery of claim 1, wherein, D / δ is less than 0.8.

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