A negative electrode sheet and a lithium ion battery

Abstract

The present application relates to the technical field of lithium ion batteries, and provides a negative electrode sheet and a lithium ion battery. In the width direction of the negative electrode sheet, the negative electrode active material layer comprises a first coating layer and a second coating layer at the two side edges; the first coating layer and the second coating layer independently comprise a first non-active material; and / or the negative electrode sheet comprises a tab; the surface of at least one side of the negative electrode current collector is provided with a tab groove; a tab adhesive layer covers the tab groove, and the tab adhesive layer comprises a second non-active material; the first non-active material and the second non-active material independently comprise at least one of polyimide, polyetherimide and polyamide-imide. The negative electrode sheet can reduce the generation of lithium precipitation and lithium dendrites at the edge of the negative electrode, improve the edge lithium precipitation window, reduce the risk of thermal runaway caused by lithium dendrites piercing the separator, and improve the cycle performance of the battery; and the negative electrode sheet uses a tab adhesive layer containing a non-active material to replace the traditional tab protective adhesive, which can reduce the overall thickness of the battery cell and improve the energy density.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a negative electrode sheet and a lithium ion battery. BACKGROUND

[0002] With the rapid development of electric vehicles and smart devices, higher requirements are put forward for the rapid charging capability of batteries. Rapid charging can significantly shorten the charging time and improve user experience, which is an important direction for the development of battery industry. During rapid charging, a large polarization may be generated inside the battery, leading to the growth of lithium dendrites and an increased risk of thermal runaway. How to reduce the safety risk of the battery is an important research direction for the development of battery technology. SUMMARY

[0003] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a negative electrode sheet and a lithium ion battery comprising the same. The two side edges of the negative electrode sheet are coated with a non-active material, which can reduce the generation of lithium precipitation and lithium dendrites at the edge of the negative electrode, improve the edge lithium precipitation window, reduce the risk of thermal runaway caused by lithium dendrites piercing the separator, and improve the cycle performance of the battery; and / or, the negative electrode sheet is replaced with a tab adhesive layer comprising a non-active material instead of the traditional tab protective adhesive, which can reduce the overall thickness of the battery cell, improve the energy density, and at the same time reduce the risk of lithium precipitation at the edge of the tab.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode sheet, comprising: a negative electrode current collector, and a negative electrode active material layer arranged on the opposite two side surfaces of the negative electrode current collector; in the width direction of the negative electrode sheet, the negative electrode active material layer comprises a first coating area and a second coating area at the two side edges; the first coating area is provided with a first coating layer, and the second coating area is provided with a second coating layer; the first coating layer and the second coating layer independently comprise a first non-active material; the first non-active material comprises at least one of polyimide, polyetherimide and polyamide-imide;

[0005] And / or, the negative electrode sheet comprises a tab, the tab protrudes from one side of the negative electrode current collector in the width direction, and the tab is electrically connected to the negative electrode current collector; the surface of at least one side of the negative electrode current collector is provided with a tab slot, and the bottom of the tab slot is exposed to the negative electrode current collector; the tab comprises a first tab area and a second tab area protruding out of the tab slot, and the first tab area is located in the tab slot; the negative electrode sheet comprises a tab adhesive layer, the tab adhesive layer covers the tab slot, and the tab adhesive layer comprises a second non-active material; the second non-active material comprises at least one of polyimide, polyetherimide and polyamide-imide.

[0006] The second aspect of the present application provides a lithium ion battery, comprising the negative electrode sheet of the first aspect of the present application.

[0007] In some embodiments, the battery comprises a jelly-roll type battery cell, the jelly-roll type battery cell comprising a negative electrode sheet, a positive electrode sheet and a separator, the negative electrode sheet, the separator and the positive electrode sheet are sequentially stacked and wound along the length direction from one end to form a jelly-roll type battery cell;

[0008] The jelly-roll type battery cell comprises a circular arc region and a flat region extending between the circular arc regions, the circular arc region comprises a first circular arc region and a second circular arc region; along the width direction of the jelly-roll type battery cell, the positive electrode sheet comprises a first circular arc segment and a second circular arc segment located at the outermost two ends; the first circular arc segment is located in the first circular arc region, and the second circular arc segment is located in the second circular arc region;

[0009] The outermost circle of the jelly-roll type battery cell is a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, and a first positive electrode active layer and a second positive electrode active layer arranged on the opposite sides of the positive electrode current collector in the thickness direction; along the winding direction of the jelly-roll type battery cell, the tail end of the first positive electrode active layer exceeds the tail end of the second positive electrode active layer to form a double-sided positive electrode region and a single-sided positive electrode region;

[0010] The positive electrode sheet in the first circular arc segment is a single-sided positive electrode region, and the positive electrode sheet in the second circular arc segment is a hollow foil region; the surface of the single-sided positive electrode region in the first circular arc segment away from the negative electrode sheet is provided with a third coating layer; and / or, the surface of the hollow foil region in the second circular arc segment away from the negative electrode sheet is provided with a fourth coating layer;

[0011] The third coating layer and / or the fourth coating layer independently comprise a third non-active substance; the third non-active substance comprises at least one of polyimide, polyetherimide and polyamide-imide.

[0012] The technical scheme has the following beneficial effects:

[0013] (1) In the negative electrode sheet provided by the present application, the two side edges of the negative electrode sheet are coated with a coating layer containing a non-active substance, which can reduce the generation of lithium precipitation and lithium dendrite at the edge of the negative electrode, improve the edge lithium precipitation window, reduce the risk of thermal runaway caused by lithium dendrite piercing the separator, and improve the cycle performance of the battery;

[0014] (2) In the negative electrode sheet provided by the present application, the tab rubber layer containing a non-active substance is used to replace the traditional tab protection rubber (insulating rubber paper), which can reduce the overall thickness of the battery cell, improve the energy density, and reduce the risk of lithium precipitation at the edge of the tab.

[0015] (2) In the lithium ion battery provided by the present application, the surface of the positive electrode sheet at the outermost side in the circular arc region is further coated with a non-active substance, which can reduce material damage and structural damage caused by mechanical stress, reduce the deformation of the battery cell, and improve the structural stability and cycle performance of the battery.

[0016] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as implicitly split into this precise range without method of interpolation between the described values when it is clear from the context that such data values are used only as data points for extrapolation to a range of values. Any numerical range recited herein is intended to include all sub-ranges of the same numbers except specifically stated otherwise. For example, a range of 1 to 10 is specifically intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, all sub-ranges White including individual values from the range of 1 to 6 or from the range of 4 to 8, in addition to sub-ranges having an explicit terminal value of either 1 or 10. All individual values were included within the ranges if specifically stated so. Ranges of values recited herein are intended to include the endpoints of the range and any values between the recited endpoints. Ranges of values recited herein are intended to include the endpoints of the range and any values between the recited endpoints. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0018] Figure 2 A structure schematic view of a vertical section of a winding type battery cell in an example of the present application is shown.

[0019] Figure 3 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown. Figure 4 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0020] Figure 4 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0021] Figure 5 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0022] Figure 6 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0023] Figure 7 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0024] Figure 8 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0025] Figure 9 A structure schematic view of a cross section of a winding type battery cell in an example of the present application is shown.

[0026] Reference signs: 1 - positive electrode sheet; 11 - positive electrode current collector; 12 - first positive electrode active layer; 13 - second positive electrode active layer; 14 - first circular arc segment; 141 - third coating layer; 15 - second circular arc segment; 151 - fourth coating layer; 2 - negative electrode sheet; 21 - negative electrode current collector; 22 - negative electrode active material layer; 221 - first coating layer; 222 - second coating layer; 3 - separator; 4 - tab; 41 - first tab area; 42 - second tab area; 5 - tab groove; 6 - tab adhesive layer. DETAILED DESCRIPTION

[0027] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0028] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0029] In the present application, the terms "battery", "lithium battery", "lithium ion battery", "lithium ion secondary battery" all have the same meaning, and all refer to lithium ion secondary batteries, which generally include an electrode assembly (e.g., a positive electrode sheet, a negative electrode sheet, and a separator), a container (a case) that houses the electrode assembly, and an electrolyte.

[0030] In the present application, the term "non-active material" refers to a material that does not participate in an electrochemical reaction during charging and discharging of a battery, and which hinders the transport of lithium ions.

[0031] The first aspect of the present application provides a negative electrode sheet, the negative electrode sheet comprising: a negative electrode current collector, and a negative electrode active material layer disposed on opposite side surfaces of the negative electrode current collector;

[0032] In the width direction of the negative electrode sheet, the negative electrode active material layer includes a first coating area and a second coating area at both side edges; the first coating area is provided with a first coating layer, and the second coating area is provided with a second coating layer; the first coating layer and the second coating layer independently include a first non-active material; the first non-active material includes at least one of polyimide, polyetherimide, and polyamide-imide;

[0033] And / or, the negative electrode sheet comprises a tab, the tab protrudes from one side of the negative electrode current collector in the width direction, and the tab is electrically connected to the negative electrode current collector; the surface of at least one side of the negative electrode current collector is provided with a tab slot, and the bottom of the tab slot is exposed to the negative electrode current collector; the tab comprises a first tab area and a second tab area protruding out of the tab slot, and the first tab area is located in the tab slot; the negative electrode sheet comprises a tab adhesive layer, the tab adhesive layer covers the tab slot, and the tab adhesive layer comprises a second inactive substance; the second inactive substance comprises at least one of polyimide, polyetherimide, and polyamide-imide.

[0034] In the present application, the first coating layer and the second coating layer containing the first inactive substance are coated on the two side edges of the negative electrode sheet, and the first coating layer and the second coating layer are coated on the surface of the negative electrode active material layer. On the one hand, the interface side reaction between the electrolyte and the negative electrode surface is weakened, the transmission rate of lithium ions in the edge area of the negative electrode sheet is oriented and controlled, the transmission of lithium ions in the edge area of the negative electrode sheet is hindered or isolated, the lithium precipitation window is improved, the generation of lithium precipitation and lithium dendrite in the edge of the negative electrode is reduced, and the risk of thermal runaway caused by lithium dendrite piercing the separator is reduced. On the other hand, since the first inactive substance has good adhesion, mechanical properties and thermal stability, the volume expansion of the negative electrode can be inhibited, the structural integrity of the electrode and the cycle life of the battery can be improved.

[0035] In addition, in the present application, the tab adhesive layer containing the second inactive substance is coated in the tab slot, which can replace the traditional tab protective adhesive, reduce the overall thickness of the battery cell, improve the energy density, and reduce the risk of lithium precipitation in the edge of the tab.

[0036] In some embodiments, the first coating layer and the second coating layer independently comprise a first inactive substance, that is, the inactive substance coated in the first coating layer and the inactive substance in the second coating layer can be the same or different, preferably the same.

[0037] In some embodiments, the pore diameter D1 of the first coating layer and the second coating layer is independently 0.5 nm to 1.5 nm, for example, independently 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, or any point value in the range composed of any two of the above point values. The pore diameter of the first coating layer and the second coating layer can be the same or different. When the pore diameter of the first coating layer and the second coating layer is in the above range, the transmission rate of lithium ions on the edge area of the negative electrode sheet can be controlled by adjusting the pore diameter, further improving the lithium precipitation problem of the electrode sheet and improving the capacity retention rate during the cycle process.

[0038] In some embodiments, as Figure 3 and Figure 4As shown, the negative electrode sheet 2 includes a negative electrode current collector 21, and a negative electrode active material layer 22 disposed on the opposite two side surfaces of the negative electrode current collector 21. In the width direction of the negative electrode sheet 2, the negative electrode active material layer 22 includes a first coating area and a second coating area at the two side edges; the first coating area is provided with a first coating layer 221, the width of the first coating layer 221 is d1, and the thickness is h1. The second coating area is provided with a second coating layer 222, the width of the second coating layer 222 is d2, and the thickness is h2. The first coating layer and the second coating layer coat non-active substances, which can reduce the generation of lithium precipitation and lithium dendrites at the edges of the negative electrode, and reduce the risk of thermal runaway caused by lithium dendrites piercing the separator.

[0039] In some embodiments, in the width direction of the negative electrode sheet, the width d1 of the first coating layer is 0.1 mm-15 mm, for example, d1 can be 0.1 mm, 1 mm, 2 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15 mm, or any point value in the range consisting of any two of the above point values. The width d2 of the second coating layer is 0.1 mm-15 mm, for example, d2 can be 0.1 mm, 1 mm, 2 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15 mm, or any point value in the range consisting of any two of the above point values. The width d1 of the first coating layer and the width d2 of the second coating layer can be the same or different, preferably the same. When the width d1 of the first coating layer and the width d2 of the second coating layer are in the above range, the non-active substance is not coated too widely, which reduces the effective utilization area of the active substance and reduces the capacity of the battery.

[0040] In some embodiments, in the thickness direction of the negative electrode sheet, the thickness h1 of the first coating layer is 0.1 μm-10 μm, for example, h1 can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any point value in the range consisting of any two of the above point values. The thickness h2 of the second coating layer is 0.1 μm-10 μm, for example, h2 can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any point value in the range consisting of any two of the above point values. The thickness h1 of the first coating layer and the thickness h2 of the second coating layer can be the same or different, preferably the same. When the thickness h1 of the first coating layer and the thickness h2 of the second coating layer are in the above range, the coating layer is not too thick, which causes uneven volume change of the battery during charging and discharging, thereby causing damage to the electrode structure and shortening the cycle life of the battery; and the coating layer is not too thin, which may not effectively prevent the transmission of lithium ions in the edge area, and the effect of improving negative electrode lithium precipitation is not good.

[0041] In some embodiments, in the length direction of the negative electrode sheet, the length of the first coating layer is ≤ the length of the negative electrode sheet, and the length of the second coating layer is ≤ the length of the negative electrode sheet. Preferably, the length of the first coating layer = the length of the negative electrode sheet, and the length of the second coating layer = the length of the negative electrode sheet.

[0042] In some embodiments, the negative electrode sheet comprises a tab, the tab protrudes from one side of the negative electrode current collector in the width direction of the negative electrode current collector, and the tab is electrically connected to the negative electrode current collector; at least one side of the negative electrode current collector is provided with a tab slot, and the bottom of the tab slot is exposed to the negative electrode current collector; the tab comprises a first tab area and a second tab area protruding from the tab slot, and the first tab area is located in the tab slot; the negative electrode sheet comprises a tab adhesive layer, the tab adhesive layer covers the tab slot, and the tab adhesive layer comprises a second inactive substance; the second inactive substance comprises at least one of polyimide, polyetherimide, and polyamide-imide.

[0043] In some embodiments, as shown in Figure 7 and Figure 8 As shown in the drawings, a tab 4 is provided on one side of the negative electrode sheet in the width direction of the negative electrode sheet, the tab 4 protrudes from one side of the negative electrode current collector 21 in the width direction of the negative electrode current collector 21, and the negative electrode current collector 21 is provided with a tab slot 5 near the edge of the tab 4. The tab 4 comprises a first tab area 41 and a second tab area 42, the first tab area 41 is located in the tab slot 5, and the second tab area 42 protrudes from the tab slot 5. The surface of the tab slot 5 is covered with a tab adhesive layer 6, and the size of the tab adhesive layer 6 is greater than the size of the tab slot 5.

[0044] In some embodiments, in the width direction of the negative electrode sheet, the size d5 of the tab adhesive layer is 0.1 mm-15 mm, and d5 may, for example, be 0.1 mm, 1 mm, 2 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15 mm, or any point value in the range consisting of any two of the above point values. In the thickness direction of the negative electrode sheet, the thickness h5 of the tab adhesive layer is 0.5 μm-20 μm, and h5 may, for example, be 0.5 μm, 1 μm, 2 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any point value in the range consisting of any two of the above point values. The present application uses a tab adhesive layer containing a third inactive substance to replace the conventional tab protective adhesive (insulating adhesive paper), the thickness of the tab adhesive layer is less than the thickness of the insulating adhesive paper (>20 μm), which can reduce the overall thickness of the battery cell, improve the energy density, and at the same time reduce the risk of lithium precipitation at the edge of the tab.

[0045] In some embodiments, the size of the tab adhesive layer is greater than or equal to the size of the tab slot in the length direction of the negative electrode sheet; and the size of the tab adhesive layer is greater than or equal to the size of the tab slot in the width direction of the negative electrode sheet. The size of the tab adhesive layer being greater than the size of the tab slot can ensure that the tab adhesive layer completely covers the tab slot, effectively isolating the tab from the external environment and preventing short circuiting.

[0046] In some embodiments, the first inactive substance and the second inactive substance can be the same or different.

[0047] In some embodiments, the first inactive substance comprises a polyimide adhesive; and / or the second inactive substance comprises a polyimide adhesive.

[0048] Preferably, the first inactive substance is a polyimide adhesive (PI) and the second inactive substance is a polyimide adhesive. The polyimide adhesive can hinder or isolate the transmission of lithium ions in the negative electrode sheet, reducing the lithium precipitation of the negative electrode. Moreover, the polyimide adhesive has high mechanical properties and thermal stability, which can reduce the deformation of the battery cell, improve the structural stability of the battery, and comprehensively improve the safety performance and cycle performance of the battery.

[0049] In some embodiments, the chemical formula of the polyimide adhesive is [-R1-CO-NH-R2-CO-] n , R1 and R2 respectively represent the groups of different dianhydrides and diamines, and n is the degree of polymerization, representing the number of repeating units, and n has a value in the range of 40-720.

[0050] In some embodiments, the polyimide adhesive can be prepared or purchased. For example, the polyimide adhesive can be prepared by a solution polycondensation method. Dianhydride and diamine are subjected to polycondensation reaction in a polar solvent to generate polyimide acid, and then the polyimide acid is subjected to dehydration and cyclization by heating or chemical method to form a polyimide adhesive (PI). The dianhydride includes at least one of pyromellitic dianhydride, cyclobutane tetra carboxylic dianhydride, hexafluoroisopropyl phthalic anhydride, maleic anhydride, and acetic anhydride, and the diamine includes at least one of 1,2-diaminopropane, diphenyl ethylenediamine, o-xylylenediamine, m-xylylenediamine, and p-xylylenediamine.

[0051] In some embodiments, by designing and synthesizing cross-linked dianhydride, the size of the micropores of the polyimide adhesive coating network, i.e., the pore size of the coating layer, can be adjusted, and thus the transmission rate of lithium ions on the electrode sheet can be controlled. Reducing the pore size of the coating layer can reduce the transmission of lithium ions in the edge region and the circular arc region of the negative electrode sheet, and reduce the lithium precipitation of the negative electrode.

[0052] In some embodiments, the infrared spectrum of the polyimide adhesive is as shown in Figure 9 The infrared spectrum of the polyimide adhesive is related to the structure of its chemical groups. The infrared spectrum shows the following characteristic peaks: imidazole ring characteristic peak: at about 1400 cm-1 occurs at 1634 cm-1, representing the C=N vibration within the imidazole ring; imide bond characteristic peak: occurs at 1634 cm -1 -1, representing the C=O vibration of the imide; N-H vibration of the imide: occurs at 3309 cm -1 -1, representing the C=C vibration of the benzene ring. -1

[0053] In some embodiments, the glass transition temperature (Tg) of the polyimide adhesive is 200-430℃, for example, can be 200℃, 220℃, 250℃, 280℃, 300℃, 320℃, 350℃, 380℃, 400℃, 420℃, 430℃, or any point value in the range consisting of any two of the above point values. Adjusting the Tg of the polyimide adhesive can improve the flexibility of the negative electrode sheet, easily buffer the deformation of the battery cell during the cycle process, improve the stability of the battery structure, help the battery maintain efficient ion transmission during the charging and discharging process, and thus improve the energy density.

[0054] In some embodiments, the specific surface area of the first coating layer, the second coating layer, and the tab adhesive layer is independently 280-700 m 2 / g. When the specific surface area of the first coating layer, the second coating layer, and the tab adhesive layer is in the above range, it will appropriately promote the transmission of lithium ions and reduce the purple stain caused by complete blockage of lithium ion transmission.

[0055] In some embodiments, the first non-active substance and the second non-active substance are independently grafted with a group containing a sulfur element. In the normal coating area of the non-active substance, the lithium ion transmission rate is low, and if the lithium ion transmission rate is too low, it will cause the problem of purple stain of the electrode sheet. The present application grafts a specific group on the non-active substance, and because S has high electronegativity, it can produce strong electrostatic attraction with lithium ions (Li + ). This attraction helps to accelerate the transmission of lithium ions and avoid the problem of purple stain of the electrode sheet caused by too slow lithium ion transmission.

[0056] Preferably, the content of S element in the first coating layer, the second coating layer, and the tab adhesive layer is independently 0.05-0.6%. When the content of S element is in the above range, the coating layer containing the non-active substance can have a moderate barrier effect on the transmission of lithium ions, avoiding the problem of lithium precipitation caused by too fast lithium ion transmission, and also avoiding the problem of purple stain of the electrode sheet caused by too low lithium ion transmission.

[0057] In some embodiments, the group containing a sulfur element includes at least one of a sulfonic acid group (-SO3H), a mercapto group (-SH), a sulfoxide group (-SO-R), and a thione group (-C(=S)-SR).

[0058] ​The content of element S is tested by the following method: 0.5 g of the sample is weighed, 5 ml of HNO3 is added, and the sample is digested at 350 DEG C for 10 min. After cooling and filtering, the sample is diluted to 50 ml, and then tested by inductively coupled plasma optical emission spectrometer (ICP-OES) to obtain the result.

[0059] In some embodiments, the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon material; preferably, the mass percentage of silicon in the negative electrode active material is 3% to 85%, for example, 3%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 85%, preferably 5% to 40%. The silicon negative electrode has the advantage of high specific capacity, which is beneficial to improve the energy density of the battery. However, the negative electrode prepared from the silicon material is prone to swelling, and is prone to lithium precipitation and deformation of the battery. The present application can reduce lithium precipitation at the edge of the negative electrode by arranging the first coating and the second coating in the edge area, and can reduce the deformation caused by the swelling of the silicon negative electrode by arranging the third coating and the fourth coating in the arc area, thereby inhibiting the volume expansion of the silicon particles and improving the structural integrity of the electrode and the cycle life of the battery.

[0060] The mass percentage of silicon can be obtained by acid treatment of the negative electrode active material and then ICP analysis and calculation. Alternatively, the mass percentage of silicon can be tested by thermogravimetric analysis, for example, using Shimadzu DTG-60 thermal gravimetric analyzer, and the test conditions are as follows: sample amount 5 mg, air as the atmosphere, temperature rising rate 10 DEG C / min from room temperature to 900 DEG C and constant temperature for 40 min. The relationship between the mass percentage of silicon-carbon material (x) and the final weight residue percentage (y) of the entire test is x = 7y / 15.

[0061] In some embodiments, the silicon material comprises at least one of silicon oxide, silicon-carbon, nano-silicon, and silicon alloy.

[0062] In some embodiments, the thickness of the negative electrode sheet is 40 μm to 200 μm, for example, 40 μm, 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm, or 200 μm. When the thickness of the negative electrode sheet is within the above range, the risk of internal short circuit of the battery caused by too thin negative electrode sheet can be avoided, and at the same time, the diffusion rate of lithium ions and the charge-discharge performance of the battery can be avoided.

[0063] In some embodiments, the porosity of the negative electrode sheet is 25% to 65%. When the porosity of the negative electrode sheet is within the above range, the electrolyte can be sufficiently infiltrated and the lithium ions can be rapidly diffused in the case of reducing lithium precipitation of the negative electrode.

[0064] In the present application, the porosity can be tested by a gas adsorption method (BET method), and the specific testing method is as follows: the sample is weighed, the sample tube and the analysis port Dewar bottle are installed; the gas cylinder pressure reducing table is set to 15-18 psia (0.1 Mpa), the vacuum pump provides a vacuum degree lower than 20 μm; the Dewar bottle is filled with liquid nitrogen to complete the degassing treatment; the analysis is started and the analysis result list file is output, the pore volume and pore size distribution are calculated, and then the porosity is obtained.

[0065] In some embodiments, the negative current collector can adopt at least one of copper foil, nickel foil, composite current collector or carbon-based current collector. The middle layer of the composite current collector is organic matter (such as PET / PP / PI and other high molecular materials), and the upper and lower layers are copper or aluminum plating layers. The carbon-based current collector refers to the current collector based on carbon materials (such as carbon nanotubes, graphene, carbon fibers, etc.). The thickness of the negative current collector is 4 μm-10 μm. The negative current collector can improve its electrochemical performance by surface coating. The surface carbon coating of the negative current collector can provide additional electrical conductivity and mechanical stability, reduce the crushing of silicon materials during volume expansion, and thus improve the cycle stability of the battery.

[0066] In some embodiments, the negative active material layer includes a binder, and the binder includes at least one of carboxymethyl cellulose salt, polyacrylic acid, polyacrylic acid salt, styrene butadiene rubber, styrene propylene rubber, polyurethane, polyvinyl pyrrolidone, polyaniline, polyamide-imide, polysiloxane, epoxy resin, polyester resin, polyurethane resin or polyfluorene. The mass percentage content of the binder in the negative active material layer is 0.5% to 12%.

[0067] In some embodiments, the negative active material layer includes a conductive agent, and the conductive agent includes at least one of conductive carbon black, Ketjen black, conductive graphite, graphene, carbon aerogel, MXene material, three-dimensional mesoporous carbon, carbon nanotube or carbon fiber. The mass percentage content of the conductive agent in the negative active material layer is 0.01% to 10%.

[0068] In some embodiments, the negative active material layer includes a thickening agent, and the thickening agent includes at least one of lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose and hydroxyethyl cellulose.

[0069] In some embodiments, the mass ratio of the negative active material, the conductive agent, the binder and the thickening agent in the negative active material layer can be (90.2-97.8):(0.05-10):(1.2-8):(0.2-1), and any other suitable mass ratio can also be used.

[0070] The second aspect of the present application provides a lithium ion secondary battery, which includes the negative electrode sheet of the first aspect of the present application.

[0071] The battery provided by the application has the advantages of less lithium precipitation, good safety performance and good cycle performance due to the negative electrode sheet.

[0072] In some embodiments, the battery comprises a jelly-roll type battery cell, the jelly-roll type battery cell comprises a negative electrode sheet, a positive electrode sheet and a separator, the negative electrode sheet, the separator and the positive electrode sheet are sequentially stacked and wound from one end along the length direction to form the jelly-roll type battery cell. Figure 1 As shown in the figure, a jelly-roll type battery cell comprises a positive electrode sheet 1, a negative electrode sheet 2 and a separator 3, the positive electrode sheet 1, the separator 3 and the negative electrode sheet 2 are sequentially stacked and wound from one end along the length direction to form the jelly-roll type battery cell.

[0073] In some embodiments, the battery comprises a jelly-roll type battery cell, the jelly-roll type battery cell comprises a negative electrode sheet, a positive electrode sheet and a separator, the negative electrode sheet, the separator and the positive electrode sheet are sequentially stacked and wound from one end along the length direction to form the jelly-roll type battery cell;

[0074] The jelly-roll type battery cell comprises a circular arc region and a flat region extending between the circular arc regions, the circular arc region comprises a first circular arc region and a second circular arc region; along the width direction of the jelly-roll type battery cell, the positive electrode sheet comprises a first circular arc segment and a second circular arc segment located at the two outermost ends; the first circular arc segment is located in the first circular arc region, and the second circular arc segment is located in the second circular arc region;

[0075] The outermost circle of the jelly-roll type battery cell is a positive electrode sheet, the positive electrode sheet comprises a positive electrode current collector, and a first positive electrode active layer and a second positive electrode active layer arranged on the opposite sides of the thickness direction of the positive electrode current collector; along the winding direction of the jelly-roll type battery cell, the tail end of the first positive electrode active layer exceeds the tail end of the second positive electrode active layer to form a double-sided positive electrode region and a single-sided positive electrode region;

[0076] The positive electrode sheet in the first circular arc segment is a single-sided positive electrode region, and the positive electrode sheet in the second circular arc segment is a hollow foil region; the surface of the single-sided positive electrode region in the first circular arc segment away from the negative electrode sheet is provided with a third coating layer; and / or, the surface of the hollow foil region in the second circular arc segment away from the negative electrode sheet is provided with a fourth coating layer;

[0077] The third coating layer and / or the fourth coating layer independently comprise a third non-active substance; the third non-active substance comprises at least one of polyimide, polyetherimide and polyamide-imide.

[0078] In some embodiments, the surface of the single-sided positive electrode region in the first circular arc segment away from the positive electrode current collector of the negative electrode sheet is provided with a third coating layer; the surface of the hollow foil region in the second circular arc segment away from the positive electrode current collector of the negative electrode sheet is provided with a fourth coating layer. Alternatively, only the surface of the single-sided positive electrode region in the first circular arc segment away from the negative electrode sheet is provided with a third coating layer; or only the surface of the hollow foil region in the second circular arc segment away from the negative electrode sheet is provided with a fourth coating layer. Preferably, the third coating layer and the fourth coating layer are provided at the same time, so that the surface of the positive electrode current collector of the outermost positive electrode sheet in the circular arc region of the winding type battery cell is coated with non-active material. The non-active material has good mechanical properties and thermal stability, can better withstand the volume expansion and contraction during the charging and discharging process of the battery, reduce material damage and structural damage caused by mechanical stress, reduce the deformation of the battery cell, and improve the structural stability and cycle performance of the battery.

[0079] In some embodiments, the pore diameter D2 of the third coating layer and / or the fourth coating layer is independently 0.5 nm to 1.5 nm, for example, independently 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, or any point value in the range formed by any two of the above point values. The pore diameters of the third coating layer and the fourth coating layer can be the same or different. When the pore diameters of the third coating layer and the fourth coating layer are in the above range, the internal stress during the expansion of the battery can be dispersed, the deformation of the winding core circular arc region can be reduced, the structural stability of the battery can be improved, and the cycle performance of the battery can be improved.

[0080] In some embodiments, the test method of the pore diameter in the first coating layer, the second coating layer, the third coating layer, and the fourth coating layer includes using an atomic force microscope (AFM), installing the sample on the sample stage of the AFM device, selecting a suitable scanning mode, and analyzing parameters such as pore diameter, pore structure, and pore size distribution through the AFM image.

[0081] In some embodiments, as shown in Figure 1 and Figure 2 The winding type battery cell includes a circular arc region and a flat region extending between the circular arc regions, and the circular arc region includes a first circular arc region and a second circular arc region. In the width direction of the winding core, the positive electrode sheet includes a first circular arc segment 14 and a second circular arc segment 15 away from the flat region; the first circular arc segment 14 is located in the first circular arc region, and the second circular arc segment 15 is located in the second circular arc region. The surface of the positive electrode current collector in the first circular arc segment 14 is provided with a third coating layer 141; the surface of the positive electrode current collector in the second circular arc segment 15 is provided with a fourth coating layer 151.

[0082] In some embodiments, as shown in Figure 1 , Figure 5 and Figure 6As shown, the positive electrode sheet 1 includes a positive electrode current collector 11, and a first positive electrode active layer 12 and a second positive electrode active layer 13 arranged on opposite sides of the positive electrode current collector 11 in the thickness direction of the positive electrode sheet; along the length direction of the positive electrode sheet, the tail end of the first positive electrode active layer 12 exceeds the tail end of the second positive electrode active layer 13. Along the length direction of the positive electrode sheet 1, a third coating layer 141 is arranged on the first arc segment 14, the width of the third coating layer 141 is d3, and the thickness of the third coating layer 141 is h3. A fourth coating layer 151 is arranged on the second arc segment 15, the width of the fourth coating layer 151 is d4, and the thickness of the fourth coating layer 151 is h4. The third coating layer and the fourth coating layer are coated with non-active substances, which can reduce the deformation of the battery cell and improve the structural stability and cycle performance of the battery.

[0083] In some embodiments, along the length direction of the positive electrode sheet, the size d3 (width d3) of the third coating layer is 0.1 mm-15 mm, for example, d3 can be 0.1 mm, 1 mm, 2 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15 mm, or any point value in the range consisting of any two of the above point values. The size d4 of the fourth coating layer is 0.1 mm-15 mm, for example, d4 can be 0.1 mm, 1 mm, 2 mm, 4 mm, 5 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 15 mm, or any point value in the range consisting of any two of the above point values. The width d3 of the third coating layer and the width d4 of the fourth coating layer can be the same or different, preferably the same. When the width d3 of the third coating layer and the width d4 of the fourth coating layer are in the above range, the non-active substance is not coated too widely, which avoids increasing the volume of the battery cell and reducing the overall energy density.

[0084] In some embodiments, along the thickness direction of the positive electrode sheet, the thickness h3 of the third coating layer is 0.1 μm-10 μm, for example, h3 can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any point value in the range consisting of any two of the above point values. The thickness h4 of the fourth coating layer is 0.1 μm-10 μm, for example, h4 can be 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any point value in the range consisting of any two of the above point values. The thickness h3 of the third coating layer and the thickness h4 of the fourth coating layer can be the same or different, preferably the same. When the thickness h3 of the third coating layer and the thickness h4 of the fourth coating layer are in the above range, the coating layer is not too thick, which avoids uneven volume change of the battery during charging and discharging, thereby causing damage to the electrode structure and shortening the cycle life of the battery.

[0085] In some embodiments, the size of the third coating layer is ≤ the width of the positive electrode sheet (i.e., the length of the third coating layer is ≤ the width of the positive electrode sheet) over the width of the positive electrode sheet. The size of the fourth coating layer is ≤ the width of the positive electrode sheet (i.e., the length of the fourth coating layer is ≤ the width of the positive electrode sheet). Preferably, the length of the third coating layer = the width of the positive electrode sheet, and the length of the fourth coating layer = the width of the positive electrode sheet.

[0086] In some embodiments, d1 = d2 < d3 = d4, i.e., the width of the first coating layer d1 = the width of the second coating layer d2, the width of the third coating layer d3 = the width of the fourth coating layer d4, and the width of the first coating layer (or the second coating layer) is less than the width of the third coating layer (or the fourth coating layer), i.e., the size of the edge region coated with the non-active substance is less than the size of the circular arc region coated with the non-active substance, which can reduce the lithium precipitation on the negative electrode edge, improve the safety performance of the battery, and increase the energy density of the battery, while reducing the deformation of the battery cell, improving the stability of the battery structure, and improving the capacity retention rate and cycle performance of the battery.

[0087] In some embodiments, the first non-active substance, the second non-active substance, and the third non-active substance can be the same or different.

[0088] In some embodiments, the third non-active substance includes a polyimide glue. The polyimide glue has high mechanical properties and thermal stability, which can reduce the deformation of the battery cell, improve the structural stability of the battery, and comprehensively improve the safety performance and cycle performance of the battery.

[0089] In some embodiments, the specific surface area of the third coating layer and the fourth coating layer is independently 280 m 2 / g to 700 m 2 / g. When the specific surface area of the third coating layer and the fourth coating layer is within the above range, a uniform and effective covering layer can be formed on the surface of the winding core, so that the deformation of the battery cell structure can be reduced when the battery cell is subjected to external extrusion or impact mechanical force.

[0090] In some embodiments, the battery further includes a positive electrode sheet and a separator, and the positive electrode sheet and the negative electrode sheet are separated by the separator arranged therebetween while allowing lithium ions to pass through, thereby preventing the battery from overheating.

[0091] In some embodiments, the positive electrode tab includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer is disposed on one or both surfaces of the positive electrode current collector. The positive electrode current collector can be an aluminum foil, or other positive electrode current collectors commonly used in the art. The thickness of the positive electrode current collector can be 1-15 μm. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material can include at least one of lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium iron phosphate (LFP), a ternary material (lithium nickel cobalt manganese oxide (NCM) and lithium nickel cobalt aluminum oxide (NCA)), lithium aluminum oxide, or lithium manganese oxide. The conductive agent includes at least one of conductive carbon black, conductive graphite, graphene, or carbon nanotubes. The binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, a polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate salt, a polyvinyl acetate, a polyvinylpyrrolidone, a polyvinyl ether, a polymethyl methacrylate, a polytetrafluoroethylene, or a polyhexafluoropropylene. The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is (95-98.5):(0.1-3):(0.1-5), or any other suitable mass ratio.

[0092] In some embodiments, the separator film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyethylene terephthalate, polyimide, or aramid. The thickness of the separator film is 3-12 μm. The surface of the separator film can further include a porous layer disposed on at least one surface of the separator film, and the porous layer includes inorganic particles selected from at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate, and a binder. The pore size of the pores in the separator film ranges from 0.01-1 μm. The binder of the porous layer includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a polyamide, a polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate salt, a carboxymethyl cellulose salt, a polyvinylpyrrolidone, a polyvinyl ether, a polymethyl methacrylate, a polytetrafluoroethylene, or a polyhexafluoropropylene.

[0093] In some embodiments, the lithium ion secondary battery further includes an electrolyte including a non-aqueous solvent and a lithium salt.

[0094] Exemplarily, the non-aqueous solvent includes a carbonate compound, a carboxylic ester compound, an ether compound, another organic solvent, or a combination thereof. The carbonate compound can be at least one of a chain carbonate compound, a cyclic carbonate compound, a fluoro-carbonate compound, or a combination thereof. The lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the concentration of the lithium salt is 1 mol / L to 2 mol / L, and the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.06-5. The electrolyte solution can further include the non-aqueous solvent.

[0095] The electrolyte solution includes at least one of a fluoro-ether, a fluoro-carbonate vinyl ester, or an ether nitrile.

[0096] Exemplarily, the chain carbonate compound includes at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), or a combination thereof. The cyclic carbonate compound includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or a combination thereof. The fluoro-carbonate compound includes at least one of fluoro-ethylene carbonate (FEC), 1,2-difluoro-ethylene carbonate, 1,1-difluoro-ethylene carbonate, 1,1,2-trifluoro-ethylene carbonate, 1,1,2,2-tetrafluoro-ethylene carbonate, 1-fluoro-2-methyl-ethylene carbonate, 1-fluoro-1-methyl-ethylene carbonate, 1,2-difluoro-1-methyl-ethylene carbonate, 1,1,2-trifluoro-2-methyl-ethylene carbonate, trifluoromethyl-ethylene carbonate, or a combination thereof. The carboxylic ester compound includes at least one of methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, methylvaleronolactone, hexanolactone, methyl formate, or a combination thereof. The ether compound includes at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof. The other organic solvent includes at least one of dimethyl sulfoxide, 1,2-dioxolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric ester, or a combination thereof.

[0097] The lithium-ion secondary battery of this invention can be used in any electronic device known in the prior art. These electronic devices may include, but are not limited to: laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, drones, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0098] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0099] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0100] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0101] The batteries in the examples and comparative examples were prepared according to the following preparation method.

[0102] Example 1-1:

[0103] (1) Preparation of negative electrode:

[0104] Artificial graphite, SiC, lithium polyacrylate binder, carbon nanotubes, and lithium carboxymethyl cellulose were dissolved in deionized water in a weight ratio of 87.03:9.67:2.0:0.6:0.7 to form a negative electrode slurry. The negative electrode slurry was coated onto both sides of a 6 μm thick copper foil as the negative electrode current collector, resulting in a coating thickness of 76 μm. After drying, cold pressing, and slitting, the negative electrode sheet with a silicon content of 9% was obtained.

[0105] PI adhesive coating: Apply PI adhesive evenly to the edge area of ​​the negative electrode sheet, such as... Figure 3 and Figure 4 As shown, the coating width d1 = d2 = 6.2 mm, the coating thickness h1 = h2 = 4.3 mm, the PI adhesive micropore diameter D1 is 0.8 nm, and the PI adhesive specific surface area is 530 m². 2 / g, the glass transition temperature (Tg) of PI adhesive is 312℃.

[0106] (2) Preparation of positive electrode sheet:

[0107] The positive electrode active material lithium cobaltate, the conductive agent conductive graphite, and the binder polyvinylidene fluoride (PVDF) were dissolved in N-methyl pyrrolidone (NMP) solution at a weight ratio of 97.2:1.1:1.7 to form a positive electrode slurry. An 8 μm thick aluminum foil was used as the positive electrode current collector, and the positive electrode slurry was coated on both sides of the positive electrode current collector with a coating thickness of 49 μm. After drying, cold pressing, and slitting, the positive electrode sheet was obtained.

[0108] (3) Preparation of separator film: The separator film substrate was 7 μm thick polyethylene (PE), and 2 μm aluminum oxide ceramic layers were coated on both sides of the separator film substrate. Finally, 2 μm of the binder polyvinylidene fluoride (PVDF) was coated on both sides of the ceramic layer and dried.

[0109] (4) Preparation of electrolyte: In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and non-aqueous organic solvent (ethylene carbonate (EC): propylene carbonate (PC): polypropylene (PP): diethyl carbonate (DEC) = 1:1:1:1, mass percentage) were prepared into an electrolyte with a lithium salt concentration of 1.05 mol / L.

[0110] (5) Preparation of lithium ion battery: The positive electrode sheet, the separator film, and the negative electrode sheet were sequentially stacked in order with the separator film between the positive electrode sheet and the negative electrode sheet to play a separating role, and the electrode assembly (winding type battery cell) was obtained by winding. The electrode assembly was placed in an outer packaging aluminum plastic film, and after removing the water at 80°C, the above-mentioned electrolyte was injected and packaged. After processes such as formation, degassing, shaping, and capacity distribution, the lithium ion battery was obtained.

[0111] The batteries obtained in the examples and comparative examples were subjected to the following performance tests:

[0112] (i) Lithium precipitation test

[0113] At 25°C, the lithium ion battery was charged to 4.5 V at X (X = 1, 2, 3) C constant current, and then charged to 0.05 C at 4.5 V constant voltage, and then rested for 5 min. Then discharged to 3.0 V at 1 C constant current, and then rested for 5 min. This was one cycle, and after 10 cycles, the battery was disassembled at full charge to obtain the negative electrode sheet. If any one of the regions of the PI coated area of the negative electrode sheet was greater than or equal to 2 mm 2 , lithium precipitation was determined to occur in the negative electrode sheet, and the unit was C. The higher the lithium precipitation level, the lower the degree of lithium precipitation at the same charge rate.

[0114] (ii) Energy density test

[0115] The lithium ion battery (finished lithium ion battery after formation) was charged at 25℃ with 1C constant current to 4.5V, rested for 10 minutes, discharged with 1C constant current to the cut-off voltage 3.0V (5 batteries per group), to obtain the energy of the lithium ion battery. The energy density (Wh / L) of the lithium ion battery = the energy of the lithium ion battery / the volume of the lithium ion battery.

[0116] (iii) 25℃ cycle performance test

[0117] 25℃±5℃ test the sample state voltage, internal resistance, thickness, DC internal resistance;

[0118] ① 25℃±2℃ rest for 10min;

[0119] ② 0.2C discharge to the lower limit voltage, rest for 10min;

[0120] ③ 0.7C charge to the upper limit voltage, cut off 0.025C, rest for 10min;

[0121] ④ 0.2C discharge to the lower limit voltage; (do initial capacity test);

[0122] ⑤ rest for 10min;

[0123] ⑥ 2C charge 4.25V (cut off 1.5C) 1.5C charge 4.3V (cut off 1C) 1C charge 4.5V (cut off 0.25C) test the first full charge data, voltage, internal resistance, thickness, DC internal resistance;

[0124] ⑦ 25℃±2℃ rest for 10min;

[0125] ⑧ 0.7C discharge to the lower limit voltage; rest for 10min;

[0126] ⑨ 2C charge 4.25V (cut off 1.5C) 1.5C charge 4.3V (cut off 1C) 1C charge 4.5V (cut off 0.25C), rest for 10min;

[0127] ⑩ 8-9 step cycle 500 times, record the test results.

[0128] Example group 1-3 group reference example 1-1, the main difference is shown in Table 1. Among them, the first coating and the second coating in the example group 1 change the aperture D1; the first coating and the second coating in the example group 2 change the width d1 and the width d2; the first coating and the second coating in the example group 3 change the thickness h1 and the thickness h2.

[0129] Table 1

[0130]

[0131]

[0132] As can be seen from Table 1, coating the first coating layer and the second coating layer containing PI glue on both side edges of the negative electrode sheet, adjusting the aperture, width and thickness of the first coating layer and the second coating layer within the protection scope of the present application can improve the lithium precipitation window of the edge, improve the capacity retention rate of the battery and reduce the cycle expansion rate.

[0133] The Example 4 group and the Comparative Example 1 reference Example 1-1, the main difference is shown in Table 2. In the Example 4 group, the tab slot is coated with a tab glue, while in Example 1-1, the tab slot is attached with a conventional acrylic adhesive tape with a thickness of 15 μm. Among them, the thickness of the tab glue layer is changed in Example 4-1 to Example 4-4; only the tab glue layer is set in Example 4-5 without the first coating layer and the second coating layer; and no first coating layer, second coating layer or tab glue layer is set in Comparative Example 1.

[0134] Table 2

[0135]

[0136] As can be seen from Table 2, the tab glue layer containing PI is coated in the tab slot instead of the conventional tab protection glue, which can improve the high energy density of the battery, improve the lithium precipitation window of the edge, improve the capacity retention rate of the battery and reduce the cycle expansion rate.

[0137] The Example 5 group to the Example 7 group reference Example 1-1, the main difference is shown in Table 3. Among them, the PI glue with different glass transition temperatures is selected in the Example 5 group; the PI glue with different specific surface areas and aperture (the same) is selected in the first coating layer and the second coating layer in the Example 6 group; and the PI glue is grafted with sulfonic acid groups with different S element contents in the Example 7 group.

[0138] Table 3

[0139]

[0140] As can be seen from Table 3, when the glass transition temperature, specific surface area and aperture of the PI glue in the first coating layer and the second coating layer are within the appropriate range, the lithium precipitation window of the edge can be improved, the capacity retention rate of the battery can be improved and the cycle expansion rate can be reduced. In addition, when the S element content of the PI glue grafted with a group containing sulfur elements is controlled within the appropriate range, the lithium precipitation window of the edge can be improved, the capacity retention rate of the battery can be improved and the cycle expansion rate can be reduced.

[0141] Example 8 group-10 group and example 11 reference example 1-1, on the basis of example 1-1, the outermost two sides of the core of the arc coated PI glue, the main difference see table 4. Among them, the third coating and the fourth coating of example 8 group change the aperture D2;The third coating width d3 and the fourth coating width d4 of example 9 group are changed;The third coating thickness h3 and the fourth coating thickness h4 of example 10 group are changed;In example 11, d1=d2>d3=d4 is set, the width of the arc region coated is smaller than the edge region coated.

[0142] Table 4

[0143]

[0144]

[0145] It can be seen from table 4 that coating PI on the two side arc surfaces of the outermost winding type battery can release the internal stress generated by expansion and reduce damage, reduce the deformation of the core, improve the cycle capacity retention rate of the battery and reduce the cycle expansion rate.

[0146] Example 12 group reference example 8-1, the main difference see table 5. Among them, the PI glue with different glass transition temperature is selected in example 12 group.

[0147] Table 5

[0148]

[0149] It can be seen from table 5 that when the glass transition temperature of PI glue in the third coating and the fourth coating is in the appropriate range, the edge lithium precipitation window can be improved, the capacity retention rate of the battery can be improved and the cycle expansion rate can be reduced.

[0150] Example 13 group reference example 8-1, the main difference see table 6. Among them, the content of silicon element in the negative active material and the type of silicon material are changed in example 13 group.

[0151] Table 6

[0152]

[0153]

[0154] It can be seen from table 6 that setting the first coating and the second coating in the edge region of the negative plate can reduce the negative edge lithium precipitation and reduce the lithium precipitation window, and setting the third coating and the fourth coating in the arc region of the outer side of the core can reduce the deformation caused by the expansion of silicon negative electrode, improve the capacity retention rate of the battery and reduce the cycle expansion rate.

[0155] It is to be understood that the terminology "including", "containing" or any other variation thereof does not exclude the presence of other elements or steps than those listed in the process, method, article, or apparatus. It is further understood that the steps and elements recited in any of the examples herein can be combined, removed or arranged in various ways without departing from the scope of the application. Further, the features described in relation to one example can be combined with features described in relation to other examples.

[0156] The above description is merely illustrative of the application and does not in any way delimit the scope of the application. Any modification, equivalent replacement or the like made within the spirit and principle of the application shall fall within the scope of the application.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes: a negative electrode current collector, and a negative electrode active material layer disposed on opposite sides of the negative electrode current collector; In the width direction of the negative electrode sheet, the negative electrode active material layer includes a first coating area and a second coating area on both sides; the first coating area is provided with a first coating layer, and the second coating area is provided with a second coating layer; the first coating layer and the second coating layer independently include a first inactive material; the first inactive material includes at least one of polyimide, polyetherimide, and polyamide-imide; The negative electrode sheet includes a tab that protrudes from one side of the negative current collector in the width direction and is electrically connected to the negative current collector. At least one surface of the negative current collector has a tab groove, the bottom of which exposes the negative current collector. The tab includes a first tab region and a second tab region extending out of the tab groove, the first tab region being located within the tab groove. The negative electrode sheet includes a tab adhesive layer that covers the tab groove, the tab adhesive layer including a second inactive material. The second inactive material includes at least one of polyimide, polyetherimide, and polyamide-imide. The pore size D1 of the first coating and the second coating is independently 0.5 nm-1.5 nm; In the width direction of the negative electrode sheet, the width d1 of the first coating is 0.1 mm-15 mm, and the width d2 of the second coating is 0.1 mm-15 mm; In the thickness direction of the negative electrode sheet, the thickness h1 of the first coating is 0.1 µm-10 µm, and the thickness h2 of the second coating is 0.1 µm-10 µm; The first inactive substance and / or the second inactive substance are independently grafted with sulfur-containing groups.

2. The negative electrode sheet according to claim 1, characterized in that, Along the length of the negative electrode sheet, the length of the first coating is less than or equal to the length of the negative electrode sheet, and the length of the second coating is less than or equal to the length of the negative electrode sheet.

3. The negative electrode sheet according to claim 1, characterized in that, In the width direction of the negative electrode sheet, the dimension d5 of the tab adhesive layer is 0.1 mm-15 mm; And / or, in the thickness direction of the negative electrode sheet, the thickness h5 of the tab adhesive layer is 0.5 µm-20 µm; And / or, in the length direction of the negative electrode sheet, the size of the tab adhesive layer is greater than or equal to the size of the tab groove; in the width direction of the negative electrode sheet, the size of the tab adhesive layer is greater than or equal to the size of the tab groove.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, The first inactive substance comprises polyimide adhesive; and / or the second inactive substance comprises polyimide adhesive.

5. The negative electrode sheet according to claim 4, characterized in that, The glass transition temperature of the polyimide adhesive is 200℃-430℃.

6. The negative electrode sheet according to any one of claims 1-3, characterized in that, The specific surface area of ​​the first coating, the second coating, and the tab adhesive layer is independently 280 m². 2 / g~700 m 2 / g.

7. The negative electrode sheet according to any one of claims 1-3, characterized in that, Based on the total mass of the first coating, the second coating, and the tab adhesive layer, the sulfur content in each of the first coating, the second coating, and the tab adhesive layer is independently 0.05%-0.6%.

8. The negative electrode sheet according to any one of claims 1-3, characterized in that, The sulfur-containing groups include at least one of sulfonic acid group, mercapto group, sulfoxide group, and thionyl group.

9. The negative electrode sheet according to any one of claims 1-3, characterized in that, The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes silicon material.

10. The negative electrode sheet according to claim 9, characterized in that, In the negative electrode active material, the mass percentage of silicon is 3%-85%.

11. The negative electrode sheet according to claim 9, characterized in that, The silicon material includes at least one of silicon oxide, silicon carbon, nano-silicon, and silicon alloy.

12. The negative electrode sheet according to any one of claims 1-3, wherein the thickness of the negative electrode sheet is 40 µm-200 µm; and / or, the porosity of the negative electrode sheet is 25%-65%.

13. A lithium-ion battery, characterized in that, The battery includes the negative electrode sheet according to any one of claims 1-12.

14. The battery according to claim 13, characterized in that, The battery includes a wound cell, which includes a negative electrode, a positive electrode, and a separator. The negative electrode, separator, and positive electrode are stacked in sequence and wound from one end along the length direction to form a wound cell. The wound battery cell includes an arc region and a straight region extending within the arc region. The arc region includes a first arc region and a second arc region. Along the width direction of the wound battery cell, the positive electrode includes a first arc segment and a second arc segment located at the outermost two ends. The first arc segment is located within the first arc region, and the second arc segment is located within the second arc region. The outermost ring of the wound battery cell is a positive electrode sheet, which includes a positive current collector and a first positive active layer and a second positive active layer disposed on opposite sides of the thickness direction of the positive current collector. Along the winding direction of the wound battery cell, the tail end of the first positive active layer extends beyond the tail end of the second positive active layer to form a double-sided positive electrode region and a single-sided positive electrode region. The positive electrode in the first arc segment is a single-sided positive electrode region, and the positive electrode in the second arc segment is an empty foil region; a third coating is provided on the surface of the single-sided positive electrode region in the first arc segment away from the negative electrode; and / or, a fourth coating is provided on the surface of the empty foil region in the second arc segment away from the negative electrode. The third coating and / or the fourth coating independently include a third inactive substance; the third inactive substance includes at least one of polyimide, polyetherimide, and polyamide-imide.

15. The battery according to claim 14, characterized in that, The pore size D2 of the third coating and / or the fourth coating is independently 0.5 nm to 1.5 nm.

16. The battery according to claim 14, characterized in that, Along the length of the negative electrode sheet, the dimensions d3 of the third coating and / or d4 of the fourth coating are independently 0.1 mm to 15 mm. And / or, in the thickness direction of the negative electrode sheet, the thickness h3 of the third coating and / or the thickness h4 of the fourth coating is 0.1 µm-10 µm; And / or, on the width side of the negative electrode sheet, the size of the third coating is ≤ the width of the negative electrode sheet, and / or the size of the fourth coating is ≤ the width of the negative electrode sheet.

17. The battery according to claim 16, characterized in that, d1=d2<d3=d4.

18. The battery according to any one of claims 15-17, characterized in that, The third inactive substance includes polyimide gel; And / or, the specific surface area of ​​the third coating and the fourth coating is independently 280 m². 2 / g~700 m 2 / g.

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