A negative electrode sheet and a lithium ion battery

Abstract

The present disclosure provides a negative electrode sheet and a lithium ion battery. The negative electrode sheet provided by the present disclosure comprises a negative electrode current collector and an active material layer coated on the surface of the negative electrode current collector, wherein the active material layer comprises a first active material layer and a second active material layer stacked in a direction away from the negative electrode current collector, the coating weight and the compaction density of the first active material layer and the second active material layer are different, and the coating weight and the compaction density of the first active material layer and the second active material layer are designed according to the characteristic parameters of the negative electrode current collector. The negative electrode sheet and the lithium ion battery provided by the present disclosure comprehensively consider the deformation risk and the compaction density of the electrode sheet, on the basis of reducing the deformation risk of the electrode sheet, the compaction density of the whole electrode sheet can be maximized, and the energy density of the lithium ion battery can be improved.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery technology, and more particularly to a negative electrode sheet and a lithium-ion battery. Background Technology

[0002] With the advent of 5G communication technology, users are paying more and more attention to the battery life of electronic products, and battery capacity has become a factor that users must consider when choosing electronic products.

[0003] Currently, battery capacity is often increased by increasing the compaction density of the active material on the electrodes. However, increasing the compaction density inevitably increases the risk of battery deformation. Summary of the Invention

[0004] This disclosure provides a negative electrode and a lithium-ion battery to address the shortcomings of related technologies.

[0005] According to a first aspect of the present disclosure, a negative electrode sheet is provided, comprising a negative electrode current collector and an active material layer coated on the surface of the negative electrode current collector, wherein...

[0006] The active material layer includes a first active material layer and a second active material layer stacked along a direction away from the negative electrode current collector. The coating weight and compaction density of the first active material layer and the second active material layer are different, and the coating weight and compaction density of the multilayer active material layer are selected and designed according to the characteristic parameters of the negative electrode current collector.

[0007] Furthermore, the characteristic parameters include the first stress of the negative electrode current collector under the first reference strain and the second stress of the negative electrode current collector under the second reference strain;

[0008] Wherein, the first reference strain is the deformation of the first test battery under the overcharge test after the first test battery is subjected to an overcharge test; wherein, the negative electrode sheet of the first test battery is coated with an active material layer with a coating weight of W and a compaction density of a first preset compaction density.

[0009] The second reference strain is the deformation of the second test battery under the overcharge test after the second test battery is subjected to an overcharge test; wherein, the negative electrode sheet of the second test battery is coated with an active material layer with a coating weight of W and a compaction density of a second preset compaction density; the first preset compaction density is less than the second preset compaction density.

[0010] Furthermore, the sum of the coating weight of the first active material layer and the coating weight of the second active material layer is equal to W;

[0011] the larger one of the first stress and the second stress is greater than or equal to the larger one of a first reference stress corresponding to the first reference strain and a second reference stress corresponding to the second reference strain, a coating weight of the first active material layer is greater than or equal to 1 / 2W, and a compaction density of the first active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density;

[0012] a compaction density of the second active material layer is greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer.

[0013] Further, a sum of the coating weight of the first active material layer and the coating weight of the second active material layer is equal to the W.

[0014] the larger one of the first stress and the second stress is greater than the smaller one of a first reference stress corresponding to the first reference strain and a second reference stress corresponding to the second reference strain and less than the larger one of the first reference stress and the second reference stress, a coating weight of the first active material layer is less than 1 / 2W;

[0015] the compaction density of the first active material layer and the compaction density of the second active material layer are greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer. Further, a sum of the coating weight of the first active material layer and the coating weight of the second active material layer is equal to the W.

[0016] the larger one of the first stress and the second stress is less than or equal to the smaller one of a first reference stress corresponding to the first reference strain and a second reference stress corresponding to the second reference strain, a coating weight of the first active material layer is less than 1 / 2W, and a compaction density of the first active material layer is less than the first preset compaction density;

[0017] a compaction density of the second active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density.

[0018] Further, the negative electrode current collector is a copper foil, a nickel foil, or a carbon foil.

[0019] Further, the negative electrode current collector has a thickness of 4 μm to 20 μm.

[0020] Further, the first preset compaction density has a value in a range of 1.55 g / cc to 1.78 g / cc.

[0021] The second preset compaction density is in a range of 1.35 g / cc to 1.85 g / cc.

[0022] According to a second aspect of the embodiments of the present disclosure, a lithium ion battery is provided, including the negative electrode sheet as described in any one of the preceding embodiments.

[0023] Further, the lithium ion battery is a soft package lithium ion battery.

[0024] The technical solutions provided by the embodiments of the present disclosure can include the following beneficial effects:

[0025] As can be seen from the above embodiments, the negative electrode sheet and the lithium ion battery provided by the present disclosure, by coating the first active material layer and the second active material layer on the surface of the negative electrode current collector, and making the coating weight and the compaction density of the first active material layer and the second active material layer different, and designing the coating weight and the compaction density of the first active material layer and the second active material layer according to the characteristic parameters of the negative electrode current collector, thus comprehensively considering the deformation risk and the compaction density of the sheet, on the basis of reducing the deformation risk of the sheet, the compaction density of the whole sheet can be maximized, and the energy density of the lithium ion battery can be improved.

[0026] It should be understood that the foregoing general description and the following detailed description are only exemplary and explanatory, and cannot limit the present disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate embodiments consistent with the present disclosure and, together with the description, serve to explain the principles of the disclosure.

[0028] Figure 1 FIG. 1 is a schematic diagram of a negative electrode sheet according to an exemplary embodiment of the present disclosure;

[0029] Figure 2 FIG. 3 is a schematic diagram of a calibration method for a negative electrode sheet according to an exemplary embodiment of the present disclosure;

[0030] Figure 3 FIG. 6 is a schematic diagram of an electronic device according to an exemplary embodiment of the present disclosure. DETAILED DESCRIPTION

[0031] The exemplary embodiments will be described in detail herein with reference to the attached drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present disclosure. Instead, they are merely examples of apparatuses and methods consistent with some aspects of the present disclosure as detailed in the appended claims.

[0032] Figure 1 This is a schematic diagram illustrating a negative electrode sheet according to an exemplary embodiment of the present disclosure. Please refer to... Figure 1 The negative electrode sheet provided in this embodiment includes a negative electrode current collector 1 and an active material layer 2 coated on the surface of the negative electrode current collector 1, wherein...

[0033] The active material layer 2 includes a first active material layer 21 and a second active material layer 22 stacked along a direction away from the negative electrode current collector 1. The coating weight and compaction density of the first active material layer 21 and the second active material layer 22 are different, and the coating weight and compaction density of the first active material layer 21 and the second active material layer 22 are selected and designed according to the characteristic parameters of the negative electrode current collector.

[0034] Specifically, the negative electrode current collector 1 is a copper foil, nickel foil, or carbon foil. Preferably, the negative electrode current collector is a copper foil.

[0035] Furthermore, the thickness of the negative electrode current collector 1 can be 4 μm to 20 μm. Preferably, the thickness of the negative electrode current collector 1 is 3 μm to 8 μm.

[0036] Specifically, the active material layer can be a silicon-carbon active material layer, which may include: 80% to 97% (by mass) silicon-carbon active material, 1% to 10% conductive agent and 2% to 15% adhesive.

[0037] It should be noted that the components and contents of the first active material layer and the second active material layer can be the same or different. In this embodiment, this is not limited.

[0038] Furthermore, the silicon-carbon active material may include one or more of the following substances: carbon nanotubes, carbon fibers, graphene, acetylene black; the adhesive may include one or more of the following substances: polytetrafluoroethylene, polyvinylidene fluoride, carboxymethyl cellulose, styrene rubber, silane coupling agent, titanate coupling agent, methyl cellulose, and polyacrylic acid.

[0039] Specifically, refer to Figure 1 The active material layer 2 includes a first active material layer 21 and a second active material layer 22 stacked along the direction away from the negative electrode current collector. The coating weight and compaction density of the first active material layer 21 and the second active material layer are different, and the coating weight and compaction density of the first active material layer and the second active material layer can be designed according to the characteristic parameters of the negative electrode current collector.

[0040] The negative pole piece provided by the embodiment is coated with the first active material layer and the second active material layer arranged in layers on the surface of the negative pole current collector, the coating weight and the compaction density of the first active material layer and the second active material layer are different, and the coating weight and the compaction density of the first active material layer and the second active material layer are designed according to the characteristic parameters of the negative pole current collector. In this way, the deformation risk and the compaction density of the pole piece can be comprehensively considered, the compaction density of the whole pole piece is maximally improved on the basis of reducing the deformation risk of the pole piece, and the energy density of the lithium ion battery is improved.

[0041] The coating weight and the compaction density of the first active material layer and the second active material layer are designed according to the characteristic parameters of the negative pole current collector as follows:

[0042] Specifically, the characteristic parameters include a first stress of the negative pole current collector under a first reference strain and a second stress of the negative pole current collector under a second reference strain.

[0043] The first reference strain is the deformation of the first test battery under an overcharge test after the overcharge test is performed on the first test battery, the active material layer with the coating weight W and the first preset compaction density is coated on the negative pole piece of the first test battery.

[0044] The second reference strain is the deformation of the second test battery under an overcharge test after the overcharge test is performed on the second test battery, the active material layer with the coating weight W and the second preset compaction density is coated on the negative pole piece of the second test battery, and the second preset compaction density is greater than the first preset compaction density.

[0045] It should be noted that the first stress value of the negative pole current collector under the first reference strain refers to the stress corresponding to the first reference strain in the tensile curve (stress-strain curve corresponding to the material of the negative pole current collector) of the negative pole current collector. Correspondingly, the second stress value of the negative pole current collector under the second reference strain refers to the stress corresponding to the second reference strain in the tensile curve of the negative pole current collector.

[0046] It should be noted that in the embodiment, the specific structure of the first test battery and the second test battery is not limited, as long as the active material layer with the coating weight W and the first preset compaction density is coated on the negative pole piece of the first test battery, and the active material layer with the coating weight W and the second preset compaction density is coated on the negative pole piece of the second test battery.

[0047] Further, the first preset compaction density has a value range of 1.55 g / cc-1.78 g / cc; and the second preset compaction density has a value range of 1.35 g / cc-1.85 g / cc. For example, in an embodiment, the negative pole piece of the first test battery is coated with an active material layer having a compaction density of 1.35 g / cc, and the negative pole piece of the second test battery is coated with an active material layer having a compaction density of 1.80 g / cc.

[0048] The overcharge test is briefly introduced as follows:

[0049] Specifically, the overcharge rate of the overcharge test can be 150%, 160%, etc. In this embodiment, it is not limited. For example, in an embodiment, the overcharge rate can be 150%.

[0050] In a specific implementation, the test battery is charged at a current of 1C under the condition that the ambient temperature is 20°C±5°C, and when the charging voltage reaches the charging limit voltage, the charging mode is changed to constant voltage charging until the charging current is less than or equal to 0.02C, and the maximum charging time is not greater than 1.5 hours.

[0051] It should be noted that the deformation of the test battery under the overcharge test can be the expansion rate of the negative pole piece of the test battery in the width direction under the overcharge test. Further, how to determine the deformation of the test battery under the overcharge test is described as follows:

[0052] In a specific implementation, some calibration points can be calibrated on the negative pole piece of the test battery before the overcharge test, and then the deformation of the test battery can be determined based on the position change of the calibration points after the overcharge test. For example, Figure 2 The implementation principle of the calibration method of the negative pole piece according to an exemplary embodiment of the present disclosure is shown. Refer to Figure 2 Before assembling the test battery, a preset number (the preset number is set according to actual needs, for example, in an embodiment, the preset number can be 10) of calibration points can be calibrated on the negative pole piece along the width direction of the negative pole piece, and the distance L1 between two adjacent calibration points is recorded.

[0053] Further, the test battery is assembled, and after the test battery is assembled, the test battery is subjected to the overcharge test according to the foregoing method, and after the test is completed, the test battery is disassembled, the previous calibration points are found, and the distance L2 between two adjacent calibration points is re-measured, and then the expansion rate is calculated based on L1 and L2. For example, in an embodiment, the expansion rate can be calculated based on the average value of L1 and the average value of L2, and the expansion rate=(average value of L2-average value of L1) / average value of L1.

[0054] The following will introduce in detail how to design the coating weight and the compaction density of the first active material layer and the second active material layer according to the characteristic parameters of the negative electrode current collector.

[0055] Specifically, the sum of the first coating weight of the first active material layer and the coating weight of the second active material layer is equal to the W.

[0056] In one embodiment, when the larger one of the first stress and the second stress is greater than or equal to the larger one of the first reference stress corresponding to the first reference strain and the second reference stress corresponding to the second reference strain, the coating weight of the first active material layer is greater than or equal to 1 / 2W, and the compaction density of the first active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density.

[0057] The compaction density of the second active material layer is greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer.

[0058] It should be noted that the first reference stress corresponding to the first reference strain refers to the stress corresponding to the first reference strain in the tensile curve of the negative electrode current collector of the first test battery (the strain-stress curve corresponding to the material of the negative electrode current collector of the first test battery).

[0059] The second reference stress corresponding to the second reference strain refers to the stress corresponding to the second reference strain in the tensile curve of the negative electrode current collector of the second test battery (the strain-stress curve corresponding to the material of the negative electrode current collector of the second test battery).

[0060] The following will be described by taking "the first reference strain is ε1, the first reference stress is N1, the second reference strain is ε2, the first reference stress is N2, the first stress of the selected negative electrode current collector material under the first reference strain ε1 is F1, and the first stress of the selected negative electrode current collector material under the second reference strain ε2 is F2" as an example.

[0061] According to the foregoing description, assuming that the larger one of N1 and N2 is N2, when the larger one of F1 and F2 is greater than N2, at this time, it indicates that the selected negative electrode current collector material has a greater ability to withstand elastic deformation than the negative electrode current collector material corresponding to the second test battery, at this time, the coating weight of the first active material layer can be greater than or equal to 1 / 2W, and the compaction density of the first active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density; and the compaction density of the second active material layer is greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer.

[0062] In this way, the first active layer adopts thick coating and high pressure density, and the second active layer adopts thin coating and low pressure density, which not only reduces the risk of deformation and improves the overall compaction density of the pole piece, but also improves the wettability of the electrolyte of the pole piece due to the low pressure density of the upper layer, thereby improving the kinetic performance of the pole piece.

[0063] Further, in another embodiment, when the larger one of the first stress and the second stress is greater than the smaller one of the first reference stress corresponding to the first reference strain and the second reference stress corresponding to the second reference strain, and is less than the larger one of the first reference stress and the second reference stress, the coating weight of the first active material layer is less than 1 / 2W.

[0064] The compaction densities of the first active material layer and the second active material layer are both greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than that of the first active material layer.

[0065] In combination with the previous example, that is, when the larger one of F1 and F2 is greater than N1 and less than N2, at this time, it is indicated that the selected negative current collector material has an elastic deformation capacity between the negative current collector material of the first test battery and the negative current collector material corresponding to the second test battery, at this time, the coating weight of the first active material layer can be less than 1 / 2W.

[0066] And the compaction densities of the first active material layer and the second active material layer are both greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than that of the first active material layer.

[0067] In this way, the first active layer adopts thick coating and high pressure density, and the second active layer adopts thin coating and low pressure density, which not only reduces the risk of deformation and improves the overall compaction density of the pole piece, but also improves the wettability of the electrolyte of the pole piece due to the low pressure density of the upper layer, thereby improving the kinetic performance of the pole piece.

[0068] For another example, in still another embodiment, the larger one of the first stress and the second stress is less than or equal to the smaller one of the first reference stress corresponding to the first reference strain and the second reference stress corresponding to the second reference strain, the coating weight of the first active material layer is less than 1 / 2W, and the compaction density of the first active material layer is less than the first preset compaction density.

[0069] The compaction density of the second active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density.

[0070] In the above example, when the larger one of F1 and F2 is less than or equal to N1, it indicates that the selected negative current collector material has a lower ability to withstand elastic deformation than the negative current collector material of the first test battery. In this case, the coating weight of the first active material layer can be less than 1 / 2W.

[0071] The first active material layer has a compaction density less than the first preset compaction density, and the second active material layer has a compaction density greater than the first preset compaction density and less than or equal to the second preset compaction density.

[0072] In this way, the first active layer is thin-coated and low-compacted, and the second active layer is thick-coated and high-compacted, which not only reduces the risk of deformation but also improves the overall compaction density of the pole piece.

[0073] The present disclosure also provides a lithium ion battery comprising the negative pole piece according to any one of the preceding embodiments.

[0074] Further, the lithium ion battery is a soft-pack lithium ion battery.

[0075] The present disclosure also provides an electronic device comprising the lithium ion battery according to any one of the preceding embodiments.

[0076] Figure 3 FIG. 1 is a schematic diagram of an electronic device according to an example embodiment of the present disclosure. For example, the electronic device 300 can be a mobile phone, a computer, a digital broadcast terminal, a messaging device, a game console, a tablet device, a medical device, a fitness device, a personal digital assistant, etc.

[0077] Referring to Figure 3 The electronic device 300 can include one or more of the following components: a processing component 302, a memory 304, a power supply component 306, a multimedia component 308, an audio component 310, an input / output (I / O) interface 312, a sensor component 314, and a communication component 316. The lithium ion battery according to any one of the preceding embodiments is also included.

[0078] The processing component 302 generally controls the overall operations of the electronic device 300, such as operations associated with display, telephone calls, data communications, camera operations, and recording operations. The processing component 302 can include one or more processors 320 to execute instructions. In addition, the processing component 302 can include one or more modules to facilitate the interaction between the processing component 302 and other components. For example, the processing component 302 can include a multimedia module to facilitate the interaction between the multimedia component 308 and the processing component 302.

[0079] The memory 304 is configured to store various types of data to support the operation of the electronic device 300. Examples of such data include instructions for any application or method operating on the electronic device 300, contact data, phonebook data, messages, pictures, videos, etc. The memory 304 can be implemented by any type of volatile or nonvolatile memory, or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic memory, flash memory, magnetic disc, or optical disc.

[0080] The power supply component 306 supplies power for various components of the electronic device 300. The power supply component 306 can include a power management system, one or more power supplies, and other components associated with generating, managing, and distributing power for the electronic device 300.

[0081] The multimedia component 308 includes a screen providing an output interface between the electronic device 300 and a user. In some embodiments, the screen can include a liquid crystal display (LCD) and a touch panel (TP). If the screen includes a touch panel, the screen can be implemented as a touch screen to receive an input signal from a user. The touch panel includes one or more touch sensors to sense a touch, a slide, and a gesture on the touch panel. The touch sensor can not only sense a boundary of a touching or a sliding action, but also detect duration and pressure related to the touching or sliding action. In some embodiments, the multimedia component 308 includes a front camera and / or a back camera. The front camera and / or the back camera can receive external multimedia data when the electronic device 300 is in an operation mode, such as a photographing mode or a video mode. Each of the front camera and the back camera can be a fixed optical lens system or have a focal length and optical zoom capability.

[0082] The audio component 310 is configured to output and / or input an audio signal. For example, the audio component 310 includes a microphone (MIC) configured to receive an external audio signal when the electronic device 300 is in an operation mode, such as a call mode, a recording mode, and a voice recognition mode. The received audio signal can be further stored in the memory 304 or transmitted via the communication component 316. In some embodiments, the audio component 310 also includes a speaker for outputting an audio signal.

[0083] The I / O interface 312 provides an interface between the processing component 302 and peripheral interface modules, which can be a keypad, a click wheel, buttons, etc. The buttons can include, but are not limited to, a home button, a volume button, a start button, and a lock button.

[0084] The sensor component 314 includes one or more sensors to provide the electronic device 300 with state assessments of various aspects. For example, the sensor component 314 can detect an open / closed state of the electronic device 300, relative positioning of components, such as a display and a keypad of the electronic device 300, a change in position of the electronic device 300 or a component of the electronic device 300, presence or absence of user contact with the electronic device 300, orientation or acceleration / deceleration / g-force and temperature changes of the electronic device 300. The sensor component 314 can include an accelerometer, a gyroscope sensor, a magnetic sensor, a pressure sensor or a temperature sensor.

[0085] The communication component 316 is configured to facilitate wired or wireless communication between the electronic device 300 and other devices. The electronic device 300 can access a wireless network based on a communication standard, such as WiFi, 2G or 3G, 4G LTE, 5G NR, or a combination thereof. In an example embodiment, the communication component 316 receives broadcast signals or broadcast-related information from an external broadcast management system via a broadcast channel. In an example embodiment, the communication component 316 further includes a Near Field Communication (NFC) module to facilitate short-range communication. For example, the NFC module can be implemented based on Radio Frequency Identification (RFID) techniques, infrared data association (IrDA) techniques, ultra-wideband (UWB) techniques, Bluetooth (BT) techniques, and other techniques.

[0086] In an example embodiment, the electronic device 300 can be implemented using one or more application-specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), controllers, micro-controllers, microprocessors or other electronic elements.

[0087] In an example embodiment, a non-transitory computer-readable storage medium including instructions, such as the memory 304 including instructions, is also provided, which can be executed by the processor 320 of the electronic device 300. For example, the non-transitory computer-readable storage medium can be a ROM, a random access memory (RAM), a CD-ROM, a magnetic tape, a floppy disc, and an optical data storage device, etc.

[0088] Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the features disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.

[0089] It is to be understood that the disclosure is not limited to the precise structures herein described and illustrated in the drawings, and that various modifications and changes can be made without departing from its scope. The scope of the disclosure is limited only by the claims that follow.

Claims

1. A negative electrode sheet, characterized by, The active material layer includes a first active material layer and a second active material layer stacked in a direction away from the negative current collector, the coating weight and the compaction density of the first active material layer and the second active material layer are different, and the coating weight and the compaction density of the first active material layer and the second active material layer are designed according to the characteristic parameters of the negative current collector. The characteristic parameters include a first stress of the negative current collector under a first reference strain and a second stress of the negative current collector under a second reference strain; the first reference strain is the deformation of the first test battery under an overcharge test after the overcharge test on the negative electrode sheet of the first test battery, wherein the coating weight of the active material layer on the negative electrode sheet of the first test battery is W, and the compaction density is a first preset compaction density; the second reference strain is the deformation of the second test battery under an overcharge test after the overcharge test on the negative electrode sheet of the second test battery, wherein the coating weight of the active material layer on the negative electrode sheet of the second test battery is W, and the compaction density is a second preset compaction density; the second preset compaction density is greater than the first preset compaction density; The sum of the coating weight of the first active material layer and the coating weight of the second active material layer is equal to W; the coating weight and the compaction density of the first active material layer, the coating weight and the compaction density of the second active material layer are determined as follows: The larger one of the first stress and the second stress is greater than or equal to the larger one of the first reference stress corresponding to the first reference strain and the second reference stress corresponding to the second reference strain, the coating weight of the first active material layer is greater than or equal to 1 / 2W, and the compaction density of the first active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density; the compaction density of the second active material layer is greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer; or, The larger one of the first stress and the second stress is greater than the smaller one of the first reference stress corresponding to the first reference strain and the second reference stress corresponding to the second reference strain and less than the larger one of the first reference stress and the second reference stress, the coating weight of the first active material layer is less than 1 / 2W; the compaction densities of the first active material layer and the second active material layer are both greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer; or, ​ The greater one of the first stress and the second stress is less than or equal to the greater one of a first reference stress corresponding to the first reference strain and a second reference stress corresponding to the second reference strain, the coating weight of the first active material layer is less than 1 / 2W, and the compaction density of the first active material layer is less than the first preset compaction density; the compaction density of the second active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density.

2. The negative electrode sheet according to claim 1, characterized by The negative current collector is a copper foil, a nickel foil or a carbon foil.

3. The negative electrode sheet according to claim 1, wherein The thickness of the negative current collector is 4-20 μm.

4. The negative electrode sheet according to claim 1, wherein When the coating weight and the compaction density of the first active material layer and the coating weight and the compaction density of the second active material layer are determined based on the following manners, the first preset compaction density has a value range of 1.55-1.78 g / cc; and the second preset compaction density has a value range of 1.35-1.85 g / cc: The greater one of the first stress and the second stress is greater than or equal to the greater one of a first reference stress corresponding to the first reference strain and a second reference stress corresponding to the second reference strain, the coating weight of the first active material layer is greater than or equal to 1 / 2W, and the compaction density of the first active material layer is greater than the first preset compaction density and less than or equal to the second preset compaction density; the compaction density of the second active material layer is greater than the first preset compaction density and less than the second preset compaction density, and the compaction density of the second active material layer is less than the compaction density of the first active material layer.

5. A lithium-ion battery, characterized by The negative electrode sheet comprises the negative electrode as claimed in any one of claims 1-4.

6. The lithium-ion battery of claim 5, wherein, The lithium ion battery is a soft package lithium ion battery.

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