Negative plate, battery and vehicle

Abstract

The invention discloses a negative plate, a battery and a vehicle. The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer located on one side or two sides of the negative electrode current collector, the negative electrode plate further comprises a bottom coating located between the negative electrode current collector and the negative electrode active material layer, and the bottom coating comprises magnesium salt. According to the negative plate provided by the invention, the negative impedance can be reduced, and the bonding force between the negative active material layer and the negative current collector is increased.

Description

Technical Field

[0001] The present application relates to a negative electrode sheet, a battery and a vehicle. Background Art

[0002] At present, the negative electrode sheet of the battery is generally formed by directly coating the negative electrode slurry on a smooth negative electrode collector, such as copper foil, to form a negative electrode active material layer. As a result, the adhesion between the negative electrode active material layer and the negative electrode collector is poor. During the battery production process and subsequent battery use, as the volume of the negative electrode sheet changes and the internal stress is released, the negative electrode active material layer is prone to fall off from the negative electrode collector, which may cause battery failure. Summary of the invention

[0003] The present application provides a negative electrode sheet, a battery and a vehicle, which can reduce the negative electrode impedance and increase the adhesion between the negative electrode active material layer and the negative electrode current collector.

[0004] In a first aspect, an embodiment of the present application provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer located on one side or both sides of the negative electrode current collector, the negative electrode sheet also comprising a primer layer located between the negative electrode current collector and the negative electrode active material layer, and the primer layer comprises a magnesium salt.

[0005] In some embodiments, the magnesium salt comprises one or more of magnesium ammonium phosphate, magnesium hydrogen phosphate, magnesium nitrate, magnesium carbonate, magnesium silicate and magnesium sulfate. In some embodiments, the magnesium salt has an amount of 3wt%-25wt% based on the total weight of the primer layer.

[0006] In some embodiments, based on the total weight of the primer layer, the content of the magnesium salt is 4 wt %-20 wt %.

[0007] In some embodiments, the primer layer further includes a first conductive agent, a first adhesive, and a first graphite.

[0008] In some embodiments, based on the total weight of the primer layer, the content of the first conductive agent is 0.5 wt %-10 wt %.

[0009] In some embodiments, based on the total weight of the primer layer, the content of the first binder is 0.3 wt %-1.5 wt %.

[0010] In some embodiments, based on the total weight of the primer layer, the content of the first graphite is ≥ 70 wt %.

[0011] In some embodiments, the first conductive agent includes one or more of conductive carbon black, Ketjen black, carbon nanotubes, acetylene black, and graphene.

[0012] In some embodiments, the first adhesive includes one or more of styrene-butadiene rubber, polytetrafluoroethylene, acrylate, lithium carboxymethyl cellulose, polyvinyl alcohol, and polyvinylidene fluoride.

[0013] In some embodiments, the first graphite includes natural graphite.

[0014] In some embodiments, the volume distribution particle size Dv90 of the first graphite is 2-30 μm.

[0015] In some embodiments, the primer layer has a thickness of 1-10 μm.

[0016] In some embodiments, the primer layer has a thickness of 2-5 μm.

[0017] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes one or more of a second graphite, soft carbon, hard carbon, silicon, silicon oxide, and silicon carbide.

[0018] In some embodiments, the second graphite includes one or more of natural graphite and artificial graphite.

[0019] In a second aspect, an embodiment of the present application provides a battery, comprising the negative electrode sheet of the first aspect of the embodiment of the present application.

[0020] In a third aspect, an embodiment of the present application provides a vehicle, comprising the battery of the second aspect of the embodiment of the present application, wherein the battery is used to provide electrical energy to the vehicle.

[0021] The negative electrode sheet of the embodiment of the present application includes a negative electrode current collector and a negative electrode active material layer located on one side or both sides of the negative electrode current collector, and the negative electrode sheet also includes a primer layer located between the negative electrode current collector and the negative electrode active material layer, and the primer layer includes a magnesium salt. Magnesium salt has a high surface roughness and a large specific capacity, so after adding magnesium salt to the primer layer, the surface roughness of the primer layer can be improved, so that the primer layer and the negative electrode active material layer are more closely combined, so that by adding magnesium salt to the primer layer of the negative electrode sheet, the negative electrode impedance can be reduced and the adhesion between the negative electrode active material layer and the negative electrode current collector can be increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only drawings of some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 A schematic diagram of the structure of the negative electrode sheet provided in some embodiments of the present application.

[0024] Description of Reference Numerals

[0025] 101. Negative electrode current collector; 102. Negative electrode active material layer; 103. Undercoat layer. DETAILED DESCRIPTION

[0026] The features and exemplary embodiments of various aspects of the present application will be described in detail below. In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain the present application, rather than to limit the present application. For those skilled in the art, the present application can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present application by illustrating the examples of the present application.

[0027] It should be noted that, in this application, the terms "first", "second", etc. are used to distinguish similar objects, and are not used to describe a specific order or sequence. Moreover, the term "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprising..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0028] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application). Unless otherwise specified, the test temperature of the parameters mentioned in this application is 25° C. and the test pressure is standard atmospheric pressure.

[0029] A list of items connected by the term "one or more of" may mean any combination of the listed items. The term "plurality" means more than two.

[0030] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this application.

[0031] Dvm refers to the particle size that reaches m% of the volume accumulation from the small particle size side in the volume-based particle size distribution. Dv90 refers to the particle size that reaches 90% of the volume accumulation from the small particle size side in the volume-based particle size distribution. For example, if Dv90 is 30μm, then the ratio of the volume of particles ≤30μm to the total volume is 90%.

[0032] In order to reduce the impact of the shedding of the negative electrode active material layer on the battery performance, the commonly used method is to add a layer of graphite coating with good adhesion and small particles between the negative electrode active material layer and the negative electrode current collector. However, since there is usually a passivation film on the surface of the negative electrode current collector, the contact resistance between the negative electrode active material layer and the graphite coating and the negative electrode current collector is large, resulting in poor conductivity between the negative electrode active material layer and the negative electrode current collector, which affects the battery performance.

[0033] In view of this, the inventors improved the negative electrode sheet.

[0034] Figure 1 This is a schematic diagram of the structure of the negative electrode sheet provided in some embodiments of the present application. Figure 1 As shown, the negative electrode sheet includes a negative electrode collector 101 and a negative electrode active material layer 103 located on one side or both sides of the negative electrode collector 101 , and the negative electrode sheet also includes an undercoat layer 102 located between the negative electrode collector 101 and the negative electrode active material layer 103 , and the undercoat layer 102 includes a magnesium salt.

[0035] Magnesium salt has a high surface roughness. Therefore, after adding magnesium salt to the bottom coating, the surface roughness of the bottom coating can be improved, so that the bottom coating and the negative electrode active material layer are more closely combined, thereby enhancing the adhesion between the negative electrode active material layer and the negative electrode current collector, and reducing the risk of the negative electrode active material layer falling off from the negative electrode current collector; in addition, after adding magnesium salt to the bottom coating, the interface impedance of the negative electrode can also be reduced. Therefore, after adding magnesium salt to the bottom coating, the internal resistance of the battery can be reduced, and the cycle performance and rate performance of the battery can be improved.

[0036] In some embodiments, the magnesium salt may include one or more of magnesium ammonium phosphate (MgNH4PO4), magnesium hydrogen phosphate (MgHPO4), magnesium nitrate (Mg(NO3)2), magnesium carbonate (MgCO3), magnesium silicate (MgSiO3) and magnesium sulfate (MgSO4). When the type of magnesium salt is within the above range, the internal resistance of the battery can be further reduced, and the cycle performance and rate performance of the battery can be improved.

[0037] In some embodiments, the magnesium salt may include one or both of magnesium ammonium phosphate (MgNH4PO4) and magnesium hydrogen phosphate (MgHPO4).

[0038] In some embodiments, the specific capacity of the magnesium salt may be greater than or equal to 500 mAh / g. The use of magnesium salts with high specific capacity can increase the ionic conductivity of the negative electrode, reduce the internal resistance of the battery, and improve the cycle performance and rate performance of the battery.

[0039] In some embodiments, based on the total weight of the primer layer, the content of the magnesium salt can be 3wt%-25wt%, for example, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 20wt%, 25wt%, or a range consisting of any two of the above values.

[0040] In some embodiments, based on the total weight of the primer layer, the content of the magnesium salt may be 4wt%-20wt%, 5wt%-15wt%, or 5wt%-8wt%.

[0041] When the content of magnesium salt in the undercoat layer is within the above range, the negative electrode sheet can have higher bonding strength and higher electronic conductivity, thereby further reducing the risk of the negative electrode active material layer falling off the negative electrode current collector, and further reducing the internal resistance of the battery, thereby improving the cycle performance and rate performance of the battery.

[0042] In some embodiments, the primer layer may further include a first conductive agent, a first adhesive, and a first graphite.

[0043] In some embodiments, based on the total weight of the primer layer, the content of the first conductive agent can be 0.5wt%-10wt%, for example, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, or a range consisting of any two of the above values.

[0044] When the content of the first conductive agent in the undercoat layer is within the above range, the negative electrode sheet can have a higher electronic conductivity, thereby further reducing the negative electrode impedance, reducing the internal resistance of the battery, and improving the cycle performance and rate performance of the battery.

[0045] In some embodiments, the content of the first adhesive may be 0.3-1.5wt%, for example, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, or a range consisting of any two of the above values.

[0046] When the content of the first binder in the undercoat layer is within the above range, the negative electrode sheet can have a higher bonding strength, thereby further reducing the risk of the negative electrode active material layer falling off from the negative electrode current collector.

[0047] In some embodiments, the content of the first graphite may be ≥70 wt %, ≥80 wt %, ≥90 wt %.

[0048] In some embodiments, the content of the first graphite may be 70 wt %-96 wt %, 73.2 wt %-95.2 wt %, or 78.2 wt %-94.2 wt %.

[0049] When the content of the first graphite in the undercoat layer is within the above range, the negative electrode sheet can have a higher ion conductivity, and the internal resistance of the battery can be further reduced, thereby improving the cycle performance and rate performance of the battery.

[0050] In some embodiments, the first conductive agent may include one or more of conductive carbon black, Ketjen black, carbon nanotubes, acetylene black, and graphene.

[0051] In some embodiments, the first adhesive may include one or more of styrene-butadiene rubber, polytetrafluoroethylene, acrylate, lithium carboxymethyl cellulose, polyvinyl alcohol, and polyvinylidene fluoride.

[0052] In some embodiments, the first graphite may include natural graphite.

[0053] Natural graphite has small particle size, high specific capacity, high degree of graphitization, and is not easy to agglomerate. Using it in the base coat can improve the consistency of the base coat, improve the ionic conductivity of the negative electrode, reduce the negative electrode interface impedance, reduce the internal resistance of the battery, and improve the battery's cycle performance and rate performance.

[0054] Magnesium salt has high electrical conductivity and specific capacity. Combining magnesium salt with the first conductive agent and the first graphite can further reduce the negative electrode impedance, further reduce the internal resistance of the battery, and further improve the cycle performance and rate performance of the battery.

[0055] In some embodiments, the volume distribution particle size Dv90 of the first graphite can be 2-30 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or a range consisting of any two of the above values.

[0056] In some embodiments, the thickness of the primer layer may be 1-10 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or a range consisting of any two of the above values.

[0057] In some embodiments, the primer layer may have a thickness of 2-5 μm.

[0058] When the thickness of the primer layer is within the above range, the negative electrode impedance can be further reduced, the internal resistance of the battery can be reduced, and the cycle performance and rate performance of the battery can be improved.

[0059] The thickness of the primer layer can be obtained by using conventional testing instruments and testing methods in the art. For example, it can be obtained by using a scanning electron microscope. During the test, multiple positions (for example, more than 10) can be randomly selected in the negative electrode sheet for measurement, and the vertical distance between the surface of the primer layer close to the negative electrode active material layer and the surface of the primer layer in contact with the negative electrode current collector is taken, and then the average value of the multiple positions is taken as the thickness of the primer layer.

[0060] In the present application, the thickness of the primer layer refers to the thickness of the primer layer located on the negative electrode current collector side.

[0061] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material may include one or more of a second graphite, soft carbon, hard carbon, silicon, silicon oxide, and silicon carbide.

[0062] In some embodiments, the second graphite may include one or more of natural graphite and artificial graphite.

[0063] In some embodiments, the negative electrode active material layer may further include a negative electrode conductive agent, which may include but is not limited to one or more of conductive carbon black, Ketjen black, carbon nanotubes, acetylene black and graphene.

[0064] In some embodiments, the negative electrode active material layer may further include a negative electrode binder, which may include butadiene styrene rubber, polytetrafluoroethylene, acrylate, lithium carboxymethyl cellulose, polyvinyl alcohol, and polyvinylidene fluoride.

[0065] The present application does not impose any limitation on the thickness of the negative electrode active material layer, and the thickness may be the thickness of a common negative electrode active material layer for batteries in the art.

[0066] The present application has no particular restrictions on the material of the negative electrode current collector, and a material with electronic conductivity can be selected. For example, the negative electrode current collector can be made of copper foil or copper alloy foil.

[0067] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the primer slurry can be coated on the negative electrode current collector, dried, and then the negative electrode slurry can be coated on the primer, dried, and rolled to obtain the negative electrode sheet.

[0068] In some embodiments, the undercoat slurry may include a magnesium salt, a first conductive agent, a first binder, a first graphite, and a solvent.

[0069] In some embodiments, the solvent in the base coating slurry may be water, such as deionized water, but the embodiments of the present application are not limited thereto.

[0070] In some embodiments, the primer slurry can be prepared as follows: the first adhesive and the solvent are fully stirred and mixed to obtain a mixed solution A; the first conductive agent is fully mixed with the mixed solution A to form a good conductive network, and then magnesium salt is added and mixed to obtain a mixed solution B; the first graphite and the first adhesive are mixed and stirred to obtain a mixed solution C; the mixed solution C and the mixed solution B are fully stirred and mixed to obtain the primer slurry.

[0071] In some embodiments, the negative electrode slurry may include a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a solvent. The solvent may be water, such as deionized water, but the embodiments of the present application are not limited thereto.

[0072] The embodiment of the present application also provides a battery, which includes the negative electrode sheet provided in the embodiment of the present application.

[0073] The battery also includes a positive electrode sheet. The material, composition and manufacturing method of the positive electrode sheet may include any technology known in the prior art.

[0074] In some embodiments, the positive electrode sheet may include a positive electrode current collector and a positive electrode active material layer located on one side or both sides of the positive electrode current collector.

[0075] The present application has no particular restrictions on the material of the positive electrode current collector, and a material with electronic conductivity can be selected. For example, the positive electrode current collector can be made of aluminum foil or aluminum alloy foil.

[0076] The positive electrode active material layer includes a positive electrode active material. The positive electrode active material can be selected from materials that can absorb and release lithium. The specific type of the positive electrode active material is not specifically limited and can be selected according to needs. As an example, the positive electrode active material can include but is not limited to one or more of lithium iron phosphate, lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and their respective modified compounds. These materials can be used alone or in combination of two or more.

[0077] The modified compounds of the above-mentioned positive electrode active materials may be modified by doping, surface coating, or both doping and coating.

[0078] In some embodiments, the positive electrode active material layer may include a positive electrode conductive agent, which may include, but is not limited to, one or more of conductive carbon black, Ketjen black, carbon nanotubes, acetylene black, and graphene.

[0079] In some embodiments, the positive electrode active material layer may further include a positive electrode binder, which may include but is not limited to one or more of polytetrafluoroethylene, acrylate, and polyvinylidene fluoride.

[0080] The battery also includes an electrolyte, which can be a solid electrolyte, a gel electrolyte or a liquid electrolyte (also known as an electrolyte).

[0081] In some embodiments, the electrolyte may be an electrolyte solution. The electrolyte solution may include an electrolyte salt and a solvent, and the electrolyte salt contains lithium ions. The types of the electrolyte salt and the solvent are not specifically limited and can be selected according to needs.

[0082] In some embodiments, as examples, the electrolyte salt may include, but is not limited to, one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorooxalatoborate, and lithium dioxalatoborate.

[0083] In some embodiments, as examples, the solvent may include, but is not limited to, one or more of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0084] The battery may also include a separator, which may be disposed between the positive electrode sheet and the negative electrode sheet, and mainly serves to prevent the positive electrode and the negative electrode from short-circuiting.

[0085] In some embodiments, the separator may include a polyethylene film, a polypropylene film, or a composite film thereof.

[0086] In some embodiments, the surface of the separator may further have a coating, such as an inorganic coating, an organic coating, or an organic-inorganic composite coating.

[0087] An embodiment of the present application also provides a vehicle, which includes the battery provided in the embodiment of the present application.

[0088] The vehicle provided in the embodiment of the present application may be a pure electric vehicle, a hybrid electric vehicle, or an extended-range vehicle, etc., and the embodiment of the present application is not limited to this.

[0089] Example

[0090] The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0091] Test Section

[0092] (1) Test of the adhesion of the negative electrode

[0093] The rolled negative electrode sheet is made into several rectangular electrode sheet samples with a length of 260mm and a width of 37mm. A double-sided tape (model NITTO.5000NS0) with a length and width of 10mm is attached to the head of the negative electrode active material layer of the sample; the sample to be tested is placed in the tensile test device of the electronic universal testing machine to measure the adhesion between the negative electrode active material layer and the bottom coating and the negative electrode current collector. The pulling speed of the tensile test device is 50mm / min, the tensile displacement is 150mm, the accuracy of the tensile sensor in the tensile test device is ±0.1N, and the pulling direction is 60°.

[0094] (2) Battery DC internal resistance test

[0095] At 25°C, charge the battery at 1C constant current to a voltage of 4.35V, then charge at a constant voltage to a current of 0.05C, at which point the battery is fully charged, i.e., 100% SOC; let stand for 30 minutes, discharge the battery at 1C to adjust the battery to 70% SOC, at which point the voltage is U0; discharge the battery at a current pulse of 400A for 10s, and record the voltage after discharge U1. The battery's DC internal resistance DCR (mohm) = (U0-U1) / 400A. The test equipment can be a Xinwei charge and discharge tester.

[0096] (3) Battery cycle performance test

[0097] At 25℃, charge the battery at 1C constant current to 4.35V, then charge at constant voltage to 0.05C. At this time, the battery is fully charged. Record the charging capacity at this time, which is the charging capacity of the first cycle. After standing for 30 minutes, discharge the battery at 1C constant current to 2.8V. After standing for 30 minutes, record the discharge capacity at this time, which is the discharge capacity of the first cycle. Repeat the above steps to perform cyclic charge and discharge tests, and record the discharge capacity after 800 cycles. Battery capacity retention rate after 800 cycles = discharge capacity after 800 cycles / discharge capacity of the first cycle × 100%.

[0098] (4) Battery rate performance test

[0099] At 25°C, the battery was charged to 4.35V at a constant current of 0.33C, and then charged to a current of 0.05C at a constant voltage. After standing for 30 minutes, the battery was discharged to 2.8V at a constant current of 0.33C. After standing for 30 minutes, the discharge capacity of the battery was recorded as C0.

[0100] At 25°C, the battery was charged at a constant current of 1C to a voltage of 4.35V; then charged at a constant voltage to a current of 0.05C; after standing for 30 minutes, the battery was discharged at a constant current of 2C to 2.8V; after standing for 30 minutes, the discharge capacity of the battery was recorded as C1.

[0101] Battery 2C rate discharge capacity retention rate = C1 / C0×100%.

[0102] Example 1

[0103] (1) Preparation of negative electrode

[0104] Preparation of primer slurry: fully stir and mix the first adhesive styrene-butadiene rubber with a content of 0.8wt% and the solvent deionized water to obtain a mixed solution A; fully mix the first conductive agent conductive carbon black (Super P) with a content of 0.5wt% and the mixed solution A to form a good conductive network, and then add MgHPO4 with a content of 5wt% and mix and stir to obtain a mixed solution B; mix the first graphite with a content of 93.2wt% of natural graphite, a degree of graphitization of 90%, a particle size Dv90 of 12μm, and a content of 0.5wt% of the first adhesive styrene-butadiene rubber to obtain a mixed solution C; fully stir and mix the mixed solution C with the mixed solution B to obtain a primer slurry.

[0105] Preparation of negative electrode slurry: The negative electrode active material is artificial graphite (particle size Dv90 is 35μm), the negative electrode conductive agent is conductive carbon black (Super P), and the negative electrode binder is styrene-butadiene rubber and lithium carboxymethyl cellulose. The above components are mixed in a weight ratio of 96.5:0.8:1.7:1 to obtain an initial mixture, and then deionized water is used as a solvent to prepare a negative electrode slurry.

[0106] The obtained primer slurry is evenly coated on both surfaces of the copper foil and dried to obtain a primer layer with a thickness of 3 μm. The negative electrode slurry is then coated on the primer layer, and the negative electrode sheet is obtained after drying and rolling.

[0107] (2) Preparation of positive electrode

[0108] The positive electrode active material LiNi 0.5 Co 0.2 Mn 0.3 O2, positive electrode conductive agent conductive carbon black (Super P), and positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 96.8:1.9:1.3, and NMP is added as a solvent to prepare a positive electrode slurry. The obtained positive electrode slurry is evenly coated on both surfaces of the aluminum foil, and the positive electrode sheet is obtained after drying and rolling.

[0109] (3) Preparation of electrolyte

[0110] In a dry argon atmosphere, solvents ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are mixed in a weight ratio of 2:2:1, and then lithium hexafluorophosphate (LiPF6) is added to the solvent and mixed evenly to obtain an electrolyte. The molar concentration of LiPF6 in the electrolyte is 1.1 mol / L.

[0111] (4) Preparation of batteries

[0112] The positive electrode sheet, separator and negative electrode sheet prepared above are wound, and then placed in an aluminum shell, injected with the prepared electrolyte and packaged, and then subjected to processes such as formation and degassing to obtain a battery. The battery size is 52×148×106mm.

[0113] Example 2

[0114] Except for the different contents of MgHPO4 and natural graphite in the undercoat slurry, the rest of the preparation process is the same as that of Example 1.

[0115] The content of MgHPO4 is 8wt%, and the content of natural graphite is 90.2wt%.

[0116] Example 3

[0117] Except for the different contents of MgHPO4 and natural graphite in the undercoat slurry, the rest of the preparation process is the same as that of Example 1.

[0118] The content of MgHPO4 is 4wt%, and the content of natural graphite is 94.2wt%.

[0119] Example 4

[0120] Except for the different contents of MgHPO4 and natural graphite in the undercoat slurry, the rest of the preparation process is the same as that of Example 1.

[0121] The content of MgHPO4 is 20wt%, and the content of natural graphite is 78.2wt%.

[0122] Example 5

[0123] Except for the different contents of MgHPO4 and natural graphite in the undercoat slurry, the rest of the preparation process is the same as that of Example 1.

[0124] The content of MgHPO4 is 3wt%, and the content of natural graphite is 95.2wt%.

[0125] Example 6

[0126] Except for the different contents of MgHPO4 and natural graphite in the undercoat slurry, the rest of the preparation process is the same as that of Example 1.

[0127] The content of MgHPO4 is 25wt%, and the content of natural graphite is 73.2wt%.

[0128] Comparative Example 1

[0129] Except that no magnesium salt is added to the primer layer, the content of natural graphite is 98.2wt%, and the rest of the preparation process is the same as that of Example 1.

[0130] The compositions of the primer layers of Examples 1-6 and Comparative Example 1 are shown in Table 1.

[0131] The test results of the negative electrode sheet and the battery are shown in Table 2.

[0132] Table 1

[0133]

[0134] Table 2

[0135]

[0136]

[0137] It can be seen from the test results in Table 2 that when the undercoat layer includes magnesium salt, the adhesion between the negative electrode active material layer and the negative electrode current collector can be increased, the internal resistance of the battery can be reduced, and the cycle performance and rate performance of the battery can be improved.

[0138] It can also be seen from the test results in Table 2 that when the content of magnesium salt in the undercoat layer is between 3-25wt%, and can be optionally between 4-20wt%, the negative electrode sheet can have a higher bonding strength and a higher electronic conductivity, thereby further reducing the risk of the negative electrode active material layer falling off from the negative electrode current collector, and further reducing the internal resistance of the battery, thereby improving the cycle performance and rate performance of the battery.

[0139] Example 7

[0140] Except for the different types of magnesium salt in the base coating slurry, the rest of the preparation process is the same as that of Example 1.

[0141] The magnesium salt in the base coating slurry is MgNH4PO4.

[0142] Example 8

[0143] Except for the different types of magnesium salt in the base coating slurry, the rest of the preparation process is the same as that of Example 1.

[0144] The magnesium salt in the base coating slurry is Mg(NO3)2.

[0145] Example 9

[0146] Except for the different types of magnesium salt in the base coating slurry, the rest of the preparation process is the same as that of Example 1.

[0147] The magnesium salt in the base coating slurry is MgCO3.

[0148] Example 10

[0149] Except for the different types of magnesium salt in the base coating slurry, the rest of the preparation process is the same as that of Example 1.

[0150] The magnesium salt in the base coating slurry is MgSiO3.

[0151] Embodiment 11

[0152] Except for the different types of magnesium salt in the base coating slurry, the rest of the preparation process is the same as that of Example 1.

[0153] The magnesium salt in the base coating slurry is MgSO4.

[0154] Comparative Example 2

[0155] Except that the magnesium salt in the undercoat slurry is replaced by LiZnBO3, the rest of the preparation process is the same as that of Example 1.

[0156] Comparative Example 3

[0157] Except that the magnesium salt in the undercoat slurry is replaced by Ni3V2O8, the rest of the preparation process is the same as that of Example 1.

[0158] The compositions of the primer layers of Example 1, Examples 7-11 and Comparative Examples 2-3 are shown in Table 3.

[0159] The test results of the negative electrode sheet and the battery are shown in Table 4.

[0160] Table 3

[0161]

[0162] Table 4

[0163]

[0164]

[0165] It can be seen from the test results in Table 4 that when the content of magnesium salt in the primer layer is the same and the type of magnesium salt is within the scope of this application, the addition of magnesium salt has slight differences in reducing the internal resistance of the battery and improving the cycle performance and rate performance of the battery, but both can reduce the internal resistance of the battery and improve the cycle performance and rate performance of the battery.

[0166] It can also be seen from the test results in Table 4 that when the type of magnesium salt in the undercoat layer is outside the scope of this application, it can neither improve the negative electrode adhesion well, nor reduce the battery internal resistance and improve the battery's cycle performance and rate performance.

[0167] Example 12

[0168] Except for the thickness of the primer layer, the rest of the preparation process is the same as that of Example 1.

[0169] The thickness of the primer layer was 1 μm.

[0170] Example 13

[0171] Except for the thickness of the primer layer, the rest of the preparation process is the same as that of Example 1.

[0172] The thickness of the primer layer was 2 μm.

[0173] Embodiment 14

[0174] Except for the thickness of the primer layer, the rest of the preparation process is the same as that of Example 1.

[0175] The thickness of the primer layer was 5 μm.

[0176] Embodiment 15

[0177] Except for the thickness of the primer layer, the rest of the preparation process is the same as that of Example 1.

[0178] The thickness of the primer layer was 10 μm.

[0179] The compositions of the primer layers of Examples 12-15 and Example 1 are shown in Table 5.

[0180] The test results of the negative electrode sheet and the battery are shown in Table 6.

[0181] Table 5

[0182]

[0183]

[0184] Table 6

[0185]

[0186] It can be seen from the test results in Table 6 that when the type and content of magnesium salt in the primer layer are the same, the thickness of the primer layer is in the range of 1-10 μm, and can be selected as 2-5 μm, which can further reduce the negative electrode impedance, reduce the internal resistance of the battery, and improve the cycle performance and rate performance of the battery.

[0187] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any technician familiar with the technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer located on one side or both sides of the negative electrode current collector, characterized in that: The negative electrode sheet further includes an undercoat layer between the negative electrode current collector and the negative electrode active material layer, and the undercoat layer includes a magnesium salt.

2. The negative electrode sheet according to claim 1, characterized in that: The magnesium salt includes one or more of magnesium ammonium phosphate, magnesium hydrogen phosphate, magnesium nitrate, magnesium carbonate, magnesium silicate and magnesium sulfate; and / or, Based on the total weight of the primer layer, the content of the magnesium salt is 3wt%-25wt%.

3. The negative electrode sheet according to claim 2, characterized in that: Based on the total weight of the primer layer, the content of the magnesium salt is 4wt%-20wt%.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: The primer layer further includes a first conductive agent, a first adhesive, and a first graphite.

5. The negative electrode sheet according to claim 4, characterized in that: Based on the total weight of the primer layer, The content of the first conductive agent is 0.5wt%-10wt%, and / or, The content of the first adhesive is 0.3wt%-1.5wt%, and / or, The content of the first graphite is ≥70wt%.

6. The negative electrode sheet according to claim 4, characterized in that: The first conductive agent includes one or more of conductive carbon black, Ketjen black, carbon nanotubes, acetylene black and graphene; and / or, The first adhesive comprises one or more of styrene-butadiene rubber, polytetrafluoroethylene, acrylate, lithium carboxymethyl cellulose, polyvinyl alcohol and polyvinylidene fluoride; and / or, The first graphite comprises natural graphite; and / or, The volume distribution particle size Dv90 of the first graphite is 2-30 μm.

7. The negative electrode sheet according to claim 1, characterized in that: The thickness of the primer layer is 1-10 μm.

8. The negative electrode sheet according to claim 7, characterized in that: The thickness of the primer layer is 2-5 μm.

9. The negative electrode sheet according to claim 4, characterized in that: The negative electrode active material layer includes a negative electrode active material, wherein the negative electrode active material includes one or more of a second graphite, soft carbon, hard carbon, silicon, silicon oxide and silicon carbide, and the second graphite includes one or more of natural graphite and artificial graphite.

10. A battery comprising the negative electrode sheet according to any one of claims 1 to 9.

11. A vehicle comprising the battery according to claim 10, wherein the battery is used to provide electrical energy for the vehicle.

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