Negative electrode sheet, secondary battery and method for manufacturing the same, battery module, battery pack, and electric device

Abstract

The application provides a negative electrode sheet, a secondary battery and a preparation method thereof, a battery module, a battery pack and a power utilization device, and belongs to the technical field of batteries. The negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, and the negative electrode film layer comprises a negative electrode active material, a metal hydride, a conductive agent and a binder, wherein the negative electrode active material comprises a silicon-based negative electrode active material. The use of the negative electrode sheet of the application can significantly improve the capacity retention rate of the secondary battery, thereby significantly improving the cycle performance of the secondary battery.

Description

[0001] Cross-references

[0002] This application is the text of the entry into the Chinese national phase of the international patent application filed on August 30, 2022, entitled "Negative electrode sheet, secondary battery and preparation method thereof, battery module, battery pack and power device", with international application number PCT / CN2022 / 115810, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a negative electrode sheet, a secondary battery and its preparation method, a battery module, a battery pack and an electrical device. Background Technology

[0004] In recent years, secondary batteries have been increasingly widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in various fields such as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. Due to the significant development of secondary batteries, higher requirements have been placed on their energy density, cycle performance, and safety performance. However, the cycle performance and other aspects of secondary batteries used in existing technologies urgently need further improvement. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a negative electrode sheet that enables a secondary battery containing the negative electrode sheet to have improved cycle performance.

[0006] To achieve the above objectives, a first aspect of this application provides a negative electrode sheet, comprising a negative current collector and a negative electrode film layer on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material, a metal hydride, a conductive agent and a binder, wherein the negative electrode active material comprises a silicon-based negative electrode active material.

[0007] In any embodiment, the metal hydride has the general formula MH. x M is selected from at least one of Na, Mg, Ca and Al, and optionally M is Mg, x is an integer from 1 to 5, and optionally x is 1, 2 or 3; further optionally, the metal hydride is magnesium hydride.

[0008] In any embodiment, the metal hydride accounts for 5% to 35% of the mass of the negative electrode film, optionally 8% to 32%, further optionally 10% to 30%, and even more optionally 16% to 24%.

[0009] In any embodiment, the mass ratio of the silicon-based anode active material to the metal hydride is 1:(0.5-3.5), optionally 1:(0.8-3.2), further optionally 1:(1-3), and even more optionally 1:(1.6-2.4).

[0010] In any embodiment, the negative electrode active material further comprises a carbon-based negative electrode active material.

[0011] In any embodiment, the mass ratio of the silicon-based anode active material to the carbon-based anode active material is 1:(4-10), optionally 1:(5-8), and further optionally 1:(6-7).

[0012] In any embodiment, the silicon-based anode active material is selected from at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy; and / or, the particle size Dv50 of the silicon-based anode active material is from 3 μm to 10 μm, optionally from 4 μm to 8 μm; and / or, the silicon-based anode active material accounts for 3% to 20% of the mass of the anode film, optionally from 5% to 15%.

[0013] In any embodiment, the carbon-based anode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, and hard carbon; and / or, the particle size Dv50 of the carbon-based anode active material is from 5 μm to 30 μm, optionally from 10 μm to 20 μm; and / or, the carbon-based anode active material accounts for 30% to 80% of the mass of the anode film, optionally from 40% to 78%, and further optionally from 50% to 77%.

[0014] The second aspect of this application provides a secondary battery comprising a positive electrode, a separator, an electrolyte, and the negative electrode described in the first aspect of this application.

[0015] A third aspect of this application provides a method for preparing the secondary battery described in the second aspect of this application, comprising a formation step, wherein the formation step includes constant voltage discharge treatment at 0.45±0.1V, optionally 0.45±0.05V, and at 0.23±0.1V, optionally 0.23±0.05V, for 0.5 hours to 1.5 hours, optionally 0.8 hours to 1.2 hours respectively.

[0016] A fourth aspect of this application provides a secondary battery prepared according to the method described in the third aspect of this application, wherein in the negative electrode sheet, the surface of the silicon-based negative electrode active material particles comprises a metal or a lithium metal alloy and lithium hydride, wherein the metal is selected from at least one of Na, Mg, Ca and Al.

[0017] The fifth aspect of this application provides a battery module including a secondary battery as described in the second or fourth aspect of this application or a secondary battery prepared according to the method described in the third aspect of this application.

[0018] A sixth aspect of this application provides a battery pack including the battery module described in the fifth aspect of this application.

[0019] A seventh aspect of this application provides an electrical device comprising at least one of the secondary battery described in the second or fourth aspect of this application, the battery module described in the fifth aspect of this application, or the battery pack described in the sixth aspect of this application.

[0020] Since the power supply device of this application includes at least one of the secondary battery, battery module or battery pack provided in this application, it has at least the same advantages as the secondary battery. Attached Figure Description

[0021] Figure 1 The cross-section of the negative electrode obtained in Example 1 of this application is shown in an electron microscope image taken using a LEO-1530 scanning electron microscope, which reveals the morphology of the silicon particles.

[0022] Figure 2 The silicon elemental distribution map of the cross-section of the negative electrode obtained in Example 1 of this application was obtained using a Ultima IV X-ray diffractometer.

[0023] Figure 3 The magnesium element distribution map of the cross-section of the negative electrode obtained in Example 1 of this application was obtained using a Ultima IV X-ray diffractometer.

[0024] Figure 4 The X-ray diffraction patterns of the negative electrode film of the secondary battery obtained by Example 1 of this application are compared before and after 200 charge-discharge cycles. The magnesium hydride disappears after cycling.

[0025] Figure 5 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0026] Figure 6 yes Figure 5 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0027] Figure 7 This is a schematic diagram of a battery module according to one embodiment of this application.

[0028] Figure 8 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0029] Figure 9 yes Figure 8An exploded view of a battery pack according to one embodiment of this application is shown.

[0030] Figure 10 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0033] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the negative electrode sheet, secondary battery, method for preparing the same, battery module, battery pack, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0034] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0036] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0039] Unless otherwise specified, all operations in this application are performed at room temperature (25°C) and normal pressure (101 kPa).

[0040] The inventors discovered that in existing technologies, the reaction of metal hydrides and silicon oxides to generate silicon anodes only involves the preparation of the anode active material and does not involve the solid electrolyte interphase (SEI) layer on its surface. Unexpectedly, the inventors found that by adding metal hydrides to the anode active material containing silicon-based materials, a solid electrolyte interphase layer generated in situ on the surface of silicon particles can be obtained, resulting in a significantly improved capacity retention rate and enhanced cycle performance of the secondary battery.

[0041] Regardless of any particular theory, it is currently believed that existing silicon-based materials exhibit significant volume expansion and structural fragility during cycling, resulting in a substantial SEI layer. This application addresses this issue by adding metal hydrides to the negative electrode active material. Since the lithiation processes of the metal hydride and the silicon-based material occur at different potentials, both lead to significant volume expansion, resulting in intense internal stress within the electrode. Under this intense internal stress, the lithiation products of the metal hydride—namely, metal and lithium hydride—migrate to the fractured silicon particles and gradually transform into a conductive matrix containing ionicly conductive lithium hydride and electronically conductive partially reversibly lithilated metal. The silicon particles are confined within this mixed conductive matrix of lithium hydride and metal or a lithium metal alloy, thus ensuring superior cycling performance of the silicon negative electrode.

[0042] Therefore, a first aspect of this application provides a negative electrode sheet, including a negative current collector and a negative electrode film layer on at least one surface of the negative current collector, the negative electrode film layer comprising a negative electrode active material, a metal hydride, a conductive agent and a binder, wherein the negative electrode active material comprises a silicon-based negative electrode active material.

[0043] In some embodiments, the metal hydride has the general formula MH x M is selected from at least one of Na, Mg, Ca, and Al, and optionally M is Mg, x is an integer from 1 to 5, and optionally x is 1, 2 or 3; further optionally, the metal hydride is magnesium hydride.

[0044] In some embodiments, the particle size Dv50 of the metal hydride is from 50 nm to 200 nm, and can be selected from 100 nm to 150 nm.

[0045] Dv50 has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a laser particle size analyzer (e.g., Master Size 3000) in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0046] In some embodiments, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0047] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0048] In some embodiments, the metal hydride accounts for 5% to 35% of the mass of the negative electrode film, optionally 8% to 32%, further optionally 10% to 30%, and even more optionally 16% to 24%.

[0049] When the content of metal hydrides is within the above-mentioned range, the particles of the silicon anode active material can be better protected and restricted, thus preventing particle breakage due to expansion during cycling and improving the cycle performance of the secondary battery. Advantageously, it can also prevent the local agglomeration of metal hydrides and reaction products, thereby improving the stability and specific capacity of the anode sheet.

[0050] In some embodiments, the mass ratio of the silicon-based anode active material to the metal hydride is 1:(0.5-3.5), optionally 1:(0.8-3.2), further optionally 1:(1-3), further optionally 1:(1.5-2.8), and even more optionally 1:(1.6-2.4).

[0051] When the mass ratio of silicon-based anode active material to metal hydride is within the above range, it can, on the one hand, improve the continuity and integrity of the composite highly conductive and ion-conducting solid electrolyte layer on the surface of silicon particles, and better limit the volume expansion of silicon particles during cycling; on the other hand, it can better avoid the agglomeration of excess metal hydride and reaction products, and ensure the capacity utilization and cycling stability of the entire active material.

[0052] In some embodiments, the negative electrode active material further comprises a carbon-based negative electrode active material.

[0053] In some embodiments, the mass ratio of the silicon-based anode active material to the carbon-based anode active material is 1:(4-10), optionally 1:(5-8), further optionally 1:(6-7), and even more optionally 1:(6.1-6.8).

[0054] In some embodiments, the silicon-based anode active material is selected from at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy; and / or, the particle size Dv50 of the silicon-based anode active material is 3 μm to 10 μm, optionally 4 μm to 8 μm; and / or, the silicon-based anode active material accounts for 3% to 20% of the mass of the anode film, optionally 5% to 15%, and even more optionally 7% to 12%.

[0055] In some embodiments, the carbon-based anode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, and hard carbon; and / or, the particle size of the carbon-based anode active material is 5 μm to 30 μm, optionally 10 μm to 20 μm, and even more optionally 12 μm to 18 μm; and / or, the carbon-based anode active material accounts for 30% to 80% of the mass of the anode film, optionally 40% to 78%, further optionally 50% to 77%, even more optionally 55% to 76.5%, and even more optionally 65% ​​to 71%.

[0056] In some embodiments, the negative electrode film layer further includes a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0057] In some embodiments, the conductive agent accounts for 0.4% to 1.5% of the mass percentage of the negative electrode film, optionally 0.6% to 1.0%.

[0058] In some embodiments, the negative electrode film layer further includes a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0059] In some embodiments, the binder constitutes 0.5% to 1.5% of the negative electrode film by mass, optionally 0.6% to 1.2%.

[0060] In some embodiments, the negative electrode film layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Optionally, the thickener accounts for 0.6% to 2% of the mass percentage of the negative electrode film layer, and optionally 1% to 1.5%.

[0061] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, metal hydride, conductive agent, binder and any other components, in an organic solvent to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0062] The second aspect of this application provides a secondary battery comprising a positive electrode, a separator, an electrolyte, and the negative electrode described in the first aspect of this application.

[0063] A third aspect of this application provides a method for preparing the secondary battery described in the second aspect of this application, comprising a formation step, wherein the formation step includes constant voltage discharge treatment at 0.45±0.1V, optionally 0.45±0.05V, and at 0.23±0.1V, optionally 0.23±0.05V, for 0.5 hours to 1.5 hours, optionally 0.8 hours to 1.2 hours respectively.

[0064] In some implementations, taking magnesium hydride as an example, the following reactions can occur at different potentials during silicon anode cycling:

[0065] At 0.45V:

[0066] At 0.32V:

[0067] At 0.23V:

[0068] At 0.16V:

[0069] At 0.04V:

[0070] During the first discharge cycle, the initial plateau at approximately 0.45V is due to the conversion of MgH2 into Mg and LiH, while the volume expansion of the MgH2 particles generates a strong internal stress. Secondly, the lithiation of Si leads to a rapid volume expansion of the Si particles, accompanied by internal stress driving the lithiation products Mg and LiH to migrate into the gaps between the cracked Si particles. A partial reversible alloying reaction between Mg and Li forms an electrochemically inert LixMg alloy (x is 0.5 to 2). During discharge, the volume contraction caused by delithiation causes the silicon particles to break. Simultaneously, as the reaction continues, MgH2 is gradually consumed until the reaction plateau completely disappears, representing the complete conversion from MgH2 to LixMg and LiH. This MgH2 acts as a mixed conductive matrix surrounding the broken Si particles, limiting further expansion of the silicon particles and improving the cycle performance of the silicon anode.

[0071] Optionally, to ensure the complete conversion of MgH2 to LixMg and LiH, in conjunction with the above reaction equations (1) and (3), a constant voltage discharge process of 0.5 to 1.5 hours, or optionally 0.8 to 1.2 hours, needs to be applied during the first discharge process. This allows MgH2 to be completely consumed and converted into the conductive matrix of LixMg and LiH in the first cycle, and migrate to the surface of silicon particles. This fully demonstrates the role of the composite conductive matrix in limiting volume expansion and high ionic conductivity, ensuring the structural integrity and excellent electrochemical performance of the silicon anode in subsequent cycles.

[0072] A fourth aspect of this application provides a secondary battery prepared according to the method described in the third aspect of this application, wherein in the negative electrode sheet, the surface of the silicon-based negative electrode active material particles comprises a metal or a lithium metal alloy and lithium hydride, wherein the metal is selected from at least one of Na, Mg, Ca and Al.

[0073] Because the solid electrolyte interface layer formed on the surface of silicon particles contains metal or lithium metal alloy and lithium hydride, where lithium hydride has high ionic conductivity and the metal or lithium metal alloy has high electrical conductivity, the silicon anode's particle integrity and rapid electrochemical reaction are ensured when the silicon particles are confined within the solid electrolyte interface layer of lithium hydride and the metal or lithium metal alloy, thus improving the electrochemical performance of the silicon anode. Here, the phrase "containing metal or lithium metal alloy and lithium hydride" should be understood as meaning that the metal or lithium metal alloy and lithium hydride are attached to the surface of the silicon particles and do not disrupt the overall structure of the silicon particles.

[0074] Secondary batteries

[0075] A rechargeable battery is a battery that can be recharged after it has been discharged, allowing the active materials to be reactivated and the battery to continue to be used.

[0076] Typically, a secondary battery includes a positive electrode, the negative electrode as described in this application, a separator, and an electrolyte. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, serves as a barrier. The electrolyte, located between the positive and negative electrodes, conducts ions.

[0077] [Positive electrode plate]

[0078] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0079] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0080] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0081] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0082] In some embodiments, the positive electrode active material accounts for 93% to 98% of the mass of the positive electrode film layer, and optionally 95% to 97%.

[0083] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0084] In some embodiments, the binder comprises 1% to 5% by mass in the positive electrode film layer, optionally 2% to 4%.

[0085] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some embodiments, the conductive agent comprises 1% to 4% by mass in the positive electrode film layer, optionally 2% to 3%.

[0087] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0088] [Electrolytes]

[0089] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0090] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0091] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0092] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0093] In some embodiments, the electrolyte salt content in the solvent is 10% to 15%, optionally 12% to 13%, based on the weight of the solvent.

[0094] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0095] [Isolation membrane]

[0096] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0097] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0098] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0099] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0100] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0101] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 This is an example of a square-structured secondary battery 5.

[0102] In some implementations, refer to Figure 6 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0103] The fifth aspect of this application provides a battery module including a secondary battery as described in the second or fourth aspect of this application or a secondary battery prepared according to the method described in the third aspect of this application.

[0104] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0105] Figure 7 This is battery module 4, used as an example. (See reference...) Figure 7In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0106] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0107] A sixth aspect of this application provides a battery pack including the battery module described in the fifth aspect of this application.

[0108] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0109] Figure 8 and Figure 9 This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0110] A seventh aspect of this application provides an electrical device, including at least one of the secondary battery described in the second or fourth aspect of this application, the battery module described in the fifth aspect of this application, or the battery pack described in the sixth aspect of this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0111] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0112] Figure 10 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0113] The beneficial effects of this application are further illustrated below with reference to the embodiments.

[0114] [Example]

[0115] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0116] Example 1

[0117] Preparation of silicon anode sheets

[0118] Active material silicon particles (Dv50 = 6 μm), magnesium hydride (Dv50 = 120 nm), artificial graphite (Dv50 = 14 μm), conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were dissolved in N-methylpyrrolidone solvent at a weight ratio of 10:20:67.2:0.8:0.8:1.2 and mixed evenly to prepare a negative electrode slurry with a solid content of 48%. The negative electrode slurry was uniformly coated on the negative electrode current collector copper foil, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0119] Preparation of Electrolyte

[0120] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3 / 7. 12.5% ​​LiPF6 lithium salt by mass was dissolved in the organic solvent and stirred evenly to obtain the electrolyte of Example 1.

[0121]

Isolation Film

[0122] Polypropylene film is used as the separator.

[0123] [Preparation of Lithium-ion Batteries]

[0124] The silicon anode sheet, separator, and lithium metal electrode are stacked in sequence, with the separator acting as a separator between the silicon anode sheet and the lithium metal electrode. The resulting structure is then wound to obtain a bare cell. Tabs are welded to the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. This non-charged battery undergoes a series of processes including settling, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1. During the formation process, constant voltage discharge treatments of 0.45V and 0.23V are applied for 1 hour each.

[0125] Example 2

[0126] Except for changing the weight ratio of silicon particles, magnesium hydride, and artificial graphite in the negative electrode sheet to 10:10:76.2, the other steps in Example 2 are the same as in Example 1.

[0127] Example 3

[0128] Except for changing the weight ratio of silicon particles, magnesium hydride, and artificial graphite in the negative electrode sheet to 10:15:71.2, the other steps in Example 3 are the same as in Example 1.

[0129] Example 4

[0130] Except for changing the weight ratio of silicon particles, magnesium hydride, and artificial graphite in the negative electrode sheet to 10:25:61.2, the other steps in Example 4 are the same as in Example 1.

[0131] Example 5

[0132] Except for changing the weight ratio of silicon particles, magnesium hydride, and artificial graphite in the negative electrode to 10:30:56.2, the other steps in Example 5 are the same as in Example 1.

[0133] Example 6

[0134] Except that the constant voltage discharge treatment processes applied at 0.45V and 0.23V during the formation process were changed to 0h and 0h respectively, the other steps of Example 6 were the same as those of Example 1.

[0135] Example 7

[0136] Except that the constant voltage discharge treatment process applied at 0.45V and 0.23V during the formation process was changed to 0h and 1h respectively, the other steps of Example 7 were the same as those of Example 1.

[0137] Example 8

[0138] Except that the constant voltage discharge treatment process applied at 0.45V and 0.23V during the formation process was changed to 1h and 0h respectively, the other steps of Example 8 were the same as those of Example 1.

[0139] Comparative Example 1

[0140] The preparation method is similar to that in Example 1, except that magnesium hydride is not used, and the weight ratio of active material silicon particles, artificial graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) is 10:87.2:0.8:0.8:1.2, and no constant voltage discharge treatment is applied during the formation process.

[0141] [Silicon Anode Plate Testing]

[0142] The relevant parameter testing process for the silicon anode sheets in the embodiments and comparative examples of this application is as follows:

[0143] 1. Morphological testing

[0144] The silicon anode sheet was tested using a LEO-1530 scanning electron microscope to observe the morphology of the silicon particles.

[0145] 2. X-ray diffraction test

[0146] The silicon anode sheet was tested using a Ultima IV X-ray diffractometer to detect the phase composition of the silicon anode sheet.

[0147] Battery performance test

[0148] Battery capacity retention test

[0149] At 25°C, the lithium-ion batteries prepared in the examples and comparative examples were discharged at a constant current of 0.1C to 0.01V, and then discharged at 0.1C to 1.0V. The resulting capacity was recorded as the initial capacity C0. The above steps were repeated for the same battery, and the discharge capacity Cn of the battery after the nth cycle was recorded. The capacity retention rate after each cycle, Pn = Cn / C0 * 100%, was calculated. After 200 cycles, C200 was recorded, and P200 = C200 / C0 * 100%.

[0150] Table 1: Performance test conditions and results of Examples 1-8 and Comparative Example 1

[0151]

[0152]

[0153] As can be seen from Table 1, by using the metal hydride of this application in the silicon-containing anode active material, especially in conjunction with the formation treatment of this application, the cycle capacity retention of the battery can be significantly improved.

[0154] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A negative electrode sheet, characterized in that, The device includes a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector. The negative electrode film layer comprises a negative electrode active material, a metal hydride, a conductive agent, and a binder. The negative electrode active material comprises a silicon-based negative electrode active material. In the negative electrode sheet, the particle surface of the silicon-based negative electrode active material comprises a metal and lithium hydride; or the particle surface of the silicon-based negative electrode active material comprises a lithium metal alloy and lithium hydride. The metal is selected from at least one of Na, Mg, Ca, and Al.

2. The negative electrode sheet according to claim 1, characterized in that, The metal hydride has the general formula MH x , where M is selected from at least one of Na, Mg, Ca and Al; x is an integer from 1 to 5.

3. The negative electrode sheet according to claim 1, characterized in that, The metal hydride has the general formula MH x M is Mg; x is an integer from 1 to 5.

4. The negative electrode sheet according to claim 1, characterized in that, The metal hydride has the general formula MH x M is selected from at least one of Na, Mg, Ca and Al; x is 1, 2 or 3.

5. The negative electrode sheet according to claim 1, characterized in that, The metal hydride is magnesium hydride.

6. The negative electrode sheet according to claim 1, characterized in that, The metal hydride accounts for 5% to 35% of the mass of the negative electrode film.

7. The negative electrode sheet according to claim 1, characterized in that, The metal hydride accounts for 8% to 32% of the mass of the negative electrode film.

8. The negative electrode sheet according to claim 1, characterized in that, The metal hydride accounts for 10% to 30% of the mass of the negative electrode film.

9. The negative electrode sheet according to claim 1, characterized in that, The metal hydride accounts for 16% to 24% of the mass of the negative electrode film.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, The mass ratio of the silicon-based anode active material to the metal hydride is 1:(0.5-3.5).

11. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, The mass ratio of the silicon-based anode active material to the metal hydride is 1:(0.8-3.2).

12. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, The mass ratio of the silicon-based anode active material to the metal hydride is 1:(1-3).

13. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, The mass ratio of the silicon-based anode active material to the metal hydride is 1:(1.6-2.4).

14. The negative electrode sheet according to claim 10, characterized in that, The negative electrode active material also includes carbon-based negative electrode active materials.

15. The negative electrode sheet according to claim 14, characterized in that, The mass ratio of the silicon-based anode active material to the carbon-based anode active material is 1:(4-10).

16. The negative electrode sheet according to claim 14, characterized in that, The mass ratio of the silicon-based anode active material to the carbon-based anode active material is 1:(5-8).

17. The negative electrode sheet according to claim 14, characterized in that, The mass ratio of the silicon-based anode active material to the carbon-based anode active material is 1:(6-7).

18. The negative electrode sheet according to claim 14, characterized in that, The silicon-based anode active material is selected from at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy; and / or, the particle size Dv50 of the silicon-based anode active material is 3 μm to 10 μm; and / or, the silicon-based anode active material accounts for 3% to 20% of the mass of the anode film.

19. The negative electrode sheet according to claim 18, characterized in that, The particle size Dv50 of the silicon-based anode active material is 4 μm to 8 μm; and / or, the silicon-based anode active material accounts for 5% to 15% of the mass of the anode film.

20. The negative electrode sheet according to claim 18, characterized in that, The carbon-based anode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, and hard carbon; and / or, the particle size Dv50 of the carbon-based anode active material is 5 μm to 30 μm; and / or, the carbon-based anode active material accounts for 30% to 80% of the mass of the anode film.

21. The negative electrode sheet according to claim 18, characterized in that, The particle size Dv50 of the carbon-based anode active material is 10 μm to 20 μm; and / or, the carbon-based anode active material accounts for 40% to 78% of the mass of the anode film.

22. The negative electrode sheet according to claim 18, characterized in that, The carbon-based anode active material accounts for 50% to 77% of the mass of the anode film.

23. A secondary battery, characterized in that, It comprises a positive electrode, a separator, an electrolyte, and a negative electrode as described in any one of claims 1 to 22.

24. A method for preparing the secondary battery according to claim 23, characterized in that, The process includes a formation step, wherein the formation step includes constant voltage discharge treatment at 0.45±0.1V and 0.23±0.1V for 0.5 hours to 1.5 hours respectively.

25. The secondary battery prepared according to claim 24, characterized in that, The formation process includes constant voltage discharge treatment at 0.45±0.05V and at 0.23±0.05V for 0.8 hours to 1.2 hours respectively.

26. The secondary battery prepared according to claim 24, characterized in that, In the negative electrode sheet, the surface of the silicon-based negative electrode active material particles contains a metal and lithium hydride; or the surface of the silicon-based negative electrode active material particles contains a lithium metal alloy and lithium hydride; the metal is selected from at least one of Na, Mg, Ca and Al.

27. A battery module, characterized in that, This includes the secondary battery according to claim 23 or the secondary battery prepared by the method according to claim 24.

28. A battery pack, characterized in that, Includes the battery module according to claim 27.

29. An electrical appliance, characterized in that, It includes at least one of the secondary battery according to claim 23, the battery module according to claim 27, or the battery pack according to claim 28.

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