Negative plate and preparation method thereof, secondary battery, battery pack and electric equipment

Abstract

The invention provides a negative plate and a preparation method thereof, a secondary battery, a battery pack and electric equipment. The negative plate comprises a negative current collector and a negative active material layer existing on at least one side surface of the negative current collector; and the negative active material layer comprises polyborosiloxane which is polymerized in situ. The negative plate provided by the invention can effectively absorb the volume expansion stress of negative silicon particles, so that the local compression stress of silicon volume expansion on the diaphragm is improved, the collapse of diaphragm pores is relieved, the ion transmission blockage and electrochemical performance degradation caused by diaphragm failure are avoided, and the cycle performance and fast charge performance of the secondary battery are comprehensively improved.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, and particularly relates to a negative electrode sheet and its preparation method, a secondary battery, a battery pack, and electrical equipment. Background Technology

[0002] Against the backdrop of the deepening global push for carbon neutrality, secondary batteries, as the core energy storage carrier for energy structure transformation, directly determine the development potential of strategic industries such as new energy vehicles, smart grids, and consumer electronics. As the main reaction medium for the insertion / extraction of active ions in the battery system, the intrinsic kinetic characteristics and structural stability of anode materials have become key factors affecting the overall performance of batteries.

[0003] Silicon-based anode materials, with a theoretical specific capacity as high as 4200 mAh / g, are considered an ideal choice for breaking through the current energy density bottleneck and show broad prospects in fields such as electric vehicles, large-scale energy storage, and high-end consumer electronics. However, silicon in silicon-based anode materials exhibits significant volume expansion (>300%) during charge and discharge, which can easily lead to problems such as electrode structure failure and separator performance degradation, thereby affecting the battery's cycle performance and fast-charging performance, and seriously restricting its commercial application.

[0004] Therefore, there is a need to develop an anode material that can further improve the cycle performance of secondary batteries. Summary of the Invention

[0005] This invention provides a negative electrode sheet that effectively suppresses silicon negative electrode expansion through a stress dissipation mechanism, preventing electrode pulverization and separator damage, thereby significantly improving the cycle performance and fast charging performance of secondary batteries.

[0006] This invention provides a method for preparing a negative electrode sheet. The negative electrode sheet prepared by this method can effectively suppress the expansion of silicon negative electrode, prevent electrode pulverization and separator damage, thereby significantly improving the cycle performance and fast charging performance of secondary batteries.

[0007] The present invention also provides a secondary battery with excellent cycle performance and fast charging performance.

[0008] The present invention also provides a battery pack with excellent cycle performance and fast charging performance.

[0009] The present invention also provides an electrical device that has the advantages of long service life and fast charging.

[0010] A first aspect of the present invention provides a negative electrode sheet, comprising a negative electrode current collector and a negative electrode active material layer present on at least one side surface of the negative electrode current collector; the negative electrode active material layer comprises in-situ polymerized polyborosiloxane.

[0011] The negative electrode as described above, wherein the polyborosiloxane is polymerized from raw materials including a boron source and a siloxane compound.

[0012] The negative electrode as described above, wherein the boron source includes at least one of boric acid and borate ester compounds; and / or, the siloxane compound includes at least one of alkoxysilane and silanol.

[0013] A second aspect of the present invention provides a method for preparing the aforementioned negative electrode sheet, comprising:

[0014] (1) A composite slurry is prepared by mixing raw materials including negative electrode active material, boron source and siloxane compound with solvent;

[0015] (2) The composite slurry is coated on at least one side of the surface of the negative electrode current collector and subjected to a polymerization reaction to obtain the negative electrode sheet; wherein the composite slurry is dried during the polymerization reaction to form a negative electrode active material layer, and the boron source and siloxane compound are polymerized in situ during the polymerization reaction to form the polyborosiloxane present in the negative electrode active material layer.

[0016] In the preparation method described above, the negative electrode active material layer further includes a binder and a conductive agent.

[0017] In the preparation method described above, the negative electrode active material layer comprises, by mass percentage: 88%-95% negative electrode active material, 0.1%-3% conductive agent, 2%-5% binder, 0.05%-2% boron source and 0.2%-5% siloxane compound.

[0018] In the preparation method described above, the polymerization reaction is carried out at a temperature of 60-110°C.

[0019] A third aspect of the present invention provides a secondary battery comprising the negative electrode sheet described in the first aspect above, or the negative electrode sheet prepared by the preparation method described in the second aspect above.

[0020] A fourth aspect of the present invention provides a battery pack comprising the negative electrode sheet described in the first aspect above, or the negative electrode sheet prepared by the preparation method described in the second aspect above, or the secondary battery provided in the third aspect above.

[0021] The fifth aspect of the present invention provides an electrical device comprising the negative electrode sheet described in the first aspect above, or the negative electrode sheet prepared by the preparation method described in the second aspect above, or the secondary battery provided in the third aspect above, or the battery pack provided in the fourth aspect above.

[0022] The negative electrode sheet provided by this invention can effectively absorb the volume expansion stress of the negative electrode silicon particles, thereby improving the local compressive stress on the separator caused by the silicon volume expansion, alleviating the collapse of the separator pores, avoiding the obstruction of ion transport and the degradation of electrochemical performance caused by separator failure, and thus comprehensively improving the cycle performance and fast charging performance of the secondary battery. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] Figure 1 This is a schematic diagram of the negative electrode sheet provided in Embodiment 1 of the present invention;

[0025] Figure 2 The diagram shows the cycle performance of the secondary batteries made from the negative electrode sheets of Examples 1-3 and Comparative Example 1 of this invention.

[0026] Figure label:

[0027] 1-Negative electrode current collector; 2-Negative electrode active material layer.

[0028] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0030] In silicon-based anode materials, silicon undergoes significant volume expansion during charging and discharging, which can easily lead to electrode structure pulverization and damage to the pore structure of the separator. To alleviate this problem, existing technologies typically use carbon materials (such as graphene, carbon nanotubes, or carbon shells) to coat silicon particles, utilizing the elasticity of the carbon layer to buffer the expansion stress of silicon. The inventors conducted in-depth research on the mechanism by which carbon materials suppress silicon particle expansion and discovered that the process is as follows: During charging, as the silicon particles expand, the outer carbon material undergoes elastic deformation to adapt to the volume change; during discharging, as the silicon particles contract, the carbon layer recovers to some extent. However, the recovery degree of the carbon layer is poor, and with the increase of cycle number, the carbon layer exhibits fatigue effects under repeated stress, gradually generating microcracks. These microcracks further expand, eventually leading to the rupture of the carbon coating layer, which loses its protective function and triggers a series of chain problems: the electrode structure becomes pulverized, the contact between the active material and the current collector deteriorates, and the contact resistance increases significantly; at the same time, the expansion stress of silicon is directly transmitted to the separator, causing its pore structure to collapse, severely hindering lithium-ion transport, resulting in an increase in polarization voltage and a rapid decline in battery performance.

[0031] Therefore, the inventors hoped to find a material with better deformation recovery during discharge. Initially, they attempted to add elastomeric additives (such as styrene-butadiene rubber) to the active material layer to improve deformation recovery after discharge. However, they found that such materials were insufficient to effectively resist the enormous stress generated by the expansion of silicon particles.

[0032] Based on this, such as Figure 1 As shown, the first aspect of the present invention provides a negative electrode sheet, including a negative electrode current collector 1 and a negative electrode active material layer 2 present on at least one side surface of the negative electrode current collector; the negative electrode active material layer 2 includes polyboron siloxane polymerized in situ.

[0033] It should be noted that polyborosiloxanes are very soft in their natural state. When subjected to stress and impact, the boron-oxygen bonds provide very strong resistance, and the greater the stress, the greater the resistance. They can undergo phase transitions from a viscous flow state to a highly elastic state, or even a glassy state. Macroscopically, this is manifested as a sharp increase in modulus, thus enabling them to better resist stress deformation and absorb energy. When the stress disappears, the polyborosiloxane returns to its original state.

[0034] The negative electrode sheet provided by this invention effectively suppresses silicon negative electrode expansion through a stress dissipation mechanism, preventing electrode pulverization and separator damage, thereby significantly improving the cycle performance and fast-charging performance of the secondary battery. The fundamental reason lies in the introduction of polyborosiloxane into the negative electrode sheet. This polymer possesses unique "stress response-modulus enhancement" characteristics, meaning its BO dynamic covalent bonds can undergo reversible breakage and repositioning under stress. Through a "soft-to-hard" mechanism, stress buffering and energy dissipation are achieved, thus suppressing electrode structure pulverization. Simultaneously, polyborosiloxane can disperse macroscopic silicon expansion stress into localized elastic deformation, preventing stress concentration from being transmitted to the separator, thereby maintaining the long-term stability of the separator's pore structure. Furthermore, the reversible recovery of the dynamic properties of polyborosiloxane prevents permanent separator damage caused by stress accumulation. These synergistic effects jointly ensure the performance and structural integrity of the secondary battery during long-cycle operation.

[0035] To further enhance the ability of the negative electrode to absorb and dissipate stress, the structure, modulus, and molecular weight of polyborosiloxane can be controlled.

[0036] In one specific embodiment, the polyborosiloxane is polymerized from raw materials including a boron source and a siloxane compound. The polyborosiloxane obtained from the boron source and the siloxane compound can better suppress the pulverization problem of the electrode structure, block the impact of silicon expansion stress on the separator, maintain the integrity and high porosity of the separator's pore structure, and further improve the cycle performance and fast-charging performance of the secondary battery.

[0037] Polyborosiloxanes possess a cross-linked structure. This cross-linked structure is a three-dimensional cross-linked network structure, composed of BO coordination bonds and Si-O-Si bonds, as shown in formula... ,Mode ,Mode Its dynamic cross-linking mechanism is as follows: the empty p orbital of the B atom can reversibly accept the lone pair of electrons from the O atom to form a dynamic BO coordinate bond with a bond energy of about 25-30 kcal / mol, which has reversible breaking / recombining characteristics.

[0038] Mode

[0039] Mode

[0040] Mode .

[0041] In one specific embodiment, the boron source includes at least one of boric acid and borate esters. The -OH group of boric acid undergoes dehydration condensation with the -Si-OH group of the siloxane compound to form a BO crosslink.

[0042] This invention does not specifically limit the types of borate esters. In one embodiment, the borate esters include... R1 and R2 are each independently selected from hydrogen or hydrocarbon groups, and R3 is a hydrocarbon group or an oxygen-containing group.

[0043] In one specific embodiment, the siloxane compound includes at least one of alkoxysilane and silanol. The aforementioned siloxane compound can be rapidly polymerized with a boron source to obtain polyborosiloxane.

[0044] This invention does not specifically limit the types of alkoxysilanes and silanols, including but not limited to tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), phenyltrimethoxysilane (PTMS), phenyltriethoxysilane (PTES), trimethylsilanol ((CH3)3SiOH), triethylsilanol ((C2H5)3SiOH), triphenylsilanol ((C6H5)3SiOH), dimethylsilanediol ((CH3)2Si(OH)2), methylsilanetriol (CH3Si(OH)3), ethylsilanetriol (CH3CH2Si(OH)3), and phenylsilanetriol (C6H5Si(OH)3).

[0045] A second aspect of the present invention provides a method for preparing a negative electrode sheet, comprising:

[0046] (1) A composite slurry is prepared by mixing raw materials including negative electrode active material, boron source and siloxane compound with solvent;

[0047] (2) The composite slurry is coated on at least one side of the surface of the negative electrode current collector 1 and subjected to a polymerization reaction to obtain a negative electrode sheet; wherein the composite slurry is dried during the polymerization reaction to form a negative electrode active material layer 2, and the boron source and siloxane compound are polymerized in situ during the polymerization reaction to form polyboron siloxane present in the negative electrode active material layer 2.

[0048] This invention does not impose specific limitations on the addition method of the negative electrode active material, boron source and siloxane compound, as long as a uniform composite slurry can be prepared.

[0049] In one embodiment, a silicon source and a siloxane compound are first mixed evenly, and then mixed with a negative electrode active material to obtain a composite slurry.

[0050] In one specific embodiment, the negative electrode active material layer 2 also includes a binder and a conductive agent.

[0051] This invention does not specifically limit the types of conductive agents and binders in the negative electrode active material layer; conventional conductive agents and binders in the art can be used.

[0052] In one embodiment, the conductive agent in the negative electrode active material layer includes at least one of natural carbon black, acetylene black, Ketjen black, carbon fiber, and graphene.

[0053] In one embodiment, the binder in the negative electrode active material layer includes at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0054] In one specific embodiment, the negative electrode active material layer 2, by mass percentage, comprises: 88%-95% negative electrode active material, 0.1%-3% conductive agent, 2%-5% binder, 0.05%-2% boron source, and 0.2%-5% siloxane compound. The content of each component in the negative electrode active material layer within this range further balances the cycle performance, fast charging performance, and energy density of the secondary battery.

[0055] For example, by mass percentage, the negative electrode active material accounts for 88%, 90%, 91%, 92%, 93%, 94% or 95% of the mass of the negative electrode active material layer, or a range of any two of these values.

[0056] For example, the conductive agent accounts for 0.1%, 1%, 1.5%, 2%, 2.5% or 3% of the mass of the negative electrode active material layer, or a range of any two of these values, by mass percentage.

[0057] For example, the binder accounts for 2%, 3%, 4% or 5% of the mass of the negative electrode active material layer, or any combination of two of these values, by mass percentage.

[0058] For example, the boron source accounts for 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2% of the mass of the negative electrode active material layer, or a range of any two of these values, by mass percentage.

[0059] For example, the siloxane compound accounts for 0.2%, 1%, 2%, 3%, 4% or 5% of the mass of the negative electrode active material layer, or a range of any two of these values, by mass percentage.

[0060] In one specific embodiment, the polymerization reaction temperature is 60-110°C. Within this temperature range, the resulting polyborosiloxane exhibits a crosslinked structure with a higher crosslinking density.

[0061] For example, the polymerization temperature is 60°C, 65°C, 75°C, 85°C, 95°C, 100°C, 105°C, or 110°C, or a range of any two of these values.

[0062] A third aspect of the present invention provides a secondary battery comprising the negative electrode sheet described in the first aspect, or a negative electrode sheet prepared by the method described in the second aspect. This secondary battery exhibits excellent cycle performance and fast-charging performance.

[0063] In addition to the aforementioned negative electrode, the secondary battery of the present invention also includes a positive electrode, an electrolyte, and a separator.

[0064] This invention does not impose any particular limitation on the positive electrode sheet; any conventional positive electrode sheet in the art can be used. For example, the positive electrode sheet includes a positive current collector and a positive active material layer.

[0065] This invention does not impose any particular limitation on the positive electrode current collector; any conventional positive electrode current collector in the art can be used. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil, carbon-coated aluminum foil, composite current collector, etc.

[0066] This invention does not strictly limit the positive electrode active material in the positive electrode sheet. It can be any positive electrode active material commonly used in secondary batteries, such as at least one composite oxide of lithium with cobalt, manganese, nickel, or combinations thereof. More specifically, it can be lithium nickel cobalt manganese oxide (such as NCM9505, NCM811, NCM622, NCM613, NCM523, NCM532, NCM111, etc.), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate, Na2Fe[Fe(CN)6], sodium iron phosphate, Na... 2 / 3 Ni 1 / 3 Mn 1 / 3 At least one of O2 and sodium vanadium phosphate. In addition, the positive electrode active material may also contain at least one of other elements, such as fluorine, phosphorus, boron, nitrogen, chlorine, silicon, sulfur, titanium, zinc, magnesium, calcium, strontium, lanthanum, cerium, and praseodymium. These elements can further improve the stability, ionic conductivity, cycle performance, and fast charging performance of the positive electrode active material.

[0067] This invention does not impose particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer. For example, the thickness of the positive electrode current collector is 5-20 μm, preferably 6-15 μm. The thickness of the single-sided positive electrode active material layer is 20-180 μm, preferably 30-120 μm.

[0068] This invention does not strictly limit the choice of electrolyte, and may include one or more solvents commonly used in current battery electrolytes, as well as lithium salts commonly used in current electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0069] This invention does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0070] This invention does not specifically limit the preparation method of the secondary battery; conventional preparation methods in the art can be used. In one embodiment, the preparation method of the lithium-ion battery includes: winding or stacking a positive electrode sheet, a separator, and the aforementioned negative electrode sheet to obtain a bare cell, and encapsulating the bare cell in a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85°C, electrolyte is injected into the dried battery. After the battery undergoes resting, formation, and secondary sealing, the preparation of the lithium-ion battery is completed.

[0071] A fourth aspect of the present invention provides a battery pack comprising the negative electrode sheet described in the first aspect, or the negative electrode sheet prepared by the method described in the second aspect, or the secondary battery described in the third aspect. This battery pack exhibits excellent cycle performance and fast-charging performance.

[0072] The battery pack of the present invention may include two or more batteries, and the specific number can be selected by those skilled in the art according to actual needs.

[0073] It should be noted that the individual cells that make up the battery pack can be electrically connected by conventional methods in the art, such as series connection, parallel connection, or a hybrid connection that includes both of these connection methods, and there are no particular limitations on this.

[0074] A fifth aspect of the present invention provides an electrical device comprising the negative electrode sheet described in the first aspect, or the negative electrode sheet prepared by the method described in the second aspect, or the secondary battery described in the third aspect, or the battery pack described in the fourth aspect. This electrical device has a long service life and fast charging.

[0075] The electrical equipment provided by this invention can be conventional electrical equipment in the field, such as power equipment (e.g., electric vehicles, electric cars), electrical equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no particular limitations on them.

[0076] The present invention will be further described below through specific embodiments.

[0077] Example 1

[0078] The method for preparing the negative electrode sheet in this embodiment includes:

[0079] (1) Add boric acid (BA) and phenyltrimethoxysilane (PTMS) to deionized water and stir to form a homogeneous mixture;

[0080] (2) Add negative electrode active material (graphite and silicon carbide material) to the above mixture, stir and wet thoroughly, then add conductive agent (carbon nanotube and conductive carbon black), binder (acrylic acid and styrene-butadiene rubber) and deionized water, stir evenly to obtain negative electrode slurry; wherein, the mass ratio of graphite, silicon carbide material, carbon nanotube, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane and deionized water is 77:15:0.1:0.9:2.5:1:0.5:3:90.

[0081] (3) Using copper foil as the negative electrode current collector, the above negative electrode slurry is coated on both sides of the copper foil, and the negative electrode sheet is obtained after baking / polymerization. The baking (polymerization reaction) temperature is 80°C.

[0082] Example 2

[0083] This embodiment is basically the same as Embodiment 1, except that:

[0084] The mass ratio of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane, and deionized water is 74.5:15:0.1:0.9:2.5:1:0.5:5:90.

[0085] In (3), the baking (polymerization reaction) temperature is 60℃.

[0086] Example 3

[0087] This embodiment is basically the same as Embodiment 1, except that:

[0088] The mass ratio of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane, and deionized water is 77.45:15:0.1:0.9:2.5:1:0.05:3:90.

[0089] In (3), the baking (polymerization reaction) temperature is 110℃.

[0090] Example 4

[0091] This embodiment is basically the same as Embodiment 1, except that:

[0092] The mass ratio of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane, and deionized water is 74.5:15:0.1:0.9:2.5:1:1:5:90.

[0093] Example 5

[0094] This embodiment is basically the same as Embodiment 1, except that:

[0095] The mass ratio of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane, and deionized water is 75.5:15:0.1:0.9:2.5:1:2:3:90.

[0096] Example 6

[0097] This embodiment is basically the same as Embodiment 1, except that:

[0098] The baking temperature is 50℃.

[0099] Example 7

[0100] This embodiment is basically the same as Embodiment 1, except that:

[0101] The baking temperature is 130℃.

[0102] Example 8

[0103] This embodiment is basically the same as Embodiment 1, except that:

[0104] The mass ratio of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane, and deionized water is 80.3:15:0.1:0.9:2.5:1:0.1:0.1:90.

[0105] Comparative Example 1

[0106] This comparative example is basically the same as Example 1, except that:

[0107] No mixture is prepared, and no mixture is added in step (2). The mass ratio of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane and deionized water is 80.5:15:0.1:0.9:2.5:1:0:0:90.

[0108] Test case

[0109] 1. The mass ratios (abbreviated as mass ratios) of graphite, silicon carbide, carbon nanotubes, conductive carbon black, acrylic acid, styrene-butadiene rubber, boric acid, phenyltrimethoxysilane and deionized water and the baking temperature during the preparation of the negative electrode sheets in the examples and comparative examples are shown in Table 1.

[0110] Table 1

[0111]

[0112] 2. The negative electrode sheets from the examples and comparative examples were used to prepare secondary batteries, and the cycle performance, AC resistance (ohmic impedance), and separator permeability of the secondary batteries were tested. The results are shown in Table 2. The cycle performance graphs of the secondary batteries prepared from the negative electrode sheets of Examples 1-3 and Comparative Example 1 are shown in Table 2. Figure 2 .

[0113] Fabrication of pouch cells:

[0114] The negative electrode, NCM811 positive electrode, separator, and electrolyte from the examples and comparative examples were assembled into a soft-pack battery cell with a designed capacity of 18.5Ah. The single-sided coating areal density of the positive electrode was 19 mg / cm³. 2 The compacted density is 3.5 g / cm³. 3 The surface density of the single-sided coating on the negative electrode is 7.8 mg / cm³. 2 The compacted density is 1.55 g / cm³. 3 The electrolyte injection coefficient is 2.5 g / Ah. The electrolyte solvent consists of ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and fluoroethylene carbonate (FEC), mixed in a volume ratio of EC:DEC:EMC:FEC = 1:1:1:0.3 to prepare 1 L of electrolyte. 1 mol of lithium hexafluorophosphate (LiPF6) is added to prepare a 1 mol / L basic electrolyte. The separator uses commercially available PE substrate coated with alumina ceramic layers on both sides, with the PE substrate being 9 μm thick and the alumina ceramic coating being 2 μm thick.

[0115] Test method:

[0116] At 25℃, charge at a constant current rate of 1C to 4.20V, then charge at a constant voltage until the current reaches 0.05C and is cut off. After resting for 15 minutes, discharge at a rate of 1C to 2.5V, and then rest for another 15 minutes. Repeat the above cycle 500 times, and the charge / discharge tester automatically records the discharge capacity of each cycle.

[0117] (1) Capacity retention test

[0118] The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 500th cycle were measured. 500 .

[0119] The capacity retention rate Qr after 500 cycles is calculated using the following formula:

[0120] Capacity retention rate Qr=Q 500 / Q1*100%.

[0121] (2) AC resistance (ohmic impedance)

[0122] Before the battery cycle test at 25℃, the battery was charged to 3.8V at a constant current rate of 0.1C and then left to stand for 30 minutes. The initial impedance R of the battery cell was then measured using an AC impedance meter. AC1 After 500 battery cycles, charge the battery to 3.8V at a constant current rate of 0.1C, let it rest for 30 minutes, and then test the AC impedance R after cycling. AC500 The impedance growth rate ζ after 500 cycles is calculated using the following formula:

[0123] Impedance growth rate ζ=R AC500 / R AC1 *100%.

[0124] 2) Diaphragm air permeability test

[0125] A Gurley permeability meter was used to measure the time it took for 100 mL of nitrogen to pass through the diaphragm, assessing the diaphragm's gas permeability. A lower permeability value indicates less resistance to gas permeation by the diaphragm's pore structure. When pore closure or pore structure collapse occurs, the diaphragm's permeability increases.

[0126] Cells were collected before and after 500 cycles. The separators were removed and immersed in DMC (dimethyl carbonate) solvent to remove residual electrolyte. After drying, the separators were cut to standard size (28 mm diameter). The samples were placed in a Gurley permeability meter, and the instrument was calibrated using a standard permeability membrane. The test conditions were set as follows: high-purity N2 gas, pressure 1.225 kPa (corresponding to 100 mmH2O), and volume 100 mL. The instrument was then started, and the time (in seconds) for gas to permeate through the separator was recorded. The separator permeability of the cells before and after 500 cycles was recorded as P1 and P2, respectively. 500And calculate the air permeability growth rate:

[0127] Air permeability growth rate η = P1 / P 500 *100%.

[0128] Table 2

[0129]

[0130] From Table 2, Figure 2 As can be seen, compared with the comparative example, the embodiments of the present invention can effectively improve the cycle capacity retention rate of the battery cell and reduce the rate of increase of impedance after long cycles. Through disassembly and testing of the diaphragm permeability, it was found that the present invention can effectively inhibit the increase of diaphragm permeability and alleviate diaphragm failure.

[0131] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A negative electrode sheet, characterized in that, It includes a negative electrode current collector and a negative electrode active material layer present on at least one side surface of the negative electrode current collector; the negative electrode active material layer includes in-situ polymerized polyborosiloxane.

2. The negative electrode sheet according to claim 1, characterized in that, The polyborosiloxane is polymerized from raw materials including a boron source and a siloxane compound.

3. The negative electrode sheet according to claim 2, characterized in that, The boron source includes at least one of boric acid and borate esters; and / or, the siloxane compound includes at least one of alkoxysilane and silanol.

4. A method for preparing a negative electrode sheet according to any one of claims 1-3, characterized in that, include: (1) A composite slurry is prepared by mixing raw materials including negative electrode active material, boron source and siloxane compound with solvent; (2) The composite slurry is coated on at least one side of the surface of the negative electrode current collector and subjected to a polymerization reaction to obtain the negative electrode sheet; wherein the composite slurry is dried during the polymerization reaction to form a negative electrode active material layer, and the boron source and siloxane compound are polymerized in situ during the polymerization reaction to form the polyborosiloxane present in the negative electrode active material layer.

5. The preparation method according to claim 4, characterized in that, The negative electrode active material layer also includes a binder and a conductive agent.

6. The preparation method according to claim 5, characterized in that, The negative electrode active material layer comprises, by mass percentage: 88%-95% negative electrode active material, 0.1%-3% conductive agent, 2%-5% binder, 0.05%-2% boron source and 0.2%-5% siloxane compound.

7. The preparation method according to claim 4, characterized in that, The polymerization reaction is carried out at a temperature of 60-110℃.

8. A secondary battery, characterized in that, Includes the negative electrode sheet according to any one of claims 1-3, or the negative electrode sheet prepared by the preparation method according to any one of claims 4-7.

9. A battery pack, characterized in that, It includes the negative electrode sheet according to any one of claims 1-3, or the negative electrode sheet prepared by the preparation method according to any one of claims 4-7, or the secondary battery according to claim 8.

10. An electrical appliance, characterized in that, It includes the negative electrode sheet according to any one of claims 1-3, or the negative electrode sheet prepared by the preparation method according to any one of claims 4-7, or the secondary battery according to claim 8, or the battery pack according to claim 9.

Images