Batteries and electrical equipment

Abstract

This application discloses a battery and an electrical device, relating to the field of battery technology. The battery includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer includes silicon. The mass percentage of silicon in the negative electrode active material layer is A%. When the battery is discharged at a 5C rate, the time it takes to discharge from 30% SOC to the lower limit voltage is B, in minutes. The condition is satisfied that 0.33 ≤ A / B ≤ 26.08, thus solving the problem in the prior art where batteries cannot simultaneously achieve both energy density and fast charging performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a battery and an electrical device. Background Technology

[0002] Batteries, due to their advantages of small size, light weight, and environmental friendliness, are widely used in new energy vehicles and 3C electronic products. With the rapid development and widespread application of new energy vehicles, higher demands are being placed on battery energy density. The negative electrode active material is a crucial component of lithium-ion batteries, and its performance directly affects the electrochemical performance of the battery. Currently, silicon-based negative electrode active materials have attracted widespread attention due to their higher theoretical specific capacity. However, silicon itself has low electronic conductivity, meaning that the electron transfer efficiency between active ions (such as lithium ions) and silicon is not high during charging and discharging, which limits the battery's charging and discharging speed and fast-charging capability. Furthermore, the reaction between silicon and active ions during charging and discharging is accompanied by significant volume changes, leading to increased internal stress, which can cause silicon particle breakage and electrode structure damage. This structural damage not only reduces the utilization rate of active materials but also accelerates electrolyte consumption and unstable SEI film growth. Under fast-charging conditions, the high-speed transport requirements of lithium ions conflict with the low kinetic performance of silicon, resulting in reduced fast-charging performance. Summary of the Invention

[0003] The main objective of this application is to provide a battery and electrical device to solve the problem that existing batteries cannot simultaneously achieve energy density and fast charging performance.

[0004] To achieve the above objectives, according to a first aspect of this application, a battery is provided, including a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer including silicon.

[0005] The mass percentage of silicon in the negative electrode active material layer is A%.

[0006] The battery is discharged at a 5C rate. The time B for the battery to discharge from 30% SOC to the lower limit voltage is measured in minutes. The condition is: 0.33 ≤ A / B ≤ 26.08.

[0007] Furthermore, 1.2 ≤ A / B ≤ 6.957.

[0008] Furthermore, 1 ≤ A ≤ 15; and / or, 0.5 ≤ B ≤ 3.6.

[0009] Furthermore, 3 ≤ A ≤ 8; and / or, 1 ≤ B ≤ 3.

[0010] Furthermore, the negative electrode active material layer includes a first active layer and a second active layer. The first active layer is disposed on the surface of the negative electrode current collector, and the second active layer is disposed on the surface of the first active layer away from the negative electrode current collector. The mass percentage of silicon in the first active layer is greater than the mass percentage of silicon in the second active layer, and the thickness ratio of the first active layer to the second active layer is (1~4):(1~4).

[0011] Furthermore, the thickness of the negative electrode active material layer is 40μm~110μm.

[0012] Furthermore, the thickness of the first active layer is 24 μm to 86 μm.

[0013] Furthermore, the thickness of the second active layer is 24 μm to 86 μm.

[0014] Furthermore, the mass percentage of silicon in the first active layer is 3% to 25%.

[0015] Furthermore, the mass percentage of silicon in the second active layer is 1% to 15%.

[0016] Furthermore, the negative electrode active material layer includes a silicon-based material, which includes at least one of silicon-carbon materials and silicon-oxygen materials.

[0017] Furthermore, the Dv50 particle size of the silicon-based material in the first active layer is 5μm~10μm.

[0018] Furthermore, the Dv50 particle size of the silicon-based material in the second active layer is 5μm~10μm.

[0019] Furthermore, the negative electrode active material layer includes graphite material and silicon-carbon material, with the mass ratio of silicon-carbon material in the negative electrode active material layer being 1.8% to 31%.

[0020] Furthermore, the lateral density of the negative electrode active material layer is 80 g / m². 2 ~120g / m 2 .

[0021] Furthermore, the compaction density of the negative electrode active material layer is 1.1 g / cm³. 3 ~1.65g / cm 3 .

[0022] Furthermore, the battery also includes a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

[0023] Furthermore, the positive electrode active material includes lithium nickel cobalt manganese oxide material, and the one-sided lateral density of the positive electrode active material layer is 110 g / m².2 ~250g / m 2 The compacted density is 1.5 g / cm³. 3 ~3.8g / cm 3 .

[0024] Furthermore, the thickness of the positive electrode active material layer is 60μm~145μm.

[0025] Furthermore, the battery also includes a separator, which is disposed between the positive electrode and the negative electrode, and the porosity of the separator is 35% to 48%.

[0026] According to a second aspect of this application, an electrical device is provided, which includes the battery provided in the first aspect.

[0027] By applying the technical solution of this application, the relationship between the mass ratio of silicon element in the negative electrode active material layer and the fast discharge time is controlled to satisfy: 0.33≤A / B≤26.08. This ensures the high capacity advantage of silicon and finds a balance between silicon content and the internal dynamic performance of the battery. Even under fast charge and discharge conditions, the lithium ion diffusion and electron conduction paths inside the battery remain unobstructed, thereby improving both the energy density and fast charging capability of the battery. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0029] As described in the background section of this application, existing batteries suffer from the problem of difficulty in simultaneously achieving high energy density and fast charging performance. To address this issue, in a typical embodiment of this application, a battery is provided, comprising a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector. The negative electrode active material layer comprises silicon; the mass percentage of silicon in the negative electrode active material layer is A%, and the battery discharges at a 5C rate, with the time B for discharging from 30% SOC to the lower limit voltage, satisfying: 0.33 ≤ A / B ≤ 26.08.

[0030] The battery in this application is a secondary battery, also known as a rechargeable battery or storage battery, which refers to a battery that can be used again after being discharged by recharging to activate the active materials.

[0031] The battery of this application includes a negative electrode sheet for accepting electrons and storing active ions (e.g., lithium ions). The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector. Specifically, the negative current collector has two opposing surfaces, and the negative active material layer may be disposed on one or both surfaces; this application does not impose further limitations on this. This application does not specifically limit the type of negative current collector; in some embodiments, as an example, the negative current collector may be a conventional negative current collector such as copper foil. The negative active material layer includes silicon, which can store more active ions and has a higher specific capacity.

[0032] It should be noted that the battery needs to be capacitated before being discharged at a 5C rate to obtain its capacity. The specific steps for capacitating are as follows: At 25℃, charge at a constant current of 0.33C to the upper limit voltage, then charge at a constant voltage until the current is less than or equal to 0.05C; then discharge at 0.33C to the lower limit voltage, completing one cycle. After three cycles of charge and discharge, the discharge capacity of the third cycle is taken as the battery capacity. After capacitating the battery, charge it again at 0.33C to the upper limit voltage to ensure the battery is in a 100% SOC initial state, then discharge it at 0.33C to 30% SOC, and then rapidly discharge it at a 5C current to the lower limit voltage. The time taken to discharge from 30% SOC to the lower limit voltage is B (in minutes). The value of B reflects the battery's high-rate charge and discharge capability. The larger the value of B, the smaller the battery polarization, the lower the internal resistance, and the better the lithium-ion insertion and extraction migration kinetics. Under high current, the voltage drop is slower, and it is less likely to reach the lower limit voltage of 2.5V in advance, thus enabling it to continuously release more power at a 5C current.

[0033] It should be noted that the upper and lower voltage limits for different battery systems are as follows: LFP system (lithium iron phosphate): upper voltage limit is 3.65V, lower voltage limit is 2.5V; NCM system (nickel-cobalt ternary material): upper voltage limit is 4.25V, lower voltage limit is 2.5V; LFMP system (lithium iron phosphate manganese): upper voltage limit is 4.25V, lower voltage limit is 2.5V; lithium nickel manganese oxide system: upper voltage limit is 4.8V, lower voltage limit is 3.5V.

[0034] To improve the energy density of the battery, this application introduces silicon into the negative electrode active material layer. However, silicon has poor intrinsic electronic conductivity, and its significant volume expansion during charging and discharging leads to particle breakage and increased contact resistance, thus significantly reducing kinetic performance and consequently deteriorating the battery's fast-charging performance. This is particularly true for silicon located at the bottom of the negative electrode, where the longer ion transport path exacerbates the kinetic performance degradation, becoming a bottleneck limiting overall fast-charging capability. B directly reflects the battery's discharge kinetics at high rates. Specifically, when the silicon content in the negative electrode active material layer is high, although the energy density is improved, in the later stages of 30% SOC discharge, the poor electronic / ionic conductivity of silicon and the increased SEI film impedance cause a sharp increase in lithium-ion transport resistance within the negative electrode, leading to a rapid drop in the voltage plateau. This manifests as a significantly shortened discharge time B or difficulty in maintaining stable high-current discharge, thus limiting fast-charging performance. Conversely, if the silicon content is too low, although the kinetic performance is acceptable, the high capacity advantage of silicon cannot be fully utilized, resulting in insufficient overall battery energy density. Therefore, according to the research in this application, by controlling 0.33≤A / B≤26.08, it is possible to ensure that the negative electrode active material layer has sufficient silicon content to improve energy density, while ensuring that the battery still has good ion transport dynamics and low polarization voltage at a high rate of 5C, thereby achieving the best balance between battery fast charging performance and energy density, so that the battery has both high energy density and excellent fast charging performance.

[0035] Specifically, A / B can be a range consisting of 0.33, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.5, 0.52, 0.54, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 26.08 or any two of these values.

[0036] To further improve the fast charging performance and cycle life of the battery, in some embodiments, 1.2 ≤ A / B ≤ 6.957.

[0037] This application does not impose any particular restrictions on the negative electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can use, for example, copper foil; or copper foil that has been surface-treated with one of carbon, nickel, titanium, silver, etc.

[0038] In some embodiments, 1≤A≤15. By controlling 1≤A≤15, it is helpful to ensure that the battery's fast charging performance is further improved while the energy density is increased.

[0039] Specifically, the mass percentage A of silicon in the negative electrode active material layer can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof. In some preferred embodiments, 3 ≤ A ≤ 8.

[0040] In some embodiments, 0.5 ≤ B ≤ 3.6. B represents the time range within which the battery rapidly discharges from 30% SOC to the lower limit voltage at a 5C rate. Controlling 0.5 ≤ B ≤ 3.6 indicates that the battery exhibits excellent kinetic characteristics, enabling it to release a large amount of electrical energy in a short time, thus improving its fast-charging capability. While ensuring fast-charging performance, this also helps prevent kinetic damage to the battery during extremely high-rate charging and discharging, reduces stress on electrode materials, avoids the shedding of active materials, thereby maintaining the integrity and stability of the electrode structure and extending the battery's cycle life.

[0041] Specifically, when the battery is discharged at a 5C rate, the time B min for discharging from 30% SOC to the lower limit voltage can be a range of 0.5 min, 0.6 min, 0.8 min, 0.9 min, 1 min, 1.2 min, 1.4 min, 1.5 min, 1.8 min, 2 min, 2.2 min, 2.5 min, 2.8 min, 3 min, 3.2 min, 3.4 min, 3.6 min, or any combination thereof. In some preferred embodiments, 1 ≤ B ≤ 3. This application can control the time B min for the battery to discharge from 30% SOC to the lower limit voltage at a 5C rate by adjusting the pressure during the rolling process of the negative electrode sheet preparation. For example, during the negative electrode sheet preparation process, the rolling pressure is 30T~74T. When the rolling pressure increases, the negative electrode active material particles are further compacted, the compaction density of the negative electrode sheet increases, and the porosity decreases. By adjusting the rolling pressure to 30T~74T, the pore structure and ion transport resistance of the negative electrode can be finely adjusted, thereby controlling parameter b within the target range.

[0042] This application can also control the time (B min) for the battery to discharge from 30% SOC to the lower limit voltage by adjusting the concentration of lithium salt in the electrolyte at a 5C rate. For example, the concentration of lithium salt LiPF6 in the electrolyte is controlled between 0.8 mol / L and 1.5 mol / L. To facilitate the control of lithium salt concentration, the organic solvent of the electrolyte is preferably a mixed solvent with a mass ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): ethyl carbonate (EA) = 20:10:40:30. This solvent system has good low-temperature performance and a high dielectric constant, which is conducive to the dissociation of lithium salt. Furthermore, by synergistically controlling the rolling pressure of the negative electrode and the lithium salt concentration of the electrolyte, this application can control parameter B within the range of 0.5 to 3.6.

[0043] In some embodiments, the negative electrode active material layer includes a first active layer and a second active layer. The first active layer is disposed on the surface of the negative electrode current collector, and the second active layer is disposed on the surface of the first active layer away from the negative electrode current collector. The mass percentage of silicon in the first active layer is greater than that in the second active layer, and the thickness ratio of the first active layer to the second active layer is (1~4):(1~4). By controlling the thickness ratio of the first active layer to the second active layer within the above range, it is helpful to adjust the distribution of silicon and optimize the battery dynamics performance. Secondly, the first active layer with a relatively high silicon content helps to improve the overall energy density, while the second active layer with a lower silicon content helps to improve the electronic conductivity and lithium-ion transport rate of the battery, ensuring that the battery can still maintain good performance under fast charging conditions. In addition, a reasonable thickness ratio helps to maintain the structural stability and mechanical strength of the negative electrode sheet, avoiding active material layer peeling or electrode delamination caused by uneven stress during cycling.

[0044] Specifically, the ratio of the thickness of the first active layer to the thickness of the second active layer can be 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, or any combination thereof.

[0045] In some embodiments, the thickness of the negative electrode active material layer is 40 μm to 110 μm. An excessively thin negative electrode active material layer may result in insufficient areal density, affecting the overall energy storage capacity of the battery; while an excessively thick layer may increase the resistance to lithium-ion transport, affecting the battery's kinetic performance. By controlling the thickness of the negative electrode active material layer to 40 μm to 110 μm, it is helpful to maintain a good lithium-ion diffusion rate, ensuring an efficient charge-discharge process. Simultaneously, it helps to mitigate the volume effect of the negative electrode material during lithiation and delithiation processes, reducing the risk of the negative electrode active material layer peeling off from the current collector, thereby improving cycle stability.

[0046] Specifically, the thickness of the negative electrode active material layer can be within the range of 40μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, or any combination thereof.

[0047] In some embodiments, the thickness of the first active layer is 24 μm to 86 μm. By controlling the thickness of the first active layer to be 24 μm to 86 μm, the first active layer contains a high proportion of silicon, which helps to increase the total energy storage capacity of the battery and improve the energy density of the battery. While maintaining a high energy density, it also helps to maintain a good lithium-ion transport rate and electronic conductivity, ensuring that the battery has excellent kinetic performance under high-rate charge and discharge conditions.

[0048] Specifically, the thickness of the first active layer can be within the range of 24μm, 25μm, 28μm, 30μm, 32μm, 34μm, 35μm, 38μm, 40μm, 42μm, 45μm, 48μm, 50μm, 52μm, 55μm, 58μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 86μm, or any combination thereof.

[0049] In some embodiments, the thickness of the second active layer is 24 μm to 86 μm. The second active layer is located on the surface of the negative electrode. By controlling the thickness of the second active layer to be 24 μm to 86 μm, it is ensured that the second active layer can provide the required ion channels and electron conduction network, without increasing the additional resistance to lithium-ion transport due to excessive thickness of the second active layer, thereby optimizing the kinetic performance of the battery.

[0050] Specifically, the thickness of the second active layer can be within the range of 24 μm, 25 μm, 28 μm, 30 μm, 32 μm, 34 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, 48 μm, 50 μm, 52 μm, 55 μm, 58 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 86 μm, or any combination thereof.

[0051] In some embodiments, the mass percentage of silicon in the first active layer is 3% to 25%. Excessive silicon content may lead to decreased conductivity, affecting the battery's fast-charging capability, while insufficient content will prevent full utilization of silicon's high capacity characteristics. Controlling the mass percentage of silicon in the first active layer to 3% to 25% helps to find a balance between increasing capacity and maintaining good kinetic performance. Furthermore, controlling the mass percentage of silicon in the first active layer to 3% to 25% helps reduce the risk of structural damage caused by volume changes in silicon during charging and discharging, maintaining the stability of the electrode structure and improving battery lifespan.

[0052] Specifically, the mass percentage of silicon in the first active layer is 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any combination thereof.

[0053] In some embodiments, the silicon content in the second active layer is 1% to 15% by mass. In the battery, the second active layer is in direct contact with the electrolyte. By controlling the silicon content in the second active layer to 1% to 15% by mass, it helps optimize the electronic conductivity and lithium-ion transport rate of the negative electrode surface, while reducing resistance during charging and discharging, thus improving the battery's fast-charging performance. Furthermore, controlling the silicon content in the second active layer to 1% to 15% by mass helps mitigate volume changes during charging and discharging, reducing the risk of surface cracks and peeling, and enhancing the structural stability of the negative electrode.

[0054] Specifically, the mass percentage of silicon in the second active layer is 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any combination thereof.

[0055] In some embodiments, the negative electrode active material layer includes a silicon-based material, which includes at least one of silicon-carbon material and silicon-oxygen material.

[0056] When the negative electrode active material layer includes silicon-carbon material, this application can control the mass percentage (A%) of silicon in the negative electrode active material layer by adjusting the silicon content of the silicon-carbon material itself. The mass percentage of silicon in the negative electrode active material layer can be controlled by adjusting the silicon content in the silicon-carbon material. For example, in the preparation process of silicon-carbon material, the silicon content mainly depends on the conditions of silane introduction. Specifically, the flow rate of silane, the ratio of silane to carrier gas (carrier gas ratio), and the introduction time jointly determine the amount of silicon deposited on the carbon matrix. The higher the silane flow rate, the longer the introduction time, or the higher the silane percentage, the higher the silicon content in the silicon-carbon material, and the greater the mass percentage (A%) of silicon in the negative electrode active material layer. For example, the silicon-carbon material is prepared by vapor deposition combined with high-temperature calcination. The specific preparation steps are as follows: Step S1, pretreatment and oxygen removal: The porous carbon material is added to the rotary furnace as a carbon matrix. First, nitrogen is introduced for oxygen removal treatment, and the flow rate of nitrogen is controlled at 10L / min~20L / min. The rotary kiln is then heated at a rate of 5℃ / min to 10℃ / min, with the calcination temperature controlled between 480℃ and 540℃. The rotation speed of the rotary kiln is controlled between 0.5 rpm and 3 rpm to ensure uniform heating of the carbon matrix and removal of surface impurities. Step S2, silicon source deposition: Maintaining the calcination temperature (or finely adjusting according to the specific process), a mixed gas is introduced into the furnace. The mixed gas includes nitrogen and silane, with a nitrogen to silane volume ratio of 1:(1~4). The total flow rate of the mixed gas is controlled between 0.2 L / min and 0.6 L / min, and the introduction time is controlled between 60 min and 170 min. During this stage, silane decomposes and deposits on the surface of the carbon matrix, initially forming silicon components. Step S3, high-temperature reaction and coating: After the silicon source deposition is completed, the silane gas is turned off, and only nitrogen continues to be introduced. Under a nitrogen atmosphere, the calcination temperature is increased to 550℃~600℃ and maintained at this temperature for 60min~180min to promote the bonding of the silicon-carbon matrix interface and eliminate stress. When the temperature fluctuation inside the furnace gradually becomes constant, it indicates that the reaction is stabilizing. Step S4, carbon layer coating: At a deposition temperature of 500℃~600℃, acetylene gas is introduced for the reaction. The acetylene gas flow rate is set to 1L / min~3L / min, and the reaction time (deposition time) is controlled at 10h~18h. Acetylene gas decomposes on the surface of silicon particles to form an amorphous carbon layer, achieving effective coating of silicon particles, thereby buffering the volume expansion of silicon during charging and discharging and improving conductivity. Step S5, cooling and collection: After the reaction is completed, all gases are turned off, and the rotary kiln is allowed to cool naturally to room temperature under a nitrogen atmosphere. After complete cooling, the product is collected and demagnetized (to remove any introduced metallic impurities), finally obtaining silicon-carbon material.

[0057] In some embodiments, the Dv50 particle size of the silicon-based material in the first active layer is 5 μm to 10 μm. By controlling the Dv50 particle size of the silicon-based material in the first active layer to be 5 μm to 10 μm, it is helpful to control the volume expansion of the particles during lithiation, reduce the stress on the particles caused by the charge and discharge rate, thereby reducing electrode expansion and structural damage, and extending the cycle life of the battery.

[0058] In some embodiments, the Dv50 particle size of the silicon-based material in the second active layer is 5 μm to 10 μm. By controlling the Dv50 particle size of the silicon-based material in the second active layer to be 5 μm to 10 μm, it is helpful to accelerate the transport rate of lithium ions and electrons, improve the surface dynamics of the negative electrode, and thus enhance the fast charging performance of the battery.

[0059] In some embodiments, the negative electrode active material layer further includes, but is not limited to, carbon materials. In some embodiments, carbon-based materials may include, but are not limited to, natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof.

[0060] In a preferred embodiment of the present invention, the negative electrode active material layer comprises graphite material and silicon-carbon material. The graphite material can be selected from one or more of natural graphite, artificial graphite, and mesophase carbon microspheres. In this application, the mass percentage of silicon in the negative electrode active material layer can be precisely controlled by adjusting the proportion of silicon-carbon material added to the negative electrode active material; for example, the mass percentage of silicon-carbon material in the negative electrode active material layer can be 1.8% to 31%.

[0061] In this invention, given a fixed silicon content in the silicon-carbon material, the A value can be adjusted by changing the mass ratio of silicon-carbon material to graphite material. The higher the proportion of silicon-carbon material in the negative electrode active material, the greater the mass percentage A% of silicon in the negative electrode active material layer.

[0062] In preparing the negative electrode sheet, the negative electrode active material, the first conductive agent, and the first binder can be dispersed in an appropriate amount of water and thoroughly stirred to form a uniform negative electrode slurry. An appropriate amount of the negative electrode slurry is taken as the first negative electrode slurry, and the silicon-carbon content in the first negative electrode slurry is adjusted so that the mass ratio of silicon elements after drying meets the requirements of the first active layer. When the negative electrode sheet is a double-layer coating, an appropriate amount of the negative electrode slurry is taken as the second negative electrode slurry, and the silicon-carbon content in the second negative electrode slurry is adjusted so that the mass ratio of silicon elements after drying meets the requirements of the second active layer. The first negative electrode slurry is coated on the surface of the negative electrode current collector, and after drying, the first active layer is obtained. The second slurry is coated on the surface of the first active layer, and after drying, rolling, and slitting, the negative electrode sheet is obtained. In one specific embodiment, the mass ratio of the negative electrode active material, the first conductive agent, and the first binder is (70~99):(0.5~15):(0.5~15). Furthermore, the mass ratio of the negative electrode active material, the first conductive agent, and the first binder is (95~99):(0.2~2):(0.8~3).

[0063] The first conductive agent may be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the first binder may be selected from at least one of carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride (PVC), carboxylated polyvinyl chloride (CPVC), ethylene oxide-containing polymers, polyvinylpyrrolidone (PVP), polyurethane (PU), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyethylene (PE), polypropylene (PP), polyvinyl alcohol (PVA), and sodium polyacrylate (PAA).

[0064] In some embodiments, the areal density of the negative electrode active material layer is 80 g / m². 2 ~120g / m 2 The areal density of the negative electrode active material layer refers to the density of one side surface. Areal density reflects the amount of active material loaded per unit area. A higher areal density means more active material is loaded, which can improve the battery's energy density. However, excessively high areal density increases the resistance to lithium-ion and electron transport, reduces the battery's kinetic performance, and affects fast charging and discharging rates. By controlling the areal density of the negative electrode active material layer to 80 g / m²... 2 ~120g / m 2 This ensures that the battery has sufficient capacity while also possessing a good charge / discharge rate. Furthermore, a suitable areal density helps maintain good porosity, thereby optimizing electrolyte wettability, promoting rapid lithium-ion transport and stable SEI film formation, and improving battery cycle performance and safety.

[0065] In some embodiments, the compaction density of the negative electrode active material layer is 1.1 g / cm³. 3~1.65g / cm 3 By controlling the compaction density of the negative electrode active material layer to 1.1 g / cm³ 3 ~1.65g / cm 3 This indicates that the contact between the negative electrode active material layer and the negative electrode current collector is tight, which helps to keep the porosity within a suitable range, ensures that the electrolyte fully wets the negative electrode sheet, promotes the formation of the SEI (solid electrolyte interface) film, helps to improve the lithium ion transport rate, and thus optimizes the battery's charge and discharge efficiency and kinetic performance.

[0066] In some embodiments, the battery further includes a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, which can be any existing publicly disclosed positive active material or an optimized positive active material based on existing materials. For example, the positive active material includes ternary materials such as lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.

[0067] In some embodiments, the positive electrode active material is lithium nickel cobalt manganese oxide, and the one-sided lateral density of the positive electrode active material layer is 110 g / m². 2 ~250g / m 2 The compacted density is 1.5 g / cm³. 3 ~3.8g / cm 3 The thickness of the positive electrode active material layer is 60μm~145μm. By controlling the unilateral surface density, compaction density, and thickness range of the positive electrode active material layer, the volumetric energy density of the battery is improved while the ion transport dynamics are effectively optimized, thereby further enhancing the fast charging performance of the battery.

[0068] In some embodiments, the positive electrode sheet can be prepared by: forming a positive electrode slurry by mixing the above-mentioned components for preparing the positive electrode sheet, such as the positive electrode active material, the second conductive agent, the second binder, and a solvent (e.g., N-methylpyrrolidone); coating the positive electrode slurry onto a positive electrode current collector; and obtaining the positive electrode sheet after drying, rolling, and cutting. The mass ratio of the positive electrode active material, the second conductive agent, and the second binder is (70~99):(0.5~15):(0.5~15). Further, the mass ratio of the positive electrode active material, the second conductive agent, and the second binder is (94~99):(0.5~1.8):(0.9~2.2).

[0069] In this application, the second binder is used to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. This application does not particularly limit the type of binder for the positive electrode sheet; the binder can be any conventional choice in the battery field. Specifically, the second binder can be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC), or sodium alginate. The second conductive agent can be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, graphene, and carbon nanotubes.

[0070] This application does not impose any particular restrictions on the positive electrode current collector, as long as it is conductive and will not cause adverse chemical changes in the battery, and can be made of, for example: stainless steel, aluminum, nickel, titanium, sintered carbon; or aluminum or stainless steel that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0071] In some embodiments, the battery further includes a separator disposed between the positive and negative electrode plates, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. 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. As an example, the separator can be one of PP, PE, or PP / PF; the separator can also be a structure with a coating on the surface of a base film, wherein the base film coating can be one of PP, PE, or PP / PF, and the coating can be an inorganic coating and / or an organic coating. The inorganic coating can be selected from alumina ceramic layers, boehmite, etc., and the organic coating can be selected from PVDF, etc.

[0072] In some embodiments, the porosity of the separator is 35% to 48%. The porosity of the separator directly determines the lithium-ion transport efficiency. By controlling the separator porosity to 35% to 48%, sufficient pathways for lithium ions to pass through can be provided, reducing internal resistance during battery charging and discharging, thereby optimizing the battery's kinetic performance and improving fast charging and fast discharging capabilities. Simultaneously, sufficient porosity ensures that the electrolyte can uniformly wet the entire separator, which not only improves the lithium-ion transport rate but also contributes to the stable formation of the SEI (solid electrolyte interface) film, reducing side reactions and improving battery safety and cycle life.

[0073] In this application, the secondary battery also includes an electrolyte and an outer packaging shell. A positive electrode, a negative electrode, and a separator are assembled to form an electrode assembly. The electrode assembly and the electrolyte are assembled inside the outer packaging shell. During battery charging and discharging, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrode plates. The electrolyte, located between the positive and negative electrode plates, primarily serves to conduct active ions.

[0074] As an example, the preparation process of a secondary battery is as follows: the positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, the electrodes are wound or stacked to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0075] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. As an example, the electrolyte in this application can be any electrolyte suitable for electrochemical energy storage devices in the art. The electrolyte includes an electrolyte and a solvent; the electrolyte typically includes a lithium salt, and additives may also be added to the electrolyte.

[0076] Specifically, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). The concentration of the electrolyte in the electrolyte solution can be from 0.5 mol / L to 5 mol / L.

[0077] Specifically, the solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0078] In some embodiments, as an example, the additive may be a conventional electrolyte additive such as fluoroethylene carbonate (FEC), chloroethylene carbonate (CEC), or vinylene carbonate (VC). In some embodiments, based on the mass of the electrolyte, the solvent accounts for 60% to 80% by mass, and the additive accounts for 2% to 8% by mass.

[0079] Another aspect of this application provides an electrical device including the battery described above.

[0080] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0081] Example 1

[0082] The battery preparation method of this embodiment includes the following steps:

[0083] I. Preparation of the positive electrode sheet

[0084] LiNi cathode material 0.91 Co 0.05 Mn 0.04 O2 is mixed with binder PVDF and carbon black (SP) at a mass ratio of 98:1.1:0.9 and dispersed in NMP to obtain a positive electrode slurry. The positive electrode slurry is coated on aluminum foil to obtain a double-sided coated positive electrode sheet. Then it is rolled and cut to obtain a positive electrode sheet with a thickness of 99μm.

[0085] II. Preparation of the negative electrode sheet

[0086] The preparation method of silicon-carbon material is as follows: Step S1, porous carbon material is added to a rotary furnace as a carbon matrix, and nitrogen is introduced for oxygen removal. The flow rate of nitrogen is controlled at 15 L / min. Then, the rotary furnace is heated at a heating rate of 8 °C / min, and the calcination temperature is controlled at 520 °C. The rotation speed of the rotary furnace is 2 rpm. Step S2, while keeping the calcination temperature constant, a mixed gas is introduced into the furnace. The mixed gas includes nitrogen and silane, wherein the volume ratio of nitrogen to silane is 1:2, the total flow rate of the mixed gas is 0.4 L / min, and the introduction time of the mixed gas is 87 min. Step S3: After the silicon source deposition is completed, the silane gas is turned off, and only nitrogen gas is continued to be introduced. Under the nitrogen atmosphere, the calcination temperature is raised to 550℃ and maintained at this temperature for 100 min. Step S4: While maintaining the deposition temperature of 550℃, acetylene gas is introduced to carry out the reaction. The flow rate of acetylene gas is set to 2 L / min, and the reaction time is 15 h. Step S5: After the reaction is completed, all gases are turned off, and the rotary kiln is allowed to cool naturally to room temperature under the nitrogen atmosphere. After the cooling is complete, the product is collected and demagnetized. After crushing, silicon-carbon material with a Dv50 particle size of 8 μm is obtained.

[0087] Preparation of the negative electrode sheet: Artificial graphite, the aforementioned silicon carbon material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) were dissolved in deionized water at a mass ratio of 87.87:8.13:0.6:2.4:1 to form the first negative electrode slurry. Artificial graphite, the aforementioned silicon carbon material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) were dissolved in deionized water at a mass ratio of 93.97:2.03:0.6:2.4:1 to form the second negative electrode slurry. The first negative electrode slurry was first uniformly coated onto a 4.5 μm thick copper foil and then vacuum-dried at 120°C to form a preliminary first active layer. The second negative electrode slurry was then coated onto the surface of the first active layer and vacuum-dried at 120°C to form a preliminary second active layer. After rolling under a pressure of 66.9T, a single-sided lateral density of 120 g / m² was obtained. 2 The negative electrode sheet; wherein the thickness ratio of the first active layer to the second active layer is 2:1, and the mass ratio of silicon elements in the first active layer to silicon elements in the second active layer is 4:1.

[0088] III. Preparation of Electrolyte

[0089] Ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC): ethyl carbonate (EA) were mixed in a mass ratio of 20:10:40:30 to obtain an organic solvent. Then, fully dried lithium salt LiPF6, 1,3-propanesulfonate lactone (DTD), fluoroethylene carbonate (FEC), and tris(trimethylsilane) phosphate (TMSP) were dissolved in the mixed organic solvent to prepare an electrolyte with a LiPF6 concentration of 0.94 mol / L. The amount of 1,3-propanesulfonate lactone (DTD), fluoroethylene carbonate (FEC), and tris(trimethylsilane) phosphate (TMSP) added was 5%.

[0090] IV. Preparation of the separating membrane

[0091] The diaphragm used is a 7μm PE base membrane with 2μm ceramic layers coated on both sides. The porosity of the diaphragm is 38%.

[0092] V. Battery Preparation

[0093] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing and standing for 24 hours, it is formed at 45°C to obtain the battery of this embodiment.

[0094] Example 2

[0095] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 124 minutes.

[0096] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 74.4:21.6:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 90.6:5.4:0.6:2.4:1; the rolling pressure is 64.8T.

[0097] In the preparation of the electrolyte, the concentration of LiPF6 was 0.96 mol / L.

[0098] Example 3

[0099] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 101 min.

[0100] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 86.4:9.6:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 93.6:2.4:0.6:2.4:1; the rolling pressure is 38.5T.

[0101] In the preparation of the electrolyte, the concentration of LiPF6 was 1.4 mol / L.

[0102] Example 4

[0103] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 92 minutes.

[0104] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 87.6:8.4:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 93.9:2.1:0.6:2.4:1; the rolling pressure is 44.9T.

[0105] In the preparation of the electrolyte, the concentration of LiPF6 was 1.06 mol / L.

[0106] Example 5

[0107] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 110 minutes.

[0108] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 82.5:13.5:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 92.6:3.4:0.6:2.4:1; the rolling pressure is 52.7T.

[0109] In the preparation of the electrolyte, the concentration of LiPF6 is 1 mol / L.

[0110] Example 6

[0111] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 115 minutes.

[0112] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 78.5:17.5:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 91.6:4.4:0.6:2.4:1; the rolling pressure is 59.8T.

[0113] In the preparation of the electrolyte, the concentration of LiPF6 was 0.98 mol / L.

[0114] Example 7

[0115] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 105 min.

[0116] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 84.8:11.2:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 93.2:2.8:0.6:2.4:1; the rolling pressure is 41.4T.

[0117] In the preparation of the electrolyte, the concentration of LiPF6 was 1.1 mol / L.

[0118] Example 8

[0119] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 78 minutes.

[0120] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 90.5:5.5:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 94.6:1.4:0.6:2.4:1; the rolling pressure is 72.6T.

[0121] In the preparation of the electrolyte, the concentration of LiPF6 was 0.86 mol / L.

[0122] Example 9

[0123] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 138 minutes.

[0124] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 71.7:24.3:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 89.9:6.1:0.6:2.4:1; the rolling pressure is 35.7T.

[0125] In the preparation of the electrolyte, the concentration of LiPF6 was 1.36 mol / L.

[0126] Example 10

[0127] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 128 minutes.

[0128] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 73.6:22.4:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 90.4:5.6:0.6:2.4:1; the rolling pressure is 58.4T.

[0129] In the preparation of the electrolyte, the concentration of LiPF6 was 0.99 mol / L.

[0130] Example 11

[0131] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas is introduced for 96 minutes.

[0132] In the preparation of the negative electrode, artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber and conductive graphite (KS-6) are dissolved in deionized water in a mass ratio of 89.6:6.4:0.6:2.4:1 to form a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil with a thickness of 4.5μm, dried under vacuum at 120℃, and rolled under a pressure of 40.8T to obtain the negative electrode.

[0133] In the preparation of the electrolyte, the concentration of LiPF6 was 1.12 mol / L.

[0134] Example 12

[0135] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 119 minutes.

[0136] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 75.2:20.8:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 90.8:5.2:0.6:2.4:1; the rolling pressure is 65.6T.

[0137] In the preparation of the electrolyte, the concentration of LiPF6 was 0.95 mol / L.

[0138] Example 13

[0139] The difference from Example 1 is that the mixed gas was introduced for 82 minutes in the preparation of the silicon-carbon material;

[0140] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 89.1:6.9:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 94.3:1.7:0.6:2.4:1; the rolling pressure is 36.2T.

[0141] In the preparation of the electrolyte, the concentration of LiPF6 was 1.38 mol / L.

[0142] Example 14

[0143] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas is introduced for 60 minutes.

[0144] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 92.9:3.1:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 95.2:0.8:0.6:2.4:1; the rolling pressure is 38.1T.

[0145] In the preparation of the electrolyte, the concentration of LiPF6 was 1.39 mol / L.

[0146] Example 15

[0147] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 147 minutes.

[0148] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 61.2:34.8:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 87.3:8.7:0.6:2.4:1; the rolling pressure is 74T.

[0149] In the preparation of the electrolyte, the concentration of LiPF6 was 0.82 mol / L.

[0150] Example 16

[0151] The difference from Example 1 is that the mixed gas was introduced for 102 min in the preparation of the silicon-carbon material;

[0152] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 54.7:41.3:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 85.7:10.3:0.6:2.4:1; the rolling pressure is 69.1T.

[0153] In the preparation of the electrolyte, the concentration of LiPF6 was 0.9 mol / L.

[0154] Example 17

[0155] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 133 minutes.

[0156] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 73.5:22.5:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 90.4:5.6:0.6:2.4:1; the rolling pressure is 30T.

[0157] In the preparation of the electrolyte, the concentration of LiPF6 was 1.24 mol / L.

[0158] Example 18

[0159] The difference from Example 1 is that, in the preparation of the positive electrode, LiNi is used... 0.91 Co 0.05 Mn 0.04 O2 replaced with LiNi 0.65 Co 0.15 Mn 0.2 O2;

[0160] In the preparation of silicon-carbon materials, the mixed gas is introduced for 73 minutes.

[0161] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 93.1:2.9:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 95.3:0.7:0.6:2.4:1; the rolling pressure is 33.4T.

[0162] In the preparation of the electrolyte, the concentration of LiPF6 was 1.32 mol / L.

[0163] Example 19

[0164] The difference from Example 1 is that, in the preparation of the positive electrode, LiNi is used... 0.91 Co 0.05 Mn 0.04 O2 replaced with LiNi 0.65 Co 0.15 Mn 0.2 O2;

[0165] In the preparation of silicon-carbon materials, the mixed gas is introduced for 160 minutes.

[0166] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 57.7:38.3:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 86.4:9.6:0.6:2.4:1; the rolling pressure is 73.1T.

[0167] In the preparation of the electrolyte, the concentration of LiPF6 was 0.84 mol / L.

[0168] Example 20

[0169] The difference from Example 1 is that, in the preparation of the positive electrode, LiNi is used... 0.91 Co 0.05 Mn 0.04 O2 replaced with LiNi 0.65 Co 0.15 Mn 0.2 O2;

[0170] In the preparation of silicon-carbon materials, the mixed gas was introduced for 142 minutes.

[0171] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 70.1:25.9:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 89.5:6.5:0.6:2.4:1; the rolling pressure is 69.4T.

[0172] In the preparation of the electrolyte, the concentration of LiPF6 was 0.89 mol / L.

[0173] Example 21

[0174] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas is introduced for 50 minutes.

[0175] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 93.9:2.1:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 95.5:0.5:0.6:2.4:1; the rolling pressure is 69.6T.

[0176] In the preparation of the electrolyte, the concentration of LiPF6 was 0.88 mol / L.

[0177] Example 22

[0178] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas is introduced for 165 minutes.

[0179] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 53.2:42.8:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 85.3:10.7:0.6:2.4:1; the rolling pressure is 71.6T.

[0180] In the preparation of the electrolyte, the concentration of LiPF6 was 0.87 mol / L.

[0181] Comparative Example 1

[0182] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas was introduced for 156 minutes.

[0183] In the preparation of the negative electrode, artificial graphite, silicon carbon material, sodium carboxymethyl cellulose, styrene-butadiene rubber and conductive graphite (KS-6) are dissolved in deionized water in a mass ratio of 66.6:29.4:0.6:2.4:1 to form a negative electrode slurry. The negative electrode slurry is uniformly coated on a copper foil with a thickness of 4.5μm, dried under vacuum at 120℃, and rolled under a pressure of 73.7T to obtain the negative electrode.

[0184] In the preparation of the electrolyte, the concentration of LiPF6 was 0.83 mol / L.

[0185] Comparative Example 2

[0186] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas is introduced for 55 minutes.

[0187] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 93.7:2.3:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 95.4:0.6:0.6:2.4:1; the rolling pressure is 27.2T.

[0188] In the preparation of the electrolyte, the concentration of LiPF6 was 1.2 mol / L.

[0189] Comparative Example 3

[0190] The difference from Example 1 is that, in the preparation of silicon-carbon materials, the mixed gas is introduced for 170 minutes.

[0191] In the preparation of the negative electrode sheet, the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the first negative electrode slurry is 53:43:0.6:2.4:1, and the mass ratio of artificial graphite, silicon carbide material, sodium carboxymethyl cellulose, styrene-butadiene rubber, and conductive graphite (KS-6) in the second negative electrode slurry is 85.3:10.7:0.6:2.4:1; the rolling pressure is 74.4T.

[0192] In the preparation of the electrolyte, the concentration of LiPF6 was 0.8 mol / L.

[0193] Test methods

[0194] 1. Silicon content test

[0195] The battery was discharged to its lower limit voltage at 0.33C. The negative electrode was then removed and immersed in dimethyl carbonate (DMC) solution at room temperature for 4 hours. After vacuum drying, the active material powder on the surface of the electrode was scraped off with a ceramic scraper. The silicon content was tested using the alkaline dissolution-ICP method. The scraped powder sample was weighed and placed in a nickel crucible pre-filled with potassium hydroxide. A small amount of potassium hydroxide was added to cover the sample surface, and two drops of ethanol were added. The crucible was heated on an electric furnace until the potassium hydroxide melted and dehydrated. Then, it was transferred to a muffle furnace at 1100℃ and kept at that temperature for 8 hours. After the crucible was removed and cooled slightly, it was placed in a 300mL plastic beaker, and hot water was added for extraction. The crucible was then washed. Hydrochloric acid was added to the extract for acidification, followed by the addition of a mixed acid consisting of hydrogen peroxide and hydrochloric acid to further convert the silicon-containing compounds into silicon ions. After cooling, the extract was washed with water and transferred to a 100 mL volumetric flask for dilution and shaking. After standing, the solution was transferred to another 100 mL volumetric flask for dilution and shaking, and then allowed to stand to clarify to obtain the test solution. At the same time, a blank solution without powder was prepared according to the same procedure as a control to eliminate operational interference. Finally, the experimental conditions were set according to the sample characteristics, and the detection wavelength of Si element was selected as 288.158 nm. The content A of silicon element in the test solution and the blank control solution was tested by ICP.

[0196] The upper and lower voltage limits for different battery systems are as follows: LFP system (lithium iron phosphate): upper voltage limit is 3.65V, lower voltage limit is 2.5V; NCM system (nickel-cobalt ternary material): upper voltage limit is 4.25V, lower voltage limit is 2.5V; LFMP system (lithium iron phosphate manganese): upper voltage limit is 4.25V, lower voltage limit is 2.5V; lithium nickel manganese oxide system: upper voltage limit is 4.8V, lower voltage limit is 3.5V.

[0197] 2. Particle size test

[0198] The test method refers to GB / T 19077-2016. It can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd. in the UK, where the cumulative 50% diameter in the volumetric reference distribution is Dv50.

[0199] 3. Porosity test

[0200] The diaphragm was cut into 100mm × 100mm samples, and the thickness of the samples was measured and recorded using a precision thickness gauge. The samples were then weighed on an electronic balance and their dry mass was recorded. Next, the samples were completely immersed in a n-butanol solution for at least 30 minutes to ensure that the micropores inside the diaphragm were fully filled with liquid and that there were no residual air bubbles on the surface. After that, the immersed samples were removed, the free liquid on the surface was gently absorbed with filter paper, and the samples were weighed immediately and the wet mass was recorded. Finally, the open porosity of the diaphragm was calculated by combining the n-butanol density, sample area, and sample thickness with the mass difference between the wet and dry masses.

[0201] 4. Compacted density

[0202] The powder compaction density test was conducted according to the method specified in GB / T 24533. A Sansi Zongheng UTM7305 testing instrument was used. The diameter of the test mold was 12.83 mm, and the base area was 1.292 cm². The sample mass was controlled within 1 g ± 0.005 g. The pressurization holding time was set to 30 s, the depressurization holding time to 10 s, and the applied pressure was 5 T (tons).

[0203] 5. Measurement of the time required to discharge from 30% SOC to the lower limit voltage.

[0204] At 25℃, the battery is charged at a constant current of 0.33C to the upper limit voltage, then charged at a constant voltage until the current is less than or equal to 0.05C; then discharged at 0.33C to the lower limit voltage, completing one cycle. After three charge-discharge cycles, the discharge capacity of the third cycle is taken as the battery capacity. After the battery is capped, it is charged again at 0.33C to the upper limit voltage, then discharged at 0.33C to 30% SOC, and then rapidly discharged at 5C to the lower limit voltage. The time taken to discharge from 30% SOC to the lower limit voltage is B (in minutes).

[0205] 6. Constant current ratio test

[0206] After achieving a constant capacity at room temperature (the constant capacity process involves charging at 0.33C at 25℃ to the upper limit voltage, then charging at constant voltage until the current is less than or equal to 0.05C; then discharging at 0.33C to the lower limit voltage, completing one cycle; after three charge-discharge cycles, the discharge capacity of the third cycle is taken as the battery capacity); then a 1C charge test is performed. Under the conditions of a 1C charge rate, the battery is charged at a constant current to the upper limit voltage, then charged at constant voltage to the cutoff current of 0.05C, and then discharged at a 0.33C rate to the lower limit voltage. The 1C constant current ratio = 1C constant current charging capacity / 1C total charging capacity.

[0207] The test results are shown in Table 1.

[0208] Table 1

[0209]

[0210] As shown in Table 1, compared with Comparative Examples 1-3, the batteries of Examples 1-22 all satisfy the condition: 0.33≤A / B≤26.08, while the batteries of Comparative Examples 1-3 do not satisfy the condition: 0.33≤A / B≤26.08. Compared with Comparative Examples 1-3, the batteries of Examples 1-22 simultaneously satisfy the conditions of constant current ratio ≥75% and energy density ≥738Wh / L, indicating that the batteries of Examples 1-22 have both high energy density and excellent fast charging performance.

[0211] Furthermore, compared to Examples 4, 11, 13-16, 18-19, and 21-22, Examples 1-7 further satisfy 1.2≤A / B≤6.957. Compared to Examples 11, 13-16, 18-19, and 21-22, the constant current ratio and energy density of the battery in Examples 1-7 are further improved, especially achieving a constant current ratio ≥84.3% and an energy density ≥826.7Wh / L.

[0212] Furthermore, compared to Examples 8-10, Examples 1-7 further satisfy 3≤A≤8. Compared to Examples 8-10, the constant current ratio and energy density of the battery in Examples 1-7 are further improved, especially the constant current ratio ≥84.3% and the energy density ≥826.7Wh / L can be achieved.

[0213] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A battery, characterized in that, The negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, the negative electrode active material layer comprising silicon. The mass percentage of silicon in the negative electrode active material layer is A%. The battery is discharged at a 5C rate, and the time it takes to discharge from 30% SOC to the lower limit voltage is B, in minutes. The condition is satisfied that 0.33 ≤ A / B ≤ 26.

08.

2. The battery according to claim 1, characterized in that, 1.2≤A / B≤6.

957.

3. The battery according to claim 1, characterized in that, 1 ≤ A ≤ 15; and / or, 0.5 ≤ B ≤ 3.

6.

4. The battery according to claim 3, characterized in that, 3≤A≤8; and / or, 1≤B≤3.

5. The battery according to claim 2, characterized in that, The negative electrode active material layer includes a first active layer and a second active layer. The first active layer is disposed on the surface of the negative electrode current collector, and the second active layer is disposed on the surface of the first active layer away from the negative electrode current collector. The mass percentage of silicon in the first active layer is greater than the mass percentage of silicon in the second active layer, and the thickness ratio of the first active layer to the second active layer is (1~4):(1~4).

6. The battery according to claim 5, characterized in that, The thickness of the negative electrode active material layer is 40μm~110μm.

7. The battery according to claim 5, characterized in that, The thickness of the first active layer is 24μm~86μm.

8. The battery according to claim 5, characterized in that, The thickness of the second active layer is 24μm~86μm.

9. The battery according to claim 5, characterized in that, The mass percentage of silicon in the first active layer is 3% to 25%.

10. The battery according to claim 5, characterized in that, The silicon element in the second active layer accounts for 1% to 15% of the total mass.

11. The battery according to any one of claims 5 to 10, characterized in that, The negative electrode active material layer includes a silicon-based material, which includes at least one of silicon-carbon material and silicon-oxygen material.

12. The battery according to claim 11, characterized in that, The Dv50 particle size of the silicon-based material in the first active layer is 5μm~10μm.

13. The battery according to claim 11, characterized in that, The Dv50 particle size of the silicon-based material in the second active layer is 5μm~10μm.

14. The battery according to claim 11, characterized in that, The negative electrode active material layer includes graphite material and silicon carbon material, and the mass percentage of silicon carbon material in the negative electrode active material layer is 1.8% to 31%.

15. The battery according to any one of claims 5 to 10, characterized in that, The lateral density of the negative electrode active material layer is 80 g / m². 2 ~120g / m 2 .

16. The battery according to any one of claims 1 to 10, characterized in that, The compaction density of the negative electrode active material layer is 1.1 g / cm³. 3 ~1.65g / cm 3 .

17. The battery according to any one of claims 1 to 10, characterized in that, The battery further includes a positive electrode sheet, which includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, which includes lithium nickel cobalt manganese oxide and / or lithium nickel cobalt aluminum oxide.

18. The battery according to claim 17, characterized in that, The positive electrode active material includes lithium nickel cobalt manganese oxide material, and the one-sided lateral density of the positive electrode active material layer is 110 g / m². 2 ~250g / m 2 The compacted density is 1.5 g / cm³. 3 ~3.8g / cm 3 .

19. The battery according to claim 17, characterized in that, The thickness of the positive electrode active material layer is 60μm~145μm.

20. The battery according to claim 17, characterized in that, The battery also includes a separator disposed between the positive electrode and the negative electrode, the separator having a porosity of 35% to 48%.

21. An electrical appliance, characterized in that, The electrical equipment includes the battery according to any one of claims 1 to 20.

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