A lithium-ion battery and its application

Abstract

This application provides a lithium-ion battery and its application. The lithium-ion battery includes a cell and a casing, with the cell encapsulated in a cavity within the casing. The cell includes a positive electrode sheet, which includes a positive electrode active material layer. The positive electrode active material layer includes a positive electrode active material, which includes lithium iron phosphate material and a catalyst. The catalyst includes catalyst elements, including at least one of Mo, Co, and Cu. The lithium-ion battery satisfies the following condition: 120 ≤ a / b ≤ 1910, where a is the ratio of the area of ​​the cell opening to the area of ​​the casing opening; b is the mass percentage of the catalyst in the positive electrode active material. This application improves the cycle performance and fast-charging performance of the battery by controlling the inverse relationship between a and b. When b increases, the active lithium loss compensation is improved while gas production increases, and a is decreased to ensure gas discharge. When b decreases, gas production is reduced while the active lithium loss compensation is reduced, and a is increased to ensure energy density, thus synergistically improving the battery's cycle performance and fast-charging performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium-ion battery and its applications. Background Technology

[0002] With the global energy structure transformation and the rapid development of the new energy industry, lithium-ion batteries have become a core energy solution in energy storage systems, electric vehicles, and consumer electronics due to their high energy density, long cycle life, and environmental friendliness. Among them, lithium iron phosphate is widely used in large-scale energy storage systems and medium-to-low range electric vehicles due to its excellent thermal stability, low cost, and resource sustainability.

[0003] However, lithium iron phosphate batteries face the problem of continuous loss of active lithium ions during long-term charge and discharge, leading to a decrease in battery capacity retention and a shortened cycle life. Current technologies generally employ the addition of lithium replenishing agents to compensate for this loss. However, commonly used lithium replenishing agents often generate a large amount of gas during battery operation. These gases, trapped inside the cell, participate in the repeated formation and rupture of the solid electrolyte interphase (SEI) film, thereby accelerating the increase in interfacial impedance and reducing the battery's fast-charging capability.

[0004] Therefore, how to effectively compensate for the loss of active lithium and improve cycle performance while ensuring the fast charging performance of the battery has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] This application provides a lithium-ion battery with excellent cycle performance and fast charging performance.

[0006] This application also provides an electrical device that includes the aforementioned lithium-ion battery, which has excellent cycle performance and fast charging performance.

[0007] The first aspect of this application provides a lithium-ion battery, the lithium-ion battery comprising a cell and a casing, the cell being encapsulated in a cavity of the casing; the cell comprising a positive electrode sheet, the positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising a positive electrode active material, the positive electrode active material comprising lithium iron phosphate material and a catalyst; the catalyst comprising a catalyst element, the catalyst element comprising at least one of Mo, Co, and Cu;

[0008] The lithium-ion battery satisfies: 120 ≤ a / b ≤ 1910.

[0009] Wherein, 'a' is the ratio of the area of ​​the cell opening to the area of ​​the shell opening; and 'b' is the mass percentage of the catalyst in the positive electrode active material.

[0010] The lithium-ion battery as described above, wherein 290 ≤ a / b ≤ 470.

[0011] In the lithium-ion battery described above, the thickness of the cell is 30~70mm, and 310≤a / b≤450.

[0012] The lithium-ion battery described above, wherein the cell is a wound cell, and 290≤a / b≤460.

[0013] The lithium-ion battery described above, wherein the cell is a stacked cell, and 300≤a / b≤470.

[0014] In the lithium-ion battery described above, the casing includes a first sidewall disposed opposite to the opening surface of the cell, and the distance between the opening surface of the cell and the first sidewall is 0.3~3mm.

[0015] In the lithium-ion battery described above, 0.87 ≤ a ≤ 0.955 and 0.05% ≤ b ≤ 0.7%.

[0016] In the lithium-ion battery described above, 0.89 ≤ a ≤ 0.94 and 0.15% ≤ b ≤ 0.4%.

[0017] In the lithium-ion battery described above, the catalyst comprises an oxide or carbide of the catalyst element.

[0018] In the lithium-ion battery described above, the ratio of the mass percentage of the catalyst to the mass percentage of Fe element, based on the positive electrode active material, is 0.58 to 0.65%.

[0019] In the lithium-ion battery described above, the Fe element has a mass percentage content of 32-36% based on the positive electrode active material.

[0020] In the lithium-ion battery described above, the lithium iron phosphate material includes a lithium iron phosphate matrix and a first carbon coating layer disposed on at least a portion of the surface of the lithium iron phosphate matrix.

[0021] In the lithium-ion battery described above, the thickness of the first carbon coating layer is 0.5~120 nm.

[0022] In the lithium-ion battery described above, the surface of the lithium iron phosphate substrate further includes a catalytic coating layer, the catalytic coating layer comprising the catalyst.

[0023] In the lithium-ion battery described above, the catalytic coating layer is located on the surface of the first carbon coating layer.

[0024] In the lithium-ion battery described above, the surface of the lithium iron phosphate substrate further includes a second carbon coating layer, the second carbon coating layer including the catalyst.

[0025] In the lithium-ion battery described above, the second carbon coating layer is located on the surface of the catalyst coating layer; and / or,

[0026] The thickness of the second carbon coating layer is 2~20nm.

[0027] In the lithium-ion battery described above, the average particle size of the lithium iron phosphate material is 0.5~1.5μm.

[0028] In the lithium-ion battery described above, the positive electrode active material further includes a doping element, wherein the doping element includes at least one selected from Ti, V, Mn, Na, Cr, Mg, Al, Zr, Nb, Ni, and Zn.

[0029] Based on the positive electrode active material, the mass content of the doped element is 300~30000ppm.

[0030] In the lithium-ion battery described above, when the lithium-ion battery is in a 100% SOC charging state, the ratio of the mass content of LiC6 to the mass content of the negative electrode active material layer is 0.74 to 0.97 based on the cell.

[0031] In the lithium-ion battery described above, the ratio of the mass content of LiC6 to the mass content of the negative electrode active material layer, based on the cell, is 0.77 to 0.90 when the lithium-ion battery is in a 100% SOC charging state.

[0032] A second aspect of this application provides an electrical device including the lithium-ion battery of the first aspect.

[0033] The lithium-ion battery of this application includes a cell and a casing, wherein the cell is encapsulated in a cavity of the casing; the cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes lithium iron phosphate material and a catalyst; the catalyst includes a catalyst element, the catalyst element including at least one of Mo, Co, and Cu; the lithium-ion battery satisfies: 120≤a / b≤1910, where a is the ratio of the area of ​​the cell opening to the area of ​​the casing opening; b is the mass percentage content of the catalyst in the positive electrode active material. This application controls the inverse relationship between the ratio of the cell opening area to the casing opening area (a) and the mass percentage content of the catalyst in the positive electrode active material (b). When b increases, lithium oxalate compensates for the loss of active lithium while increasing decomposition gas production; a decrease in a ensures gas discharge. When b decreases, the decomposition gas production of lithium oxalate decreases while the compensation effect for active lithium loss decreases; an increase in a ensures the cell assembly utilization rate, thus synergistically improving the cycle performance and fast charging performance of the battery. Attached Figure Description

[0034] Figure 1 A top view of a wound lithium-ion battery cell;

[0035] Figure 2 This is a side view of a wound lithium-ion battery cell.

[0036] Figure 3 A top view of a stacked lithium-ion battery cell;

[0037] Figure 4 This is a side view of a stacked lithium-ion battery cell. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0039] Lithium iron phosphate (LFP) batteries are widely used in large-scale energy storage systems and low-to-medium range electric vehicles due to their excellent thermal stability, low cost, and resource sustainability. However, LFP batteries face the problem of continuous loss of active lithium ions during long-term charge-discharge cycles, leading to decreased battery capacity retention and shortened cycle life. Current technologies generally employ the addition of lithium replenishing agents to compensate for this loss. Lithium oxalate replenishing agents have advantages such as low cost, good air stability, and the ability to release active lithium through self-sacrificing properties. However, they generate a large amount of gas during battery operation. These gases, trapped inside the cell, participate in the repeated formation and rupture of the negative electrode SEI film, thereby accelerating the increase in interfacial impedance and reducing the battery's fast-charging capability.

[0040] The inventors believe that only by reducing gas production and preventing gas from participating in the negative electrode film formation can the cycle performance of the battery be improved through lithium supplementation. To this end, the inventors conducted research and found that by controlling the mass percentage content of lithium oxalate supplementation, excessive decomposition of lithium oxalate and gas production can be avoided; by controlling the ratio of the area of ​​the cell opening to the area of ​​the casing opening, gas can be discharged between the cell and the casing, reducing the participation of gas in the negative electrode film formation.

[0041] Since lithium oxalate completely decomposes in the battery after exerting its lithium replenishment effect, the mass percentage of lithium oxalate lithium replenishment cannot be measured. The catalyst and lithium oxalate lithium replenishment are added at a fixed mass ratio during the battery preparation stage, and the catalyst is structurally stable and does not participate in consumption and decomposition during the subsequent reaction process. Therefore, the mass percentage of the catalyst can be measured. Thus, the mass percentage of the catalyst can be used to indirectly reflect the mass percentage of lithium oxalate lithium replenishment.

[0042] Furthermore, the inventors believe that by achieving a dynamic balance between the ratio of the cell opening area to the shell opening area and the mass percentage of the catalyst, the cycle performance and fast charging performance of lithium-ion batteries can be synergistically improved.

[0043] Based on this, the first aspect of this application provides a lithium-ion battery, which includes a cell and a casing, wherein the cell is encapsulated in a cavity of the casing; the cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes lithium iron phosphate material and a catalyst; the catalyst includes a catalyst element, which includes at least one of Mo, Co and Cu.

[0044] Lithium-ion batteries satisfy the following condition: 120 ≤ a / b ≤ 1910.

[0045] Where a is the ratio of the area of ​​the cell opening to the area of ​​the shell opening; b is the mass percentage of the catalyst in the positive electrode active material.

[0046] Lithium iron phosphate material is a composite oxide mainly composed of Li, Fe, P, and O. It has advantages such as stable structure, long cycle life, low cost, and environmental friendliness. This application does not limit the number of atoms of each element or whether element doping is performed. The catalyst has a stable structure during battery operation and does not participate in consumption and decomposition. Its mass percentage can indirectly reflect the mass percentage of lithium oxalate replenishing agent. This application does not limit the catalyst, as long as it includes the above-mentioned catalyst elements.

[0047] The area of ​​the cell opening refers to the area of ​​the upper end face of the cell facing the opening of the casing, specifically the projected area of ​​the cell end face in the direction perpendicular to the cell axis; the area of ​​the casing opening refers to the end face area of ​​the casing used to accommodate the cell, specifically the projected area of ​​the casing opening in the direction perpendicular to the casing axis.

[0048] Lithium-ion batteries typically have a hexahedral structure, and their cells generally include two types: wound cells and laminated cells. When the cell is a wound cell, such as... Figure 1 The image shown is a top view of a wound lithium-ion battery cell. Figure 2The image shows a side view of a wound-type lithium-ion battery cell. In this view, 1 represents the area of ​​the cell's open surface, 2 represents the area of ​​the casing's open surface, 3 represents the composite of the positive electrode, separator, and negative electrode, and 4 represents the casing's open surface. The red circle indicates that the electrode is completely covered by the separator. When the cell is a stacked cell, as shown... Figure 3 The image shown is a top view of a stacked lithium-ion battery cell. Figure 4 The image shows a side view of a stacked lithium-ion battery cell. In the image, 1 represents the area of ​​the cell opening, 2 represents the area of ​​the casing opening, 3 represents the positive electrode, 4 represents the negative electrode, 5 represents the separator, and 6 represents the casing opening. The red circle indicates that the electrode is not completely covered by the separator.

[0049] In lithium-ion batteries, continuous loss of active lithium ions and gas participation in negative electrode film formation are key factors limiting performance improvement. By synergistically controlling two parameters—the ratio of the cell opening area to the shell opening area and the mass percentage of catalyst in the positive electrode active material—an optimized match can be achieved at both the physical structure and electrochemical reaction levels. This reduces gas production while compensating for the loss of active lithium ions and minimizes gas participation in negative electrode film formation.

[0050] Specifically, the ratio of the area of ​​the cell opening to the area of ​​the casing opening essentially regulates the emission efficiency of the gas inside the cell, determines the amount of gas retained inside the cell, and thus affects whether the gas will participate in the formation of the negative electrode film, which is crucial to the fast charging performance of the battery; the mass percentage of the catalyst in the positive electrode active material indirectly determines the lithium replenishment intensity and gas production of the lithium oxalate replenishing agent, thereby affecting the compensation effect of active lithium and the cycle stability of the battery.

[0051] When the mass percentage of catalyst in the positive electrode active material increases, the gas production from lithium oxalate decomposition increases. This necessitates increasing the gap between the cell and the casing by reducing the ratio of the cell opening area to the casing opening area to ensure gas escape. Conversely, when the mass percentage of catalyst in the positive electrode active material decreases, the active lithium loss compensation effect decreases. This necessitates increasing the ratio of the cell opening area to the casing opening area to compact the assembly space and ensure energy density. Therefore, a and b exhibit an inverse proportional relationship.

[0052] By ensuring 120 ≤ a / b ≤ 1910, synergistic optimization of cycle performance and fast charging performance can be achieved. The inventors believe that if the formula is too low, it means the ratio of the cell opening area to the casing opening area is too small, resulting in low gas emission efficiency and a large amount of gas remaining inside the cell. This gas will participate in the repeated formation and rupture of the negative electrode SEI film, accelerating the increase in interfacial impedance and reducing the battery's fast charging performance. Alternatively, it could indicate an excessively high mass percentage of catalyst in the positive electrode active material, or excessive use of lithium oxalate supplementer. Excessive lithium oxalate decomposition will generate a large amount of gas, further exacerbating gas participation in negative electrode film formation. Conversely, if the formula is too high, it means the ratio of the cell opening area to the casing opening area is too large, potentially leading to electrolyte evaporation or the entry of external impurities, affecting battery sealing and safety. Alternatively, it could indicate an excessively low mass percentage of catalyst in the positive electrode active material, or insufficient use of lithium oxalate supplementer, failing to effectively compensate for active lithium loss and reducing battery cycle performance.

[0053] It should be noted that a) the control can be achieved by adjusting the number of layers in the cell during the preparation of lithium-ion batteries; b) the control can be achieved by adjusting the amount of lithium oxalate added during the preparation of the positive electrode active material.

[0054] Therefore, this application controls the inverse relationship between the ratio 'a' of the cell opening area to the shell opening area and the mass percentage 'b' of the catalyst in the positive electrode active material. When 'b' increases, lithium oxalate compensates for the loss of active lithium while increasing decomposition gas production. Matching a decrease ensures gas discharge. When 'b' decreases, lithium oxalate decomposition gas production decreases while the active lithium loss compensation effect decreases. Matching a increase ensures cell assembly utilization rate, thus synergistically improving the battery's cycle performance and fast charging performance.

[0055] In one specific embodiment, a lithium-ion battery is prepared by a method comprising the following process:

[0056] First, iron phosphate and lithium source 1 are mixed at a ratio of n(Li):n(Fe) = 1.03~1.05, and then carbon source 1 is added to obtain slurry 1. Slurry 1 is then subjected to coarse and fine grinding using a sand mill to obtain slurry 2 (average particle size 350~440nm). Slurry 2 is then spray-dried to obtain lithium iron phosphate precursor. The lithium iron phosphate precursor is then sintered to obtain lithium iron phosphate material.

[0057] The lithium source 1 includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source 1 includes at least one of glucose, sucrose, and polyethylene glycol; the solid content of the slurry 1 is 25-45%; and the sintering temperature is 700-850℃.

[0058] Then, lithium source 2 and solvent 1 are mixed at a mass ratio of 1:9~199 to obtain solution 1; carbon source 2, solution 1 and lithium iron phosphate material are mixed at a mass ratio of 0.6~30:10~140:100 to obtain slurry 3; catalyst, dispersant and solvent 2 are mixed at a mass ratio of 1:0.03~0.3:60~80 to obtain slurry 4; slurry 3 and slurry 4 are mixed at a mass ratio of 3~45:1 to obtain slurry 5; slurry 5 is spray-dried to obtain a positive electrode active material precursor; the positive electrode active material precursor is dried at a constant temperature to obtain the positive electrode active material;

[0059] Among them, lithium source 2 is lithium oxalate, solvent 1 includes at least one of pure water and ethanol, carbon source 2 includes at least one of carbon black, carbon nanotubes and graphene, catalyst includes at least one of cobalt tetroxide, molybdenum carbide, molybdenum dioxide, molybdenum trioxide and cobalt hydroxyoxide, dispersant includes at least one of CMC, PVP and polyether polyester-phosphate, solvent 2 includes at least one of pure water and ethanol, and the temperature of constant temperature drying treatment is 150~240℃ and the time is 12~36h;

[0060] Then, the positive electrode active material, conductive agent, binder, and dispersant are dispersed in an appropriate amount of N-methylpyrrolidone (NMP), and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, rolling, and slitting, a positive electrode sheet (area density 350~450 g / m²) is obtained. 2 Compacted density 2~3 g / cm³ 3 );

[0061] The positive electrode active material layer comprises, by weight percentage, 95-98 wt% positive electrode active material, 0-2 wt% conductive agent, 0.5-3 wt% binder, and 0-0.5 wt% dispersant.

[0062] The positive electrode current collector material can be at least one of aluminum foil and nickel foil; the conductive agent can be at least one of conductive carbon black, carbon nanotubes, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane; and the dispersant includes at least one of acrylic acid, acrylate, polyether ester, phosphate ester, small molecule alkanolamine, polyurethane, modified styrene / maleic anhydride, HNBR, PVP, and polyethylene glycol (PEG).

[0063] Then, the negative electrode active material, conductive agent, binder, and dispersant are dispersed in an appropriate amount of water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet (area density 160~200g / m²) is obtained. 2 The compacted density is 1.4~1.8 g / cm³. 3 );

[0064] The negative electrode active material layer comprises, by weight percentage, 95-99 wt% negative electrode active material, 0.3-3 wt% conductive agent, 2-3 wt% binder, and 0.5-4 wt% dispersant.

[0065] The material of the negative electrode current collector layer can be at least one of copper foil, nickel foam, and copper foam; the conductive agent can be at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the binder can be 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; and the dispersant includes at least one of sodium carboxymethyl cellulose, acrylic acid, acrylate, polyether ester, phosphate ester, small molecule alkanolamine, polyurethane, modified styrene / maleic anhydride, HNBR, and PVP.

[0066] Finally, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a square aluminum shell. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. After the battery is placed, formed, and resealed, a lithium-ion battery is obtained.

[0067] Furthermore, 290 ≤ a / b ≤ 470. By controlling a / b within the above range, on the one hand, it can ensure that the active lithium released by the lithium oxalate supplement fully compensates for the active lithium ions lost during the charging and discharging of the lithium iron phosphate material, effectively improving the battery capacity retention rate and extending the battery cycle life. At the same time, it avoids excessive use of lithium oxalate supplement decomposition and gas generation, reducing the amount of gas generated from the source. On the other hand, it can ensure that the gas can be efficiently discharged into the gap between the cell and the casing, preventing the gas from remaining inside the cell and participating in the negative electrode film formation, thereby suppressing the growth of interface impedance, ensuring the battery's fast charging capability, and achieving synergistic optimization of battery cycle performance and fast charging performance.

[0068] Furthermore, the cell thickness is 30~70mm, and 310≤a / b≤450. By limiting the cell thickness and a / b, on the one hand, the requirements for gas generation and emission within the cell can be optimized. This ensures that gases generated during cell operation can be efficiently discharged into the gap between the cell and the casing through the opening ratio, preventing gas from stagnating inside the cell and reducing the repeated formation and rupture of the negative electrode SEI film, which is beneficial for optimizing the battery's fast-charging performance. On the other hand, it can indirectly control the amount of lithium oxalate supplement, ensuring sufficient replenishment of active lithium while avoiding excessive decomposition and gas generation of the lithium oxalate supplement, thus synergistically improving the battery's cycle performance and fast-charging performance.

[0069] In one specific embodiment, the battery cell is a wound battery cell, where 290≤a / b≤460. A wound battery cell is a battery cell made by stacking the positive electrode, separator, and negative electrode in sequence and then winding them in a spiral shape along the same axis. It has a compact structure and high space utilization.

[0070] By controlling the range of wound cells and the a / b ratio, on the one hand, the amount of lithium oxalate replenishing agent can be precisely controlled to fully compensate for the loss of active lithium in wound cells during high-rate, long-cycle processes, significantly improving capacity retention and cycle life. At the same time, the excessive decomposition and gas generation of lithium oxalate replenishing agent can be strictly controlled, reducing the risk of gas generation from the source. On the other hand, it can ensure that the gas is discharged in a timely manner, effectively preventing the gas from being trapped between the winding layers and participating in the repeated rupture and reconstruction of the negative electrode SEI film, thereby ensuring the fast-charging performance of the battery.

[0071] In addition, the battery cell is a laminated cell, with a ratio of 300 ≤ a / b ≤ 470. A laminated cell is a cell made by stacking positive electrode plates, separators, and negative electrode plates alternately in sequence, and adopts a continuous integrated separator layout, resulting in a flat structure and uniform internal resistance.

[0072] By controlling the range of stacked cells and the a / b ratio, on the one hand, the amount of lithium oxalate replenishing agent can be precisely controlled to fully compensate for the loss of active lithium ions during long-term charging and discharging of the stacked cells, effectively improving the battery capacity retention rate and cycle life. At the same time, it avoids the excessive decomposition of lithium oxalate replenishing agent to generate a large amount of gas, controlling the risk of gas generation from the source. On the other hand, it can prevent gas from lingering between the stacked layers, preventing gas from participating in the repeated rupture and reconstruction of the SEI film, thereby reducing the interface impedance and further ensuring the battery's fast charging capability.

[0073] To further improve gas discharge efficiency, the casing can include a first sidewall positioned opposite the opening of the battery cell, with a distance of 0.3~3mm between the opening and the first sidewall. The first sidewall refers to a sidewall structure on the casing that is parallel to and corresponds to the opening of the battery cell. Its core function is to facilitate gas discharge in conjunction with the opening of the battery cell, while also providing lateral support and protection for the battery cell. It is one of the key structures forming the gas-accommodating gap between the battery cell and the casing.

[0074] Adjusting the distance between the cell opening and the first sidewall can, on the one hand, create a reasonable gas containment and flow gap between the cell opening and the first sidewall, ensuring that the gas can diffuse smoothly within this gap after being discharged from the cell, avoiding gas stagnation inside the cell or at the opening, effectively preventing gas from participating in the repeated formation and rupture of the negative electrode SEI film, thereby suppressing the increase in interface impedance and ensuring the fast charging performance of the battery; on the other hand, it can provide stable support for the cell, reduce the deformation of the cell during charging and discharging, and further improve the structural stability and cycle reliability of the battery.

[0075] In one specific implementation, 0.87 ≤ a ≤ 0.955, and 0.05% ≤ b ≤ 0.7%. Adjusting a increases the effective proportion of the gas emission channel, ensuring that gas generated inside the cell can be quickly and smoothly discharged to the buffer space between the cell and the casing. This physically prevents gas from stagnating inside the cell and participating in negative electrode film formation, effectively suppressing interfacial impedance growth and ensuring excellent fast-charging performance. Adjusting b indirectly limits the amount of lithium oxalate replenishing agent, achieving a balance between efficient lithium replenishment and moderate gas production. This fully compensates for the loss of active lithium ions while reducing the risk of additional gas production, synergistically improving the battery's cycle performance and fast-charging performance.

[0076] Furthermore, 0.89 ≤ a ≤ 0.94, 0.15% ≤ b ≤ 0.4%. By controlling 'a' within the above range, the area ratio of the cell opening surface to the casing opening surface can be precisely optimized, enabling an efficient gas emission matching relationship between the two. This effectively prevents gas from stagnating inside the cell, reduces gas participation in negative electrode film formation, and ensures stable fast charging capability of the battery. By controlling 'b' within the above range, the amount of lithium oxalate supplement can be more precisely controlled, ensuring that the amount of active lithium released by the lithium oxalate supplement is more suitable for the active lithium loss requirements of lithium iron phosphate materials, precisely alleviating battery capacity decay and further improving cycle life. At the same time, strictly controlling excessive decomposition and gas production of lithium oxalate supplement achieves synergistic optimization of battery cycle performance and fast charging performance.

[0077] In one specific embodiment, the catalyst includes an oxide or carbide of a catalyst element. The oxide or carbide of the catalyst element exhibits stronger chemical and structural stability. On the one hand, it can exert a catalytic effect, accelerating the redox reaction rate during the charging and discharging process of the positive electrode active material, promoting the insertion and extraction of lithium ions, and effectively improving the charging and discharging efficiency of the battery. On the other hand, it can maintain structural integrity during long-term charging and discharging of the battery, not participating in reaction consumption or decomposition, and stably exerting a catalytic effect over a long period.

[0078] Furthermore, based on the positive electrode active material, the mass percentage ratio of the catalyst to the Fe element is 0.58~0.65%. Limiting this ratio ensures a stable release of active lithium from the lithium oxalate supplement to compensate for battery degradation, while preventing excessive catalyst content (i.e., excessive lithium oxalate supplement) leading to lithium oxalate decomposition and gas production. This synergistically optimizes the battery's cycle performance and fast-charging performance, while also ensuring the structural stability of the positive electrode active material, thereby extending the battery's cycle life.

[0079] Furthermore, based on the positive electrode active material, the mass percentage of Fe element is 32-36%. By controlling the mass percentage of Fe element within this range, the integrity and stability of the lithium iron phosphate lattice structure can be guaranteed, preventing the positive electrode active material from pulverizing and detaching during long-term charge and discharge, thus ensuring the long-term service stability of the positive electrode active material. Simultaneously, it can reduce the resistance during lithium-ion diffusion, widen the lithium-ion transport channels, accelerate the insertion and extraction rate of lithium ions within the positive electrode active material, ensure smooth lithium-ion transport, and synergistically optimize the battery's cycle performance and fast-charging performance.

[0080] In one specific embodiment, the lithium iron phosphate material includes a lithium iron phosphate substrate and a first carbon coating layer disposed on at least a portion of the surface of the lithium iron phosphate substrate. The first carbon coating layer can improve the electronic conductivity of the lithium iron phosphate substrate, accelerate electron transport, alleviate the problem of poor conductivity of the lithium iron phosphate substrate itself, and at the same time form a first physical barrier, reducing direct contact between the lithium iron phosphate substrate and the electrolyte, reducing gas generation, and further preventing gas from participating in the formation of the negative electrode film, thereby optimizing the fast charging performance of the battery.

[0081] It should be added that the thickness of the first carbon coating layer is 0.5~120nm. The thickness of the first carbon coating layer can be controlled by adjusting the amount of carbon source added during the preparation of lithium iron phosphate material. Controlling the thickness of the first carbon coating layer within the above range ensures that the coating layer has sufficient electronic conductivity and barrier function, thereby improving the conductivity of the lithium iron phosphate matrix while suppressing side reaction gas production and further improving the fast charging performance of the battery.

[0082] In addition, the surface of the lithium iron phosphate substrate also includes a catalytic coating layer, which comprises a catalyst. The catalyst can promote the redox reaction of the lithium iron phosphate substrate during battery charging and discharging, promote the rapid insertion and extraction of lithium ions, and significantly improve the charging and discharging efficiency of the battery. At the same time, the catalytic coating layer can form an auxiliary protective barrier, reduce the direct contact between the lithium iron phosphate substrate and the electrolyte, suppress the generation of side reactions and gases, and ensure the fast charging performance of the battery.

[0083] Furthermore, the catalytic coating layer is located on the surface of the first carbon coating layer. By placing the catalytic coating layer on the surface of the first carbon coating layer, functional synergy and complementary advantages between the two layers can be achieved. The first carbon coating layer has a certain porous structure and active sites, providing a stable adhesion substrate for the catalytic coating layer. This allows the catalytic coating layer to adhere tightly to the surface of the first carbon coating layer, preventing stress caused by volume expansion and contraction during long-term charging and discharging of the battery, which could lead to detachment or peeling of the catalytic coating layer. This ensures the structural integrity of both the catalytic coating layer and the first carbon coating layer. Simultaneously, the tightly bonded layered structure reduces the interfacial gap between the two layers, lowers interfacial impedance, further optimizes the electron and lithium-ion transport efficiency, and synergistically optimizes the battery's cycle performance and fast-charging performance.

[0084] In one specific embodiment, the surface of the lithium iron phosphate substrate further includes a second carbon coating layer, which comprises a catalyst. The second carbon coating layer is a coating layer disposed on at least a portion of the surface of the lithium oxalate substrate, forming a dense physical barrier that isolates the lithium oxalate substrate from the electrolyte, preventing premature reaction between lithium oxalate and the electrolyte, reducing ineffective loss of active lithium, ensuring precise release of active lithium during battery charging and discharging, improving lithium replenishment efficiency, and thus enhancing the cycle stability of the battery. The catalyst catalyzes the decomposition and activation reactions of lithium oxalate, lowers the active lithium extraction energy barrier, promotes precise lithium replenishment at the first irreversible loss site, improves lithium replenishment efficiency and utilization, and further optimizes the battery's cycle performance.

[0085] Furthermore, the second carbon coating layer is located on the surface of the catalytic coating layer. This second carbon coating layer allows for functional synergy and complementary advantages between the two layers. The catalytic coating layer provides a stable adhesion base for the second carbon coating layer, preventing it from detaching or peeling off during long-term charge-discharge cycles, thus ensuring the lithium replenishment effect of the lithium oxalate matrix. Simultaneously, the close adhesion between the second carbon coating layer and the catalytic coating layer effectively reduces interfacial impedance, promotes lithium-ion transport, and ensures the battery's fast-charging performance.

[0086] It should be added that the thickness of the second carbon coating layer is 2~20 nm. The thickness of the second carbon coating layer can be controlled by adjusting the amount of carbon source added during the preparation of the lithium oxalate supplement. By controlling the thickness of the second carbon coating layer within the above range, it is possible to ensure that the coating layer has sufficient density and integrity, effectively exerting the insulating effect of the coating layer and improving the cycle performance and fast charging performance of the battery; at the same time, it is also possible to ensure the migration of active lithium and effectively improve the lithium ion transport efficiency.

[0087] In one specific embodiment, the average particle size of the lithium iron phosphate material is 0.5~1.5 μm. Limiting the average particle size of the lithium iron phosphate material ensures that it has a suitable specific surface area. On the one hand, this promotes full wetting of the electrolyte, shortens the lithium ion transport path, and improves the lithium ion migration rate and the rate performance of the battery. On the other hand, it prevents the agglomeration of lithium iron phosphate particles, ensures full exposure of active sites, and further improves the electrochemical performance of the battery.

[0088] In addition, the positive electrode active material also includes doping elements, including at least one of Ti, V, Mn, Na, Cr, Mg, Al, Zr, Nb, Ni, and Zn. These doping elements are incorporated into the lithium iron phosphate lattice in the form of elemental doping, partially replacing Fe or Li sites in the lithium iron phosphate lattice. This suppresses lattice distortion, phase transitions, and volume stress during charging and discharging, alleviates the generation of microcracks and pulverization of particles, and significantly improves the cycle stability of the positive electrode active material.

[0089] Based on the cathode active material, the mass content of the doping element is 300~30000ppm. Limiting the mass content of the doping element can ensure that the doping element effectively enters the lithium iron phosphate lattice sites, thereby stabilizing the crystal framework structure, widening the lithium-ion diffusion channels, improving the intrinsic conductivity of the cathode active material, suppressing lattice distortion and particle pulverization during cycling, and further improving the long-term cycle stability of the battery.

[0090] In one specific embodiment, the lithium-ion battery further includes an electrolyte comprising a lithium salt and an additive. The lithium salt includes at least one selected from lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate, and the additive includes at least one selected from vinylene carbonate and fluoroethylene carbonate. In the electrolyte system, the lithium salt is responsible for providing high ionic conductivity, and the additive is responsible for forming a stable SEI film on the negative electrode surface.

[0091] Lithium hexafluorophosphate (LiPF6) exhibits excellent ionic conductivity balance in organic carbonate solvents and can form a stable passivation film on the surface of aluminum current collectors to prevent corrosion. Lithium bis(fluorosulfonyl)imide (LiFSI) has the advantages of high ionic conductivity and good thermal stability, which can effectively reduce the risk of electrolyte decomposition and gas generation at high temperatures. Lithium difluorophosphate (LiDFP) has good ionic conductivity, which can provide a stable lithium-ion transport channel for battery charging and discharging, ensuring efficient lithium-ion transport and improving battery charging and discharging efficiency.

[0092] Vinylene carbonate (VC) can form a flexible and dense SEI film on the negative electrode surface, effectively inhibiting the continuous decomposition of the electrolyte and significantly improving the cycle life of lithium-ion batteries; fluoroethylene carbonate (FEC) participates in the formation of a stable, LiF-containing SEI film, and the LiF component is conducive to the rapid transport of lithium ions and has high mechanical strength.

[0093] It should be added that the lithium salt content in the electrolyte is 8-16% by mass, and the additive content is 0.001-5% by mass. Limiting the lithium salt content in the electrolyte provides a sufficient number of free lithium ions, while maintaining an optimal balance between ion interactions and electrolyte viscosity, thus achieving the highest ionic conductivity. This is the physical basis for supporting fast charging and discharging. Limiting the additive content in the electrolyte allows for complete coverage and formation of a dense, stable solid electrolyte interface film on both the positive and negative electrode surfaces, reducing battery gas generation and improving the battery's fast charging performance.

[0094] Furthermore, the lithium salt includes lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium difluorophosphate, with a mass ratio of 100:3~8:1~2. This mass ratio design can synergistically improve the ionic conductivity of the electrolyte, while LiDFP can assist in the formation of a dense and stable SEI film, inhibiting lithium dendrite growth and improving the cycle performance of the battery.

[0095] In one specific embodiment, the electrolyte further includes a solvent, which includes at least one of ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, and γ-butyrolactone; the solvent has a mass percentage of 45-87.5% in the electrolyte.

[0096] In one specific embodiment, the battery cell further includes a separator, which comprises a separator substrate and a ceramic functional layer disposed on at least a portion of the surface of the separator substrate. The ceramic functional layer includes at least one of alumina, boehmite, and zirconium oxide. The ceramic functional layer possesses excellent thermal stability and high-temperature resistance, effectively increasing the thermal runaway temperature of the separator and preventing short circuits between the positive and negative electrodes caused by separator melting and shrinkage under high-temperature conditions or during long-term cycling, thus further improving the cycle stability of the battery. Simultaneously, the ceramic functional layer exhibits good mechanical strength, enhancing the separator's puncture resistance and tensile strength, ensuring the structural stability of the battery.

[0097] Furthermore, the separator's air permeability is 30~400 s / 100mL, and the ceramic functional layer thickness is 2~8μm. The separator's air permeability is determined using the bubble point test, which measures the time required for a certain volume of air to pass through the separator under a specified pressure. Limiting the separator's air permeability ensures suitable pore flow efficiency, allowing lithium ions in the electrolyte to smoothly pass through the separator pores, guaranteeing efficient lithium ion transport between the positive and negative electrodes, and further improving the battery's charge / discharge efficiency and fast-charging performance. Limiting the thickness of the ceramic functional layer effectively insulates against heat, prevents thermal shrinkage of the separator substrate, prevents lithium dendrites from penetrating the separator and causing short circuits, extending the battery's cycle life, and also ensures the electrolyte's wettability to the separator, improving the battery's fast-charging performance.

[0098] This application does not limit the membrane substrate. In one specific embodiment, the membrane substrate includes at least one of polypropylene membrane (PP), polyethylene membrane (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), and polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP).

[0099] In one specific embodiment, the battery cell further includes a negative electrode sheet. This application does not strictly limit the negative electrode active material in the negative electrode sheet; it can be any negative electrode active material commonly used in lithium-ion batteries, including graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrodes), tin-based negative electrode materials (mainly including tin and tin alloys), and lithium titanate (Li4Ti5O4). 12 At least one of the following.

[0100] In one specific embodiment, at 100% SOC, the mass ratio of LiC6 to the negative electrode active material layer in the lithium-ion battery cell is 0.74 to 0.97. Further, at 100% SOC, the mass ratio of LiC6 to the negative electrode active material layer in the lithium-ion battery cell is 0.77 to 0.90. The lithium-ion battery is charged at a constant current of 0.33C to 3.65V, and then charged at a constant voltage of 3.65V until the current drops to 0.05C (cutoff). The mass ratio of LiC6 to the negative electrode active material layer is determined by X-ray photoelectron spectroscopy (XPS) analysis, specifically by measuring the characteristic peak intensity of LiC6 using XPS and calculating the LiC6 mass content using a calibration curve; simultaneously, the mass content of the negative electrode active material layer is determined by weighing, and the final ratio is calculated.

[0101] LiC6 is the main lithium intercalation product formed after lithium ions are inserted into the negative electrode. The ratio of the mass content of LiC6 to the mass content of the negative electrode active material layer directly determines the degree of lithium intercalation and capacity utilization of the negative electrode. By controlling the ratio of the mass content of LiC6 to the mass content of the negative electrode active material layer within the above-mentioned range, the amount of LiC6 generated is optimally matched with the lithium storage capacity of the negative electrode active material. This ensures that the negative electrode is fully lithium-intercalated to release the full capacity of the battery, while maintaining the uniform distribution of LiC6 in the negative electrode active material layer. This reduces the negative electrode volume expansion and structural damage caused by excessive local lithium intercalation during the lithium intercalation process, ensuring the long-term stability of the negative electrode structure and thus improving the cycle stability of the battery.

[0102] When a lithium-ion battery comprises a cell, a casing, and an electrolyte, and the cell comprises a positive electrode, a negative electrode, and a separator, and the positive electrode comprises a positive active material layer, the positive active material layer comprises a positive active material, and the positive active material comprises lithium iron phosphate material (which, from the core to the outermost layer, comprises a lithium iron phosphate matrix, a first carbon coating layer, a catalyst coating layer, and a second carbon coating layer), a catalyst, and doping elements, the lithium-ion battery is prepared by a method comprising the following processes:

[0103] First, iron phosphate and lithium source 1 are mixed at a ratio of n(Li):n(Fe) = 1.03~1.05, and then carbon source 1 and dopant are added to obtain slurry 1. Slurry 1 is then subjected to coarse and fine grinding using a sand mill to obtain slurry 2 (average particle size 350~440nm). Slurry 2 is then spray-dried to obtain lithium iron phosphate precursor. Finally, the lithium iron phosphate precursor is sintered to obtain lithium iron phosphate material.

[0104] The lithium source 1 includes at least one of lithium carbonate, lithium hydroxide, and lithium acetate; the carbon source 1 includes at least one of glucose, sucrose, and polyethylene glycol; the dopant includes at least one of tungsten trioxide, vanadium pentoxide, titanium dioxide, zinc carbonate, zinc oxide, niobium pentoxide, zirconium dioxide, tin dioxide, manganese dioxide, sodium carbonate, magnesium carbonate, and aluminum oxide; the slurry 1 has a solid content of 25-45%; and the sintering temperature is 700-850℃.

[0105] Then, lithium source 2 and solvent 1 are mixed at a mass ratio of 1:9~199 to obtain solution 1; carbon source 2, solution 1 and lithium iron phosphate material are mixed at a mass ratio of 0.6~30:10~140:100 to obtain slurry 3; catalyst, dispersant and solvent 2 are mixed at a mass ratio of 1:0.03~0.3:60~80 to obtain slurry 4; slurry 3 and slurry 4 are mixed at a mass ratio of 3~45:1 to obtain slurry 5; slurry 5 is spray-dried to obtain a positive electrode active material precursor; the positive electrode active material precursor is dried at a constant temperature to obtain the positive electrode active material;

[0106] Among them, lithium source 2 is lithium oxalate, solvent 1 includes at least one of pure water and ethanol, carbon source 2 includes at least one of carbon black, carbon nanotubes and graphene, catalyst includes at least one of cobalt tetroxide, molybdenum carbide, molybdenum dioxide, molybdenum trioxide and cobalt hydroxyoxide, dispersant includes at least one of CMC, PVP and polyether polyester-phosphate, solvent 2 includes at least one of pure water and ethanol, and the temperature of constant temperature drying treatment is 150~240℃ and the time is 12~36h;

[0107] Then, the positive electrode active material, conductive agent, binder, and dispersant are dispersed in an appropriate amount of N-methylpyrrolidone (NMP), and thoroughly stirred to form a uniform positive electrode slurry. The positive electrode slurry is then uniformly coated onto the positive electrode current collector, and after drying, rolling, and slitting, a positive electrode sheet (area density 350~450 g / m²) is obtained. 2 Compacted density 2~3 g / cm³ 3 );

[0108] The positive electrode active material layer comprises, by weight percentage, 95-98 wt% positive electrode active material, 0-2 wt% conductive agent, 0.5-3 wt% binder, and 0-0.5 wt% dispersant.

[0109] The positive electrode current collector material can be at least one of aluminum foil and nickel foil; the conductive agent can be at least one of conductive carbon black, carbon nanotubes, acetylene black, graphene, Ketjen black, and carbon fiber; the binder can be at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane; and the dispersant includes at least one of acrylic acid, acrylate, polyether ester, phosphate ester, small molecule alkanolamine, polyurethane, modified styrene / maleic anhydride, HNBR, PVP, and polyethylene glycol (PEG).

[0110] Then, the negative electrode active material, conductive agent, binder, and dispersant are dispersed in an appropriate amount of water and thoroughly stirred to form a uniform negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode sheet (area density 160~200g / m²) is obtained. 2 The compacted density is 1.4~1.8 g / cm³. 3 );

[0111] The negative electrode active material layer comprises, by weight percentage, 95-99 wt% negative electrode active material, 0.3-3 wt% conductive agent, 2-3 wt% binder, and 0.5-4 wt% dispersant.

[0112] The material of the negative electrode current collector layer can be at least one of copper foil, nickel foam, and copper foam; the conductive agent can be at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, and graphene; the binder can be 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; and the dispersant includes at least one of sodium carboxymethyl cellulose, acrylic acid, acrylate, polyether ester, phosphate ester, small molecule alkanolamine, polyurethane, modified styrene / maleic anhydride, HNBR, and PVP.

[0113] Finally, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a square aluminum shell. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. After the battery is placed, formed, and resealed, a lithium-ion battery is obtained.

[0114] A second aspect of this application provides an electrical device that includes the lithium-ion battery of the first aspect.

[0115] Thanks to the excellent cycle performance and fast charging performance of this lithium-ion battery, the electrical device can achieve efficient and long-lasting operation by relying on its stable energy supply and efficient charge and discharge characteristics, effectively improving the device's battery life and user experience, and has a wide range of application scenarios. The electrical device of this application may include, but is not limited to, electric vehicles (such as pure electric vehicles, hybrid electric vehicles, and electric bicycles), consumer electronic devices (such as smartphones, laptops, and wearable devices), energy storage devices (such as home energy storage cabinets, industrial energy storage systems, and photovoltaic energy storage power stations), and power tools (such as electric drills, electric wrenches, and electric saws).

[0116] The present application will be further described below through specific embodiments.

[0117] Example 1

[0118] 1) Iron phosphate and lithium carbonate were mixed at a ratio of n(Li):n(Fe) = 1.03, and then glucose and vanadium pentoxide were added to obtain slurry 1 with a solid content of 38%; slurry 1 was coarsely ground and finely ground using a sand mill to obtain slurry 2 (average particle size 350 nm); slurry 2 was spray-dried to obtain lithium iron phosphate precursor; the lithium iron phosphate precursor was sintered at 750℃ to obtain lithium iron phosphate material;

[0119] 2) Lithium oxalate and pure water were mixed at a mass ratio of 1:19 to obtain solution 1; carbon nanotubes, solution 1, and lithium iron phosphate were mixed at a mass ratio of 3.75:135:100 to obtain slurry 3; cobalt tetroxide, polyether polyester-phosphate, and pure water were mixed at a mass ratio of 1:0.3:78 to obtain slurry 4; slurry 3 and slurry 4 were mixed at a mass ratio of 7:1 to obtain slurry 5; slurry 5 was spray-dried to obtain a positive electrode active material precursor; the positive electrode active material precursor was dried at a constant temperature of 180℃ for 24 hours to obtain the positive electrode active material.

[0120] 3) The positive electrode active material, SP, CNT, PVDF, and PVP are mixed in a weight ratio of 96.8%:0.5%:0.5%:2%:0.2%, and the mixture is dispersed in NMP to obtain a positive electrode slurry; the slurry is coated onto an aluminum foil current collector, with a positive electrode areal density of 402 g / m³. 2 The positive electrode sheet was prepared by rolling (compacted density 2.62 g / cm³). 3 );

[0121] 4) Artificial graphite, SP, SBR, and CMC are mixed in a weight ratio of 96.4%:0.6%:2.4%:0.6%, and the mixture is dispersed in water to obtain a negative electrode slurry. The slurry is coated onto a copper current collector, followed by rolling and drying to obtain a negative electrode sheet (area density 194 g / m²). 2Compacted density 1.6 g / cm³ 3 );

[0122] 5) Assemble the positive electrode, negative electrode, and separator into a battery and inject electrolyte; wherein, the electrolyte is mixed at a volume ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 1:1:1, and then 5% of fluoroethylene carbonate (FEC) (by mass of the total electrolyte), 13% of lithium hexafluorophosphate (LiPF6) (by mass of the total electrolyte), and 2% of vinylene carbonate (VC) (by mass of the total electrolyte) (by mass of the total electrolyte) are added; the battery is then left to stand, formed, and resealed to obtain a lithium-ion battery;

[0123] The formation temperature is 45℃, and the formation steps are: 0.02C constant current charging for 5 hours, 0.05C constant current charging for 4 hours, 0.1C constant current charging to 4.8V, and 0.02C constant current charging to 4.9V.

[0124] The lithium-ion battery includes a cell (the cell has 99 layers) and a casing. The casing includes a first sidewall that is disposed opposite to the opening surface of the cell, and the distance between the opening surface of the cell and the first sidewall is 0.5 mm.

[0125] Example 2

[0126] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:38:100 to obtain slurry 3; and in step 5), the number of layers of the cell is 106.

[0127] Example 3

[0128] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:45:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0129] Example 4

[0130] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:74:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 98.

[0131] Example 5

[0132] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:60:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 104.

[0133] Example 6

[0134] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:70:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0135] Example 7

[0136] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:67:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 95.

[0137] Example 8

[0138] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:69:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 106.

[0139] Example 9

[0140] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:63:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 102.

[0141] Example 10

[0142] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:69:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 97.

[0143] Example 11

[0144] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:63:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 104.

[0145] Example 12

[0146] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:67:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 101.

[0147] Example 13

[0148] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:38:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 105.

[0149] Example 14

[0150] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:130:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0151] Example 15

[0152] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:76:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0153] Example 16

[0154] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:58:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0155] Example 17

[0156] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:80:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0157] Example 18

[0158] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:69:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0159] Comparative Example 1

[0160] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:145:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 86.

[0161] Comparative Example 2

[0162] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:9:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 100.

[0163] Comparative Example 3

[0164] The preparation method of this comparative example is basically the same as that of Example 1. The difference is that in step 2), carbon nanotubes, solution 1 and lithium iron phosphate material are mixed in a mass ratio of 3.75:8:100 to obtain slurry 3; and in step 5), the number of layers of the battery cell is 110.

[0165] Experimental Example 1

[0166] The ratio of the cell opening area to the casing opening area and the mass percentage of catalyst in the positive electrode active material of all examples and comparative examples of lithium-ion batteries were tested, and the results are shown in Table 1.

[0167] 1) The ratio a of the area of ​​the cell opening to the area of ​​the casing opening.

[0168] Take the lithium-ion battery to be tested, measure the length and width of the opening of the casing with a ruler, calculate the area of ​​the opening, repeat the measurement 5 times and take the average value, recorded as S1; after breaking the casing of the lithium-ion battery to be tested, take out the cell, measure the length and width of the opening of the cell with a ruler, calculate the area of ​​the opening of the cell, repeat the measurement 5 times and take the average value, recorded as S2; a=S2 / S1. The ruler accuracy is 1mm, and the test is carried out at room temperature.

[0169] 2) Mass percentage of catalyst in positive electrode active material b

[0170] Take the lithium-ion battery to be tested, discharge it to 2.5V at 0.33C and then disassemble the positive electrode sheet; soak the positive electrode sheet in dimethyl carbonate (DMC) at room temperature for 60 minutes and then take it out and air dry it at room temperature with humidity ≤15%; scrape the positive electrode active material powder off the positive electrode sheet.

[0171] Weigh 0.2g of positive electrode active material powder, disperse it in 20mL of water, add 10mL of nitric acid, mix well, and then heat it. After the positive electrode active material powder is completely dissolved, dilute it to 100mL with water to obtain the test solution.

[0172] Before performing ICP testing on the test solution, a standard solution (with a linear correlation coefficient above 0.999) needs to be prepared. Dilute the 1000 mg / L standard solution with deionized water to 0, 1 mg / 100 mL, 2 mg / 100 mL, and 3 mg / 100 mL, respectively. Select the elemental detection wavelength and set the operating conditions: gas flow rate 0.5 mL / min, power 1150 W. The ICP testing software's self-analysis function can read the catalyst element content *m* and the Fe element content *d*. b = (m / x·A) r (M))·M r (M y O z / M y C z ) / (d / A r (Fe))·M r (LiFePO4), where A r (M) represents the relative atomic mass of the catalyst element, A r (Fe) represents the relative atomic mass of Fe, M r (M x O y / M y C z M represents the molar mass of the catalyst. r (LiFePO4) represents the molar mass of LiFePO4, and x represents the number of catalyst atoms in the catalyst's chemical formula.

[0173] Table 1

[0174]

[0175] Experimental Example 2

[0176] The cycle performance and fast-charging performance of the lithium-ion batteries in all embodiments and comparative examples were tested, and the results are shown in Table 2.

[0177] 1) Cyclic performance (capacity retention)

[0178] Fixed capacity: At 25℃, charge at 0.33C to the upper limit voltage of 3.65V, then charge at constant voltage to the cutoff current of 0.05C, let stand for 30 minutes, and discharge at 0.33C to the lower limit voltage of 2.5V. Repeat the above operation 3 times, and use the discharge capacity of the third cycle as the fixed capacity of the battery.

[0179] Cyclic performance test: At 60℃, charge at a constant current rate of 1C to 3.65V, then charge at a constant voltage rate until the current drops to 0.05C, let stand for 30 minutes, discharge at a constant current rate of 1C to 2.5V, let stand for 30 minutes, repeat this charge-discharge cycle 200 times, and measure the discharge capacity Q1 at the first cycle and Q at the 200th cycle.200 Capacity retention rate Q = Q 200 / Q1×100%.

[0180] 2) Fast charging performance (charging time)

[0181] When assembling a lithium-ion battery, a copper wire is added to the negative electrode side;

[0182] After assembling the lithium-ion battery, let it stand for 24 hours, then charge it at 0.02C to 4.1V, then charge it at a constant current of 0.33C to 4.25V, then charge it at a constant voltage of 0.05C, let it stand for 10 minutes, and then discharge it at a constant current of 0.33C to 2.5V to complete the formation.

[0183] Then, it is charged to 4.25V with constant current discharge at a rate of 0.33C, and then charged to 0.05C with constant voltage. After standing for 10 minutes, it is discharged to 2.5V with constant current discharge at a rate of 0.33C. This is one cycle of volume determination. Two cycles of volume determination are performed to complete the volume determination.

[0184] After the initial capacity determination, the copper wire is first lithium-plated at a rate of 0.02C for 4 hours. Then, it is charged at a rate of 0.33C to 10% of the capacity of the second cycle of the initial capacity determination. Immediately afterwards, it is charged at a constant current rate of 4C until the negative electrode potential is 0 or the terminal voltage is 4.25V. Then, it is charged in a decreasing order at a rate of 0.2C, with the cutoff condition unchanged, until the charging rate drops to 0.33C or the capacity reaches 80%. Finally, it is charged at a constant current and constant voltage of 0.33C to 4.25V.

[0185] The test temperature was 25℃, the device signal acquisition frequency was 100ms, and after the test, the charging time t required for the lithium-ion battery to go from 10% to 80% SOC was calculated.

[0186] Table 2

[0187]

[0188] As shown in Table 2, the lithium-ion battery of this application has excellent cycle performance and fast charging performance.

[0189] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a cell and a casing, wherein the cell is encapsulated in a cavity of the casing; the cell includes a positive electrode sheet, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active material, the positive electrode active material includes lithium iron phosphate material and a catalyst; the catalyst includes a catalyst element, the catalyst element including at least one of Mo, Co, and Cu; The lithium-ion battery satisfies: 120 ≤ a / b ≤ 1910. Wherein, 'a' is the ratio of the area of ​​the cell opening to the area of ​​the shell opening; and 'b' is the mass percentage of the catalyst in the positive electrode active material.

2. The lithium-ion battery according to claim 1, characterized in that, 290≤a / b≤470.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The thickness of the battery cell is 30~70mm, and 310≤a / b≤450.

4. The lithium-ion battery according to claim 1 or 2, characterized in that, The battery cell is a wound battery cell, with 290≤a / b≤460.

5. The lithium-ion battery according to claim 1 or 2, characterized in that, The battery cell is a laminated cell, with a value of 300 ≤ a / b ≤ 470.

6. The lithium-ion battery according to claim 1 or 2, characterized in that, The housing includes a first sidewall disposed opposite to the opening surface of the battery cell, and the distance between the opening surface of the battery cell and the first sidewall is 0.3~3mm.

7. The lithium-ion battery according to claim 1 or 2, characterized in that, 0.87≤a≤0.955, 0.05%≤b≤0.7%.

8. The lithium-ion battery according to claim 7, characterized in that, 0.89≤a≤0.94, 0.15%≤b≤0.4%.

9. The lithium-ion battery according to claim 1 or 2, characterized in that, The catalyst comprises oxides or carbides of the catalyst element.

10. The lithium-ion battery according to claim 1 or 2, characterized in that, Based on the positive electrode active material, the ratio of the mass percentage of the catalyst to the mass percentage of Fe element is 0.58~0.65%.

11. The lithium-ion battery according to claim 10, characterized in that, Based on the positive electrode active material, the mass percentage content of the Fe element is 32-36%.

12. The lithium-ion battery according to claim 1 or 2, characterized in that, The lithium iron phosphate material includes a lithium iron phosphate matrix and a first carbon coating layer disposed on at least a portion of the surface of the lithium iron phosphate matrix.

13. The lithium-ion battery according to claim 12, characterized in that, The thickness of the first carbon coating layer is 0.5~120nm.

14. The lithium-ion battery according to claim 12, characterized in that, The surface of the lithium iron phosphate substrate also includes a catalytic coating layer, which includes the catalyst.

15. The lithium-ion battery according to claim 14, characterized in that, The catalytic coating layer is located on the surface of the first carbon coating layer.

16. The lithium-ion battery according to claim 12, characterized in that, The surface of the lithium iron phosphate substrate also includes a second carbon coating layer, which includes the catalyst.

17. The lithium-ion battery according to claim 16, characterized in that, The second carbon coating layer is located on the surface of the catalyst coating layer; and / or, The thickness of the second carbon coating layer is 2~20nm.

18. The lithium-ion battery according to claim 1 or 2, characterized in that, The average particle size of the lithium iron phosphate material is 0.5~1.5μm.

19. The lithium-ion battery according to claim 1 or 2, characterized in that, The positive electrode active material further includes doping elements, which include at least one of Ti, V, Mn, Na, Cr, Mg, Al, Zr, Nb, Ni, and Zn. Based on the positive electrode active material, the mass content of the doped element is 300~30000ppm.

20. The lithium-ion battery according to claim 1 or 2, characterized in that, When the lithium-ion battery is in a 100% SOC charging state, the ratio of the mass content of LiC6 to the mass content of the negative electrode active material layer is 0.74~0.97 based on the battery cell.

21. The lithium-ion battery according to claim 20, characterized in that, When the lithium-ion battery is in a 100% SOC charging state, the ratio of the mass content of LiC6 to the mass content of the negative electrode active material layer is 0.77~0.90 based on the battery cell.

22. An electrical appliance, characterized in that, Including the lithium-ion battery according to any one of claims 1-21.

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