Positive plate and preparation method thereof, battery monomer, battery and power utilization device

Abstract

The invention provides a positive plate and a preparation method thereof, a battery monomer, a battery and a power utilization device. The positive plate comprises a positive film layer, the positive film layer comprises mixed lithium cobalt oxide and a lithium-rich manganese-based material, and the average particle size of the lithium cobalt oxide is larger than that of the lithium-rich manganese-based material. The lithium cobalt oxide and the lithium-rich manganese-based material are mixed, and the lithium cobalt oxide is a single-crystal material and is high in mechanical structure and pressure resistance, so that the lithium-rich manganese-based material particles with small particle sizes can be dispersed among the lithium cobalt oxide particles with large particle sizes by controlling the average particle size of the lithium cobalt oxide to be greater than that of the lithium-rich manganese-based material; the lithium-rich manganese-based material is arranged in the gaps of the lithium cobalt oxide, namely the lithium-rich manganese-based material is hidden in the gaps of the lithium cobalt oxide, so that in the compaction process of the lithium cobalt oxide, the lithium cobalt oxide can protect the lithium-rich manganese-based material and prevent the lithium-rich manganese-based material from being crushed, that is, the lithium-rich manganese-based material keeps good structural integrity; therefore, the lithium-rich phase in the lithium-rich manganese-based material can exert high capacity under high voltage, and the discharge capacity of the battery is further improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a positive electrode sheet and its preparation method, a battery cell, a battery, and an electrical device. Background Technology

[0002] Regarding the positive electrode of a battery, there are three main ways to improve the energy density of the battery: the first is to increase the discharge capacity of the battery; the second is to increase the voltage plateau of the battery; and the third is to increase the compaction density of the positive electrode, so that it has a higher capacity per unit volume.

[0003] Lithium cobalt oxide (LCO) is widely used in batteries due to its significantly higher compaction density, higher voltage plateau, and discharge capacity (second only to high-nickel ternary cathode materials) compared to other cathode materials such as ternary cathodes, lithium iron phosphate, and lithium manganese oxide. However, the charging cutoff voltage of current lithium cobalt oxide batteries is approaching its limit, and the capacity improvement gained by increasing the charging cutoff voltage is becoming increasingly limited, while the challenges posed by side reactions are growing. Summary of the Invention

[0004] The embodiments of this application provide a positive electrode sheet and its preparation method, a battery cell, a battery, and an electrical device, which can improve the technical problem of difficulty in increasing battery energy density.

[0005] In a first aspect, embodiments of this application provide a positive electrode sheet, including a positive electrode film layer, the positive electrode film layer comprising a mixture of lithium cobalt oxide and lithium-rich manganese-based material, wherein the average particle size of the lithium cobalt oxide is larger than the average particle size of the lithium-rich manganese-based material.

[0006] In this embodiment, lithium cobalt oxide is mixed with lithium-rich manganese-based material. Since lithium cobalt oxide is a single-crystal material with strong mechanical structure and high compressive strength, by controlling the average particle size of lithium cobalt oxide to be larger than that of lithium-rich manganese-based material, the small-diameter lithium-rich manganese-based material particles can be dispersed between the large-diameter lithium cobalt oxide particles. In other words, the lithium-rich manganese-based material is "hidden" in the gaps of lithium cobalt oxide. Thus, during the compaction process of lithium cobalt oxide, lithium cobalt oxide can protect the lithium-rich manganese-based material and prevent it from being crushed, thereby maintaining the good structural integrity of the lithium-rich manganese-based material. In this way, the lithium-rich phase in the lithium-rich manganese-based material can exert a high capacity under high voltage, thereby improving the discharge capacity of the battery.

[0007] In one embodiment, the molecular formula of the lithium-rich manganese-based material is xLi₂MnO₃·(1-x)LiMeO₂ or Li 1+ x MeO 2+x Where 0.1≤x≤0.5, and Me includes at least one of Ni, Co and Mn.

[0008] In lithium-rich manganese-based materials, the lithium-rich phase Li₂MnO₃ can promote the improvement of the specific capacity. Here, 'x' represents the amount of lithium-rich phase in the material; a larger 'x' indicates a higher specific capacity due to the abundance of lithium-rich phase. However, excessive Li₂MnO₃ can exacerbate side reactions. Therefore, it is necessary to control the amount of lithium-rich phase in the material to keep the side reactions within an acceptable range.

[0009] In one embodiment, the mass content of the lithium-rich manganese-based material is 0.5wt%-10wt%, based on the total mass of the lithium cobalt oxide and the lithium-rich manganese-based material.

[0010] As mentioned above, lithium-rich manganese-based materials need to be "hidden" between lithium cobalt oxides. Therefore, the amount of lithium cobalt oxide should be much greater than the amount of lithium-rich manganese-based materials to effectively protect them. Otherwise, excessive lithium-rich manganese-based materials will be crushed under the appropriate compaction density for lithium cobalt oxides, thus failing to achieve the desired effect. Furthermore, lithium-rich manganese-based materials are prone to causing side reactions in the battery, so the amount used must be controlled; otherwise, the side reactions caused by excessive lithium-rich manganese-based materials will be difficult to eliminate.

[0011] In one embodiment, the lithium cobalt oxide has an average particle size of 5 μm-18 μm; and / or, the lithium-rich manganese-based material has an average particle size of 2 μm-12 μm.

[0012] The lithium-rich manganese-based material is "hidden" within lithium cobalt oxide, specifically within the gaps between lithium cobalt oxide particles. The particle size of the lithium cobalt oxide particles affects the size of the gaps between them. When the gaps between lithium cobalt oxide particles are large, the particle size of the lithium-rich manganese-based material can also be increased; conversely, when the gaps are small, the particle size of the lithium-rich manganese-based material needs to be reduced, otherwise it will be easily crushed. By controlling the average particle size of lithium cobalt oxide to 5μm-18μm and the average particle size of the lithium-rich manganese-based material to 3μm-12μm, the lithium cobalt oxide and the lithium-rich manganese-based material can be effectively combined, reducing the risk of the lithium-rich manganese-based material being crushed, thus allowing the lithium-rich manganese-based material to effectively utilize its capacity.

[0013] In one embodiment, the compaction density of the positive electrode film is 3.5 g / cm³. 3 ~4.25g / cm 3 .

[0014] Thanks to the combination of large-particle-size lithium cobalt oxide and small-particle-size lithium-rich manganese-based materials, the compaction density of the positive electrode film can be increased by compacting the lithium cobalt oxide, thereby increasing the energy density of the battery. In this process, the lithium cobalt oxide can protect the lithium-rich manganese substrate and prevent it from being crushed.

[0015] In one embodiment, the positive electrode sheet further includes a positive current collector, and the positive electrode film layer is disposed on the positive current collector.

[0016] The positive current collector serves as a carrier to support the positive electrode film layer, ensuring that the positive electrode active material can effectively participate in the electrochemical reaction during charging and discharging. At the same time, the current generated inside the positive electrode film layer is transmitted to the external circuit through the positive current collector, and a complete discharge cycle is completed through the negative electrode.

[0017] In one embodiment, the positive electrode film layer further includes at least one of a conductive agent and a binder.

[0018] The conductive agent dispersed between the positive electrode active materials and between the positive electrode active materials and the positive electrode current collector acts as a connector, forming a continuous conductive path. Simultaneously, the conductive agent also promotes the wetting of the electrode sheet by the electrolyte, thereby increasing the migration rate of lithium ions in the electrode material and reducing polarization. The binder's role is to firmly bond the various materials in the positive electrode film layer together, thus giving the positive electrode film layer a certain mechanical strength and structural stability.

[0019] Secondly, embodiments of this application provide a method for preparing a positive electrode sheet, comprising:

[0020] A cathode mixture is provided, the cathode mixture comprising lithium cobalt oxide and lithium-rich manganese-based materials;

[0021] The positive electrode mixture is subjected to a film-forming treatment to obtain a positive electrode film layer;

[0022] The positive electrode film is subjected to hot pressing to obtain a positive electrode sheet.

[0023] Because the positive electrode film maintains a high temperature during hot pressing, the stress is released simultaneously when the positive electrode film is squeezed, reducing the risk of the lithium-rich manganese-based material being crushed. In addition, hot pressing can also reduce the pressure required to compact the positive electrode film to the target compaction density.

[0024] In one embodiment, the hot pressing temperature of the hot pressing process is 60°C-120°C.

[0025] The hot-pressing temperature should not be too low, otherwise it will not be enough to effectively release the stress of the positive electrode film. Of course, if the hot-pressing temperature is too high, it will affect the stability of the material in the positive electrode film.

[0026] Thirdly, embodiments of this application provide a battery cell including a positive electrode and a negative electrode disposed opposite to each other, wherein the positive electrode is the aforementioned positive electrode, or the positive electrode is a positive electrode prepared by the aforementioned method for preparing the positive electrode.

[0027] The battery cell includes the positive electrode sheet described above or prepared by the above method. Therefore, the battery cell has all the beneficial effects of the positive electrode sheet described above or prepared by the above method, which will not be elaborated here.

[0028] In one embodiment, the negative electrode sheet includes a negative electrode film layer, which includes at least one of a carbon-based negative electrode material and a silicon-based negative electrode material.

[0029] Carbon-based anode materials not only possess good structural stability, effectively buffering volume changes and thus extending the cycle life of individual battery cells, but also exhibit high conductivity, improving battery charge-discharge efficiency. Silicon-based anode materials have a theoretical specific capacity significantly higher than carbon-based anode materials, allowing them to provide greater energy storage capacity and thus significantly enhancing battery life. Furthermore, silicon-based anode materials have a lower delithiation potential, which helps to inhibit lithium deposition, thereby reducing the risk of lithium plating.

[0030] In one embodiment, the negative electrode film layer comprises graphite and silicon carbon, wherein the mass content of silicon carbon is less than or equal to 20 wt% based on the total mass of the graphite and the silicon carbon.

[0031] Graphite is a carbon-based anode material, while silicon-carbon is a silicon-based anode material. Silicon-carbon can increase the theoretical specific capacity of the anode active material and reduce the delithiation potential, while graphite can maintain the high conductivity and low expansion rate of the anode active material. The combination of graphite and silicon-carbon can optimize the overall performance of the anode active material.

[0032] In one embodiment, the battery cell further includes a separator disposed between the positive electrode and the negative electrode.

[0033] The membrane allows ions to pass through while preventing direct contact between the positive and negative electrodes, thus preventing short circuits.

[0034] Fourthly, embodiments of this application provide a battery comprising the aforementioned battery cell.

[0035] The battery comprises the aforementioned battery cells, and therefore possesses all the beneficial effects of the aforementioned battery cells, which will not be elaborated upon here.

[0036] Fifthly, embodiments of this application provide an electrical device, including the aforementioned battery cell or the aforementioned battery.

[0037] The electrical device includes the aforementioned battery cell or battery, and therefore has all the beneficial effects of the aforementioned battery cell or battery, which will not be elaborated here. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a scanning electron microscope image of the positive electrode sheet provided in Embodiment 1 of this application;

[0040] Figure 2 This is a scanning electron microscope image of the positive electrode provided in Comparative Example 1 of this application. Detailed Implementation

[0041] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and 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. In addition, it should be understood that the specific implementation methods described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0042] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish an order.

[0043] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0044] In this application, "at least one" means one or more, and "more than one" means two or more. "One or more", "at least one of the following", or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0045] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0046] Some embodiments of this application provide an electrical device that uses a battery as a power source. This device can be, but is not limited to, vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. In this device, the battery can serve as both an operating power source and a driving power source.

[0047] Some embodiments of this application provide a battery, and an electrical device includes the battery. A battery refers to a device that can convert chemical energy into electrical energy. The battery can have different forms, such as, but not limited to, a battery cell, a battery module, and a battery pack. Typically, battery modules and battery packs each independently include multiple battery cells connected in series or parallel.

[0048] Some embodiments of this application provide a single battery cell. A single battery cell (also called a battery cell) is the basic unit for converting chemical energy into electrical energy. Optionally, the single battery cell is a secondary battery, such as a lithium-ion battery, thus enabling the interconversion of chemical energy and electrical energy.

[0049] In some embodiments of this application, the battery cell includes a housing with a receiving cavity and an electrode assembly disposed within the receiving cavity, the housing serving to protect the electrode assembly. In a common embodiment, the housing includes a shell and a cover, the cover being disposed on the shell, the shell and cover together defining the receiving cavity. The shell can be made of a metal material with good mechanical strength. As an example, the shell can be a steel shell or an aluminum shell. In another embodiment, a flexible aluminum-plastic film can be used as the shell, resulting in a pouch battery, which has advantages such as lightweight, high energy density, good safety, and flexible shape design.

[0050] To facilitate the transmission of circuits and data between the electrode assembly inside the cavity and the external circuitry outside the cavity, terminals are provided on the cover, which are connected to the electrode assembly. The external circuitry can supply power to the electrode assembly through the terminals, thus charging the individual battery cells; conversely, the electrode assembly can also supply power to the external circuitry through the terminals, thus discharging the individual battery cells.

[0051] In some embodiments of this application, the electrode assembly includes a positive electrode and a negative electrode disposed opposite to each other. The electrode assembly can be configured as a wound structure or a stacked structure.

[0052] In some embodiments of this application, the electrode assembly further includes a separator disposed between the positive and negative electrode plates to prevent short circuits caused by contact between the positive and negative electrode plates. The separator may be selected from one or more of polyolefin separators, non-woven fabric separators, ceramic-coated separators, and composite separators. As an example, a polyolefin separator includes at least one of polyethylene (PE) membranes and polypropylene (PP) membranes. The separator may be a dry-process separator or a wet-process separator, and this is not limited thereto.

[0053] In some embodiments of this application, the battery cell further includes an electrolyte used to wet the electrode assembly. The electrolyte provides ion channels during the charging and discharging process of the battery cell, enabling charge transfer between the positive and negative electrodes, thereby completing energy storage and release. The electrolyte mainly includes a non-aqueous organic solvent and an electrolyte salt. Taking a lithium-ion battery as an example, the electrolyte salt includes lithium salts, which may include at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); the non-aqueous organic solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, and ether solvents. Optionally, the electrolyte also includes functional additives. Functional additives are generally diverse and have different functions. As examples, functional additives include membrane additives, overcharge protection additives, flame retardant additives, high and low temperature additives, conductive additives, and additives for controlling water and HF content, etc. The film additive includes at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The flame retardant additive includes at least one of organophosphorus compounds, organofluorine compounds, and haloalkyl phosphates.

[0054] In some embodiments of this application, the electrode assembly further includes a solid electrolyte membrane disposed between the positive and negative electrode plates. The solid electrolyte membrane can also prevent the positive and negative electrode plates from conducting. Optionally, the solid electrolyte membrane includes at least one of oxide solid electrolyte, sulfide solid electrolyte, and polymer solid electrolyte. If the solid electrolyte membrane can completely replace the electrolyte and separator in a single battery cell, then the battery cell is an all-solid-state battery. Of course, in other embodiments, the battery cell can also be a semi-solid-state battery or a liquid battery.

[0055] In some embodiments of this application, the electrode assembly further includes tabs. Specifically, the tabs include a positive tab and a negative tab, wherein the positive tab is connected to a positive electrode plate, for example, by welding, and the negative tab is connected to a negative electrode plate, for example, by welding. A terminal post is connected to the tabs of the electrode assembly, for example, by welding. The terminal post also includes a positive terminal post and a negative terminal post, wherein the positive terminal post is connected to the positive tab, and the negative terminal post is connected to the negative tab.

[0056] In some embodiments of this application, the negative electrode sheet includes a negative electrode film layer, which contains a negative electrode active material. The negative electrode active material can be selected from at least one of carbon-based and silicon-based negative electrode materials. Carbon-based negative electrode materials not only have good structural stability, effectively buffering volume changes and thus extending the cycle life of individual battery cells, but also have high conductivity, improving the charge and discharge efficiency of the battery. Common carbon-based negative electrode materials include graphite-based materials, such as natural graphite, artificial graphite, and mesophase carbon microspheres (MCI); hard carbon materials, such as amorphous carbon; soft carbon materials, such as graphene and carbon nanotubes; and nanocarbon materials, such as graphene, carbon nanotubes, and carbon fibers. Silicon-based negative electrode materials are another type of negative electrode material different from carbon-based negative electrode materials. Silicon-based negative electrode materials use silicon as the main active material and achieve energy storage through a chemical reaction with lithium ions. Silicon-based anode materials have a theoretical specific capacity far exceeding that of carbon-based anode materials, allowing them to provide greater energy storage capacity and significantly improve battery life. Furthermore, silicon-based anode materials have a lower delithiation potential, which helps inhibit lithium deposition and reduces the risk of lithium plating. Common silicon-based anode materials include silicon-oxygen composites, silicon-carbon composites, and silicon-based alloys. However, silicon-based anode materials have low conductivity and experience significant volume expansion during charge and discharge, which can easily lead to pulverization of the anode film and instability of the SEI film, thus affecting the cycle performance and safety of the battery cell.

[0057] In some embodiments of this application, the negative electrode active material includes carbon-based negative electrode materials and silicon-based negative electrode materials. Specifically, the negative electrode film layer includes graphite and silicon-carbon. Graphite belongs to carbon-based negative electrode materials, and silicon-carbon belongs to silicon-based negative electrode materials. Silicon-carbon can increase the theoretical specific capacity of the negative electrode active material and reduce the delithiation potential, while graphite can maintain high conductivity and low expansion rate of the negative electrode active material. The combination of graphite and silicon-carbon can optimize the overall performance of the negative electrode active material. Based on the total mass of graphite and silicon-carbon, the mass content of silicon-carbon is less than or equal to 20 wt%. Excessive silicon-carbon content in the negative electrode active material will lead to serious side reactions. Optionally, based on the total mass of graphite and silicon-carbon, the mass content of silicon-carbon is 5 wt%-20 wt%. Considering the significant volume expansion of silicon-carbon, the expansion rate of the negative electrode active material is mitigated by controlling the silicon-carbon content in the negative electrode active material. As an example, based on the total mass of graphite and silicon carbon, the mass content of silicon carbon is any one or a range between any two of 5 wt%, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 14 wt%, 15 wt%, 16 wt%, 18 wt%, and 20 wt%.

[0058] In some embodiments of this application, the negative electrode film layer further comprises a conductive agent and a binder. As an example, in the negative electrode sheet, the conductive agent includes at least one of carbon black, graphite, carbon nanotubes (CNTs), graphene, and carbon fiber, and the binder includes at least one of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA).

[0059] In some embodiments of this application, the negative electrode is a self-supporting structure, and the negative electrode only includes a negative electrode film layer, without a negative electrode current collector.

[0060] In some embodiments of this application, the negative electrode sheet further includes a negative electrode current collector, and a negative electrode film layer is disposed on the negative electrode current collector. As an example, the negative electrode current collector includes copper foil.

[0061] Some embodiments of this application provide a positive electrode sheet including a positive electrode film layer. The positive electrode film layer includes a mixture of lithium cobalt oxide and lithium-rich manganese-based material, wherein the average particle size of the lithium cobalt oxide is larger than the average particle size of the lithium-rich manganese-based material.

[0062] Lithium cobalt oxide and lithium-rich manganese-based materials are two different cathode active materials. Lithium cobalt oxide (LiCoO2) has a layered structure composed of alternating layers of CoO2 and lithium ions. Lithium cobalt oxide typically exists as single-crystal primary particles, and its surface is relatively smooth with a uniform particle size distribution. These advantages result in close contact between lithium cobalt oxide particles, reducing voids and thus increasing its compaction density. The compaction density of lithium cobalt oxide is typically around 3.8 g / cm³. 3 ~4.25g / cm 3Between. The higher the compaction density of the active material, the more active material can be accommodated in the same volume, thereby increasing the energy density of the battery, especially the volumetric energy density.

[0063] Lithium-rich manganese-based materials (LMR) are composite cathode materials mainly composed of Li₂MnO₃ and LiMeO₂ (Me is usually Ni, Co, Mn, etc.). The molecular formula of lithium-rich manganese-based materials is xLi₂MnO₃·(1-x)LiMeO₂, or it can also be written as Li 1+x MeO 2+x , where 0 < x < 1, and Me includes at least one of Ni, Co, and Mn. As an example, x is a value in the range of any one or any two of 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, and 0.99.

[0064] Lithium-rich manganese-based materials exhibit high specific capacity, primarily due to the following factors: The lithium-rich phase Li₂MnO₃ is a key component contributing to the high specific capacity of these materials. Under high voltage (>4.5V), the Li₂MnO₃ phase provides additional lithium-ion insertion / extraction sites, thus achieving a higher theoretical specific capacity. In lithium-rich manganese-based materials, oxygen anions (O₂O₃)... 2 During charging and discharging, redox reactions occur, providing additional capacity. In addition to the redox reactions of oxygen anions, transition metals (such as Ni, Co, and Mn) in lithium-rich manganese-based materials also undergo redox reactions, thus providing additional capacity. In other words, lithium-rich manganese-based materials can simultaneously participate in the lithium-ion insertion / extraction and oxygen-ion redox reactions during charging and discharging, thereby significantly improving their specific capacity.

[0065] In addition, lithium-rich manganese-based materials have a wide operating voltage range (2.0V-4.8V) and a high voltage plateau around 4.5V, which enables them to maintain high energy density at high voltages.

[0066] However, it is precisely this complex two-phase structure of lithium-rich manganese-based materials that makes them prone to large interparticle voids during compaction, thus reducing their compaction density. The compaction density of lithium-rich manganese-based materials is typically 2.8 g / cm³. 3 ~3.0g / cm 3 .

[0067] Therefore, in this embodiment, lithium cobalt oxide is mixed with lithium-rich manganese-based material. Since lithium cobalt oxide is a single-crystal material with strong mechanical structure and high compressive strength, by controlling the average particle size of lithium cobalt oxide to be larger than that of lithium-rich manganese-based material, the small-diameter lithium-rich manganese-based material particles can be dispersed between the large-diameter lithium cobalt oxide particles. In other words, the lithium-rich manganese-based material is "hidden" in the gaps of lithium cobalt oxide. Thus, during the compaction process of lithium cobalt oxide, lithium cobalt oxide can protect the lithium-rich manganese-based material and prevent it from being crushed, thereby maintaining the good structural integrity of the lithium-rich manganese-based material. In this way, the lithium-rich phase in the lithium-rich manganese-based material can exert a high capacity under high voltage, thereby improving the discharge capacity of the battery.

[0068] In some embodiments of this application, the molecular formula of the lithium-rich manganese-based material is xLi2MnO3·(1-x)LiMeO2 or Li 1+ x MeO 2+x Where 0.1≤x≤0.5, and Me includes at least one of Ni, Co and Mn.

[0069] In lithium-rich manganese-based materials, the lithium-rich phase Li₂MnO₃ can promote the improvement of the specific capacity of the lithium-rich manganese-based material. x represents the amount of lithium-rich phase in the lithium-rich manganese-based material; the larger x is, the more lithium-rich phase is present in the material, and the higher the specific capacity. However, excessive lithium-rich phase Li₂MnO₃ in the lithium-rich manganese-based material can also aggravate side reactions. Therefore, it is necessary to control the amount of lithium-rich phase in the lithium-rich manganese-based material to keep the side reactions of the battery within an acceptable range. As an example, x is any one or any two of the values ​​of 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, and 0.5.

[0070] In some embodiments of this application, the mass content of the lithium-rich manganese-based material is 0.5wt%-10wt% based on the total mass of lithium cobalt oxide and lithium-rich manganese-based material.

[0071] As mentioned above, lithium-rich manganese-based materials need to be "hidden" between lithium cobalt oxides. Therefore, the amount of lithium cobalt oxide should be much greater than the amount of lithium-rich manganese-based materials to effectively protect them. Otherwise, excessive lithium-rich manganese-based materials will be crushed under the appropriate compaction density for lithium cobalt oxides, thus failing to achieve the desired effect. Furthermore, lithium-rich manganese-based materials are prone to causing side reactions in the battery, so the amount used must be controlled; otherwise, the side reactions caused by excessive lithium-rich manganese-based materials will be difficult to eliminate. As an example, based on the total mass of lithium cobalt oxide and lithium-rich manganese-based materials, the mass content of lithium-rich manganese-based materials is a range of any one or any two of the following: 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, 8wt%, 8.5wt%, 9wt%, 9.5wt%, and 10wt%.

[0072] In some embodiments of this application, the average particle size of lithium cobalt oxide is 5 μm-18 μm; and / or, the average particle size of lithium-rich manganese-based materials is 2 μm-12 μm.

[0073] The particle size of the cathode active material directly affects the lithium-ion insertion / extraction process, thus influencing the battery's electrochemical performance. Reducing the particle size of the cathode active material can increase the specific surface area and shorten the lithium-ion diffusion path, thereby improving the efficiency of the electrochemical reaction. However, excessively small particle size leads to an excessively large specific surface area, which can easily cause surface defects and side reactions, increasing the battery's internal resistance and reducing its cycle performance. Furthermore, excessively small particle size also makes the cathode active material difficult to manufacture, leading to increased material preparation costs.

[0074] As an example, the average particle size of lithium cobalt oxide is a range of any one or any two of 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm and 18 μm.

[0075] As an example, the average particle size of the lithium-rich manganese-based material is a range of any one or any two of 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm and 12μm.

[0076] Furthermore, the lithium-rich manganese-based material is "hidden" within lithium cobalt oxide, specifically within the gaps between lithium cobalt oxide particles. The particle size of the lithium cobalt oxide particles affects the size of the gaps between them. When the gaps between lithium cobalt oxide particles are large, the particle size of the lithium-rich manganese-based material can also be increased; conversely, when the gaps are small, the particle size of the lithium-rich manganese-based material needs to be reduced, otherwise it will be easily crushed. By controlling the average particle size of lithium cobalt oxide to 5μm-18μm and the average particle size of the lithium-rich manganese-based material to 3μm-12μm, the lithium cobalt oxide and the lithium-rich manganese-based material can be effectively combined, reducing the risk of the lithium-rich manganese-based material being crushed, thus allowing the lithium-rich manganese-based material to effectively utilize its capacity.

[0077] In some embodiments of this application, the compaction density of the positive electrode film is 3.5 g / cm³. 3 ~4.25g / cm 3 Thanks to the combination of large-particle-size lithium cobalt oxide and small-particle-size lithium-rich manganese-based materials, the compaction density of the cathode film can be increased by compacting the lithium cobalt oxide, thereby improving the energy density of the battery. During this process, the lithium cobalt oxide protects the lithium-rich manganese substrate, preventing it from being crushed. For example, the compaction density of the cathode film is 3.5 g / cm³. 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 3.85g / cm 3 3.95g / cm 3 4.0g / cm 3 4.05g / cm 3 4.1g / cm 3 4.15g / cm 3 4.2g / cm 3 and 4.25g / cm 3 The value can be any one or both of these values. However, the compaction density of the positive electrode film should not be too high, as lithium-rich manganese-based materials are easily crushed under excessive compaction density.

[0078] In some embodiments of this application, the positive electrode sheet further includes a positive current collector, and the positive electrode film layer is disposed on the positive current collector. The positive current collector acts as a carrier to support the positive electrode film layer, ensuring that the positive electrode active material can effectively participate in the electrochemical reaction during charging and discharging; simultaneously, the current generated inside the positive electrode film layer is transmitted to the external circuit through the positive current collector, completing a complete discharge cycle through the negative electrode. The positive current collector is made of a material with good conductivity, such as at least one of metal and carbon material. As an example, the positive current collector can be a metal current collector made of metal, such as aluminum foil; the positive current collector can also be a carbon current collector made of carbon fiber cloth or carbon nanotubes; the positive current collector can also be a composite current collector made of metal and carbon material, such as carbon-coated aluminum foil. Of course, in other embodiments, the positive electrode sheet can be a self-supporting structure, and the positive electrode sheet only includes the positive electrode film layer without a positive current collector.

[0079] In some embodiments of this application, the positive electrode film layer further includes at least one of a conductive agent and a binder. The conductive agent is dispersed between the positive electrode active materials and between the positive electrode active materials and the positive electrode current collector, acting as a connector to form a continuous conductive path; simultaneously, the conductive agent also promotes the wetting of the electrode sheet by the electrolyte, thereby increasing the migration rate of lithium ions in the electrode material and reducing polarization. As an example, in the positive electrode sheet, the conductive agent includes at least one of carbon black, graphite, carbon nanotubes (CNTs), graphene, and carbon fiber. The binder's function is to firmly bond the various materials in the positive electrode film layer together, thereby imparting a certain mechanical strength and structural stability to the positive electrode film layer. As an example, the binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE).

[0080] Some embodiments of this application provide a method for preparing a positive electrode sheet, which includes:

[0081] We provide cathode mixtures, which include lithium cobalt oxide and lithium-rich manganese-based materials.

[0082] The positive electrode mixture is subjected to a film-forming treatment to obtain a positive electrode film layer;

[0083] The positive electrode film is hot-pressed to obtain the positive electrode sheet.

[0084] The positive electrode sheet can be prepared using either a dry process or a wet process. When using a dry process, the positive electrode mixture does not contain solvent. When using a wet process, the positive electrode mixture is a positive electrode slurry, which includes solvent.

[0085] The film-forming process involves preparing a non-fixed-shape positive electrode mixture into a film structure with a fixed shape through a specific process. Film-forming methods include, but are not limited to, at least one of casting, spin coating, spraying, molding, and electrostatic processes. As an example, a positive electrode slurry is spin-coated onto a positive electrode current collector to obtain a wet film. The wet film is then dried to remove the solvent from the positive electrode slurry, thereby obtaining a pre-formed positive electrode film.

[0086] Hot pressing specifically involves heating and pressurizing the pre-formed positive electrode film obtained after film formation. The purpose is to reduce the porosity of the positive electrode film, allowing the materials within to bond more tightly together and increasing the compaction density of the positive electrode film. As an example, hot pressing is performed using hot roller pressing.

[0087] Because the positive electrode film maintains a high temperature during hot pressing, the stress is released simultaneously when the positive electrode film is squeezed, reducing the risk of the lithium-rich manganese-based material being crushed. In addition, hot pressing can also reduce the pressure required to compact the positive electrode film to the target compaction density.

[0088] In some embodiments of this application, the hot-pressing temperature is 60℃-120℃. The hot-pressing temperature should not be too low, otherwise it will be insufficient to effectively release the stress in the positive electrode film layer. Conversely, excessively high hot-pressing temperatures will affect the stability of the materials in the positive electrode film layer. For example, the binder in the positive electrode film layer may thermally decompose, and the crystal structure of the positive electrode active material in the positive electrode film layer may change, leading to the deactivation of the positive electrode active material. As an example, the hot-pressing temperature is any one or any two of the following: 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, and 120℃.

[0089] In some embodiments of this application, the positive electrode in the battery cell is the aforementioned positive electrode, and the negative electrode active material includes a silicon-based negative electrode material. Since silicon-based negative electrode materials are prone to expansion leading to film formation and consuming more active lithium, this results in the positive electrode active material having a lower specific capacity than the negative electrode active material. However, the lithium-rich manganese-based material added to the positive electrode can exhibit a high capacity under high voltage, thereby compensating for the capacity loss of the positive electrode active material in the negative electrode.

[0090] The following description is based on specific embodiments.

[0091] Example 1

[0092] Example 1 provides a lithium-ion battery. Referring to Table 1, the preparation method of this lithium-ion battery includes the following steps:

[0093] S1. Preparation of the positive electrode sheet: The positive electrode active material, conductive agent, and binder are prepared into a slurry at a mass ratio of 97:2:1 and coated onto an aluminum foil current collector. After drying, a hot pressing process is used. The steel rollers are heated to 90°C and then rolled to achieve a compaction density of 4.25 g / cm³. 3 The positive electrode is fabricated using lithium cobalt oxide (LCO) with a D50 particle size of 15.7 μm and lithium methyl methacrylate (LMR) with a D50 particle size of 6 μm (molecular formula 0.3Li₂MnO₃·0.7LiNi₂). 0.5 Mn 0.5 The mass ratio of LCO to LMR is 95:5, the conductive agent is conductive carbon black SP, and the binder is PVDF.

[0094] S2. Preparation of the negative electrode sheet: The negative electrode active material, conductive agent, and binder are prepared into a slurry in a mass ratio of 96:1:3 and coated onto a copper foil current collector. After drying, the slurry is cold-pressed to obtain the negative electrode sheet. The negative electrode active material includes graphite and silicon carbide, with a mass ratio of graphite to silicon carbide of 90:10. The conductive agent is conductive carbon black SP, and the binder is PAA.

[0095] S3. Preparation of Lithium-ion Batteries: The prepared negative electrode, positive electrode, and separator are wound into bare cells using a winding process. The separator is a PE film. The bare cells are then made into pouch cells, injected with a prepared electrolyte (1M LiPF6, solvents including EC (ethylene carbonate), PC (propylene carbonate), EP (ethyl propionate), and PP (propyl propionate) in a volume ratio of EC:PC:EP:PP = 1:1:2:7), and then packaged to obtain a lithium-ion battery.

[0096] Example 2

[0097] Example 2 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 2 and Example 1 is that in S1, the compaction density of the positive electrode sheet is 4.00 g / cm³. 3 .

[0098] Example 3

[0099] Example 3 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 3 and Example 1 is that in S1, the compaction density of the positive electrode sheet is 3.80 g / cm³. 3 .

[0100] Example 4

[0101] Example 4 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 4 and Example 1 is that in S1, the compaction density of the positive electrode sheet is 3.50 g / cm³. 3 .

[0102] Example 5

[0103] Example 5 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 5 and Example 1 is that in S1, the D50 particle size of lithium cobalt oxide (LCO) is 9.8 μm.

[0104] Example 6

[0105] Example 6 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 6 and Example 1 is that in S1, the mass ratio of LCO to LMR is 99.5:0.5.

[0106] Example 7

[0107] Example 7 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 7 and Example 1 is that in S1, the mass ratio of LCO to LMR is 97:3.

[0108] Example 8

[0109] Example 8 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 8 and Example 1 is that in S1, the mass ratio of LCO to LMR is 90:10.

[0110] Example 9

[0111] Example 9 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 9 and Example 1 is that in S1, the molecular formula of LMR is 0.5Li2MnO3·0.5LiNi. 0.5 Mn 0.5 O2.

[0112] Example 10

[0113] Example 10 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 10 and Example 1 is that in S1, the molecular formula of LMR is 0.1Li2MnO3·0.9LiNi. 0.5 Mn 0.5 O2.

[0114] Example 11

[0115] Example 11 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 11 and Example 1 is that in S1, the D50 particle size of LMR is 2 μm.

[0116] Example 12

[0117] Example 12 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 12 and Example 1 is that in S1, the D50 particle size of LMR is 3.1 μm.

[0118] Example 13

[0119] Example 13 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 13 and Example 1 is that in S1, the D50 particle size of LMR is 12 μm.

[0120] Example 14

[0121] Example 14 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 14 and Example 1 is that in S2, the mass ratio of graphite to silicon carbon is 100:0, that is, the negative electrode active material contains only graphite and does not contain silicon carbon.

[0122] Example 15

[0123] Example 15 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 15 and Example 1 is that in S2, the mass ratio of graphite to silicon carbon is 98:2.

[0124] Example 16

[0125] Example 16 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 16 and Example 1 is that in S2, the mass ratio of graphite to silicon carbon is 95:5.

[0126] Example 17

[0127] Example 17 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 17 and Example 1 is that in S2, the mass ratio of graphite to silicon carbon is 80:20.

[0128] Example 18

[0129] Example 18 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 18 and Example 1 is that in S1, the rolling temperature of the positive electrode is 60°C.

[0130] Example 19

[0131] Example 19 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 19 and Example 1 is that in S1, the rolling temperature of the positive electrode is 120°C.

[0132] Example 20

[0133] Example 20 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 20 and Example 1 is that in S1, the rolling temperature of the positive electrode is 150°C.

[0134] Example 21

[0135] Example 21 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 21 and Example 1 is as follows:

[0136] In S1, the D50 particle size of LCO is 12.6 μm, and the D50 particle size of LMR is 5.7 μm. The mass ratio of LCO to LMR is 99.5:0.5, and the rolling temperature is 60℃.

[0137] In S2, the mass ratio of graphite to silicon carbon is 95:5.

[0138] Example 22

[0139] Example 22 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 22 and Example 1 is as follows:

[0140] In S1, the compaction density of the positive electrode is 4.00 g / cm³. 3 The D50 particle size of LCO is 16.8 μm, while that of LMR is 9.8 μm. The molecular formula of LMR is 0.5Li₂MnO₃·0.5LiNi. 0.45 Co 0.05 Mn 0.5 The mass ratio of O2, LCO to LMR is 94:6, and the rolling temperature is 120℃.

[0141] In S2, the mass ratio of graphite to silicon carbon is 80:20.

[0142] Example 23

[0143] Example 23 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 23 and Example 1 is as follows:

[0144] In S1, the molecular formula of LMR is 0.1Li₂MnO₃·0.9LiNi. 0.5 Mn 0.5The mass ratio of O2, LCO, and LMR is 97:3.

[0145] Example 24

[0146] Example 24 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 24 and Example 1 is that:

[0147] In S1, the compaction density of the positive electrode is 3.8 g / cm³. 3 The D50 particle size of LCO is 6.2 μm, and the D50 particle size of LMR is 3.1 μm. The mass ratio of LCO to LMR is 97:3, and the rolling temperature is 60℃.

[0148] In S2, the mass ratio of graphite to silicon carbon is 95:5.

[0149] Example 25

[0150] Example 25 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 25 and Example 1 is as follows:

[0151] In S1, the compaction density of the positive electrode is 3.8 g / cm³. 3 The D50 particle size of LCO is 5 μm, and the D50 particle size of LMR is 3.1 μm. The mass ratio of LCO to LMR is 97:3, and the rolling temperature is 60℃.

[0152] In S2, the mass ratio of graphite to silicon carbon is 95:5.

[0153] Example 26

[0154] Example 26 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Example 26 and Example 1 is that:

[0155] In S1, the D50 particle size of LCO is 18 μm.

[0156] Comparative Example 1

[0157] Comparative Example 1 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Comparative Example 1 and Example 1 is that in S1, the D50 particle size of LCO is 3 μm.

[0158] Comparative Example 2

[0159] Comparative Example 2 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Comparative Example 2 and Example 1 is that in S1, the D50 particle size of LCO is 5.7 μm.

[0160] Comparative Example 3

[0161] Comparative Example 3 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Comparative Example 3 and Example 1 is that in S1, the D50 particle size of LCO is 15 μm and the D50 particle size of LMR is also 15 μm.

[0162] Comparative Example 4

[0163] Comparative Example 4 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Comparative Example 4 and Example 1 is that in S1, the addition of LMR is omitted.

[0164] Comparative Example 5

[0165] Comparative Example 5 provides a lithium-ion battery. The preparation method of this lithium-ion battery can be found in Example 1 and Table 1. The difference between Comparative Example 5 and Example 1 is that in S1, LCO is omitted, and the compaction density of the positive electrode is 2.8 g / cm³. 3 .

[0166] Comparative Example 6

[0167] Comparative Example 6 provides a lithium-ion battery. The preparation method of the lithium-ion battery can be found in Example 1 and Table 1. The difference between Comparative Example 6 and Example 1 is that in S1, the rolling temperature is 25°C.

[0168] Table 1

[0169]

[0170]

[0171] The discharge capacity of the lithium-ion batteries provided in Examples 1 to 26 and Comparative Examples 1 to 6 at 0.2C in the voltage range of 3.0V to 4.55V was tested, and the test results are recorded in Table 1.

[0172] Results analysis:

[0173] Examples 1-4: As the compaction density of the positive electrode decreases, the discharge capacity of the lithium-ion battery decreases. This is because when the compaction density decreases, there is less positive electrode active material per unit volume of battery, and the overall battery capacity decreases while the unit capacity remains unchanged.

[0174] Examples 1, 5, and 26: As the D50 particle size of lithium cobalt oxide decreases, the discharge capacity of the lithium-ion battery changes only slightly. This indicates that when the D50 particle size of LMR is smaller than that of lithium cobalt oxide, changing the particle size of LCO has little impact on capacity, and the capacity of the lithium-ion battery is mainly related to the LCO content.

[0175] Examples 1, 6 to 8: As the LMR content in the positive electrode active material increases, the specific capacity of the positive electrode active material becomes higher, resulting in a higher overall capacity of the lithium-ion battery at the same compaction density. However, the LMR content in the positive electrode active material should not be too high, otherwise it will lead to severe side reactions in the lithium-ion battery, which will negatively affect the cycle performance of the lithium-ion battery.

[0176] Examples 1, 9, and 10: In LMR, Li₂MnO₃ is a lithium-rich phase. The higher the content of the lithium-rich phase, the higher the specific capacity of the positive electrode active material, resulting in a higher overall capacity of the lithium-ion battery. However, excessively high lithium-rich phase content can also lead to severe side reactions in the lithium-ion battery.

[0177] Examples 1, 11 to 13: When the D50 particle size of LMR increases, the discharge capacity of the lithium-ion battery changes only slightly. This indicates that when the D50 particle size of LMR is smaller than that of lithium cobalt oxide, changing the particle size of LMR has little impact on capacity, and the capacity of the lithium-ion battery is mainly related to the LMR content.

[0178] Examples 1, 14 to 17: As the silicon-carbon content in the negative electrode active material increases, the negative electrode sheet becomes thinner, allowing for more positive and negative electrode sheets to be placed in the lithium-ion battery, resulting in a higher overall capacity. However, silicon-carbon undergoes significant volume expansion during charging and discharging; therefore, the silicon-carbon content in the negative electrode active material should not be too high.

[0179] Examples 1, 18 to 20, and Comparative Example 6: When the rolling temperature is greater than or equal to 60°C, increasing the rolling temperature has a relatively small effect on improving the capacity of the lithium-ion battery. However, when the rolling temperature is low (25°C in Comparative Example 6), electrical performance testing is not performed due to severe breakage of LMR particles in the positive electrode sheet. It can be seen that increasing the rolling temperature during the preparation of the positive electrode sheet can help release internal stress and reduce the risk of LMR breakage; however, once the rolling temperature reaches a certain value, its effect on improving the capacity of the lithium-ion battery is minimal.

[0180] In Examples 21 to 25, when the D50 particle size of the LMR is smaller than that of the lithium cobalt oxide, protecting the LMR with lithium cobalt oxide can effectively improve the capacity of the lithium-ion battery. The relatively low capacities in Examples 24 and 25 are due to the lower compaction density of the positive electrode in these examples, indicating that the compaction density of the positive electrode has a significant impact on the battery capacity.

[0181] Compared with Comparative Examples 1 to 3, in Comparative Examples 1 and 2, the D50 particle size of LMR was larger than that of lithium cobalt oxide. In Comparative Example 3, the D50 particle size of LMR was comparable to that of lithium cobalt oxide. In Comparative Examples 1 to 3, electrical performance tests were not performed because the LMR particles in the positive electrode were severely fragmented. This indicates that when the particle size of lithium cobalt oxide is smaller than or close to that of lithium-rich manganese-based materials, it will crush the lithium-rich manganese-based materials under high compaction. Please refer to [link to details]. Figure 1 and Figure 2 , Figure 1 This is a scanning electron microscope (SEM) image of the positive electrode in Example 1. Figure 2 The image shows a scanning electron microscope (SEM) image of the positive electrode in Comparative Example 1. It can be seen that in Comparative Example 1, a large number of LMR particles are crushed, while in Example 1, most LMR particles can maintain their structural integrity relatively well.

[0182] Compared with Comparative Examples 4 to 5, Example 1 showed improved capacity because the addition of LMR increased the specific capacity of the positive electrode active material; however, compared with Comparative Example 5, Example 1 showed reduced capacity.

[0183] Further cycle performance tests were conducted on the lithium-ion batteries provided in Example 1, Comparative Example 4, and Comparative Example 5. The results showed that, compared with Comparative Example 5, Example 1 maintained a capacity retention rate of 99.4% after 50 cycles, while Comparative Example 5 maintained a capacity retention rate of only 85.6%, and Comparative Example 4 maintained a capacity retention rate of 99.5% after 50 cycles. It can be seen that although Comparative Example 5 has a high discharge capacity, the overall cycle life of the battery is poor due to the tendency for LMR to undergo side reactions.

[0184] In summary, by adding a small amount of LMR to lithium cobalt oxide and controlling the D50 particle size of LMR to be smaller than that of lithium cobalt oxide, the LMR can be protected from being crushed during the compaction process. The LMR can effectively exert its specific capacity, thereby increasing the battery capacity. At the same time, because the amount of LMR added is small, the side reactions inside the battery are easier to control, and the battery cycle performance is also better.

[0185] The embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode plate, characterized in that, It includes a positive electrode film layer, which comprises a mixture of lithium cobalt oxide and lithium-rich manganese-based material, wherein the average particle size of the lithium cobalt oxide is larger than the average particle size of the lithium-rich manganese-based material.

2. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the lithium cobalt oxide and the lithium-rich manganese-based material, the mass content of the lithium-rich manganese-based material is 0.5wt%-10wt%.

3. The positive electrode sheet according to claim 1 or 2, characterized in that, The average particle size of the lithium cobalt oxide is 5 μm-18 μm; and / or the average particle size of the lithium-rich manganese-based material is 2 μm-12 μm.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that, The compaction density of the positive electrode film is 3.5 g / cm³. 3 ~4.25g / cm 3 .

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that, The molecular formula of the lithium-rich manganese-based material is xLi₂MnO₃·(1-x)LiMeO₂ or Li 1+x MeO 2+x Where 0.1≤x≤0.5, and Me includes at least one of Ni, Co and Mn.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that, The positive electrode sheet further includes a positive current collector, and the positive electrode film layer is disposed on the positive current collector; and / or, the positive electrode film layer further includes at least one of a conductive agent and a binder.

7. A method for preparing a positive electrode sheet, used to prepare the positive electrode sheet as described in any one of claims 1 to 6, characterized in that, include: A cathode mixture is provided, the cathode mixture comprising lithium cobalt oxide and lithium-rich manganese-based materials; The positive electrode mixture is subjected to a film-forming treatment to obtain a positive electrode film layer; The positive electrode film is subjected to hot pressing to obtain a positive electrode sheet.

8. The method for preparing the positive electrode sheet according to claim 7, characterized in that, The hot pressing temperature for the hot pressing process is 60℃-120℃.

9. A single battery cell, characterized in that, It includes a positive electrode and a negative electrode arranged opposite to each other, wherein the positive electrode is the positive electrode as described in any one of claims 1 to 6, or the positive electrode is a positive electrode prepared by the method for preparing the positive electrode as described in claim 7 or 8.

10. The battery cell according to claim 9, characterized in that, The negative electrode sheet includes a negative electrode film layer, which includes at least one of carbon-based negative electrode material and silicon-based negative electrode material.

11. The battery cell according to claim 10, characterized in that, The negative electrode film layer comprises graphite and silicon carbon, and the mass content of silicon carbon is less than or equal to 20 wt% based on the total mass of the graphite and silicon carbon.

12. The battery cell according to any one of claims 9 to 11, characterized in that, The battery cell also includes a separator, which is disposed between the positive electrode and the negative electrode.

13. A battery, characterized in that, Includes the battery cell as described in any one of claims 9 to 12.

14. An electrical appliance, characterized in that, Includes the battery cell as described in any one of claims 9 to 12 or the battery as described in claim 13.

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