Positive electrode active material, positive electrode sheet, and electrochemical device

Abstract

The application relates to a positive electrode active material, a positive electrode sheet and an electrochemical device. The positive electrode active material comprises first particles, second particles and third particles with different particle sizes and specific surface areas, at least one of the first particles, the second particles and the third particles is coated on the surface and doped in the interior with preset particles; wherein the first particles have the largest particle size and the smallest specific surface area, the volume particle size is 15 mu m to 21 mu m, the specific surface area is 0.05 m 2 / g to 0.2 m 2 / g; the second particles have a particle size and a specific surface area in the middle, the volume particle size is 3 mu m to 7 mu m, the specific surface area is 0.2 m 2 / g to 1 m 2 / g; the third particles have the smallest particle size and the largest specific surface area, the volume particle size is 0.5 mu m to 3 mu m, and the specific surface area is 1 m 2 / g to 3 m 2 / g. The scheme provided by the application can meet the high energy density of the battery by matching the positive electrode active particle material with three particle sizes, different specific surface areas, and surface coating or internal doping of preset particles, while the rate performance and high and low temperature performance of the battery are considered.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to positive electrode active materials, positive electrode sheets, and electrochemical devices. Background Technology

[0002] With the development of lithium-ion batteries, consumers have increasingly higher demands for charging speed, battery life, and safety performance. However, the charging and discharging speed of traditional lithium-ion batteries still cannot meet people's needs for rapid charging and discharging. In order to improve the charging and discharging rate of batteries, a great deal of research has been conducted on cathode materials.

[0003] Studies have found that the particle size of the positive electrode active material has a significant impact on the rate performance of the battery. Smaller particle size results in better rate performance and better low-temperature performance. However, smaller particle size inevitably leads to a larger specific surface area, resulting in poor high-temperature storage performance and lower compaction density, thereby reducing energy density.

[0004] In related technologies, the energy density and rate performance of batteries are improved by mixing two positive electrode active materials with different particle sizes. However, the combination of small and large particles means that the small particles cannot fully fill the gaps between the large particles, resulting in limited improvement in compaction density and thus the energy density of the positive electrode active material cannot be effectively improved. Moreover, the small particle size and large specific surface area of ​​the small particles will aggravate the side reactions of the battery and deteriorate the high-temperature performance of the battery.

[0005] Therefore, there is an urgent need to develop a cathode material with high energy density, good rate performance, and good high and low temperature performance. Summary of the Invention

[0006] To address or partially address the problems existing in related technologies, this application provides a positive electrode active material, a positive electrode sheet, and an electrochemical device. By combining three positive electrode active particle materials with different particle sizes and specific surface areas, and with preset particles coated on the surface or doped internally, the high energy density of the battery can be achieved while also taking into account the rate performance and high and low temperature performance of the battery.

[0007] This application provides a positive electrode active material, comprising a first particle, a second particle, and a third particle with different particle sizes and specific surface areas. At least one of the first, second, and third particles is coated with a first predetermined particle and internally doped with a second predetermined particle. The first particle has the largest particle size and the smallest specific surface area, and its particle size is D1, where D1 is 15 μm to 21 μm, and its specific surface area is S. a S a It is 0.05m 2 / g~0.2m 2 / g; the second particle has a medium particle size and specific surface area, and the particle size of the second particle is D2, where D2 is 3μm~7μm, and the specific surface area is S b S b 0.2m 2 / g~1m 2 / g; the third particle has the smallest particle size and the largest specific surface area, and the particle size of the third particle is D3, where D3 is 0.5μm~3μm, and the specific surface area is S. c S c 1m 2 / g~3m 2 / g.

[0008] As an optional embodiment, the first particle accounts for 75% to 85% of the mass percentage of the positive electrode active material; and / or, the second particle accounts for 14% to 25% of the mass percentage of the positive electrode active material; and / or, the third particle accounts for 1% to 5% of the mass percentage of the positive electrode active material.

[0009] As an optional embodiment, the positive electrode active material satisfies the following relationship:

[0010] 8≤W c +W b ≤25

[0011] Wherein, the third particle accounts for W% of the mass percentage of the positive electrode active material. c The second particle accounts for W% of the mass percentage of the positive electrode active material. b %.

[0012] As an optional embodiment, S a It is 0.12m 2 / g~0.18m 2 / g; and / or, S b 0.4m 2 / g~0.8m 2 / g; and / or, S c 1.5m 2 / g~2.5m 2 / g.

[0013] As an optional embodiment, the surfaces of the first particle, the second particle, and the third particle are all coated with the first preset particle, and the coating amount satisfies the following relationship:

[0014] W c1 ≥W b1 ≥W a1

[0015] Wherein, the amount of coating of the first preset particle on the surface of the first particle is W.a1 ppm, the coating amount of the first preset particle on the surface of the second particle is W b1 ppm, the coating amount of the first preset particle on the surface of the third particle is W c1 ppm.

[0016] As an optional embodiment, 100ppm≤W a1 ≤1000ppm; and / or, 400ppm≤W b1 ≤1500ppm; and / or, 700ppm≤W c1 ≤2500ppm.

[0017] As an optional embodiment, the coating amount and specific surface area of ​​the positive electrode active material satisfy the following relationship:

[0018] W x1 =k×(0.25+S y )×1000+h

[0019] Among them, W x1 W a1 W b1 and W c1 One of them, X is one of a, b, c; S y S represents a S b and S c One of the following, y is one of a, b, c, and x=y; k is 0.1~1.0; h is 100~1000.

[0020] As an optional embodiment, the first particle, the second particle, and the third particle are all doped with the second preset particle, and the doping amount of the positive electrode active material satisfies the following relationship with its specific surface area:

[0021] W b2 =W a2 +(S b -S a )×1000; and / or,

[0022] W c2 =W b2 +(S c -S b )×500

[0023] Wherein, the doping amount of the second preset particle inside the first particle is W. a2 ppm; the doping amount of the second preset particle inside the second particle is W. b2 ppm; the doping amount of the second preset particle inside the third particle is W. c2ppm.

[0024] As an optional embodiment, 3000≤W a2 ≤10000.

[0025] As an optional embodiment, the first preset particle and / or the second preset particle are selected from at least one of aluminum (Al), magnesium (Mg), titanium (Ti), lanthanum (La), yttrium (Y), zirconium (Zr), and fluorine (F).

[0026] As an optional embodiment, the first particle, the second particle, and the third particle are all made of lithium cobalt oxide.

[0027] A second aspect of this application also provides a positive electrode sheet, including a positive current collector and a positive active material layer coated on at least one side of the positive current collector; the positive active material layer includes the aforementioned positive active material.

[0028] A third aspect of this application provides an electrochemical device including the aforementioned positive electrode.

[0029] The technical solution provided in this application may include the following beneficial effects:

[0030] This application prepares a positive electrode active material by mixing three types of particles with different particle sizes in an appropriate ratio. Compared to positive electrode active materials prepared by mixing two types of particles with different particle sizes, the third particle with the smallest particle size in this application embodiment can fully fill the gaps between the first and second particles, which can greatly improve the compaction density and thus improve the energy density of the battery. At the same time, the third particle has a larger specific surface area, resulting in more contact with the electrolyte, and its small particle size makes the lithium-ion transport path shorter, which can improve the lithium-ion transport speed and thus improve the rate performance and low-temperature performance of the battery. Moreover, this application coats at least one of the first, second, and third particles with a predetermined particle inside, which can mitigate the loss caused by excessive lithium-ion insertion / extraction by surface coating or internal doping, and increase the stability of the particle surface and internal structure, thereby improving the high-temperature performance of the battery. Therefore, this application prepares a positive electrode active material by mixing three types of positive electrode particles with different particle sizes and specific surface areas, and with surface coating and internal doping of predetermined particles, which can simultaneously ensure high energy density, high rate performance, and high and low temperature performance of the battery.

[0031] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Detailed Implementation

[0032] The embodiments of this application will now be described in more detail. While embodiments of this application are shown, it should be understood that this application can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to make this application more thorough and complete, and to fully convey the scope of this application to those skilled in the art.

[0033] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0034] It should be understood that although the terms "first," "second," "third," etc., may be used in this application to describe various information, this information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0035] Studies have found that the particle size of the positive electrode active material has a significant impact on the rate performance of the battery. Smaller particle size results in better rate performance and better low-temperature performance. However, smaller particle size inevitably leads to a larger specific surface area, resulting in poor high-temperature storage performance and lower compaction density, thereby reducing energy density.

[0036] In related technologies, the energy density and rate performance of batteries are improved by mixing two positive electrode active materials with different particle sizes. However, the combination of small and large particles means that the small particles cannot fully fill the gaps between the large particles, resulting in limited improvement in compaction density and thus the energy density of the positive electrode active material cannot be effectively improved. Moreover, the small particle size and large specific surface area of ​​the small particles will aggravate the side reactions of the battery and deteriorate the high-temperature performance of the battery.

[0037] To address the aforementioned issues, this application provides a positive electrode active material that, by combining three positive electrode active particle materials with different particle sizes and specific surface areas, and which are coated or doped with preset particles, can satisfy the high energy density of the battery while also taking into account the battery's high rate performance and high and low temperature performance.

[0038] This application provides a positive electrode active material, comprising a first particle, a second particle, and a third particle with different particle sizes and specific surface areas. At least one of the first, second, and third particles has a first predetermined particle coated on its surface and is internally doped with a second predetermined particle. The first particle has the largest particle size and the smallest specific surface area, with a particle size D1 of 15 μm to 21 μm and a specific surface area S... a It is 0.05m 2 / g~0.2m 2 / g; the second particle has a medium particle size and specific surface area, and the particle size D2 of the second particle is 3μm~7μm, and the specific surface area S b 0.2m 2 / g~1m 2 / g; the third particle has the smallest particle size and the largest specific surface area, and the particle size D3 of the third particle is 0.5μm~3μm, with a specific surface area S c 1m 2 / g~3m 2 / g.

[0039] In this embodiment, the particle size and specific surface area of ​​the first particle, the second particle, and the third particle are all different, and the particle size D1 of the first particle > the particle size D2 of the second particle > the particle size D3 of the third particle, and the specific surface area S of the third particle is... c > Specific surface area S of the second particle b > Specific surface area S of the first particle a For example, the specific surface area of ​​the first particle and the second particle is not both 0.2 m². 2 / g, the specific surface area of ​​the third particle and the second particle is different, both being 1m². 2 / g, the particle size of the third particle and the second particle are different, both being 3μm.

[0040] In this context, particle size can refer to the volume average particle size (Dv50), which represents the particle size at which the cumulative volume distribution reaches 50%. It can also refer to the average particle size obtained using laser particle size distribution measurement. Specific surface area refers to the total area per unit mass of particles. Generally, the smaller the volume average particle size (Dv50), the larger the specific surface area.

[0041] For example, in the embodiments of this application, the particle size D1 of the first particle can be 15μm, 17μm, 19μm, 21μm or any value within the above-defined range, and this application does not limit it in this way. The specific surface area S of the first particle a It can be 0.05m 2 / g, 0.1m 2 / g, 0.15m 2 / g, 0.2m 2 / g or any value within the above-mentioned range, but this application does not limit it.

[0042] The particle size D2 of the second particle can be 3 μm, 3.5 μm, 5 μm, 5.5 μm, 7 μm, or any value within the above-defined range; this application does not limit this value. The specific surface area S of the second particle... b It can be 0.2m 2 / g, 0.4m 2 / g, 0.6m 2 / g, 0.8m 2 / g、1m 2 / g or any value within the above-mentioned range, but this application does not limit it.

[0043] The particle size D3 of the third particle can be 0.5 μm, 1 μm, 2 μm, 3 μm, or any value within the above-defined range; this application does not limit this value. The specific surface area S of the third particle... c It can be 1m 2 / g, 1.5m 2 / g、2m 2 / g, 2.5m 2 / g、3m 2 / g or any value within the above-mentioned range, but this application does not limit it.

[0044] This application embodiment prepares a positive electrode active material by providing three particles of different sizes and mixing them in an appropriate ratio. Compared to positive electrode active materials prepared by two particles of different sizes, the third particle with the smallest particle size in this application embodiment can fully fill the gaps between the first and second particles, which can greatly improve the compaction density and thus improve the energy density of the battery. At the same time, the third particle has a larger specific surface area, resulting in more contact with the electrolyte, and the smaller particle size of the third particle makes the lithium ion transport path shorter, which can improve the lithium ion transport speed and thus improve the rate performance and low-temperature performance of the battery. Moreover, under high voltage, the particle material will undergo lithium insertion / extraction, causing irreversible damage to the positive electrode active material itself. This application embodiment coats the surface of at least one of the first, second, and third particles and does the interior with preset particles. The surface coating or internal doping of the preset particles can improve the loss caused by excessive lithium ion insertion / extraction, increase the stability of the particle surface and internal structure, and thus improve the high-temperature performance of the battery. Therefore, the embodiments of this application prepare positive electrode active materials by mixing three positive electrode particle materials with different particle sizes and specific surface areas, and with the surface coated and the interior doped with preset particles, which can simultaneously ensure the high energy density, high rate performance and high and low temperature performance of the battery.

[0045] Furthermore, the first particle accounts for W% of the mass of the positive electrode active material. a%, W a The percentage ranges from 75% to 85%.

[0046] In this embodiment, the first particle accounts for W% of the mass percentage of the positive electrode active material. a The percentage can be 75%, 78%, 80%, 82%, 85% or any value within the above-mentioned range, and this application does not limit it in this regard.

[0047] Furthermore, the second particle accounts for W% of the mass of the positive electrode active material. b %, W b The percentage ranges from 14% to 25%.

[0048] In this embodiment of the application, the second particle accounts for W% of the mass percentage of the positive electrode active material. b The percentage can be 14%, 18%, 20%, 22%, 25% or any value within the above-mentioned range, and this application does not limit it in this regard.

[0049] Furthermore, the third particle accounts for W% of the mass of the positive electrode active material. c %, W c The percentage ranges from 1% to 5%.

[0050] In this embodiment, the third particle accounts for W% of the mass percentage of the positive electrode active material. c The percentage can be 1%, 2%, 4%, 4.5%, 5% or any value within the above-mentioned range, and this application does not limit it in this regard.

[0051] Furthermore, the positive electrode active material satisfies the following relationship:

[0052] 8≤W c +W b ≤25

[0053] The third particle accounts for W% of the mass percentage of the positive electrode active material. c The second particle accounts for W% of the mass percentage of the positive electrode active material. b %.

[0054] In this embodiment, the cooperation of the second and third particles can fully fill the large gap between the first particle with the largest particle size. Therefore, by controlling the appropriate total mass ratio of the second and third particles in the positive electrode active material, the filling rate of the particle pores can be maximized, thereby maximizing the compaction density of the positive electrode active material. When 8≤W c +W b When the value is ≤25, the compaction density of the positive electrode active material can be maximized.

[0055] Furthermore, the specific surface area of ​​the first particle is 0.12 m². 2 / g~0.18m 2 / g.

[0056] The specific surface area of ​​the first particle can be 0.12 m². 2 / g, 0.13m 2 / g, 0.15m 2 / g, 0.18m 2 / g or any value within the above-mentioned range, but this application does not limit it.

[0057] Furthermore, the specific surface area of ​​the second particle is 0.4 m². 2 / g~0.8m 2 / g.

[0058] The specific surface area of ​​the second particle can be 0.4 m². 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g or any value within the above-mentioned range, but this application does not limit it.

[0059] Furthermore, the specific surface area of ​​the third particle is 1.5 m². 2 / g~2.5m 2 / g.

[0060] The specific surface area of ​​the third particle can be 1.5 m². 2 / g、2m 2 / g, 2.2m 2 / g, 2.5m 2 / g or any value within the above-mentioned range, but this application does not limit it.

[0061] Furthermore, the surfaces of the first particle, the second particle, and the third particle are all coated with a first preset particle, and the coating amount satisfies the following relationship:

[0062] W c1 ≥W b1 ≥W a1

[0063] Wherein, the coating amount of the first preset particle on the surface of the first particle is W. a1 ppm, the coating amount of the first preset particle on the surface of the second particle is W b1 ppm, the coating amount of the first preset particle on the surface of the third particle is W c1 ppm.

[0064] The surfaces of the first particle, the second particle, and the third particle in this application embodiment are all coated with a first preset particle, which can form an isolation layer on the particle surface to isolate the electrolyte from the oxidation of the positive electrode, increase the stability of the surface structure of the positive electrode active material, and thus improve the high-temperature performance of the positive electrode active material.

[0065] Furthermore, 100ppm≤W a1 ≤1000ppm.

[0066] In this embodiment of the application, the coating amount of the first preset particle on the surface of the first particle can be 100ppm, 200ppm, 400ppm, 600ppm, 800ppm, 1000ppm or any value within the above-defined range, and this application does not limit it.

[0067] Furthermore, 400ppm≤W b1 ≤1500ppm.

[0068] In this embodiment of the application, the coating amount of the first preset particle on the surface of the second particle can be 400ppm, 600ppm, 800ppm, 1000ppm, 1300ppm, 1500ppm or any value within the above-defined range, and this application does not limit it.

[0069] Furthermore, 700ppm≤W c1 ≤2500ppm.

[0070] In this embodiment of the application, the coating amount of the first preset particle on the surface of the third particle can be 700ppm, 900ppm, 1000ppm, 1500ppm, 2000ppm, 2500ppm or any value within the above-defined range, and this application does not limit it.

[0071] Furthermore, the coating amount and specific surface area of ​​the positive electrode active material satisfy the following relationship:

[0072] W x1 =k×(0.25+S y )×1000+h

[0073] Among them, W x1 W a1 W b1 and W c1 One of them, X is one of a, b, c; S y S represents a S b and S c One of the following, y is one of a, b, c, and x=y; k is 0.1~1.0; h is 100~1000.

[0074] Specifically, W a1 =k×(0.25+S a )×1000+h, W b1 =k×(0.25+S b )×1000+h, W c1 =k×(0.25+S c )×1000+h.

[0075] In this embodiment of the application, due to the specific surface area S of the third particle c > Specific surface area S of the second particle b > Specific surface area S of the first particle a Based on the above relationship, the coating amount W of the third particle c1 > Coating amount W of the second particle b1 > Coating amount W of the first particle a1 This is because smaller particles release more lithium from their surface under high voltage, resulting in more severe structural damage. Therefore, this application embodiment limits the relationship between the coating amount and specific surface area of ​​the positive electrode active material, coating more first preset particles with particles having a larger specific surface area, thereby improving the stability of the overall external structure of the positive electrode active material and thus improving the overall high-temperature performance of the positive electrode active material.

[0076] Furthermore, the first, second, and third particles are all doped with second preset particles, and the doping amount of the positive electrode active material satisfies the following relationship with the specific surface area:

[0077] W b2 =W a2 +(S b -S a )×1000; and / or,

[0078] W c2 =W b2 +(S c -S b )×500

[0079] Wherein, the doping amount of the second preset particle inside the first particle is W. a2 ppm; The doping amount of the second preset particle inside the second particle is W b2 ppm; the doping amount of the second preset particle inside the third particle is W. c2 ppm; the specific surface area of ​​the first particle is S a m 2 / g; the specific surface area of ​​the second particle is S b m 2 / g; the specific surface area of ​​the third particle is S c m 2 / g.

[0080] In this embodiment of the application, due to the specific surface area S of the third particle c > Specific surface area S of the second particle b > Specific surface area S of the first particle a Based on the above relationship, the doping amount W of the third particle c2 > Doping amount W of the second particle b2 > Doping amount W of the first particle a2 This is because smaller particles release more lithium from their surface under high voltage, resulting in more severe structural damage. Therefore, this application embodiment limits the relationship between the doping amount and specific surface area of ​​the positive electrode active material, and uses a first preset particle with a larger doping amount inside a particle with a larger specific surface area to improve the stability of the overall internal structure of the positive electrode active material, thereby improving the overall high-temperature performance of the positive electrode active material.

[0081] Furthermore, 3000≤W a2 ≤10000.

[0082] This application embodiment can be based on W a2 Based on the relationship between the doping amount and specific surface area of ​​the positive electrode active material, W was determined. b2 and W c2 .

[0083] Furthermore, the first preset particle and / or the second preset particle are selected from at least one of aluminum (Al), magnesium (Mg), titanium (Ti), lanthanum (La), yttrium (Y), zirconium (Zr), and fluorine (F).

[0084] In this embodiment, the first preset particle and the second preset particle can be selected from the same material or from different materials. For example, the first preset particle is selected from aluminum (Al), and the second preset particle is selected from magnesium (Mg); or both the first preset particle and the second preset particle are selected from aluminum (Al). When the first preset particle and / or the second preset particle are selected from the above materials, the high-temperature performance of the positive electrode active particle material can be effectively improved when it is coated or doped.

[0085] Preferably, the first preset particles and / or the second preset particles are selected from aluminum (Al).

[0086] When positive electrode active materials, such as lithium cobalt oxide, are doped or coated with Al, the stability of the lithium cobalt oxide matrix structure and surface stability can be improved.

[0087] Furthermore, the first, second, and third particles are all made of lithium cobalt oxide.

[0088] Because other positive electrode active materials have large differences in particle size and specific surface area, while lithium cobalt oxide materials have smaller differences in particle size and specific surface area, choosing lithium cobalt oxide materials can result in higher precision in the particle size and specific surface area of ​​the first, second, and third particles.

[0089] Preferably, the third particle in the embodiments of this application can be selected from the fine powder produced during sintering and crushing in the synthesis of positive electrode active materials.

[0090] The synthesis of positive electrode active materials requires high-temperature sintering, and generally, after sintering, a crushing and powdering process is needed to prepare the positive electrode active materials into particles with the required composite particle size distribution and specific surface area. This crushing and powdering process generates byproducts such as fine powder. The third particle in this embodiment can screen particles with suitable particle size and specific surface area from the fine powder separated during the synthesis of the positive electrode active material, thus avoiding material waste, turning fine powder into a valuable resource, and reducing costs.

[0091] Corresponding to the aforementioned application function implementation method embodiments, this application also provides a positive electrode sheet and an electrochemical device, an electronic device, and corresponding embodiments.

[0092] This application also provides a positive electrode sheet, including a positive current collector and a positive active material layer coated on at least one side of the positive current collector; the positive active material layer includes the aforementioned positive active material.

[0093] In this embodiment, the positive electrode sheet includes a positive current collector and a positive active material coated on at least one side of the positive current collector.

[0094] This application does not limit the choice of positive current collector; it can be selected according to actual needs, such as copper foil.

[0095] In one specific embodiment, the positive electrode active material layer further includes a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent includes at least one of carbon materials such as natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, and graphene. The positive electrode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0096] The positive electrode sheet prepared using the positive electrode active material provided in the embodiments of this application can simultaneously ensure the high energy density, high rate performance and high and low temperature performance of the battery.

[0097] This application also provides an electrochemical device, which includes a positive electrode, a negative electrode, a separator, and an electrolyte.

[0098] This application does not impose any particular limitation on the specific type of electrochemical device, which can be a secondary battery, a power battery, an energy storage battery, etc. The battery casing can be used to encapsulate the battery cell and electrolyte. The battery casing can be a hard casing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. It can also be a soft-pack, such as a pouch-type soft-pack. The material of the soft-pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate. This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape.

[0099] In this embodiment, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. After winding and welding the tabs, a bare cell is obtained. The bare cell is then placed in an aluminum-plastic film, electrolyte is injected, and after encapsulation, a lithium-ion battery is obtained. The electrolyte in this embodiment includes an organic solvent, lithium salt, and additives.

[0100] In one specific embodiment, the diaphragm includes a porous sheet-like or non-woven material with excellent liquid retention properties. The diaphragm includes resin or glass fiber diaphragm materials, which include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc.

[0101] In this embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material coated on at least one side of the negative electrode current collector.

[0102] This application does not limit the selection of the negative electrode current collector; it can be selected according to actual needs, such as copper foil. The negative electrode active material layer of this application includes a negative electrode active material and a negative electrode binder. The negative electrode active material includes a silicon-carbon composite material, which can include carbon materials and silicon materials. This application does not limit the selection of carbon materials; it can be selected according to actual needs, such as graphite, carbon black, hard carbon, soft carbon, etc. This application does not limit the selection of silicon materials; it can be selected according to actual needs, such as silicon oxide, pre-lithiated silicon oxide, pre-magnesiated silicon oxide materials, silicon-carbon composite materials, elemental silicon, etc. The negative electrode binder of this application includes polypropylene compounds and styrene-butadiene rubber. Polypropylene compounds refer to polypropylene derivatives, such as polyacrylic acid, polyacrylonitrile, polyacrylamide, polymethyl methacrylate, etc.

[0103] In some embodiments, the electrolyte further includes a solvent, which includes ethylene carbonate, propylene carbonate, butenyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, diphenyl carbonate, methyl acetate, methyl propionate, methyl butyrate, ethyl acetate, propyl acetate, ethyl butyrate, propyl propionate, γ-butyrolactone, 1,3 At least one of dioxolane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0104] Specifically, the solvents mentioned above are mainly used to dissolve the first additive, the second additive, and the lithium salt.

[0105] In some embodiments, the electrolyte further includes a lithium salt.

[0106] Specifically, the lithium salt can be at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalate)borate, lithium difluorooxalateborate, lithium tetrafluoroborate, and lithium difluorodi(oxalate)borate.

[0107] It should be noted that this application does not impose any particular limitation on the preparation method of the electrolyte. Those skilled in the art can prepare the electrolyte using conventional technical means, such as mixing the raw materials evenly according to the specified ratio.

[0108] This application also provides an electronic device, including the aforementioned electrochemical device.

[0109] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0110] To further understand the present invention, the following embodiments are provided to illustrate the present application. These embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0111] I. Battery Preparation

[0112] 1. Preparation of positive electrode sheet

[0113] (1) The first particle, the second particle and the third particle are mixed to prepare a positive electrode active material; wherein, the physical parameters of the first particle, the second particle and the third particle in each embodiment and comparative example are shown in Table 1;

[0114] (2) The positive electrode active material, positive electrode conductive agent acetylene black SuperP and binder polyvinylidene fluoride PVDF are mixed evenly in a mass ratio of 97:1.5:1.5 and then evenly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The mixed slurry is coated on both sides of the aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0115] 2. Preparation of negative electrode sheet

[0116] The negative electrode active material graphite, the negative electrode conductive agent acetylene black SuperP, the thickener CMC and the negative electrode binder SBR are mixed evenly in a mass ratio of 94:2:1.2:2.8 and then evenly dispersed with deionized water to form a uniform negative electrode slurry. The mixed slurry is coated on both sides of the copper foil current collector, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet.

[0117] 3. Preparation of electrolyte

[0118] Ethylene carbonate EC, propylene carbonate PC, propyl propionate EP, and diethyl carbonate DEC were mixed and stirred in a mass ratio of 10:20:40:30 to form a mixed solvent. The water was removed by molecular sieve and the mixture was set aside. 1 M LiPF6 was added and mixed evenly to obtain the electrolyte.

[0119] 4. Manufacturing of lithium-ion batteries

[0120] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. After winding and welding the tabs, a bare cell is obtained. The bare cell is then placed in an aluminum-plastic film for electrolyte injection and encapsulation to obtain a lithium-ion battery. The preparation of lithium-ion batteries in each embodiment and comparative example is completed.

[0121] Table 1. Formulas and Relationships

[0122]

[0123] II. Performance Testing

[0124] The lithium-ion batteries prepared in the above embodiments and comparative examples were tested as follows, and the test results are shown in Table 2.

[0125] 1. Compacted density

[0126] The positive electrode active material, positive electrode conductive agent acetylene black (SuperP), and binder polyvinylidene fluoride (PVDF) were mixed uniformly at a mass ratio of 97:1.5:1.5, and then uniformly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a homogeneous positive electrode slurry. The slurry was coated onto both sides of an aluminum foil current collector and dried. The areal density of the foil was measured using an areal density meter. A sample of a fixed area of ​​the electrode was taken and its total areal density was measured using the areal density meter. The areal density of the coating material was obtained by subtracting the areal density of the foil from the total areal density. The thickness of the rolled electrode was measured using a micrometer, and the thickness of the coating material was obtained by subtracting the foil thickness. The compacted density of the coating material was calculated based on its areal density and thickness.

[0127] 2. Storage capacity recovery rate at 85℃

[0128] The battery capacity C1 was tested at room temperature using a fixed charge-discharge procedure. After fully charging, the battery was placed in an 85°C constant temperature chamber for 6 hours, then removed and allowed to stand at room temperature for 6 hours before being fully discharged. The battery capacity C2 was then tested again using the same fixed charge-discharge procedure. The ratio of C2 to C1 represents the capacity recovery rate. The fixed charge-discharge procedure was as follows: constant current charging at 0.7C to the upper voltage limit, then constant voltage charging until the current decreased to 0.05C, followed by a 5-minute rest period, and finally constant current discharging at 0.2C until the voltage reached 3.0V to obtain the discharge capacity.

[0129] 3. -20℃ / 25℃ discharge ratio

[0130] The battery capacity C1 was tested at room temperature (25℃) according to a fixed charge and discharge procedure. Then, it was fully charged and placed in a constant temperature chamber at -20℃ for 4 hours before being discharged to obtain the discharge capacity C3. C3 / C1 is the discharge ratio.

[0131] Table 2 Test Results

[0132]

[0133] As shown in Tables 1 and 2, providing three different particle sizes and mixing them in an appropriate ratio to prepare the positive electrode active material can significantly increase the compaction density compared to positive electrode active materials prepared from two different particle sizes, thereby increasing the battery's energy density. Simultaneously, the third particle has a larger specific surface area, resulting in more contact with the electrolyte, and its smaller particle size shortens the lithium-ion transport path, increasing the lithium-ion transport speed and thus improving the battery's rate performance and low-temperature performance. Furthermore, by coating the surface of at least one of the first, second, and third particles with predetermined particles and internally doping them, the surface coating or internal doping of the predetermined particles can mitigate losses caused by excessive lithium-ion insertion / extraction, increase the stability of the particle surface and internal structure, and thus improve the battery's high-temperature performance.

[0134] Although this application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for the elements, as long as they do not depart from the scope of this application. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of this application, as long as they do not depart from the essential scope of this application. Therefore, this application is not intended to be limited to the specific embodiments disclosed as the best mode of carrying out this application as conceived, but rather this application will include all embodiments falling within the scope of the appended claims.

[0135] All scopes disclosed in this application include endpoints, and endpoints can be combined with each other.

[0136] The various embodiments of this application have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or improvement of the technology in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A positive electrode active material, characterized by, The cathode active material comprises a first particle, a second particle, and a third particle with different particle sizes and specific surface areas. All three particles are made of lithium cobalt oxide. The first particle accounts for 75%–85% of the mass of the cathode active material, the second particle accounts for 14%–25%, and the third particle accounts for 1%–5%. At least one of the first, second, and third particles is coated with a first predetermined particle and internally doped with a second predetermined particle. The first particle has the largest particle size and the smallest specific surface area, with a particle size of D1 (15 μm–21 μm) and a specific surface area of ​​S. a S a It is 0.05m 2 / g~0.2m 2 / g; the second particle has a medium particle size and specific surface area, and the particle size of the second particle is D2, where D2 is 3μm~7μm, and the specific surface area is S b S b 0.2m 2 / g~1m 2 / g; the third particle has the smallest particle size and the largest specific surface area, and the particle size of the third particle is D3, where D3 is 0.5μm~3μm, and the specific surface area is S. c S c 1m 2 / g~3m 2 / g; The surfaces of the first particle, the second particle, and the third particle are all coated with the first preset particle, and the coating amount satisfies the following relationship: W c1 >W b1 >W a1 The first preset particles are coated on the surface of the first particles in an amount of W a1 ppm, the first preset particles are coated on the surface of the second particles in an amount of W b1 ppm, the first preset particles are coated on the surface of the third particles in an amount of W c1 ppm; and W c2 >W b2 >W a2 The doping amount of the second preset particle inside the first particle is W a2 ppm; the doping amount of the second preset particle inside the second particle is W b2 ppm; the doping amount of the second preset particle inside the third particle is W c2 ppm; the first preset particle and the second preset particle are both selected from at least one of aluminum Al, magnesium Mg, titanium Ti, lanthanum La, yttrium Y, zirconium Zr, and fluorine F.

2. The positive electrode active material according to claim 1, characterized by The positive electrode active material satisfies the following relationship: 8 < W c + W b ≤ 25 The third particles account for W% of the mass of the positive electrode active material c The second particles account for W% of the mass of the positive electrode active material b .

3. The positive electrode active material according to claim 1 or 2, characterized by S a is 0.12 m 2 / g ~ 0.18 m 2 / g; and / or, S b is 0.4 m 2 / g ~ 0.8 m 2 / g; and / or, S c is 1.5 m 2 / g ~ 2.5 m 2 / g.

4. The positive electrode active material according to claim 1, characterized by 100 ppm < W a1 ≤ 1000 ppm; and / or, 400 ppm < W b1 ≤ 1500 ppm; and / or, 700 ppm < W c1 ≤ 2500 ppm.

5. The positive electrode active material according to claim 1, characterized by The coating amount and the specific surface area of the positive electrode active material satisfy the following relationship: W x1 =k×(0.25+S y )×1000+h wherein W x1 represents one of W a1 , W b1 and W c1 , X is one of a, b, c; S y represents one of S a , S b and S c , y is one of a, b, c, and x = y; k is 0.1 to 1.0; and h is 100 to 1000.

6. The positive electrode active material according to claim 1, characterized by The first particle, the second particle and the third particle are all doped with the second preset particle inside, and the doping amount and the specific surface area of the positive electrode active material satisfy the following relationship: W b2 = W a2 + (S b - S a ) x 1000; and / or, W c2 = W b2 + (S c - S b ) x 500.

7. The positive electrode active material according to claim 6, characterized by 3000≤W a2 ≤10000。 8. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side of the positive electrode current collector; the positive electrode active material layer comprises the positive electrode active material according to any one of claims 1 to 7.

9. An electrochemical device, characterized by, The positive electrode sheet according to claim 8.

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