Positive electrode active material and preparation method therefor, positive electrode sheet, battery and electric device

Abstract

A positive electrode active material and a preparation method therefor, a positive electrode sheet, a battery, and an electric device. The positive electrode active material comprises a substrate and a coating layer; the coating layer is formed on at least part of the surface of the substrate; the coating layer comprises a surface modifier and a hydrophobic protective agent; the surface modifier comprises at least one of haloalkylsilane or alkylsilane; and the hydrophobic protective agent comprises a hydrophobic group. Since the surface modifier and the hydrophobic protective agent are provided on at least part of the surface of the positive electrode active material, an electrolyte can be isolated from the positive electrode active material, irreversible loss caused by side reactions of the positive electrode active material is reduced, the absorption of H2O and CO2 in air can be reduced, and the high-pressure durability of the positive electrode active material is improved; and the joint action of the surface modifier and the hydrophobic protective agent makes a battery have excellent cycling stability.

Description

Positive electrode active material and preparation method thereof, positive electrode sheet, battery, and electrical device

[0001] Priority information

[0002] This application claims priority and benefits of patent application 202311644258.0 filed with the State Intellectual Property Office of China on November 30, 2023, and the entire text of which is incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to positive electrode active materials and preparation methods thereof, positive electrode sheets, batteries, and electrical devices. Background Art

[0004] Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as in military equipment, aerospace and other fields.

[0005] Positive electrode active materials are a very important component of secondary batteries. However, current positive electrode active materials have poor stability, resulting in poor cycle performance of batteries containing them.

[0006] It should be noted that the above statements are only used to provide background technical information related to this application and do not necessarily constitute prior art.

[0007] Summary of the Invention

[0008] In view of the technical problems existing in the background technology, the present application provides a positive electrode active material, aiming to solve the problem of poor cycle performance of batteries containing the positive electrode active material.

[0009] In order to achieve the above-mentioned objectives, the first aspect of the present application provides a positive electrode active material, including a substrate and a coating layer, wherein the coating layer is formed on at least a portion of the surface of the substrate, the coating layer includes a surface modifier and a hydrophobic protective agent, the surface modifier includes at least one of a halogenated alkylsilane or an alkylsilane, and the hydrophobic protective agent includes a hydrophobic group.

[0010] Thus, the surface modifier and the hydrophobic protective agent are provided on at least part of the surface of the substrate, which can isolate the matrix reaction between the electrolyte and the positive electrode active material, improve the ionic conductivity of the coating layer, reduce the absorption of H2O and CO2 in the air by the positive electrode active material, and improve the high-voltage durability of the positive electrode active material. The surface modifier and the hydrophobic protective agent work together to make the battery containing it have excellent cycle stability.

[0011] In some embodiments, the surface modifier includes a hydrolyzable group, optionally comprising at least one of an ester group, an amide group, a carboxylate salt, or a sodium phenolate. This can improve the stability of the positive electrode active material and the cycle performance of a battery containing the same.

[0012] In some embodiments, the surface modifier includes at least one of heptafluorodecyltriethoxysilane, octadecylsilane, (trimethylsilyl)methyl trifluoromethanesulfonate, trimethylpentafluorophenylsilane, fluorooctylmethylsiloxane-dimethylsiloxane copolymer, N-methyl-N-(trimethylsilyl)trifluoroacetamide, or bis(3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane.

[0013] In some embodiments, at least one of the following conditions is met: the hydrophobic group includes at least one of a phenyl group, a halogen atom, a nitro group, an ester group, an ether group, or an alkyl group with 32 or fewer carbon atoms; and the hydrophobic protective agent further includes a first group, wherein the first group includes at least one of a phosphate group, a carbonate group, or a sulfonate group. This can improve the stability of the positive electrode active material and enhance the cycling performance of batteries containing the hydrophobic protective agent.

[0014] In some embodiments, the hydrophobic protective agent includes at least one of dihexadecyl phosphate, tributyl phosphate, trimethyl phosphate, triisopropyl phosphate, dibutyl phosphate, dimethyl phosphate, or isopropyl phosphate. This can improve the stability of the positive electrode active material and the cycle performance of a battery containing the hydrophobic protective agent.

[0015] In some embodiments, the matrix comprises at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. Alternatively, the matrix comprises Li x Ni a Co b M c O 2-y , wherein M includes at least one of Mn or Al, 0.6≤x≤1.2, -0.1≤y≤0.1, 0.5≤a<1, 0.1≤b≤0.3, 0<c≤0.3, and a+b+c=1. Thus, the stability of the positive electrode active material can be improved, and the cycle performance of the battery containing the positive electrode active material can be improved.

[0016] In some embodiments, the volume average particle size D of the positive electrode active material is v 50 is 10 μm-20 μm, and can be optionally 10 μm-15 μm. Thus, the stability of the positive electrode active material can be improved, and the cycle performance of the battery containing the positive electrode active material can be improved.

[0017] In the second aspect of the present application, the present application proposes a method for preparing a positive electrode active material, comprising: forming a coating layer on at least a portion of the surface of a substrate, the coating layer comprising a surface modifier and a hydrophobic protective agent, the surface modifier comprising at least one of a halogenated alkylsilane or an alkylsilane, and the hydrophobic protective agent comprising a hydrophobic group.

[0018] Therefore, the positive electrode active material prepared by the above method of the present application can improve the stability of the positive electrode active material and improve the cycle performance of the battery containing the positive electrode active material.

[0019] In some embodiments, the method comprises: preparing a surface modifier on at least a portion of the surface of the substrate by a vapor deposition method to obtain an intermediate;

[0020] The intermediate is immersed in a solution containing a hydrophobic protective agent to obtain a positive electrode active material.

[0021] This can improve the stability of the positive electrode active material and enhance the cycle performance of the battery containing the positive electrode active material.

[0022] In some embodiments, the temperature of the vapor deposition is 130° C.-200° C., thereby improving the stability of the positive electrode active material and the cycle performance of the battery containing the positive electrode active material.

[0023] In some embodiments, at least one of the following conditions is met: the mass percentage of the hydrophobic protective agent is 90%-99% of the total mass of the solution containing the hydrophobic protective agent; and the soaking time is 2 hours-6 hours. This can improve the stability of the positive electrode active material and enhance the cycling performance of the battery containing the same.

[0024] In some embodiments, based on the total mass of the solution containing the hydrophobic protective agent, the mass proportion of the hydrophobic protective agent is 90%-99%, thereby improving the stability of the positive electrode active material and the cycle performance of the battery containing the same.

[0025] In some embodiments, the immersion time is 2 hours to 6 hours, thereby improving the stability of the positive electrode active material and the cycle performance of the battery containing the positive electrode active material.

[0026] In some embodiments, the mass ratio of the substrate, the surface modifier, and the hydrophobic protective agent is 1:(0.05-0.1):(0.02-0.05), thereby improving the stability of the positive electrode active material and the cycle performance of the battery containing the same.

[0027] In a third aspect of this application, a positive electrode sheet is provided, comprising the positive electrode active material described in the first aspect of this application, or a positive electrode active material prepared using the method described in the second aspect. Thus, this positive electrode sheet possesses all the features and advantages of the aforementioned positive electrode active material and method for preparing the positive electrode active material, and no further details are given here.

[0028] In a fourth aspect of the present application, the present application provides a battery comprising the positive electrode sheet described in the third aspect of the present application, thereby having excellent cycle performance.

[0029] In a fifth aspect of the present application, the present application provides an electrical device comprising the battery described in the fourth aspect. Thus, the electrical device includes all the features and advantages of the aforementioned battery, which will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0031] FIG1 is a schematic diagram of a battery cell according to an embodiment of the present application;

[0032] FIG2 is an exploded view of a battery cell according to an embodiment of the present application shown in FIG1 ;

[0033] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0034] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0035] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0036] FIG6 is a schematic diagram of an electrical device using a battery as a power source according to an embodiment of the present application;

[0037] FIG7 is a scanning electron microscope image of the positive electrode active material of Example 1 of the present application as prepared, after being placed in the air for 7 days, and after being placed in the air for 14 days;

[0038] FIG8 is a scanning electron microscope image of the positive electrode active material of Comparative Example 1 of the present application when it is prepared, after being placed in the air for 7 days, and after being placed in the air for 14 days.

[0039] Description of reference numerals:

[0040] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 battery cell;

[0041] 51 shell; 52 electrode assembly; 53 top cover assembly. DETAILED DESCRIPTION

[0042] Below, the lithium supplement material and its preparation method, positive electrode sheet, battery, and electric device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0043] " scope " disclosed in the application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a scope with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 listed, and if the maximum range value 3,4 and 5 are listed, then the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0044] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0045] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0046] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), indicating that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0047] In the description of this application, “plurality” means two or more.

[0048] In the description of this application, "A and / or B" may include the case of A alone, the case of B alone, or any of the cases of A and B, where A and B are only used for example, and may be any technical feature connected by "and / or" in this application.

[0049] Secondary batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but are also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as in military equipment, aerospace and other fields.

[0050] As an important component of secondary batteries, positive electrode active materials play the role of providing active metal ions (such as lithium ions, sodium ions, etc.). However, on the one hand, when the battery is charging and discharging, especially at high voltage, the interface film between the positive electrode active material and the electrolyte is easily destroyed, and the positive electrode active material will continuously react with the electrolyte, causing irreversible loss of the positive electrode active material, affecting the cycle performance of the battery; on the other hand, the existing positive electrode active materials have the problem of unstable chemical environment. In the air, the surface of the positive electrode active material particles can easily absorb H2O and CO2, and H2O and CO2 react with the positive electrode active material. This process will consume active metal ions and produce inactive rock salt phase. The irreversible inactive rock salt phase blocks the diffusion channel of the active metal ions, increases the energy barrier of the active metal ion reaction, and thus deteriorates the cycle performance of the battery containing it.

[0051] In an embodiment of the present application, a coating layer is provided on at least part of the surface of the substrate, and the coating layer includes a surface modifier and a hydrophobic protective agent. The surface modifier and the hydrophobic protective agent act together. On the one hand, the provision of the coating layer can isolate the contact between the electrolyte and the substrate of the positive electrode active material, thereby reducing the side reactions between the two and reducing the irreversible consumption of the positive electrode active material. The surface modifier containing halogenated alkylsilane and / or alkylsilane is provided on the surface of the substrate. The halogenated alkylsilane and / or alkylsilane has excellent ion conductivity and can also reduce the formation of an excessively thick interface film, so that the coating layer has less effect on the transmission of active metal ions, and thus the battery impedance containing the positive electrode active material of the present application is lower. On the other hand, the hydrophobic protective agent in the coating layer can play a good hydrophobic role, which can reduce the absorption of H2O and CO2 in the air by the substrate, reduce the probability of the substrate reacting with H2O and CO2, and enhance the stability of the positive electrode active material. In summary, the positive electrode active material proposed in the present application has good stability and improves the cycle performance of the battery containing it.

[0052] The positive electrode active material disclosed in the embodiments of the present application is suitable for secondary batteries, and the battery disclosed in the embodiments of the present application can be used in electrical devices that use batteries as power sources or various energy storage systems that use batteries as energy storage elements. Electrical devices may include but are not limited to mobile phones, tablets, laptops, electric toys, power tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys may include fixed or mobile electric toys, for example, game consoles, electric car toys, electric ship toys and electric airplane toys, etc., and spacecraft may include airplanes, rockets, space shuttles and spacecraft, etc.

[0053] In a first aspect of the present application, a positive electrode active material is provided. The positive electrode active material includes a substrate and a coating layer, wherein the coating layer is formed on at least a portion of the surface of the substrate, and the coating layer includes a surface modifier and a hydrophobic protective agent. The surface modifier includes at least one of a haloalkylsilane or an alkylsilane, and the hydrophobic protective agent includes a hydrophobic group.

[0054] The present application includes at least the following beneficial effects: the positive electrode active material proposed in the present application, the setting of the coating layer can isolate the contact between the electrolyte and the matrix of the positive electrode active material, thereby reducing the side reactions of the two, reducing the side reactions of the positive electrode active material, the surface modifier is arranged on the surface of the matrix, has excellent ion conductivity, and can also reduce the formation of an excessively thick interface film, and has little effect on the transmission of active metal ions, thereby lowering the impedance of the battery containing it; on the other hand, the hydrophobic protective agent can play a good hydrophobic role, which can reduce the absorption of H2O and CO2 in the air by the matrix, reduce the probability of the matrix reacting with H2O and CO2, and enhance the stability of the positive electrode active material. In summary, the positive electrode active material proposed in the present application has good stability and improves the cycle performance of the battery containing it.

[0055] As you can understand, an alkylsilane is an organosilicon compound containing both an alkyl group and a silane group in its molecular structure. A haloalkylsilane is an alkylsilane containing a halogen atom, such as a fluorine, chlorine, bromine, or iodine atom. A hydrophobic group is a lipophilic group. These groups have no affinity for water and are insoluble or minimally soluble in water. They can reduce the absorption of H2O and CO2 from the air by the substrate.

[0056] In some embodiments, the surface modifier includes a hydrolyzable group, whereby a hydrolyzable group refers to a group that can react with water and hydrolyze. Such a hydrolyzable group facilitates the consumption of water, preventing moisture from corroding the positive electrode active material, improving the stability of the positive electrode active material, and thereby enhancing the cycling performance of batteries containing such a group. In other embodiments, the hydrolyzable group includes at least one of an ester group, an amide group, a carboxylate salt, or a sodium phenolate.

[0057] In some embodiments, the surface modifier includes at least one of heptafluorodecyltriethoxysilane, octadecylsilane, (trimethylsilyl)methyl trifluoromethanesulfonate, trimethylpentafluorophenylsilane, fluorooctylmethylsiloxane-dimethylsiloxane copolymer, N-methyl-N-(trimethylsilyl)trifluoroacetamide, or bis(3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane. Specifically, the above-mentioned substances have the characteristics of high electronegativity, good dielectric properties and good solubility, which are conducive to the transmission of active metal ions at the electrode / solid electrolyte interface (SEI film). When used in the positive electrode of the battery, it also reduces its activation energy; in addition, the above-mentioned surface modifiers can isolate the contact between the electrolyte and the matrix of the positive electrode active material, thereby reducing the side reactions between the two and reducing the irreversible consumption of the positive electrode active material. The surface modifier is arranged on the surface of the matrix, has excellent ion conductivity, and can also reduce the formation of excessively thick interface films, which has little effect on the transmission of active metal ions, and thus the battery containing it has a lower impedance, thereby improving the cycle performance of the battery.

[0058] It can be understood that (trimethylsilyl) methyl trifluoromethanesulfonate, also known as trimethylsilyl trifluoromethanesulfonate, is an important organic compound; fluorooctylmethylsiloxane-dimethylsiloxane copolymer is an organic silicon compound, which is copolymerized by fluorooctylmethylsiloxane and dimethylsiloxane and has excellent high temperature resistance, oxidation resistance, chemical corrosion resistance and other properties; the molecular formula of N-methyl-N-(trimethylsilyl) trifluoroacetamide is H2C(OMe)N(SiMe3)CF3, where Me represents methyl; bis(3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane is a chemical substance with the molecular formula C 10 H 12 F6NSi2N.

[0059] In some embodiments, the hydrophobic group includes at least one of a phenyl group, a halogen atom, a nitro group, an ester group, an ether group, or an alkyl group having a carbon number less than or equal to 32. The hydrophobic protective agent containing the above-mentioned hydrophobic group is on the surface of the substrate, which can reduce the absorption of water by the substrate, thereby improving the stability of the substrate and improving the cycle performance of the battery containing it.

[0060] In some embodiments, the hydrophobic protective agent further comprises a first group, which comprises at least one of a phosphate group, a carbonate group, or a sulfonate group. Specifically, on the surface of the substrate, the hydrophobic group tends to be away from the substrate. On the outer surface of the coating layer, the absorption of H2O and CO2 by the substrate particle surface can be reduced. Taking the positive electrode active material of a lithium-ion battery as an example, the first group tends to be close to the substrate, combining with the Li element of the substrate to form an O=DOLi- group (D can be a P element, a C element, or an S element). Inside the coating layer, the O=DOLi- group can improve the transmission coefficient of the active metal ions during the charge and discharge process. In addition, the hydrophobic protective agent containing the hydrophobic group and the first group works together with the surface modifier to give the battery excellent rate performance and cycle stability.

[0061] For example, the phosphate group can react with the matrix of the positive active material of the lithium ion battery to form O=POLi - The group improves the binding force between the hydrophobic protective agent and the substrate, reduces the risk of its detachment from the substrate surface, and can improve the ionic conductivity of the coating layer and enhance the cycle performance of the battery containing it.

[0062] In some embodiments, the hydrophobic protective agent includes at least one of dihexadecyl phosphate, tributyl phosphate, trimethyl phosphate, triisopropyl phosphate, dibutyl phosphate, dimethyl phosphate, or isopropyl phosphate. Specifically, the hydrophobic protective agent contains both a hydrophobic group and a first group, which can reduce the absorption of H2O and CO2 by the substrate particle surface while improving the transport coefficient of active metal ions during charge and discharge. Furthermore, the hydrophobic protective agent containing both a hydrophobic group and a first group, in conjunction with the surface modifier, imparts excellent rate performance and cycling stability to the battery.

[0063] In some embodiments, the volume average particle size D of the positive electrode active material is v 50 is 10 μm-20 μm, for example, the volume average particle size D of the positive electrode active material v 50 can be 10 μm-19 μm, 11 μm-18 μm, 12 μm-17 μm, 13 μm-16 μm, 14 μm-15 μm, etc. Specifically, the volume average particle size D of the positive electrode active material is v 50 is limited to the above range, which is conducive to the rapid deintercalation of active metal ions, reduces the probability of the matrix reacting with H2O and CO2, and can also reduce the probability of side reactions between the positive electrode active material and the electrolyte, thereby improving the stability of the positive electrode active material and the cycle performance of the battery containing it. In other embodiments, the volume average particle size D v 50 is 10μm-15μm.

[0064] The volume average particle size Dv 50 refers to the particle size corresponding to when the cumulative volume distribution percentage of the particles reaches 50%.

[0065] The volume average particle size D v 50" is a well-known meaning in the art and can be measured using instruments and methods known in the art. As an example, the volume average particle size D of the positive electrode active material v 50 can be measured by laser diffraction particle size analysis. Specifically, the volume average particle size D of the positive electrode active material is v 50 can be measured with reference to the standard GB / T 19077-2016 using a laser particle size analyzer (such as Malvern Master Size 3000).

[0066] In some embodiments, the substrate comprises at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. Specifically, lithium nickel cobalt manganese oxide has a high capacity, which can increase the energy density of the battery. Furthermore, lithium nickel cobalt manganese oxide readily absorbs H2O and CO2, resulting in the reduction of nickel. Combining these materials with a coating layer to form a positive electrode active material not only increases the battery's energy density, but also stabilizes the Mn-Mn bonds and O-O bonds on the substrate surface, enhancing the stability of the positive electrode active material and improving the cycling performance of batteries containing them.

[0067] In some embodiments, the matrix includes Li x Ni a Co b M c O 2-y , wherein M includes at least one of Mn or Al, 0.6≤x≤1.2, -0.1≤y≤0.1, 0.5≤a<1, 0.1≤b≤0.3, 0<c≤0.3, and a+b+c=1. For example, 0.6≤x≤1.1, 0.7≤x≤1, 0.8≤x≤0.9, etc.; -0.1≤y≤0.09, -0.1≤y≤0, 0≤y≤0.1, etc.; 0.5≤a≤0.9, 0.6≤a≤0.8, 0.7≤a≤0.8, etc.; 0.1≤b≤0.2, 0.2≤b≤0.3, etc.; 0.05≤c≤0.3, 0.1≤c≤0.3, 0.2≤c≤0.3, etc. The above matrix has a high nickel content and a high reversible capacity, thereby improving the energy density of the battery containing it.

[0068] The battery will be accompanied by the deintercalation and consumption of Li during the charge and discharge process. The molar content of Li is different when the battery is discharged to different states. Therefore, the above Li x Ni a Co b M c O 2-yIn the case of adding a lithium supplement to the matrix, x may be less than 1. In addition, when a lithium supplement is added to the matrix, x may be greater than 1.

[0069] In the enumeration of the matrix in this application, lattice oxygen release will cause the molar content of oxygen to change, so y will be greater than 0. In addition, metal dissolution in the matrix will also cause y to be less than 0.

[0070] In other embodiments, the matrix comprises LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.5 Co 0.25 Mn 0.25 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2 or LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0071] In some embodiments, when the battery is a lithium-ion battery, the substrate may be a substrate for lithium-ion batteries known in the art.

[0072] As an example, the matrix may also include at least one of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, other lithium nickel cobalt manganese oxides (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 ) and at least one of its modified compounds. Examples of olivine-structured lithium-containing phosphates may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. The modified compounds of the above materials may be modified by doping and / or surface coating the materials.

[0073] The battery's charge and discharge processes involve the intercalation and deintercalation of Li, leading to different Li molar contents at different discharge states. The molar content of Li in the matrix listed in this application refers to the initial state of the material, i.e., the state before the materials are added. When the positive electrode active material is applied to a battery system, the molar content of Li will change after charge and discharge cycles.

[0074] In the enumeration of the matrix in this application, the molar content of O is only a theoretical value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0075] In some embodiments, when the battery is a sodium ion battery, the matrix may also be a matrix for sodium ion batteries known in the art.

[0076] As an example, the matrix may include, but is not limited to, at least one of a layered transition metal oxide, a polyanion compound, and a Prussian blue analog.

[0077] Examples of the layered transition metal oxides include:

[0078] Na 1-x Cu h Fe k Mn l M 1 m O 2-y , where M 1 One or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0079] Na 0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0080] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0081] Examples of the above polyanion compounds include, for example:

[0082] A 1 f M 3 g (PO4) i O j X 1 3-j , where A 1 is one or more of H, Li, Na, K, and NH4, M 3 is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X 1 is one or more of F, Cl, and Br, 0 < f ≤ 4, 0 < g ≤ 2, 1 ≤ i ≤ 3, 0 ≤ j ≤ 2;

[0083] Na n M 4 PO4X 2 , where M 4 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, X 2 is one or more of F, Cl, and Br, 0 < n ≤ 2;

[0084] Na p M 5 q (SO4)3, where M 5 is one or more of Mn, Fe, Co, Ni, Cu, and Zn, 0 < p ≤ 2, 0 < q ≤ 2;

[0085] Na s Mn t Fe 3-t (PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3, for example, t is 0, 1, 1.5, 2, or 3.

[0086] Examples of the above Prussian blue analogs include, for example:

[0087] A u M 6 v [M 7 (CN)6] w ·xH2O, where A is H + , NH4 + , an alkali metal cation, and an alkaline earth metal cation or one or more of them, M 6 and M 7Each independently is one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + , Li + , Na + , K + , NH4 + , Rb + , Cs + , Fr + , Be 2+ , Mg 2+ , Ca 2+ , Sr 2+ , Ba 2+ and Ra 2+ One or more of those, M 6 and M 7 Each independently is a cation of one or more transition metal elements among Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn and W. [[ID=,33]]

[0088] The modified compounds of the above-mentioned materials can be doping modification and / or surface coating modification of the materials.

[0089] In the second aspect of the present application, a method for preparing a positive electrode active material is proposed. Thus, the aforementioned positive electrode active material can be prepared by a relatively simple method. Specifically, the method for preparing a positive electrode active material includes:

[0090] S100: Form a coating layer on at least part of the surface of the substrate. The coating layer includes a surface modifier and a hydrophobic protective agent. The surface modifier includes at least one of haloalkylsilane or alkylsilane, and the hydrophobic protective agent includes a hydrophobic group.

[0091] Specifically, for the positive electrode active material prepared by the method proposed in the embodiment of the present application, a coating layer is provided on at least part of the surface of the substrate. The coating layer includes a surface modifier and a hydrophobic protective agent. The coating layer formed by the surface modifier and the hydrophobic protective agent, on the one hand, can isolate the contact between the electrolyte and the substrate of the positive electrode active material, thereby reducing the side reaction between the two and reducing the side reaction of the positive electrode active material. The surface modifier is provided on the surface of the substrate and has excellent ion conduction performance. It can also reduce the formation of an overly thick interfacial film and has little influence on the transport of active metal ions. Therefore, the battery containing it has a lower impedance; on the other hand, the hydrophobic protective agent can play a good hydrophobic role, can reduce the absorption of H2O and CO2 in the air by the substrate, reduce the probability of reaction between the substrate and H2O and CO2, and enhance the stability of the positive electrode active material. In summary, the positive electrode active material proposed in the present application has good stability and improves the cycle performance of the battery containing it.

[0092] In some embodiments, a method of preparing a positive active material includes:

[0093] S101: preparing a surface modifier on at least a portion of the surface of the substrate by a vapor deposition method to obtain an intermediate;

[0094] S102: Soaking the intermediate in a solution containing a hydrophobic protective agent to obtain a positive electrode active material.

[0095] Thus, the prepared positive electrode active material can isolate the contact between the electrolyte and the positive electrode active material, reduce the irreversible loss caused by the side reaction of the positive electrode active material, reduce the absorption of H2O and CO2 in the air by the matrix, play a role of hydrophobic protection, and improve the ionic conductivity of the positive electrode active material. The two substances work together to further improve the stability of the positive electrode active material and enhance the cycle performance of the battery containing it.

[0096] Specifically, the vapor deposition method is conducive to the formation of a coating layer in which the surface modifier molecules form a single-layer molecular arrangement to form a self-assembled monolayer. The deposited surface modifier has good uniformity, can isolate the contact between the electrolyte and the positive electrode active material, reduce the irreversible loss caused by the side reactions of the positive electrode active material, and can also reduce the matrix's absorption of H2O and CO2 in the air, reducing the probability of the matrix reacting with H2O and CO2, and can also reduce the probability of side reactions between the positive electrode active material and the electrolyte, thereby improving the stability of the positive electrode active material and improving the cycle performance of the battery containing it.

[0097] Specifically, the surface modifier is evaporated into gas at a certain temperature and introduced into a reaction chamber, in which a substrate is placed, so that the surface modifier is deposited on the outer surface of the substrate.

[0098] In some embodiments, the temperature of the vapor deposition is 130°C-200°C. For example, the temperature of the vapor deposition can be 130°C-199°C, 135°C-195°C, 140°C-190°C, 145°C-185°C, 150°C-180°C, 155°C-175°C, 160°C-170°C, etc. Within the above deposition temperature range, the surface modifier molecules form a single-layer molecular arrangement to form a self-assembled monolayer. The deposited surface modifier has good uniformity, can isolate the contact between the electrolyte and the positive active material, reduce the irreversible loss caused by the side reaction of the positive active material, and can also reduce the absorption of H2O and CO2 in the air by the matrix, reduce the probability of the matrix reacting with H2O and CO2, and can also reduce the probability of side reactions between the positive active material and the electrolyte, thereby improving the stability of the positive active material and improving the cycle performance of the battery containing it.

[0099] In some embodiments, the intermediate is immersed in a solution containing a hydrophobic protective agent to obtain a positive electrode active material. This allows the hydrophobic protective agent to be evenly distributed on the surface of the substrate, increasing the deintercalation rate of the active metal ions in the substrate, isolating the electrolyte from the positive electrode active material, reducing irreversible losses caused by side reactions of the positive electrode active material, and reducing the substrate's absorption of H2O and CO2 in the air, thereby reducing the probability of the substrate reacting with H2O and CO2. It also reduces the probability of side reactions between the positive electrode active material and the electrolyte, thereby improving the stability of the positive electrode active material and the cycle performance of the battery containing it.

[0100] In some embodiments, based on the total mass of the solution containing the hydrophobic protective agent, the mass proportion of the hydrophobic protective agent is 90%-99%. For example, based on the total mass of the solution containing the hydrophobic protective agent, the mass proportion of the hydrophobic protective agent can be 90%-98.9%, 91%-98%, 92%-97%, 93%-96%, 94%-95%, etc. The mass proportion of the hydrophobic protective agent is controlled within the above range, which is conducive to the formation of a monolayer molecular arrangement of the hydrophobic protective agent molecules and the formation of a self-assembled monolayer, thereby increasing the deintercalation rate of the active metal ions of the matrix, and is sufficient to isolate the contact between the electrolyte and the positive active material, reduce the irreversible loss caused by the side reaction of the positive active material, reduce the absorption of H2O and CO2 in the air by the matrix, reduce the probability of the matrix reacting with H2O and CO2, and can also reduce the probability of side reactions between the positive active material and the electrolyte, thereby improving the stability of the positive active material and improving the cycle performance of the battery containing it.

[0101] In some embodiments, the immersion time is 2h-6h, for example, the immersion time can be 2h-5.9h, 3h-5h, 3h-4h, 4h-5h, etc. The immersion time is controlled within the above range, which can make the thickness of the coating layer thinner, which is conducive to the formation of a single-layer molecular arrangement of the hydrophobic protective agent molecules and the formation of a self-assembled monolayer, thereby improving the deintercalation rate of the active metal ions of the matrix, and is sufficient to isolate the contact between the electrolyte and the positive electrode active material, reduce the irreversible loss caused by the side reaction of the positive electrode active material, reduce the absorption of H2O and CO2 in the air by the matrix, reduce the probability of the matrix reacting with H2O and CO2, and can also reduce the probability of side reactions between the positive electrode active material and the electrolyte, thereby improving the stability of the positive electrode active material and improving the cycle performance of the battery containing it.

[0102] In some embodiments, the mass ratio of the substrate, the surface modifier and the hydrophobic protective agent is 1: (0.05-0.1): (0.02-0.05). For example, the mass ratio of the three can be 1: (0.05-0.09): (0.02-0.05), 1: (0.06-0.08): (0.02-0.05), 1: (0.05-0.1): (0.02-0.04), 1: (0.05-0.1): (0.03-0.04), etc., thereby, a thinner self-assembled monolayer can be formed on the surface of the substrate, which can improve the stability of the positive electrode active material and improve the cycle performance of the battery containing it.

[0103] In the third aspect of the present application, the present application proposes a positive electrode plate, comprising the positive electrode active material described in the first aspect of the present application, or the positive electrode active material prepared by the method described in the second aspect.

[0104] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, which includes the positive electrode active material described in the first aspect of this application, or a positive electrode active material prepared using the method described in the second aspect. Thus, the positive electrode sheet has all the features and advantages of the aforementioned positive electrode active materials and methods for preparing the positive electrode active materials, and no further details are given here.

[0105] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0106] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] In some embodiments, the positive active material layer may further optionally include a binder.

[0108] As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0109] In some embodiments, the positive active material layer may further optionally include a conductive agent.

[0110] As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0111] In some embodiments, the positive electrode sheet can be prepared by the following method: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.

[0112] In a fourth aspect of the present application, the present application provides a battery comprising the positive electrode sheet described in the third aspect. Thus, the battery includes all the features and advantages of the aforementioned positive electrode sheet, which will not be elaborated here.

[0113] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During the battery's charge and discharge processes, active ions are inserted and removed between the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing the active metal ions to pass through.

[0114] [Negative electrode]

[0115] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0116] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either or both of the two facing surfaces of the negative electrode current collector.

[0117] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. Silicon-based materials include at least one of elemental silicon, silicon oxides, silicon nitrogen complexes, silicon nitrogen complexes, and silicon alloys. Tin-based materials include at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0119] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0120] In some embodiments, the negative electrode active material layer may further include a conductive agent, which includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the negative electrode active material layer may further optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0122] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0123] [Electrolytes]

[0124] The electrolyte conducts ions between the positive and negative electrodes. This application does not specify the type of electrolyte, and the electrolyte can be selected based on the needs. For example, the electrolyte can be liquid, gel, or solid.

[0125] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0126] As an example, when the battery is a lithium-ion battery, the electrolyte lithium salt may include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0127] As an example, when the battery is a sodium ion battery, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalatoborate, sodium tetrafluoroborate, sodium bisoxalatoborate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, and sodium bis(trifluoromethylsulfonyl)imide.

[0128] As an example, the solvent may include at least one of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0129] In some embodiments of the present application, the electrolyte further includes additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0130] [Isolation film]

[0131] In some embodiments, the battery further includes a separator. The present application has no particular limitation on the type of separator, and any porous separator with good chemical and mechanical stability can be selected.

[0132] In some embodiments, the material of the separator includes at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0133] The battery of the present application includes a battery cell form, a battery module form and a battery pack form. The battery, battery module and battery pack of the present application are described below with reference to the accompanying drawings as appropriate.

[0134] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0135] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0136] In some embodiments, the battery outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the battery outer packaging may be a soft shell, such as a pouch-type soft shell. The soft shell may be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0137] The present application has no particular limitation on the shape of the battery, which can be cylindrical, square, or any other shape. For example, FIG1 shows a battery cell 5 of a square structure as an example.

[0138] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a top cover assembly 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the top cover assembly 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0139] In some embodiments, batteries may be assembled into a battery module. The number of batteries contained in the battery module may be one or more. The specific number may be selected by those skilled in the art based on the application and capacity of the battery module.

[0140] Figure 3 shows an example battery module 4. Referring to Figure 3 , within the battery module 4, multiple battery cells 5 may be arranged sequentially along the length of the battery module 4. Of course, they may also be arranged in any other manner. Furthermore, the multiple battery cells 5 may be secured together using fasteners.

[0141] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0142] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0143] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0144] In the fifth aspect of the present application, the present application provides an electrical device, comprising the battery described in the fourth aspect of the present application. Therefore, the electrical device includes all the features and advantages of the aforementioned battery, which will not be repeated here.

[0145] Batteries, battery modules, and battery packs can be used as power sources or energy storage units for electrical devices. Electrical devices may include, but are not limited to, mobile devices (e.g., mobile phones, laptops), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks), electric trains, ships, satellites, and energy storage systems.

[0146] As an electrical device, a battery, battery module or battery pack can be selected according to its usage requirements.

[0147] Figure 6 shows an example of an electric device. This device can be a pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the battery, a battery pack or battery module can be used.

[0148] Another example device may be a mobile phone, a tablet computer, a laptop computer, etc. Such a device is usually required to be light and thin, and may use a battery as a power source.

[0149] The present invention will be described below by way of specific examples. It should be noted that the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention. Specific techniques or conditions not specified in the embodiments are described in accordance with the techniques or conditions described in the literature in this area or in accordance with product specifications. Reagents or instruments not specified in the manufacturer's description are all commercially available conventional products.

[0150] Example 1

[0151] Preparation of positive electrode active materials:

[0152] The pristine LiNi was synthesized by high-temperature solid-state reaction. 0.8 Co 0.1 Mn 0.1 O2(NCM). Ni 0.8 Co 0.1 Mn 0.1 The (OH)2 precursor was mixed with LiOH·H2O in a molar ratio of 1:1.05 for thorough cleaning. Then, sufficient oxygen was introduced and the mixture was heated to 600℃ / 5h and then to 850℃ / 10h. The heating rate and O2 flow rate were 5℃min -1 and 0.5Lmin -1 , the obtained sample was labeled as original NCM (matrix).

[0153] Preparation of intermediates containing surface modifiers: Surface modifiers: heptafluorodecyltriethoxysilane (F3C(CF2)7(CH2)3Si(OCH3)3) and octadecylsilane (ODS:H3C(CH2) 17 Si(OCH3)3) was vapor deposited at a mass ratio of 1:1 at a temperature of 150°C and atmospheric pressure to form an intermediate on the surface of the NCM. The mass ratio of the NCM to the surface modifier was 1:0.08.

[0154] Preparation of positive electrode active material: A simple wet-dip method was used to coat a uniform layer of dihexadecyl phosphate [CH3(CH2) 15 O]2POOH(DHP)], to the surface of the intermediate, first, dissolve dihexadecyl phosphate in tetrahydrofuran (THF, C4H8O) solvent in a glove box and stir thoroughly for 1 hour to obtain a THF solution of DHP (based on the total mass of the THF solution of DHP, the mass of DHP accounts for 95%). Secondly, the intermediate is immersed in the dihexadecyl phosphate / THF solution and stirred for 4 hours. The mass ratio of NCM to dihexadecyl phosphate is 1:0.04. The obtained mixture is then filtered, and the excess dihexadecyl phosphate molecules are removed several times with an appropriate amount of tetrahydrofuran solution. Finally, the washed powder is vacuum dried at 80°C for 12 hours to remove excess THF.

[0155] Positive electrode preparation:

[0156] The prepared positive electrode active material, conductive agent acetylene black, and binder were mixed in a mass ratio of 98:1:1, and N-methylpyrrolidone solvent was added and stirred until the system became uniform to obtain a positive electrode slurry. The positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. The positive electrode sheet was then cut into 40 mm × 50 mm rectangles. The positive electrode surface capacity was 3.5 mAh / cm 2 .

[0157] Negative electrode preparation:

[0158] The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener carbon methyl cellulose sodium (CMC) are mixed in a deionized water solvent system in a weight ratio of 96.5:0.7:1.8:1. After being fully stirred until uniformly mixed, a negative electrode slurry is obtained. The negative electrode slurry is coated on the negative electrode current collector copper foil, dried, and cold pressed to obtain a negative electrode sheet.

[0159] Preparation of electrolyte:

[0160] At 25°C, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then LiPF6 is dissolved in the above mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 is 1 mol / L.

[0161] Preparation of the battery:

[0162] Using polypropylene film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation. The cells are then wound to form a bare cell. The bare cell is then placed in an outer packaging, injected with electrolyte, and packaged to form a battery.

[0163] The differences between Examples 2-18 and Example 1 are shown in Table 1.

[0164] In Comparative Example 1, the preparation method is the same as that of Example 1 except that the surface modifier is not prepared on the substrate surface.

[0165] In Comparative Example 2, the preparation method is the same as that of Example 1, except that the hydrophobic protective agent is not prepared on the intermediate containing the surface modifier.

[0166] Comparative Example 3 was prepared in the same manner as Example 1 except that the surface modifier and the hydrophobic protective agent were not added. See Table 1.

[0167] Table 1

[0168] The following tests were performed on the positive electrode active materials and batteries in Examples 1-18 and Comparative Examples 1-3:

[0169] 1. Scanning electron microscope image of positive electrode active material

[0170] Scanning electron microscope images were taken of the positive electrode active materials obtained in Example 1 and Comparative Example 3, and then they were exposed to air for 7 days and 14 days, and scanning electron microscope images were taken again, respectively, to obtain Figures 7 and 8, respectively.

[0171] In Figure 7, Figure a2 is a scanning electron microscope image of the positive electrode active material of Example 1 when it was prepared, and the right side of Figure a2 is an enlarged view within the box; Figure b2 is a scanning electron microscope image of the positive electrode active material of Example 1 after being placed in the air for 7 days, and the right side of Figure b2 is an enlarged view within the box; Figure c2 is a scanning electron microscope image of the positive electrode active material of Example 1 after being placed in the air for 14 days, and the right side of Figure c2 is an enlarged view within the box; it can be seen from Figure 7 that the positive electrode active material of Example 1 of the present application, when prepared, has little morphology change after being placed in the air for 7 days and 14 days, and the small particles on the surface do not show obvious breakage.

[0172] In Figure 8, Figure a1 is a scanning electron micrograph of the positive electrode active material of Comparative Example 1 as prepared, with the right side of Figure a1 being an enlarged view within the box; Figure b1 is a scanning electron micrograph of the positive electrode active material of Comparative Example 1 after being placed in air for 7 days, with the right side of Figure b1 being an enlarged view within the box; and Figure c1 is a scanning electron micrograph of the positive electrode active material of Comparative Example 1 after being placed in air for 14 days, with the right side of Figure c1 being an enlarged view within the box. As can be seen from Figure 8, compared to the positive electrode active material of Example 1 in Figure 7, the positive electrode active material of Comparative Example 1 of the present application has smooth surface particles and good morphology when prepared. After being placed in air for 7 days, the surface particles are significantly broken, and the surface particle fragmentation phenomenon is more obvious after 14 days. This can be attributed to the reaction of H2O and CO2 in the air with the surface particles of the positive electrode active material, causing microcracks and surface corrosion. It can be seen that the positive electrode active material prepared in Example 1 of the present application has good stability.

[0173] 2. Battery cycle performance test:

[0174] The battery was charged at a rate of 0.5C to a voltage of 4.4V at room temperature (25°C), and then discharged at a rate of 0.5C to a voltage of 2.5V. The reversible capacity was measured as E0. The above charge and discharge process was cycled 1000 times to obtain the reversible capacity, which was recorded as E0. n , where n = 1000. The capacity retention rate of the battery after 1000 cycles at 25 ° C is ε = (E n -E0) / E0×100%.

[0175] 3. Determination of battery impedance:

[0176] Prepare button cells:

[0177] a. Preparation of negative electrode sheet:

[0178] 96.5 wt.% of artificial graphite, 2.5 wt.% of styrene-butadiene latex (SBR) binder, and 1 wt.% of SP conductive carbon black were uniformly dispersed in deionized water to prepare a negative electrode slurry. The negative electrode slurry was coated on one side of a copper foil (thickness of 6 μm) (coating surface density of 0.15 g / 1540.25 mm 2 ), then drying and cold pressing to form a negative electrode active material layer (with a thickness of 0.15 mm) on one side of the negative electrode current collector, and finally punching to obtain a negative electrode sheet;

[0179] b. Preparation of positive electrode sheet:

[0180] The positive electrode active material, conductive carbon (SP), and binder (polyvinylidene fluoride PVDF) prepared in the above examples and comparative examples were dissolved in a solvent N-methylpyrrolidone (NMP) at a mass ratio of 96:2:2, and stirred thoroughly to prepare a positive electrode slurry. The positive electrode slurry was coated on one side of an aluminum foil (coating surface density of 0.4 g / 1540.25 mm 2 ), then drying and cold pressing to form a positive electrode active material layer (with a thickness of 0.2 mm) on one surface of an aluminum foil (15 μm), and finally punching to obtain a positive electrode sheet;

[0181] c. Preparation of isolation membrane:

[0182] A polyethylene porous polymer film was used as the separator (thickness 7 μm);

[0183] d. Preparation of electrolyte

[0184] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a mass ratio of 1:1:1 to obtain a solvent, and fully dried electrolyte salt LiPF6 is dissolved in the above solvent. After mixing evenly, an electrolyte solution with a concentration of 1 mol / L is obtained.

[0185] Assembly: Stack a single positive electrode sheet, a single separator, and a single negative electrode sheet in order (the side of the positive electrode sheet where the positive electrode active material layer is formed contacts the separator, and the side of the negative electrode sheet where the negative electrode active material layer is formed contacts the separator), so that the separator is placed between the positive and negative electrodes to serve as an isolation, and add electrolyte. Pressure packaging (50 MPa) is performed to obtain a CR2032 button-type full battery (capacity ≤ 5 mAh).

[0186] Using a VSP-300 electrochemical workstation (Bio-Logic), the button cell was connected to the workstation and electrochemical impedance spectroscopy (EIS) was performed within a frequency range of 2 MHz to 1 mHz, with a constant potential sweep of ±10 V. The impedance of the button cell was measured. The results are shown in Table 2.

[0187] Table 2

[0188] Conclusion: As can be seen from Table 2, in Examples 1-18 of the present application, the surface modifier and the hydrophobic protective agent are provided on at least part of the surface of the positive electrode active material, which makes the battery containing the surface modifier have excellent cycle stability and low impedance.

[0189] In Examples 1-18 and Comparative Examples 1-3, the surface modifier and the hydrophobic protective agent were not added at the same time, and the cycle performance of the battery was significantly reduced and the impedance increased. It can be seen that in the present application, the surface modifier and the hydrophobic protective agent work together to isolate the contact between the electrolyte and the positive electrode active material, reduce the irreversible loss caused by the side reaction of the positive electrode active material, and reduce the absorption of H2O and CO2 in the air by the matrix, thereby improving the high-voltage durability of the matrix, and making the battery containing it have excellent cycle stability and low impedance.

[0190] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, wherein The invention comprises a substrate and a coating layer, wherein the coating layer is formed on at least a part of the surface of the substrate, the coating layer comprises a surface modifier and a hydrophobic protective agent, the surface modifier comprises at least one of a halogenated alkylsilane or an alkylsilane, and the hydrophobic protective agent comprises a hydrophobic group.

2. The positive electrode active material according to claim 1, wherein The surface modifier includes a hydrolyzable group, and optionally, the hydrolyzable group includes at least one of an ester group, an amide group, a carboxylate or sodium phenolate.

3. The positive electrode active material according to claim 1 or 2, wherein The surface modifier includes at least one of heptadecafluorodecyltriethoxysilane, octadecylsilane, (trimethylsilyl)methyltrifluoromethanesulfonate, trimethylpentafluorophenylsilane, fluorooctylmethylsiloxane-dimethylsiloxane copolymer, N-methyl-N-(trimethylsilyl)trifluoroacetamide or bis(3-trifluoropropyl)-1,1,3,3-tetramethyldisilazane.

4. The positive electrode active material according to any one of claims 1 to 3, wherein At least one of the following conditions is met: The hydrophobic group includes at least one of a phenyl group, a halogen atom, a nitro group, an ester group, an ether group, or an alkyl group having a carbon number less than or equal to 32; The hydrophobic protective agent further includes a first group, wherein the first group includes at least one of a phosphate group, a carbonate group or a sulfonate group.

5. The positive electrode active material according to any one of claims 1 to 4, wherein The hydrophobic protective agent includes at least one of dihexadecyl phosphate, tributyl phosphate, trimethyl phosphate, triisopropyl phosphate, dibutyl phosphate, dimethyl phosphate or isopropyl phosphate.

6. The positive electrode active material according to any one of claims 1 to 5, wherein The matrix includes at least one of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. Optionally, the matrix includes Li x Ni a Co b M c O 2-y , wherein M includes at least one of Mn or Al, 0.6≤x≤1.2, -0.1≤y≤0.1, 0.5≤a<1, 0.1≤b≤0.3, 0<c≤0.3, a+b+c=1.

7. The positive electrode active material according to any one of claims 1 to 6, wherein The volume average particle size D of the positive electrode active material v 50 is 10μm-20μm, and can be optionally 10μm-15μm.

8. A method for preparing a positive electrode active material, wherein: include: A coating layer is formed on at least part of the surface of the substrate, wherein the coating layer comprises a surface modifier and a hydrophobic protective agent, wherein the surface modifier comprises at least one of a halogenated alkylsilane or an alkylsilane, and the hydrophobic protective agent has a hydrophobic group.

9. The method according to claim 8, wherein: include: preparing a surface modifier on at least a portion of the surface of the substrate by a vapor deposition method to obtain an intermediate; The intermediate is immersed in a solution containing a hydrophobic protective agent to obtain a positive electrode active material.

10. The method according to claim 9, wherein: The temperature of the vapor deposition is 130°C-200°C.

11. The method according to claim 9 or 10, wherein: At least one of the following conditions is met: Based on the total mass of the solution containing the hydrophobic protective agent, the mass proportion of the hydrophobic protective agent is 90%-99%; The soaking time is 2h-6h.

12. The method according to any one of claims 9 to 11, wherein: The mass ratio of the substrate, the surface modifier and the hydrophobic protective agent is 1:(0.05-0.1):(0.02-0.05).

13. A positive electrode sheet, wherein: The invention comprises the positive electrode active material according to any one of claims 1 to 7 or the positive electrode active material prepared by the method according to any one of claims 8 to 12.

14. A battery, wherein: Including the positive electrode sheet as described in claim 13.

15. An electrical device, wherein: Comprising the battery of claim 14.

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