Lithium battery monomer, positive electrode active material, preparation method of positive electrode active material, battery device and power utilization device

Abstract

The invention discloses a lithium battery monomer, a positive active material, a preparation method of the positive active material, a battery device and a power utilization device, the lithium battery monomer comprises a positive pole piece, the positive pole piece comprises a positive current collector and a positive active material film layer located on at least one side of the positive current collector, and the positive active material film layer comprises the positive active material; the positive electrode active material includes: an inner core including a lithium-containing transition metal oxide material; the polymer is at least partially located on the surface of the inner core, and the polymer comprises P-O-P bonds. The positive electrode active material polymer in the lithium battery monomer comprises P-O-P bonds, so that the high-temperature storage property and the energy density of the lithium battery monomer are improved; the invention provides the positive electrode active material with good stability and the preparation method of the positive electrode active material, and the gram volume of the positive electrode active material can be fully exerted; the invention further provides a battery device and a power utilization device which at least have the beneficial effects.

Description

Technical Field

[0001] This application belongs to the field of battery technology, specifically relating to a lithium battery cell, a positive electrode active material and its preparation method, a battery device and an electrical device. Background Technology

[0002] Batteries, represented by lithium-ion cells, utilize the insertion and extraction of lithium ions between the positive and negative electrodes to achieve charging and discharging. The positive electrode active material is a key factor affecting battery performance.

[0003] In related technologies, olivine-structured cathode materials in battery cells exhibit poor electrochemical performance in carbonate electrolyte systems. Therefore, improvements are needed. Summary of the Invention

[0004] The purpose of this application is to provide a lithium battery cell that improves the high-temperature storage performance and energy density of the lithium battery cell; this application provides a positive electrode active material with good stability and full utilization of its specific capacity and its preparation method; this application also provides a battery device and an electrical device that have at least the above-mentioned beneficial effects.

[0005] In a first aspect, embodiments of this application provide a lithium battery cell, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material film layer located on at least one side of the positive current collector, the positive active material film layer including a positive active material, the positive active material including: a core, the core including a lithium-containing transition metal oxide material; a polymer, at least partially located on the surface of the core, the main chain of the polymer including POP bonds.

[0006] In the embodiments of this application, the POP bond in the polymer has strong antioxidant capacity and can resist the oxidative degradation of the electrolyte; it remains stable under the high temperature conditions of lithium battery and is not easily decomposed, which can effectively reduce the intensity of chemical reactions in lithium-ion battery at high temperature, reduce the generation and shuttle of unstable oxidation products, help to form a more stable interface layer (CEI), and improve the high temperature storage performance of lithium battery cells.

[0007] In some alternative embodiments, the main chain of the polymer further includes PO-Si bonds, or the side chains of the polymer include PO-Si bonds.

[0008] In the embodiments of this application, the PO-Si bonds in the polymer, whether located in the main chain or the side chain, can help form a more stable interface layer (CEI), thereby improving the high-temperature storage performance of the lithium battery cell. The stable CEI can maintain its integrity under high-temperature conditions, reducing the probability of the interface layer (CEI) being damaged and reformed, reducing the consumption of active lithium ions, fully utilizing the specific capacity of the positive electrode active material, and thus improving the energy density of the lithium battery cell.

[0009] In some alternative embodiments, the polymer includes a first structural unit having the structure of formula (1):

[0010] In any of the first structural units, R1, R2, and R3 independently include C1 to C5 alkyl groups that are either unsubstituted or substituted by halogen atoms.

[0011] In the embodiments of this application, the first structural unit includes PO-Si bonds, which improves the stability of the polymer. Generally, the core surface contains some alkaline substances, which will generate certain PO-Li bonds with the first structural unit. The core reacts with the first structural unit to generate PO-Li bonds as well, which improves the binding force between the polymer and the core and improves the stability of the positive electrode active material. The PO-Li bond has a certain degree of lithium affinity, which is beneficial to the insertion and extraction of active lithium ions. In addition, the PO-Li bond itself contains a certain amount of Li element, which can reduce the consumption of lithium ions by side reactions and reduce the consumption of active lithium ions at adjacent interfaces of the polymer. Therefore, it reduces the consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and is conducive to improving the energy density of the lithium battery cell.

[0012] In some alternative embodiments, the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

[0013] In the embodiments of this application, the end group includes -Li, which improves the lithium affinity of the polymer and reduces the consumption of active lithium ions at adjacent interfaces of the polymer. Therefore, it reduces the overall consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and is beneficial to improving the energy density of the lithium battery cell.

[0014] In the embodiments of this application, the end group includes -Si(R4)4, which includes silicon and alkyl groups. It has good hydrophobicity, which reduces the oxidation or pulverization of the positive electrode active material caused by contact with water in the air, and is beneficial to the preparation of lithium battery cells.

[0015] In some alternative embodiments, the first structural unit includes any one of equations (I-1) to (I-15):

[0016]

[0017]

[0018] In the embodiments of this application, the silicon element of the first structural unit can be connected to any type of unsubstituted or halogen-substituted alkyl group. These alkyl groups (such as methyl, ethyl, propyl, etc.) affect the chemical stability and mechanical properties of the polymer, especially its thermal stability. Therefore, the first structural unit of the above type improves the high-temperature storage performance of the lithium battery cell containing the positive electrode active material. The first structural unit of the above type improves the toughness and elasticity of the polymer, improves the stability of the polymer, which is beneficial to the stability of the positive electrode electrolyte membrane (CEI membrane) in the lithium battery cell and reduces the consumption of active ions. The first structural unit includes silicon element and alkyl group, which has good hydrophobicity, reduces the oxidation or pulverization caused by the contact of the positive electrode active material with water in the air, which is beneficial to the preparation of lithium battery cells.

[0019] Furthermore, the first structural unit of the above types did not significantly reduce the conductivity of the positive electrode active material.

[0020] In some optional embodiments, the polymer comprises x first structural units and y second structural units, the first structural units having the structure of formula (2) and the second structural units having the structure of formula (3):

[0021]

[0022] Where x and y are positive integers, x is from 1 to 10, y is from 1 to 6, x+y≥3, and the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

[0023] In the embodiments of this application, the polymer has the above-described structural formula, and x and y are within the above-described range. This can increase the chemical stability of the positive electrode active material, improve the bonding degree between the polymer and the core, and enhance the high-temperature storage performance of the lithium battery cell. The polymer includes POP bonds, PO-Si bonds, and PO-Li bonds, which reduces the side reactions between the lithium-containing transition metal oxide material and the electrolyte, reduces the consumption of lithium ions by side reactions, and since it itself contains lithium, it reduces the consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and improves the energy density of the lithium battery cell.

[0024] In some alternative embodiments, the polymer includes a first structural unit and a third structural unit, the first structural unit having the structure of formula (1) and the third structural unit having the structure of formula (4):

[0025]

[0026] In each of the first structural units, R1, R2, and R3 independently include unsubstituted or halogen-substituted C1-C5 alkyl groups; R5 independently includes unsubstituted or halogen-substituted C1-C5 alkyl groups; R6 independently includes any one of hydrogen atom, halogen atom, C1-C5 alkyl group, or C1-C5 amino group; R7 is empty, oxygen atom, or chlorine atom; and R8 is oxygen atom or chlorine atom.

[0027] In the embodiments of this application, the polymer includes a first structural unit and a third structural unit. The main chain of this block polymer may include POP bonds, PO-Si bonds, and Si-O-Si bonds. These bonds have strong antioxidant capacity and can resist the oxidative degradation of the electrolyte. They can effectively reduce the intensity of chemical reactions that occur in lithium-ion batteries at high temperatures, reduce the generation and shuttle of unstable oxidation products, help form a more stable interface layer (CEI), and improve the high-temperature storage performance of lithium battery cells.

[0028] In some alternative embodiments, the number-average molecular weight of the polymer is 300 to 10,000.

[0029] A polymer with a number-average molecular weight within the aforementioned range is beneficial for forming a polymer with suitable thickness and uniform coating, resulting in appropriate polymer density. A polymer with a number-average molecular weight within the aforementioned range also provides suitable mechanical strength and toughness, offering better protection, reducing mechanical damage to the positive electrode active material caused by volume changes during charging and discharging, improving the stability of the CEI film, reducing the process of CEI film destruction and reformation, and thus helping to reduce the consumption of active lithium ions in the lithium battery cell, fully utilizing the specific capacity of the positive electrode active material. In some optional embodiments, the polymer's number-average molecular weight is between 300 and 2000.

[0030] In some optional embodiments, the polymer thickness on the core surface is between 1 nm and 10 nm. A polymer thickness within this range increases the chemical stability of the positive electrode active material and reduces adverse reactions between the lithium-containing transition metal oxide material and the electrolyte. The polymer thickness also eliminates the utilization rate of lithium-containing transition metal oxide materials, thereby improving the capacity and cycle performance of the lithium battery cell.

[0031] In some optional embodiments, the polymer content is 0.05% to 2% by mass, based on the total mass of the positive electrode active material.

[0032] According to the embodiments of this application, the mass content of the polymer in the positive electrode active material is within the above-mentioned range, which is beneficial for the direct contact between the polymer degradation electrolyte and the core, reducing the occurrence of side reactions and thus improving cycle stability. The polymer can maintain the structural stability of the lithium-containing transition metal oxide material during charge and discharge; it reduces the side reactions occurring in the lithium-containing transition metal oxide material and improves the cycle capacity retention rate of the lithium battery cell.

[0033] In some optional embodiments, at least 80% of the core surface area is coated with a polymer. This reduces side reactions between the lithium-containing transition metal oxide material and the electrolyte, increases the chemical stability of the positive electrode active material, and improves the high-temperature storage performance of the lithium-ion battery cell.

[0034] In some optional embodiments, the lithium-containing transition metal oxide material is a lithium-containing transition metal spinel material. In a lithium-ion battery cell, the lithium-containing transition metal spinel material provides a foundation for the high voltage of the entire battery system. In this high-voltage system, the POP bond has strong oxidation resistance, resisting the oxidative degradation of the electrolyte, which helps to form a more stable interface layer (CEI), reducing the capacity loss of the positive electrode active material, and improving the high-temperature storage performance of the lithium-ion battery cell.

[0035] In some optional embodiments, the chemical formula of the lithium-containing transition metal oxide material is: Li a Ni m Mn j M n O (4-c) , 0.8≤a≤1.2, m≥0, 2>j>0, 0≤n<2, 0≤c≤0.5, m+j+n≤2, M includes one or more of Sb, Al, Ti, Mg, V, Cr, Zr, Nb and W.

[0036] In the embodiments of this application, the presence of polymer, especially PO-Si, reduces the release of iron ions and manganese ions from the positive electrode in the core, reduces the precipitation of iron and manganese ions in the negative electrode, reduces the impact on the negative electrode, and improves the high-temperature storage performance of the lithium battery cell.

[0037] In some optional embodiments, to improve the high-temperature storage performance and energy density of the lithium battery cell, the specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 5m 2 / g, optionally 0.3m 2 / g to 2m 2 / g.

[0038] In some optional embodiments, to improve the high-temperature storage performance and energy density of the lithium battery cell, the powder compaction density of the positive electrode active material is 2.4 g / cm³. 3 ~3.1g / cm 3 2.6g / cm³ is an option. 3 ~2.9g / cm 3 .

[0039] In some optional embodiments, in order to balance the cost of the electrolyte in the lithium battery cell and the kinetic performance of the lithium battery cell, and to improve the high-temperature storage performance of the battery cell, the lithium battery cell includes an electrolyte, which includes a carbonate solvent; the electrolyte includes a lithium salt with a molar concentration of 0.4 mol / L to 2 mol / L.

[0040] In some optional embodiments, the cutoff voltage of the lithium battery cell is greater than or equal to 4.5V, optionally 4.7-5V. Therefore, at a higher cutoff voltage, the POP bonds in the polymer of this lithium battery cell have strong antioxidant capacity and can resist oxidative degradation by the electrolyte; it remains stable within the lithium battery operating voltage range or under high temperature conditions, is not easily decomposed, and forms a more stable interface layer (CEI). The stable interface facilitates the uniform insertion and extraction of lithium ions, further improving the high-temperature storage performance of the lithium battery cell.

[0041] Secondly, embodiments of this application provide a positive electrode active material, comprising:

[0042] The core, which includes lithium-containing transition metal oxide materials;

[0043] The polymer, at least partially located on the surface of the core, has a main chain consisting of POP bonds.

[0044] In the embodiments of this application, the POP bonds in the polymer have strong antioxidant capacity and can resist the oxidative degradation of the electrolyte. They remain stable under the working voltage range or high temperature conditions of lithium batteries and are not easily decomposed. This can effectively reduce the intensity of chemical reactions in lithium-ion batteries at high temperatures, reduce the generation and shuttle of unstable oxidation products, and help form a more stable interface layer (CEI). The stable interface helps the uniform insertion and extraction of lithium ions and improves the high-temperature storage performance of lithium battery cells.

[0045] In some alternative embodiments, the main chain of the polymer also includes PO-Si bonds, or the side chains of the polymer include PO-Si bonds.

[0046] In the embodiments of this application, the PO-Si bonds in the polymer, whether located in the main chain or the side chain, can help form a more stable interface layer (CEI). A stable CEI can maintain its integrity under high temperature or high voltage conditions, reducing the probability of the interface layer (CEI) being damaged and reformed, reducing the consumption of active lithium ions, fully utilizing the specific capacity of the positive electrode active material, and thus improving the energy density of the lithium battery cell.

[0047] In some alternative embodiments, the polymer includes a first structural unit having the structure of formula (1):

[0048]

[0049] In any of the first structural units, R1, R2, and R3 independently include C1 to C5 alkyl groups that are either unsubstituted or substituted by halogen atoms.

[0050] In the embodiments of this application, the first structural unit includes PO-Si bonds, which improves the stability of the polymer. Generally, the core surface contains some alkaline substances, which will generate certain PO-Li bonds with the first structural unit. The core reacts with the first structural unit to generate PO-Li bonds as well, which improves the binding force between the polymer and the core and improves the stability of the positive electrode active material. The PO-Li bond has a certain degree of lithium affinity, which is beneficial to the insertion and extraction of active lithium ions. In addition, the PO-Li bond itself contains a certain amount of Li element, which can reduce the consumption of lithium ions by side reactions and reduce the consumption of active lithium ions at adjacent interfaces of the polymer. Therefore, it reduces the consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and is conducive to improving the energy density of the lithium battery cell.

[0051] In some alternative embodiments, the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

[0052] In the embodiments of this application, the end group includes -Li, which improves the lithium affinity of the polymer and reduces the consumption of active lithium ions at adjacent interfaces of the polymer. Therefore, it reduces the overall consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and is beneficial to improving the energy density of the lithium battery cell.

[0053] In the embodiments of this application, the end group includes -Si(R4)4, which includes silicon and alkyl groups. It has good hydrophobicity, which reduces the oxidation or pulverization of the positive electrode active material caused by contact with water in the air, and is beneficial to the preparation of lithium battery cells.

[0054] In some alternative embodiments, the first structural unit includes any one of equations (I-1) to (I-15):

[0055]

[0056]

[0057] In the embodiments of this application, the silicon element of the first structural unit can be connected to any type of unsubstituted or halogen-substituted alkyl group. These alkyl groups (such as methyl, ethyl, propyl, etc.) affect the chemical stability and mechanical properties of the polymer, especially its thermal stability. Therefore, the first structural unit of the above type improves the high-temperature storage performance of the lithium battery cell containing the positive electrode active material. The first structural unit of the above type improves the toughness and elasticity of the polymer, improves the stability of the polymer, which is beneficial to the stability of the positive electrode electrolyte membrane (CEI membrane) in the lithium battery cell and reduces the consumption of active ions. The first structural unit includes silicon element and alkyl group, which has good hydrophobicity, reduces the oxidation or pulverization caused by the contact of the positive electrode active material with water in the air, which is beneficial to the preparation of lithium battery cells.

[0058] Furthermore, the first structural unit of the above types did not significantly reduce the conductivity of the positive electrode active material.

[0059] In some optional embodiments, the polymer comprises x first structural units and y second structural units, the first structural units having the structure of formula (2) and the second structural units having the structure of formula (3):

[0060]

[0061] Where x and y are positive integers, x is from 1 to 10, y is from 1 to 6, x+y≥3, and the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

[0062] In the embodiments of this application, the polymer has the above-mentioned structural formula, and x and y are within the above-mentioned range, which can increase the chemical stability of the positive electrode active material and further improve the high-temperature storage performance of the lithium battery cell.

[0063] In some alternative embodiments, the polymer includes a first structural unit and a third structural unit, the first structural unit having the structure of formula (1) and the third structural unit having the structure of formula (4):

[0064]

[0065] In each of the first structural units, R1, R2, and R3 independently include unsubstituted or halogen-substituted C1-C5 alkyl groups; R5 independently includes unsubstituted or halogen-substituted C1-C5 alkyl groups; R6 independently includes any one of hydrogen atom, halogen atom, C1-C5 alkyl group, or C1-C5 amino group; R7 is empty, oxygen atom, or chlorine atom; and R8 is oxygen atom or chlorine atom.

[0066] In the embodiments of this application, the polymer includes a first structural unit and a third structural unit. The main chain of this block polymer may include POP bonds, PO-Si bonds, and Si-O-Si bonds. These bonds have strong antioxidant capacity and can resist the oxidative degradation of the electrolyte; thus further improving the high-temperature storage performance of the lithium battery cell.

[0067] In some alternative embodiments, the number-average molecular weight of the polymer is 300 to 10,000.

[0068] The number-average molecular weight of the polymer is within the above range, which is conducive to forming a polymer with appropriate thickness and uniform coating, giving the polymer suitable density, reducing the contact and reaction between the electrolyte and the positive electrode active material, thereby reducing the probability of side reactions and improving the cycle stability of lithium battery cells.

[0069] Furthermore, the polymer's number-average molecular weight within the aforementioned range provides it with suitable mechanical strength and toughness, offering better protection and reducing mechanical damage to the positive electrode active material caused by volume changes during charging and discharging. This improves the stability of the CEI film, reduces the process of CEI film destruction and reformation, and helps lower the consumption of active lithium ions in the lithium battery cell, fully utilizing the specific capacity of the positive electrode active material. In some optional embodiments, the polymer's number-average molecular weight is between 300 and 2000.

[0070] In some optional embodiments, the polymer thickness on the core surface is between 1 nm and 10 nm. A polymer thickness within this range increases the chemical stability of the positive electrode active material and reduces adverse reactions between the lithium-containing transition metal oxide material and the electrolyte. The polymer thickness also eliminates the utilization rate of lithium-containing transition metal oxide materials, thereby improving the capacity and cycle performance of the lithium battery cell.

[0071] In some optional embodiments, the polymer content is 0.05% to 2% by mass, based on the total mass of the positive electrode active material.

[0072] According to the embodiments of this application, the mass content of the polymer in the positive electrode active material is within the above-mentioned range, which is beneficial for the direct contact between the polymer degradation electrolyte and the core, reducing the occurrence of side reactions and thus improving cycle stability. The polymer can maintain the structural stability of the lithium-containing transition metal oxide material during charge and discharge; it reduces the side reactions occurring in the lithium-containing transition metal oxide material and improves the cycle capacity retention rate of the lithium battery cell.

[0073] In some optional embodiments, at least 80% of the core surface area is coated with a polymer. This reduces side reactions between the lithium-containing transition metal oxide material and the electrolyte, increases the chemical stability of the positive electrode active material, and improves the high-temperature storage performance of the lithium-ion battery cell.

[0074] In some optional embodiments, the lithium-containing transition metal oxide material is a lithium-containing transition metal spinel material. In lithium-ion battery cells, the lithium-containing transition metal spinel material provides a foundation for the high voltage of the entire battery system. In this high-voltage system, the POP bond and PO-Si bond have strong antioxidant capabilities, resisting the oxidative degradation of the electrolyte, which helps to form a more stable interface layer (CEI), reducing the capacity loss of the positive electrode active material, and improving the high-temperature storage performance of the lithium-ion battery cell.

[0075] In some optional embodiments, the chemical formula of the lithium-containing transition metal oxide material is: Li a Ni m Mn j M n O (4-c) , 0.8≤a≤1.2, m≥0, 2>j>0, 0≤n<2, 0≤c≤0.5, m+j+n≤2, M includes one or more of Sb, Al, Ti, Mg, V, Cr, Zr, Nb and W.

[0076] In the embodiments of this application, the presence of polymer, especially PO-Si, reduces the release of iron ions and manganese ions from the positive electrode in the core, reduces the precipitation of iron and manganese ions in the negative electrode, reduces the impact on the negative electrode, and improves the high-temperature storage performance of the lithium battery cell.

[0077] In some optional embodiments, the specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 5m 2 / g. Therefore, it improves the high-temperature storage performance and energy density of lithium battery cells.

[0078] In some optional embodiments, the powder compaction density of the positive electrode active material is 2.4 g / cm³. 3 ~3.1g / cm 3Therefore, the high-temperature storage performance and energy density of lithium battery cells have been further improved.

[0079] Thirdly, embodiments of this application provide a method for preparing a positive electrode active material, including:

[0080] An organic polymeric monomer is placed on the core surface, wherein the organic polymeric monomer comprises an alkyl silane phosphate or a mixture of a silane monomer and a phosphate ester; the core comprises a lithium-containing transition metal oxide material;

[0081] The organic polymer monomer is subjected to a crosslinking reaction to obtain a positive electrode active material, the positive electrode active material comprising a polymer at least partially located on the surface of the core, the main chain of the polymer containing POP bonds.

[0082] In the embodiments of this application, the polymer prepared by using alkyl silane phosphate esters or a mixture of silane monomers and phosphate esters has strong anti-oxidation ability in the POP bonds of the polymer, which can resist the oxidative degradation of the electrolyte. It remains stable under the working voltage range or high temperature conditions of lithium batteries and is not easily decomposed. It can effectively reduce the intensity of chemical reactions in lithium-ion batteries at high temperatures, reduce the generation and shuttle of unstable oxidation products, and help to form a more stable interface layer (CEI). The stable interface helps the uniform insertion and extraction of lithium ions and improves the high-temperature storage performance of lithium battery cells.

[0083] In some optional embodiments, the alkylsilane phosphate includes one or more of trimethylsilane phosphate, triethylsilane phosphate, tributylsilane phosphate, triisopropylsilane phosphate, dimethylethylsilane phosphate, and trimethylsilane polyphosphate.

[0084] In some optional embodiments, the silane monomer includes one or more of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, KH570, KH560, KH550, trimethylchlorosilane, triethylchlorosilane, tributylchlorosilane, triisopropylchlorosilane, trimethylsilanol, triethylsilanol, tributylsilanol, triisopropylsilanol, methyldiethylsilanol, dimethylethylsilanol, dimethylsilanediol, diethylsilanediol, methylethylsilanediol, and hexamethylsilazaneamine.

[0085] In some alternative embodiments, the phosphate ester includes one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, methyl polyphosphate, polyethylene glycol phosphate, tris(trimethylsilane) phosphate, and trimethylsilane polyphosphate.

[0086] Thirdly, embodiments of this application provide a battery device, including a lithium battery cell as described in the first aspect or a lithium battery cell formed by preparing a positive electrode active material as described in the second aspect. The power device of this application embodiment at least has the beneficial effects of a lithium battery cell.

[0087] Fourthly, embodiments of this application provide an electrical device, including the battery device of the third aspect. The electrical device of this application embodiment at least has the beneficial effects of a battery device. Attached Figure Description

[0088] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0089] Figure 1 A schematic diagram of a battery cell provided in some embodiments of this application is shown.

[0090] Figure 2 An exploded view of a battery cell provided in some embodiments of this application is shown.

[0091] Figure 3 A schematic diagram of a battery module provided in some embodiments of this application is shown.

[0092] Figure 4 A schematic diagram of a battery pack provided in some embodiments of this application is shown.

[0093] Figure 5 It shows Figure 4 The diagram shown is an exploded view of the battery pack.

[0094] Figure 6 A schematic diagram of an electrical device provided in some embodiments of this application is shown.

[0095] Figure 7 The microstructure of the core-polymer interface in the positive electrode active material of this application embodiment is shown.

[0096] Figure 8 The elemental distribution diagram of the TEM-EDS of the positive electrode active material according to an embodiment of this application is shown.

[0097] The accompanying drawings are not necessarily drawn to scale.

[0098] The reference numerals in the attached diagram are explained as follows: 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate. Detailed Implementation

[0099] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, the positive electrode sheet, the lithium battery cell, and the power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0100] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0101] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0102] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0103] Unless otherwise specified, in this application, the term "active ion" refers to lithium ions that can be inserted and extracted back and forth between the positive and negative electrodes of a lithium battery cell.

[0104] In this application, "multiple" refers to two or more items (including two). "Multiple types" or "several kinds" in this application refers to two or more items (including two).

[0105] The battery device mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0106] In some embodiments, a battery cell assembly is typically formed by arranging multiple battery cells; as an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple battery cells into a single module. As an example, a battery module can be formed by bundling multiple battery cells together with cable ties.

[0107] A single battery cell is the smallest unit that makes up a battery device, and it can independently perform the functions of charging and discharging. A single battery cell can be cylindrical, cuboid, or other shapes, and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0108] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 2 This is a schematic diagram of battery module 4 as an example. Figure 2 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0109] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0110] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0111] Figure 3 and Figure 4 This is a schematic diagram of battery pack 1 as an example. Figure 3 and Figure 4As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0112] In some embodiments, the battery device may be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0113] The battery cells mentioned in the embodiments of this application may include lithium battery cells, such as lithium-ion battery cells, lithium metal battery cells, etc.

[0114] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode assembly. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0115] In some embodiments, such as Figure 5 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted according to requirements.

[0116] The battery cell includes an electrode assembly. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited to this.

[0117] Electrode assemblies generally include a positive electrode, a negative electrode, and a separator.

[0118] [Positive electrode plate]

[0119] The positive electrode includes a positive current collector and a positive active material film layer located on at least one side of the positive current collector. The positive active material film layer includes a positive active material, which includes:

[0120] The polymer, at least partially located on the surface of the core, has a main chain consisting of POP bonds.

[0121] In related technologies, lithium-containing transition metal oxide materials in lithium battery cells undergo continuous oxidation in carbonate electrolyte systems, failing to form a stable interface on the surface of the positive electrode. This leads to the continuous consumption of active lithium ions, and the shuttle of oxidation byproducts between the positive and negative electrodes, affecting battery life, especially high-temperature storage life.

[0122] In the embodiments of this application, the POP bond in the polymer has strong antioxidant capacity and can resist the oxidative degradation of the electrolyte; it remains stable under high temperature conditions and is not easily decomposed, which can effectively reduce the intensity of chemical reactions in lithium-ion batteries at high temperatures, reduce the generation and shuttle of unstable oxidation products, help form a more stable interface layer (CEI), and improve the high-temperature storage performance of lithium battery cells.

[0123] In some alternative embodiments, the polymer backbone includes POP bonds and PO-Si bonds, or the polymer backbone is POP bonds and the polymer side chains include PO-Si bonds.

[0124] In the embodiments of this application, the PO-Si bonds in the polymer, whether located in the main chain or the side chain, can help form a more stable interface layer (CEI), thereby improving the high-temperature storage performance of the lithium battery cell. The stable CEI can maintain its integrity under high-temperature conditions, reducing the probability of the interface layer (CEI) being damaged and reformed, reducing the consumption of active lithium ions, fully utilizing the specific capacity of the positive electrode active material, and thus improving the energy density of the lithium battery cell.

[0125] In addition, the PO-Si bonds in the polymer can prevent related byproducts from shuttling to the negative electrode. By reducing the shuttle effect of byproducts (such as manganese-containing byproducts), the capacity loss of the positive electrode active material can also be reduced.

[0126] The polymer's distribution and thickness can be observed using transmission electron microscopy (TEM). The uniformity of polymer distribution and thickness can be confirmed by randomly selecting multiple independent active material particles. The distribution of P and Si elements in the polymer can be confirmed using TEM-EDS, and the presence of POP and PO-Si can be detected using XPS and FTIR. Py-GCMS (thermal pyrolysis gas chromatography-mass spectrometry) can detect Si-O and Si-OP structural fragments, and confirm the polymer's molecular weight. In summary, the polymer's chemical structure can be determined. Furthermore, the POP structure of the polymer can be observed using XRD diffraction techniques commonly used in this field, and the proportions of structural units can be calculated comprehensively.

[0127] In some alternative embodiments, the polymer includes a first structural unit having the structure of formula (1):

[0128]

[0129] In any of the first structural units, R1, R2, and R3 independently include C1 to C5 alkyl groups that are either unsubstituted or substituted by halogen atoms.

[0130] For example, R1, R2, and R3 are each independently one of triethyl, tripropyl, triisopropyl, and tributyl.

[0131] In the embodiments of this application, the first structural unit includes PO-Si bonds, which improves the stability of the polymer. Generally, the core surface contains some alkaline substances, which will generate certain PO-Li bonds with the first structural unit. The core reacts with the first structural unit to generate PO-Li bonds as well, which improves the binding force between the polymer and the core and improves the stability of the positive electrode active material. The PO-Li bond has a certain degree of lithium affinity, which is beneficial to the insertion and extraction of active lithium ions. In addition, the PO-Li bond itself contains a certain amount of Li element, which can reduce the consumption of lithium ions by side reactions and reduce the consumption of active lithium ions at adjacent interfaces of the polymer. Therefore, it reduces the consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and is conducive to improving the energy density of the lithium battery cell.

[0132] The composition of polymers can be determined by a combination of transmission electron microscopy and XPS elemental analysis.

[0133] In some alternative embodiments, the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

[0134] In the embodiments of this application, the end group includes -Li, which improves the lithium affinity of the polymer and reduces the consumption of active lithium ions at adjacent interfaces of the polymer. Therefore, it reduces the overall consumption of active lithium ions in the lithium battery cell, fully utilizes the specific capacity of the positive electrode active material, and is beneficial to improving the energy density of the lithium battery cell.

[0135] In this embodiment, the end group includes -Si(R4)4, which comprises silicon and an alkyl group. This end group exhibits good hydrophobicity, reducing oxidation or pulverization of the positive electrode active material caused by contact with water in the air, thus facilitating the preparation of lithium battery cells. In some optional embodiments, the first structural unit includes any one of formulas (I-1) to (I-15):

[0136]

[0137]

[0138] In the embodiments of this application, the silicon element of the first structural unit can be connected to any type of unsubstituted or halogen-substituted alkyl group. These alkyl groups (such as methyl, ethyl, propyl, etc.) affect the chemical stability and mechanical properties of the polymer, especially its thermal stability. Therefore, the first structural unit of the above type improves the high-temperature storage performance of the lithium battery cell containing the positive electrode active material. The first structural unit of the above type improves the toughness and elasticity of the polymer, improves the stability of the polymer, which is beneficial to the stability of the positive electrode electrolyte membrane (CEI membrane) in the lithium battery cell and reduces the consumption of active ions. The first structural unit includes silicon element and alkyl group, which has good hydrophobicity, reduces the oxidation or pulverization caused by the contact of the positive electrode active material with water in the air, which is beneficial to the preparation of lithium battery cells.

[0139] Furthermore, the first structural unit of the above types did not significantly reduce the conductivity of the positive electrode active material.

[0140] In some optional embodiments, the polymer comprises x first structural units and y second structural units, the first structural units having the structure of formula (3) and the second structural units having the structure of formula (4):

[0141]

[0142] Where x and y are positive integers, x is from 1 to 10, y is from 1 to 6, x+y≥3, and the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

[0143] In the embodiments of this application, the polymer has the above-mentioned structural formula, and x and y are within the above-mentioned range, which can increase the chemical stability of the positive electrode active material and further improve the high-temperature storage performance of the lithium battery cell.

[0144] The polymer contains POP bonds, PO-Si bonds, and PO-Li bonds, which reduces the side reactions between lithium-containing transition metal oxide materials and electrolytes, reduces the consumption of lithium ions by side reactions, and contains lithium elements itself, which reduces the consumption of active lithium ions in lithium battery cells, fully utilizes the specific capacity of positive electrode active materials, and improves the energy density of lithium battery cells.

[0145] In some alternative embodiments, the polymer includes a first structural unit and a third structural unit, the first structural unit having the structure of formula (1) and the third structural unit having the structure of formula (4):

[0146]

[0147] In each of the first structural units, R1, R2, and R3 independently include unsubstituted or halogen-substituted C1-C5 alkyl groups; R5 independently includes unsubstituted or halogen-substituted C1-C5 alkyl groups; R6 independently includes any one of hydrogen atom, halogen atom, C1-C5 alkyl group, or C1-C5 amino group; R7 is empty, oxygen atom, or chlorine atom; and R8 is oxygen atom or chlorine atom.

[0148] The fact that R7 is empty can be understood as Si being directly connected to R5 via a bond.

[0149] In the embodiments of this application, the polymer includes a first structural unit and a third structural unit. The main chain of this block polymer may include POP bonds, PO-Si bonds, and Si-O-Si bonds. These bonds have strong antioxidant capacity and can resist the oxidative degradation of the electrolyte. They can effectively reduce the intensity of chemical reactions that occur in lithium-ion batteries at high temperatures, reduce the generation and shuttle of unstable oxidation products, help form a more stable interface layer (CEI), and improve the high-temperature storage performance of lithium battery cells.

[0150] In some optional embodiments, the number average molecular weight of the polymer is 300 to 10,000, optionally 300 to 2,000.

[0151] Optionally, the number-average molecular weight of the polymer can be any value or a range of combinations thereof from 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, and 10000.

[0152] The number-average molecular weight of the polymer is within the above range, which is conducive to forming a polymer with appropriate thickness and uniform coating, giving the polymer suitable density, reducing the contact and reaction between the electrolyte and the positive electrode active material, thereby reducing the probability of side reactions and improving the cycle stability of lithium battery cells.

[0153] Furthermore, the number-average molecular weight of the polymer is within the above range, which gives the polymer suitable mechanical strength and toughness, providing better protection, reducing mechanical damage to the positive electrode active material caused by volume changes during charging and discharging, improving the stability of the CEI film, reducing the process of CEI film destruction and reformation, which helps to reduce the consumption of active lithium ions in the lithium battery cell and fully utilize the specific capacity of the positive electrode active material.

[0154] The number-average molecular weight of the polymer has a well-known meaning in the art and can be determined using instruments and methods known in the art, such as high-temperature gel permeation chromatography (GPC). The test can be performed using a gel permeation chromatography (GPC) instrument, such as the Polymer Char GPC-IR high-temperature gel permeation chromatograph, and the number-average molecular weight of the polymer is calculated by determining the mass of the polymer and the number of molecules in the polymer. The test can be referenced to the international standard ISO 16014-1-2019.

[0155] In some alternative embodiments, the polymer thickness on the core surface is 1 nm to 10 nm.

[0156] Optionally, the thickness of the polymer can be any value or a range of combinations thereof from 1.0 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 4.0 nm, 4.5 nm, and 5.0 nm.

[0157] The polymer thickness within the above range increases the chemical stability of the positive electrode active material and reduces adverse reactions between lithium-containing transition metal oxide materials and the electrolyte; polymers with the above thickness do not have the utilization rate of lithium-containing transition metal oxide materials, thus improving the capacity and cycle performance of lithium battery cells.

[0158] The thickness of the polymer can be obtained by measuring the average value using a transmission electron microscope.

[0159] In some optional embodiments, the polymer content is 0.05% to 2% by mass, based on the total mass of the positive electrode active material.

[0160] Optionally, the mass content of the polymer can be any value or range of the following: 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35%, 0.40%, 0.45%, 0.50%, 0.55%, 0.60%, 0.65%, 0.70%, 0.75%, 0.80%, 0.85%, 0.90%, 0.95%, 1.00%, 1.5%, 2.0%.

[0161] According to the embodiments of this application, the mass content of the polymer in the positive electrode active material is within the above-mentioned range, which is beneficial for the direct contact between the polymer degradation electrolyte and the core, reducing the occurrence of side reactions and thus improving cycle stability. The polymer can maintain the structural stability of the lithium-containing transition metal oxide material during charge and discharge; it reduces the side reactions occurring in the lithium-containing transition metal oxide material and improves the cycle capacity retention rate of the lithium battery cell.

[0162] In some optional embodiments, at least 80% of the core surface area is coated with a polymer. This reduces side reactions between the lithium-containing transition metal oxide material and the electrolyte, increases the chemical stability of the positive electrode active material, and improves the high-temperature storage performance of the lithium-ion battery cell.

[0163] In some optional embodiments, the lithium-containing transition metal oxide material is a lithium-containing transition metal spinel material. In lithium-ion battery cells, the lithium-containing transition metal spinel material provides a foundation for the high voltage of the entire battery system. In this high-voltage system, the POP bond and PO-Si bond have strong antioxidant capabilities, resisting the oxidative degradation of the electrolyte, which helps to form a more stable interface layer (CEI), reducing the capacity loss of the positive electrode active material, and improving the high-temperature storage performance of the lithium-ion battery cell.

[0164] In some optional embodiments, the chemical formula of the lithium-containing transition metal oxide material is: Li a Ni m Mn j M n O (4-c) , 0.8≤a≤1.2, m>0, 2≥j>0, 0≤n<2, 0≤c≤0.5, m+j+n≤2, M includes one or more of Sb, Al, Ti, Mg, V, Cr, Zr, Nb and W.

[0165] Lithium-containing transition metal oxide materials are lithium-manganese spinel-type materials with oxygen vacancies on the surface, Mn 3+ The presence of [a specific compound] is closely related to the Jahn-Teller effect (JT effect) during the charging process. The Jahn-Teller effect is a structural distortion effect of coordination compounds, and its occurrence responds to the performance of lithium-ion battery cells. For example, Mn [a specific compound]. 3+ The existence and generation of Mn 2+ The dissolved lithium ions in the electrolyte undergo reduction and deposition at the negative electrode during high-voltage storage, catalyzing the unstable decomposition of the SEI (Sediment-Insulated Electrode). This continuously consumes active lithium at the negative electrode, reducing the lifespan of lithium-ion battery cells at high temperatures, especially under high voltage. It also affects the capacity of the positive electrode active material and the kinetic performance of the lithium-ion battery cells.

[0166] Therefore, the presence of polymers, especially PO-Si, reduces the release of manganese ions from the core, which helps maintain the stability of the core, reduces the damage of manganese ions to the solid electrolyte membrane (CEI membrane) on the surface of the positive electrode, and improves the high-temperature storage performance of the lithium battery cell. In addition, the reduced release of manganese ions from the core reduces the precipitation of manganese ions in the negative electrode, reduces the impact on the negative electrode, and thus improves the kinetic performance of the lithium battery cell.

[0167] For example, the lithium-containing transition metal oxide material can be LiNi 0.5 Mn 1.5 O4, LiNi 0.2 Mn 1.8 O4, LiNiMnO4, LiNi 0.2 Mn 1.8 O4, LiNi 1.5 Mn 0.5 O4, LiNiMnO4.

[0168] In some optional embodiments, the cutoff voltage of the lithium battery cell is greater than or equal to 4.5V, optionally from 4.7V to 5V. Therefore, at a higher cutoff voltage, the POP bonds in the polymer of this lithium battery cell have strong antioxidant capacity and can resist oxidative degradation by the electrolyte; it remains stable within the lithium battery operating voltage range or under high temperature conditions, is not easily decomposed, and forms a more stable interface layer (CEI). The stable interface facilitates the uniform insertion and extraction of lithium ions, further improving the high-temperature storage performance of the lithium battery cell.

[0169] In some optional embodiments, to improve the high-temperature storage performance and energy density of the lithium battery cell, the specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 5m 2 / g, optionally 0.3m 2 / g to 2m 2 / g.

[0170] Optionally, the specific surface area of ​​the positive electrode active material can be 0.2 m². 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.0m 2 / g, 3.5m 2 / g, 4.0m 2 / g, 4.5m 2 / g, 5.0m 2 Any value in / g or a range thereof.

[0171] In any embodiment of this application, specific surface area has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0172] In some optional embodiments, to improve the high-temperature storage performance and energy density of the lithium battery cell, the powder compaction density of the positive electrode active material is 2.4 g / cm³. 3 ~3.1g / cm 3 2.6g / cm³ is an option. 3 ~2.9g / cm 3 .

[0173] Optionally, the powder compaction density of the positive electrode active material can be 2.4 g / cm³. 3 2.5g / cm 3 2.6g / cm 3 2.7g / cm 3 2.8g / cm 3 2.9g / cm 3 3.0g / cm 3 Any value or range of 3.1 g / cm.

[0174] When the compaction density of the positive electrode active material powder is within the above range, the packing performance of the positive electrode active material powder can be improved, thereby increasing the energy density of the lithium battery cell containing the positive electrode active material; the contact degree between the positive electrode active material powders can be increased, thereby improving the conductivity of the positive electrode active material, thereby improving the kinetic performance of the lithium battery cell.

[0175] In any embodiment of this application, the powder compaction density (PD) has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using an electronic pressure testing machine (e.g., UTM7305) according to standard GB / T24533-2009. An exemplary test method is as follows: Weigh 1g of the above-mentioned positive electrode active material and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 3000 kg (equivalent to 30 kN), held for 30 seconds, then depressurized and held for 10 seconds. The compaction density of the positive electrode active material under 30 kN pressure is then recorded and calculated.

[0176] In some optional embodiments, in order to maximize the capacity of the positive electrode active material or increase the energy density of the lithium battery cell, when the graphite negative electrode is used in the embodiments, the 0.33C full cell specific capacity of the positive electrode active material is 118.4 mAh / g to 125 mAh / g, optionally 119 mAh / g to 124 mAh / g.

[0177] There are various methods for preparing lithium-containing transition metal oxide materials, which typically include solid-state methods, solution methods, co-precipitation methods, and hydrothermal methods.

[0178] The preparation methods of positive electrode active materials can generally be understood as the reprocessing of lithium-containing transition metal oxide materials. Examples include carbon coating and doping modification. Carbon coating refers to coating a layer of conductive carbon onto the surface of lithium iron phosphate particles using methods such as vapor deposition, sol-gel method, and chemical vapor deposition (CVD). Commonly used carbon sources include organic materials such as glucose, sucrose, and resins. Doping modification involves introducing other metal or non-metal ions to replace some of the iron or phosphate ions in the lithium iron phosphate lattice, altering the material's electronic structure and enhancing conductivity and ion migration rate. However, the positive electrode active materials prepared by these methods still limit the lifespan of lithium battery cells, especially their high-temperature storage life. Composite materials: By combining with other conductive materials (such as graphene, carbon nanotubes, and conductive polymers), multiphase materials are formed, enhancing the conductivity and electrochemical performance of lithium iron phosphate.

[0179] This application provides a method for preparing a positive electrode active material, including:

[0180] An organic polymeric monomer is placed on the core surface, and the organic polymeric monomer includes alkyl silane phosphates or a mixture of silane monomers and phosphate esters;

[0181] The organic polymer monomers are cross-linked to obtain a positive electrode active material, which includes a core comprising a lithium transition metal oxide material.

[0182] A polymer, at least partially covering the surface of the core; wherein the polymer backbone includes POP bonds.

[0183] In some alternative embodiments, the organic polymer monomer is placed on the core surface, and the polymer can be formed on the core surface by ball milling, liquid-phase negative pressure solvothermal coating, or liquid-phase negative pressure solvothermal coating. Liquid-phase negative pressure solvothermal coating can be understood as removing the solvent under negative pressure at low temperature and medium temperature while stirring at low speed.

[0184] In some optional embodiments, the alkylsilane phosphate includes one or more of trimethylsilane phosphate, triethylsilane phosphate, tributylsilane phosphate, triisopropylsilane phosphate, dimethylethylsilane phosphate, and trimethylsilane polyphosphate.

[0185] In some optional embodiments, the silane monomer in the mixture of silane monomer and phosphate ester includes one or more of methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, KH570, KH560, KH550, trimethylchlorosilane, triethylchlorosilane, tributylchlorosilane, triisopropylchlorosilane, trimethylsilanol, triethylsilanol, tributylsilanol, triisopropylsilanol, methyldiethylsilanol, dimethylethylsilanol, dimethylsilanediol, diethylsilanediol, methylethylsilanediol, and hexamethylsilazaneamine.

[0186] In some alternative embodiments, the phosphate ester includes one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, methyl polyphosphate, polyethylene glycol phosphate, tris(trimethylsilane) phosphate, and trimethylsilane polyphosphate.

[0187] In some alternative embodiments, the organic polymer monomers can undergo a crosslinking reaction through the action of an organic coupling agent and / or an initiator. In some alternative embodiments, the organic polymer monomers can undergo a crosslinking reaction through hydrolysis and / or hybridization.

[0188] Compared to conventional solid-phase coating, the embodiments of this application use organic polymer monomers and carry out rapid mixing treatment at medium and low temperatures, such as <150°C, which reduces the energy consumption and time consumption of the coating process.

[0189] When preparing the positive electrode sheet, the areal density of the positive active material film layer has a meaning known in the art and can be measured using instruments and methods known in the art. For example, take a positive electrode sheet that has been coated on one side and cold-pressed (if it is a positive electrode sheet coated on both sides, the positive active material film layer on one side can be wiped off first), and cut it into small circular pieces with an area of ​​S1.

[0190] Weigh it and record the weight as M1. Then wipe off the negative electrode film of the positive electrode after weighing, weigh the positive current collector and record the weight as M0. The surface density of the positive electrode film = (weight of the positive electrode M1 - weight of the positive current collector M0) / S1.

[0191] [Negative electrode plate]

[0192] The negative electrode sheet includes a negative current collector and a negative active material film layer disposed on at least one surface of the negative current collector, wherein the negative active material film layer includes a negative active material.

[0193] As an example, the negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode active material film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector. The negative electrode current collector can be made of materials such as metal foil, carbon-coated metal foil, or porous metal plate, and copper foil can be selected as an option.

[0194] As an example, the negative electrode active material film layer includes a negative electrode active material, an optional conductive agent, and an optional binder. The conductive agent is used to improve the conductivity of the negative electrode active material film layer, and the binder is used to firmly bond the negative electrode active material and the binder to the negative electrode current collector. This application does not specifically limit the types of conductive agents and binders, which can be selected according to actual needs.

[0195] As an example, the negative electrode active material can be one or more of natural graphite, artificial graphite, mesophase micro carbon spheres (MCMB), hard carbon, and soft carbon.

[0196] As an example, the conductive agent may be one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers; the binder may be one or more of styrene-butadiene rubber (SBR), styrene-butadiene rubber (SBCs), water-based acrylic resin, and carboxymethyl cellulose (CMC).

[0197] The negative electrode active material film layer may also optionally include a thickener, such as carboxymethyl cellulose (CMC). However, this application is not limited to this, and other materials that can be used as thickeners for lithium-ion battery negative electrode sheets may also be used.

[0198] [Isolation membrane]

[0199] The separator is located between the positive and negative electrodes and mainly serves to prevent internal short circuits.

[0200] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0201] In some embodiments, the material of the separator may include, but is not limited to, one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0202] [Electrolytes]

[0203] A single battery cell includes an electrolyte. The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid-state.

[0204] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and an organic solvent.

[0205] In some embodiments, the electrolyte includes anion, which may include bis(fluorosulfonyl)imide anion (FSI). - ), bis(trifluoromethanesulfonyl)imide anion (TFSI) - ), dioxaborate anion (BOB) - ), difluorooxalate borate anion (DFOB) - ), difluorodioxanol phosphate anion (DFOP) - ), tetrafluorooxalate phosphate anion (TFOP) - ), difluorophosphate anion (PO2F2) - ), hexafluorophosphate anion (PF6) - ), tetrafluoroborate anion (BF4) - ), hexafluoroarsenate anion (AsF6) - ), trifluoromethanesulfonate anion (CF3SO3) - One or more of the following.

[0206] In some embodiments, the electrolyte comprises cations, which may include lithium ions, etc.

[0207] In some optional embodiments, to balance the electrolyte cost and kinetic performance of lithium battery cells, the high-temperature storage performance of the battery cells is also improved. The lithium battery cell includes an electrolyte comprising a carbonate solvent; the electrolyte includes a lithium salt with a molar concentration of 0.4 mol / L to 2 mol / L. Optionally, the electrolyte includes a lithium salt with a mass concentration of any value or range thereof from 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.5 mol / L, and 2 mol / L.

[0208] Organic solvents may include, but are not limited to, one or more of esters, ethers, sulfones, and nitriles. Esters may include, but are not limited to, one or more of carbonates, phosphate esters, carboxylic esters, sulfate esters, and sulfonates. Carbonates may include cyclic carbonates and / or chain carbonates; optionally, carbonates may include both cyclic and chain carbonates. Chain carbonates may include low-viscosity polar chain carbonates, aliphatic branched carbonates, etc.

[0209] As an example, organic solvents may include, but are not limited to, ethylene carbonate (EC), propylene carbonate (PC), butene carbonate, 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), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), dimethyl ether tetraethylene glycol (TEGDME), ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), trimethyl phosphate, 3-methoxypropionitrile, H(CF2)2OCH3, C4F9O CH3, H(CF2)2OCH2CH3, H(CF2)2OCH2CF3, H(CF2)2CH2O(CF2)2H, CF3CHFCF2OCH3, CF3CHFCF2OCH2CH3, 2-trifluoromethylhexafluoropropyl methyl ether, 2-trifluoromethylhexafluoropropyl ethyl ether, 2-trifluoromethylhexafluoropropyl propyl ether, 3-trifluoromethyloctafluorobutyl methyl ether, 3-trifluoromethyloctafluorobutyl ethyl ether, 3-trifluoromethyloctafluorobutyl propyl ether, 4-trifluoromethyl One or more of the following: decafluoropentyl methyl ether, 4-trifluoromethyl decafluoropentyl ethyl ether, 4-trifluoromethyl decafluoropentyl propyl ether, 5-trifluoromethyl dodecylfluorohexyl methyl ether, 5-trifluoromethyl dodecylfluorohexyl ethyl ether, 5-trifluoromethyl dodecylfluorohexyl propyl ether, 6-trifluoromethyl tetradecafluoroheptyl methyl ether, 6-trifluoromethyl tetradecafluoroheptyl ethyl ether, 6-trifluoromethyl tetradecafluoroheptyl propyl ether, 7-trifluoromethyl hexadecylfluorooctyl methyl ether, 7-trifluoromethyl hexadecylfluorooctyl ethyl ether, and 7-trifluoromethyl hexadecylfluorooctyl propyl ether.

[0210] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0211] Methods for preparing battery cells are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer package, dried, and then injected with the electrolyte. After vacuum sealing, settling, and formation processes, a lithium battery cell is obtained.

[0212] Electrical appliances

[0213] This application also provides an electrical device, which includes the battery device provided in this application. The battery device can be used as the power source for the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, 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.

[0214] Electrical devices can choose the type of battery device according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0215] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0216] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0217] Example

[0218] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0219] Example 1

[0220] Preparation of positive electrode active material by ball milling and coating: The core (uncoated LiNiMnO4 material) was mixed with a tris(trimethylsilane) phosphate-ethanol mixed solution, and the mass ratio of the core to tris(trimethylsilane) phosphate was controlled at 99.5:0.5. The mixture was ball-milled at a low speed of 300 RPM for 30 min, the solution was filtered off and the material was retained, and the mixture was dried at 100℃ for 30 min to obtain the positive electrode active material. The positive electrode active material includes a core and a polymer located on the surface of the core; the polymer monomer structure is shown in formula (I-1).

[0221] Lithium-ion battery cell preparation:

[0222] Preparation of the positive electrode sheet: The above-prepared positive electrode active material, conductive agent Super P, and binder polyvinylidene fluoride were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 90:5:5. The positive electrode slurry was then uniformly coated onto one side of an aluminum foil with a thickness of 13 μm. After drying, cold pressing, and slitting, the positive electrode sheet of Example 1 was obtained, with a surface density (CW) of 350 mg / 1540.25 mm² for the positive electrode active material film. 2 .

[0223] Preparation of the negative electrode sheet: Graphite, conductive carbon black (SP), carboxymethyl cellulose, and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 96.3:0.7:1.2:1.8 and thoroughly mixed in water to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto the surface of the copper foil current collector. After drying, cooling, and slitting, the negative electrode sheet was obtained. The areal density (CW) of the negative electrode active material film layer was 142 mg / 1540.25 mm². 2 .

[0224] Electrolyte: LiPF6 is dispersed in a solvent, which is obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. The concentration of LiPF6 is 1 mol / L. Additives are added to the electrolyte: propane sulpholactone (PS), 1,3,2-dioxothiocyclo-2,2-dioxide (DTD), and fluoroethylene carbonate (FEC), with mass concentrations of 1%, 2%, and 0.5%, respectively.

[0225] Separating membrane: Polyethylene base film with a thickness of 7μm; ceramic coating is respectively set on both sides of the polyethylene base film with a thickness of 1μm; polymer coating is placed on the surface of the ceramic coating with a thickness of 1.5μm, and the main component is PVDF polymer.

[0226] Assembly: Assemble the stacked battery cells by placing them in the following order: single-sided positive electrode sheet - separator - double-sided negative electrode sheet - separator - single-sided positive electrode sheet, with the positive active material film layer of the positive electrode sheet facing the separator. Place the bare cell in an outer package, inject the electrolyte as described above, and seal it to obtain an assembled lithium battery cell.

[0227] Example 2

[0228] Example 2 differs from Example 1 in the preparation of the positive electrode active material: the core (uncoated LiNiMnO4 material) is mixed with a trimethylsilane phosphate-DEC mixed solution, controlling the mass ratio of the core to tri(trimethylsilane) phosphate to be 99.5:0.5. The mixture is ball-milled at 800 rpm for 30 min, the solution is filtered off, the remaining material is dried at 100°C for 30 min, and the positive electrode active material is obtained. This positive electrode active material comprises a polymer. The structural units in the polymer are shown in Table 1.

[0229] Examples 3 to 4

[0230] The differences between Examples 3 and 4 and Example 1 lie in the preparation of the positive electrode active material: In Example 3, the core (uncoated LiNiMnO4 material) was mixed with a tris(triethylsilane) phosphate-ethanol solution to obtain the positive electrode active material; this positive electrode active material includes a core and a polymer located on the surface of the core; the polymer's structural monomer is shown in formula (I-10). In Example 4, the core (uncoated LiNiMnO4 material) was mixed with a tris(triisopropylsilane)-ethanol mixed solution to obtain the positive electrode active material; this positive electrode active material includes a core and a polymer located on the surface of the core; the polymer's structural monomer is shown in formula (I-12). The types of polymers on the surface of the positive electrode active materials in Examples 3 and 4 are different, i.e., the structural units are different, as shown in Table 1.

[0231] Examples 5 to 6

[0232] The differences between Examples 5 and 6 and Example 1 are as follows: the preparation of the positive electrode active material is different; the quality of the raw materials is different, resulting in different mass content of the polymer in the positive electrode active material. As shown in Table 1.

[0233] Example 7

[0234] The difference between Example 7 and Example 2 is as follows: The positive electrode active material was prepared by liquid-phase negative pressure solvothermal coating: 100g of diethyl carbonate (DEC) solvent was added to a fluorinated container (TPFA) and placed on a rotary evaporator at 105℃. 100g of the core (uncoated LiNiMnO4 material) and 6mm polytetrafluoroethylene (PTFE) coated steel balls were added and ball-milled at low speed. The steel column and core were rotated at 100rpm, and a DEC-tris(trimethylsilane) phosphate solution (5% by mass of trimethylsilane phosphate) was added uniformly using a peristaltic pump. The addition was completed in 20min. Subsequently, the solvent was removed by vacuum, the powder was collected, and after vacuum drying at 105℃ for 2h, the positive electrode active material was obtained. This positive electrode active material includes a core and a polymer located on the surface. The polymer's monomer structure is shown in formula (I-1).

[0235] Example 8

[0236] The difference between Example 8 and Example 2 is that the positive electrode active material is prepared by mixed spraying. Specifically, 100g of core (uncoated LiNiMnO4 material) is stirred at high speed to make it flow while being kept at 105°C; a mixture of trimethylsilane phosphate and EMC solvent is sprayed onto the surface of the core in the form of atomization, wherein the mass content of trimethylsilane phosphate in the mixed solution is 30%, and then kept at 30min; the positive electrode active material is obtained, which includes a polymer.

[0237] Example 9

[0238] The difference between Example 9 and Example 2 is that the positive electrode active material is prepared by spray drying. Specifically, 100g of core (uncoated LiNiMnO4 material) is mixed with tris(trimethylsilane phosphate) and DEC to form a 10% wt% dispersion, and the powder is collected by spray drying at an outlet temperature of 105°C.

[0239] Examples 10 to 11

[0240] The difference between Examples 10 and 11 and Example 2 lies in the preparation of the positive electrode active material. The preparation of the positive electrode active material in Example 10 involved mixing the core (uncoated LiNiMnO4 material) with a mixed solution containing trimethylsilane phosphate-DEC and a silane monomer, wherein the silane monomer was dimethyldimethoxysilane. The mass ratio of the core, tri(trimethoxysilane) phosphate, and dimethyldimethoxysilane was controlled at 99.4:0.55:0.05. The mixture was ball-milled at 800 rpm for 30 min, the solution was filtered off, the material was retained, and the mixture was dried at 100°C for 2 h to obtain the positive electrode active material, which included a polymer located on the surface of the core. The difference between the preparation of the positive electrode active material in Example 11 and Example 10 lies in the mass ratio of the core, tri(trimethoxysilane) phosphate, and dimethyldimethoxysilane at 99:0.95:0.05. The structural units in the polymers of Examples 10 and 11 include formulas (I-1) and (5), where formulas (I-1) and (5) have portions connected by PO-Si.

[0241]

[0242] Examples 12 to 13

[0243] The difference between Examples 12 and 13 and Example 1 lies in the concentration of the electrolyte in the lithium battery cells. The concentration of LiPF6 in Example 12 is 0.5 mol / L; the concentration of LiPF6 in Example 13 is 2 mol / L.

[0244] Comparative Example 1

[0245] The difference between Comparative Example 1 and Example 1 is that the positive electrode active material is replaced with an uncoated LiNiMnO4 core, without polymer coating.

[0246] Comparative Example 2

[0247] The difference between Comparative Example 2 and Example 1 is that a solid-phase coating method is used: 0.5% of ammonium dihydrogen phosphate by mass of the core is taken and ball-milled together with the core at 800 rpm for 30 min, and sintered at 450°C for 2 h in air atmosphere to form an active material coated with lithium phosphate.

[0248] Comparative Example 3

[0249] The difference between Comparative Example 3 and Example 2 is that the preparation of the positive electrode active material is different: dimethyldimethoxysilane is used instead of tris(trimethylsilane) phosphate to form a Si-O-Si polymer coating.

[0250] Test section

[0251] The lithium battery cells prepared in the examples and comparative examples were subjected to performance testing. The specific testing methods are as follows.

[0252] 1) Testing the chemical formula of the positive electrode active material:

[0253] Weigh 0.2g of the positive electrode material into a 100mL beaker, add 10mL of 10% w / w nitric acid solution, heat and digest at 120℃ for 0.5 hours, then dilute to volume with a 100mL volumetric flask; then use a pipette to transfer 1mL to a 100mL volumetric flask and dilute to volume to obtain the test solution.

[0254] The mass fractions of lithium, manganese, iron, phosphorus, and dopant elements in the test solution were determined using an inductively coupled plasma optical emission spectrometer (ICP-OES, Agilent 5800). Based on the mass fractions of each element in the test solution of the precursor, the molar percentage of each element in the cathode material was calculated, thereby determining the chemical formula and element molar ratio.

[0255] 2) Testing of single-cell discharge capacity at 0.33C and total capacity at 0.33C.

[0256] Using the Shenzhen Xinwei Battery Testing System, the battery cells were discharged at a constant current rate of 0.33C to 3.5V, then charged at a constant voltage of 3.5V to a cutoff current of 0.04C. Next, they were charged at a constant current rate of 0.33C to a cutoff voltage of 4.95V, and then charged at a constant voltage of 4.95V to a cutoff current of 0.05C, and allowed to stand for 5 minutes. Subsequently, they were discharged at a constant current rate of 0.33C to a cutoff voltage of 3.5V. The discharge capacity of this step is recorded as C0. Dividing C0 by the mass of the active material used on the positive electrode side yields the total nominal capacity of the coating material at 0.33C.

[0257] 3) The powder compaction density of the positive electrode active materials prepared in the examples and comparative examples was tested:

[0258] The testing method refers to Appendix L of the national standard GB / T24533-2009, "Test Method for Powder Compacted Density". The density is determined using a compaction density meter. The test method is as follows: Weigh 1g of the above-mentioned positive electrode active material and add it to a container with a cross-sectional area of ​​1.298cm³. 2 In a metal cylindrical sleeve, pressure is applied to 300 kg (equivalent to 3 kN), held for 30 seconds, and then the pressure is released. The change in the height of the top column exposed outside the sleeve before and after compaction is recorded. Then, the compaction density of the active material powder under 3 kN pressure is recorded and calculated.

[0259] 4) High-temperature storage performance test of lithium battery cells

[0260] Using the Shenzhen Xinwei Battery Testing System, the battery cells were discharged at a constant current rate of 0.33C to 3.5V, then charged at a constant voltage of 3.5V to a cutoff current of 0.04C. Next, they were charged at a constant current rate of 0.33C to a cutoff voltage of 4.95V, and then charged at a constant voltage of 4.95V to a cutoff current of 0.05C. The cells were then allowed to stand for 5 minutes. Finally, they were discharged at a constant current rate of 0.33C to a cutoff voltage of 3.5V. The discharge capacity of this step is recorded as C0.

[0261] Next, the cells are stored at 45°C for n days. Afterward, the individual cells are removed and cooled to 25°C. At 25°C, they are discharged at a constant current rate of 0.33C0 to 3.5V, then discharged at a constant voltage of 3.5V to a cutoff current of 0.04C0. They are then charged at a constant current rate of 0.33C0 to a cutoff voltage of 4.95V, then charged at a constant voltage of 4.95V to a cutoff current of 0.05C0. After resting for 5 minutes, they are discharged at a constant current rate of 0.33C0 to a cutoff voltage of 3.5V, then charged at a constant voltage of 3.5V to a cutoff current of 0.04C0. The reversible capacity Cn is calculated, where n is the number of storage days, and Cn / C0 is the reversible capacity retention rate after n days of storage.

[0262] 5) Manganese Deposition Calculation: After measuring the C0 of the battery cell, it was fully charged and stored at 100% SOC in an environment of 45℃ for 14 days. After that, the battery cell was removed and cooled to 25℃. At 25℃, it was discharged at a constant current rate of 0.33C0 to 3.5V, then discharged at a constant voltage of 3.5V to the cutoff current of 0.04C0. Then, it was charged at a constant current rate of 0.33C0 to the cutoff voltage of 4.95V, then charged at a constant voltage of 4.95V to the cutoff current of 0.05C0. After standing for 5 minutes, it was discharged at a constant current rate of 0.33C0 to the cutoff voltage of 3.5V, then charged at a constant voltage of 3.5V to the cutoff current of 0.04C0. The lithium battery cell was disassembled to remove the negative electrode sheet. The negative electrode sheet was digested in nitric acid, and the Mn content was tested using ICP technology to calculate the Mn content in the negative electrode sheet.

[0263] The test results of the examples and comparative examples are shown in Tables 1 and 2.

[0264]

[0265] Figure 7 The left image in Example 1 is a transmission electron microscope (TEM) image of the uncoated LiNiMnO4 material. The white part in the left image is the outside of the material, and the black part is the uncoated LiNiMnO4 material, which illustrates that the LiNiMnO4 material has a core and a polymer surface structure.

[0266] Figure 8 The image shows the elemental distribution of the negative electrode sheet in the lithium battery cell of Example 1 using TEM-EDS. The left image shows the distribution of Mn in the LiNiMnO4 material of Example 1. The blue Mn represents the core boundary, with no enrichment at the edge. The middle and right images show the distribution of P and Si in the LiNiMnO4 material of Example 1, respectively. P and Si are enriched in obvious edge bands, indicating that there is a polymer containing P and Si on the surface, demonstrating the uniformity and consistency of the polymer on the core surface.

[0267] As can be seen from the test results in Table 1, the discharge specific capacity of the positive electrode active materials prepared using Examples 1-4 is higher than that of Comparative Examples 1-3. The reason for this may be that the polymers forming POP and PO-Si exhibit good oxidation resistance under high voltage. The polymers themselves are relatively stable, reducing side reactions at high voltage and improving the reversible capacity level. The lithium battery cells of Examples 1-4 show higher reversible capacity retention after 14 days of storage than those of Comparative Examples 1-3. This is likely because the polymers containing POP and PO-Si help form a stable SEI film, and the PO-Si bonds in the polymer can form a physical and chemical barrier, preventing related byproducts from shuttling to the negative electrode. By reducing the shuttle effect of byproducts (such as manganese-containing byproducts), the high-temperature storage performance of the lithium battery cells is improved, and the manganese content detected on the surface of the negative electrode is also relatively low.

[0268] As can be seen from Examples 1 and 3-4, different silicon and phosphorus-coated precursors can yield polymers with different molecular weights and adjust the structure of the first unit of the polymer; the differences in the surface state of the polymer cause the active material to exhibit different powder compaction, capacity and high-temperature storage properties.

[0269] As shown in Examples 1 and 5-6, while increasing the polymer content improves high-temperature storage performance at 45°C and Mn dissolution, Examples 5-6, compared to Example 1, more or less deteriorate the discharge capacity. However, compared to Comparative Example 2, the discharge capacity of Examples 5-6 is still better. Although the solid-phase coated inorganic Li3PO4 can partially improve storage and Mn dissolution, it significantly deteriorates the capacity. The reason for this may be that inorganic salts are difficult to distribute uniformly at the nanoscale through processing, which will significantly consume the active lithium coating the core, rather than the residual lithium on the surface.

[0270] Examples 1-2 and 7-9 demonstrate that different preparation process conditions result in different reaction behaviors, affecting the polymer's molecular weight and the polymer's bonding with the core. The polymer bonds with the core to form PO-Li bonds. A large portion of the Li in these PO-Li bonds originates from residual alkali on the core surface, reducing the active lithium ions consumed in the PO-Li bonding process and forming a complete and effective coating. Controlling the reaction conditions and mixing methods is crucial for achieving better results. Examples 1 and 2 show that DEC, as a solvent carrier, exhibits a higher 0.33C discharge capacity compared to ethanol. Furthermore, using a milder preparation method allows for uniform spreading of the coating precursor while minimizing damage to the core, resulting in better performance and reflecting differences in polymer molecular weight.

[0271] As demonstrated by Examples 1-2, 10-11, and Comparative Example 3, the individual silane monomer molecules were coated to form Si-O-Si bonds. In the polymers of Examples 1-2, POP bonds were formed in the main chain and PO-Si bonds in the side chains. In the polymers of Examples 10-11, POP bonds and PO-Si bonds were formed in the main chain. Comparative Example 3 did not form POP bonds or PO-Si bonds in the side chains. During the electrochemical cycling of the lithium-ion battery cell, the siloxane underwent some side reactions with the electrolyte. Therefore, the capacity of the positive electrode active material and the high-temperature storage performance of the lithium-ion battery cell in Comparative Example 3 were inferior to those in Examples 1-2 and 10-11.

[0272] As shown in Table 2, under different concentrations of lithium salt, the battery cells prepared using the positive electrode active material of Example 11 in Examples 1, 12, and 13 can achieve better levels in discharge capacity, storage life, and Mn dissolution, further improving discharge capacity and high-temperature storage performance of lithium battery cells.

[0273] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium battery cell, comprising a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive active material film layer located on at least one side of the positive current collector, the positive active material film layer comprising a positive active material, the positive active material comprising: The core comprises a lithium-containing transition metal oxide material; The polymer, at least partially located on the surface of the core, has a main chain comprising POP bonds.

2. The lithium battery cell according to claim 1, characterized in that, The main chain of the polymer also includes PO-Si bonds, or the side chains of the polymer include PO-Si bonds.

3. The lithium battery cell according to claim 1 or 2, characterized in that, The polymer includes a first structural unit having the structure of formula (1): In any one of the first structural units, R1, R2, and R3 independently include C1 to C5 alkyl groups that are either unsubstituted or substituted with halogen atoms.

4. The lithium battery cell according to claim 3, characterized in that, The first structural unit includes any one of equations (I-1) to (I-15):

5. The lithium battery cell according to any one of claims 1 to 4, characterized in that, The polymer comprises x first structural units and y second structural units, wherein the first structural units have the structure of formula (2) and the first structural units have the structure of formula (3): Wherein, x and y are positive integers, x is from 1 to 10, y is from 1 to 6, x+y≥3, and the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

6. The lithium battery cell according to any one of claims 1 to 5, characterized in that, The polymer comprises a first structural unit and a third structural unit, the first structural unit having the structure of formula (1), and the third structural unit having the structure of formula (4): In this configuration, R1, R2, and R3 in any one of the first structural units independently include unsubstituted or halogen-substituted C1-C5 alkyl groups; R5 in any one of the first structural units independently includes unsubstituted or halogen-substituted C1-C5 alkyl groups; R6 independently includes any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, or C1-C5 amino groups; R7 is empty, an oxygen atom, or a chlorine atom; and R8 is an oxygen atom or a chlorine atom.

7. The lithium battery cell according to any one of claims 1 to 6, characterized in that, The number average molecular weight of the polymer is between 300 and 10,000.

8. The lithium battery cell according to any one of claims 1 to 7, characterized in that, The number-average molecular weight of the polymer is between 300 and 2000.

9. The lithium battery cell according to any one of claims 1 to 8, characterized in that, The polymer satisfies one or more of the following conditions: 1) The thickness of the polymer on the core surface is 1 nm to 10 nm; 2) Based on the total mass of the positive electrode active material, the polymer content is from 0.05% to 2% by mass; 3) At least 80% of the surface area of ​​the core is covered with the polymer.

10. The lithium battery cell according to any one of claims 1 to 9, characterized in that, The positive electrode active material satisfies one or more of the following conditions: 1) The lithium-containing transition metal oxide material is a lithium-containing transition metal spinel material; 2) The specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 5m 2 / g; 3) The compacted density of the positive electrode active material powder is 2.4 g / cm³. 3 Up to 3.1 / cm 3 .

11. The lithium battery cell according to any one of claims 1 to 10, characterized in that, The positive electrode active material satisfies one or more of the following conditions: 1) The chemical formula of the lithium-containing transition metal oxide material is: Li a Ni m Mn j M n O (4-c) , 0.8≤a≤1.2, m≥0, 2>j>0, 0≤c≤0.5, 0≤n<2, m+j+n≤2, M includes one or more of Sb, Al, Ti, Mg, V, Cr, Zr, Nb and W; 2) The specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g to 2m 2 / g; 3) The compacted density of the positive electrode active material powder is 2.6 g / cm³. 3 Up to 2.9 g / cm 3 .

12. The lithium battery cell according to any one of claims 1 to 11, characterized in that, The lithium battery cell includes an electrolyte, which includes a carbonate solvent; the electrolyte includes a lithium salt with a molar concentration of 0.4 mol / L to 2 mol / L.

13. The lithium battery cell according to any one of claims 1 to 12, characterized in that, The cutoff voltage of the lithium battery cell is greater than or equal to 4.5V.

14. A positive electrode active material, comprising: The core comprises a lithium-containing transition metal oxide material; The polymer, at least partially located on the surface of the core, has a main chain containing POP bonds.

15. The positive electrode active material according to claim 14, characterized in that, The main chain of the polymer also includes PO-Si bonds, or the side chains of the polymer include PO-Si bonds.

16. The positive electrode active material according to claim 14 or 15, characterized in that, The polymer includes a first structural unit having the structure of formula (1): In any one of the first structural units, R1, R2, and R3 independently include C1 to C5 alkyl groups that are either unsubstituted or substituted with halogen atoms.

17. The positive electrode active material according to claim 16, characterized in that, The first structural unit includes any one of equations (I-1) to (I-15):

18. The positive electrode active material according to any one of claims 10 to 17, characterized in that, The polymer comprises x first structural units and y second structural units, wherein the first structural units have the structure of formula (2) and the first structural units have the structure of formula (3): Wherein, x and y are positive integers, x is from 1 to 10, y is from 1 to 6, x+y≥3, and the end groups of the polymer include one or more of -Li and -Si(R4)4, wherein R4 includes unsubstituted or substituted C1 to C5 alkyl groups.

19. The positive electrode active material according to any one of claims 14 to 18, characterized in that, The polymer comprises a first structural unit and a third structural unit, the first structural unit having the structure of formula (1), and the third structural unit having the structure of formula (4): In this configuration, R1, R2, and R3 in any one of the first structural units independently include unsubstituted or halogen-substituted C1-C5 alkyl groups; R5 in any one of the first structural units independently includes unsubstituted or halogen-substituted C1-C5 alkyl groups; R6 independently includes any one of hydrogen atoms, halogen atoms, C1-C5 alkyl groups, or C1-C5 amino groups; R7 is empty, an oxygen atom, or a chlorine atom; and R8 is an oxygen atom or a chlorine atom.

20. The positive electrode active material according to any one of claims 14 to 19, characterized in that, The number average molecular weight of the polymer is between 300 and 10,000.

21. The positive electrode active material according to any one of claims 14 to 19, characterized in that, The number-average molecular weight of the polymer is between 300 and 2000.

22. The positive electrode active material according to any one of claims 14 to 21, characterized in that, The polymer satisfies one or more of the following conditions: 1) The thickness of the polymer on the core surface is 1 nm to 10 nm; 2) Based on the total mass of the positive electrode active material, the polymer content is from 0.05% to 2% by mass; 3) At least 80% of the surface area of ​​the core is covered with the polymer.

23. The positive electrode active material according to any one of claims 14 to 22, characterized in that, The positive electrode active material satisfies one or more of the following conditions: 1) The lithium-containing transition metal oxide material is a lithium-containing transition metal spinel material; 2) The specific surface area of ​​the positive electrode active material is 0.2 m². 2 / g to 5m 2 / g; 3) The compacted density of the positive electrode active material powder is 2.4 g / cm³. 3 Up to 3.1 g / cm 3 .

24. The positive electrode active material according to any one of claims 14 to 23, characterized in that, The positive electrode active material satisfies one or more of the following conditions: 1) The chemical formula of the lithium-containing transition metal oxide material is: Li a Ni m Mn j M n O (4-c) , 0.8≤a≤1.2, m≥0, 2≥j>0, 0≤c≤0.5, 0≤n<2, m+j+n≤2, M includes one or more of Sb, Al, Ti, Mg, V, Cr, Zr, Nb and W; 2) The specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g to 2m 2 / g; 3) The compacted density of the positive electrode active material powder is 2.6 g / cm³. 3 Up to 2.9 g / cm 3 .

25. A method for preparing a positive electrode active material, comprising: An organic polymeric monomer is placed on the core surface, wherein the organic polymeric monomer comprises an alkyl silane phosphate or a mixture of a silane monomer and a phosphate ester; the core comprises a lithium-containing transition metal oxide material; The organic polymer monomer is subjected to a crosslinking reaction to obtain a positive electrode active material, the positive electrode active material comprising a polymer at least partially located on the surface of the core, the main chain of the polymer containing POP bonds.

26. The preparation method according to claim 25, characterized in that, The alkyl silane phosphate includes one or more of trimethylsilane phosphate, triethylsilane phosphate, tributylsilane phosphate, triisopropylsilane phosphate, dimethyl ethylsilane phosphate, and trimethylsilane polyphosphate.

27. The preparation method according to claim 25, characterized in that, The mixture of the silane monomer and the phosphate ester satisfies one or more of the following conditions: 1) The silane monomer comprises one or more of the following: methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, KH570, KH560, KH550, trimethylchlorosilane, triethylchlorosilane, tributylchlorosilane, triisopropylchlorosilane, trimethylsilanol, triethylsilanol, tributylsilanol, triisopropylsilanol, methyldiethylsilanol, dimethylethylsilanol, dimethylsilanediol, diethylsilanediol, methylethylsilanediol, and hexamethylsilazaneamine; 2) The phosphate ester includes one or more of trimethyl phosphate, triethyl phosphate, tributyl phosphate, methyl polyphosphate, polyethylene glycol phosphate, tris(trimethylsilane) phosphate, and trimethylsilane polyphosphate.

28. A battery device, characterized in that, The lithium battery cell includes any one of the lithium battery cells described in claims 1 to 13, or a lithium battery cell prepared by the positive electrode active material described in any one of claims 14 to 24 or the positive electrode active material prepared by the preparation method described in any one of claims 25 to 27.

29. An electrical appliance, characterized in that, Includes the battery device as described in claim 28.

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