Positive electrode active material and preparation method thereof, positive electrode plate, battery monomer, battery and electric device

Abstract

The invention discloses a positive active material and a preparation method thereof, a positive pole piece, a battery monomer, a battery and an electric device, and belongs to the technical field of batteries. The positive electrode active material comprises lithium-containing phosphate, the chemical formula of the lithium-containing phosphate is Li < 1 + a > Fe < 1-x-y-z > Ni < x > Sn < y > M < z > PO4, and 0 < = a < = 0.2, 0 lt; xlt; 1, 0lt; yt; Yt; 1, 0 < = zlt; 1, x + y + zlt; m comprises at least one of transition metal elements. The technical scheme provided by the embodiment of the invention is beneficial to improving the energy density and the cycle performance of the battery monomer.

Description

Technical Field

[0001] The present application relates to the technical field of batteries, and particularly to a positive electrode active material, a preparation method thereof, a positive electrode plate, a battery cell, a battery, and an electrical device. Background Art

[0002] With the increasing aggravation of environmental pollution, the new energy industry has attracted more and more attention. In the new energy industry, battery technology is an important factor related to its development.

[0003] The development of battery technology needs to consider various design factors, such as energy density, cycle performance, reliability, etc. The positive electrode active material in a battery cell is crucial for the energy density and cycle performance of the battery cell. Therefore, how to provide a positive electrode active material to improve the energy density and cycle performance of the battery cell is a technical problem to be solved urgently. Summary of the Invention

[0004] The present application is made in view of the above problems, and its purpose is to provide a positive electrode active material to improve the energy density and cycle performance of a battery cell.

[0005] To achieve the above purpose, the present application provides a positive electrode active material, a preparation method thereof, a positive electrode plate, a battery cell, a battery, and an electrical device.

[0006] In a first aspect, a positive electrode active material is provided, including: a lithium-containing phosphate, and the chemical formula of the lithium-containing phosphate is Li 1+a Fe 1-x-y-z Ni x Sn y M z PO4, where 0 ≤ a ≤ 0.2, 0 < x < 1, 0 < y < 1, 0 ≤ z < 1, x + y + z < 1, and M includes at least one of transition metal elements.

[0007] An embodiment of the present application provides a positive electrode active material, which includes a lithium-containing phosphate, and the chemical formula of the lithium-containing phosphate is Li 1+a Fe 1-x-y-z Ni x Sn y M z PO4, and 0 ≤ a ≤ 0.2, 0 < x < 1, 0 < y < 1, 0 ≤ z < 1, x + y + z < 1. By adding Ni element and Sn element to the lithium-containing phosphate, it is beneficial to improve the voltage platform and stability of the positive electrode active material, thereby being beneficial to improving the energy density and cycle performance of the battery cell.

[0008] In a possible implementation, 0.005≤x≤0.05. By setting x to satisfy the above range, it is not only convenient to dope the nickel element, but also the Ni element in the lithium-containing phosphate can have a suitable content, thereby reducing the risk of generating impurities such as nickel phosphide, thereby reducing the risk of reducing the reversible capacity of the battery cell. Optionally, 0.01≤x≤0.03. In this way, the risk of generating impurities such as nickel phosphide can be further reduced.

[0009] In a possible implementation, 0.002≤y≤0.03. By setting y to satisfy the above range, it is not only convenient to dope the tin element, but also the Sn element in the lithium-containing phosphate can have a suitable content, thereby reducing the risk of generating heterogeneous LiSnPO4, thereby reducing the risk of decreased dynamic performance and energy density of the battery cell. Optionally, 0.005≤y≤0.02. In this way, the risk of generating heterogeneous LiSnPO4 can be further reduced.

[0010] In one possible implementation, 0≤z≤0.01.

[0011] In one possible implementation, 0 <x+y+z≤0.03。

[0012] In the above technical solution, by setting the range of z, and / or the range of x+y+z, the Ni element, Sn element, and M element doped in the lithium-containing phosphate have appropriate contents, so that the Fe element in the lithium-containing phosphate has a more appropriate content, which is beneficial for the lithium-containing phosphate and the lithium iron phosphate to have the same or substantially the same crystal structure.

[0013] In a possible implementation, M includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Sr, Nb, V or Ti. By doping the lithium-containing phosphate with the corresponding M element, it is beneficial to improve the ionic conductivity, reversible capacity, kinetics and other properties of the battery cell.

[0014] In a possible implementation, the Ni element occupies at least part of the Fe position in the lithium-containing phosphate, and the Fe position is the Fe 2+ In this way, Ni 2+ At least part of the Fe sites can be occupied by solid solution substitution. On the one hand, it is beneficial to increase the electrode potential of the positive electrode active material, thereby increasing the voltage platform of the positive electrode active material; on the other hand, the lithium phosphate doped with Ni element has basically the same crystal structure as lithium iron phosphate, which can reduce the risk of producing LiNiPO4, thereby reducing the risk of the electrolyte being difficult to work stably due to the excessively high voltage platform of LiNiPO4.

[0015] In a possible implementation, the Sn element is located within the unit cell of the lithium-containing phosphate. This is beneficial for increasing the potential energy required for the dissolution of Ni 2+ and Fe 2+ Thereby, it is beneficial to improve the stability of the positive electrode active material and the cycle life of the battery cell; in addition, it is also beneficial to reduce the risk of generating the impurity phase LiSnPO4.

[0016] In a possible implementation, based on the total mass of the positive electrode active material, the mass content A of Ni e P in the positive electrode active material satisfies: A < 0.1 wt%, 0 < e < 2.4. In this way, there is very little or almost no Ni e P impurity in the positive electrode active material, thereby reducing the influence of the Ni e P impurity on the reversible capacity of the battery cell.

[0017] In a possible implementation, the specific surface area S of the positive electrode active material satisfies: 9.5 m 2 / g ≤ S ≤ 14.56 m 2 / g. In this way, the specific surface area of the positive electrode active material is relatively large, which is beneficial to improving the rate performance of the battery cell.

[0018] In a possible implementation, the volume average particle size Dv50 of the positive electrode active material satisfies: 0.61 μm ≤ Dv50 ≤ 1.80 μm. In this way, the particle size of the positive electrode active material is relatively small, which is beneficial to improving the rate performance of the battery cell.

[0019] In a possible implementation, the positive electrode active material further includes a carbon material, and the carbon material is located on the outer surface of the lithium-containing phosphate and coats the lithium-containing phosphate. In this way, the positive electrode active material has good electrical conductivity.

[0020] In a possible implementation, based on the total mass of the positive electrode active material, the mass content B of the carbon material satisfies: 0.99 wt% ≤ B ≤ 1.31 wt%. In this way, in the positive electrode active material, the carbon material has a relatively appropriate mass content, and the battery cell has good electrical conductivity.

[0021] In a second aspect, a method for preparing the positive electrode active material according to the first aspect and any one of its possible implementations is provided, including: adding lithium carbonate, phosphoric acid, iron, nickel oxide, and tin oxide into a solvent to obtain an intermediate product; performing a sintering treatment on the intermediate product to obtain the positive electrode active material. Through this method, the positive electrode active material of the embodiments of the present application can be prepared, and the positive electrode active material has a high energy density and good cycle performance.

[0022] In a possible implementation, the sintering the intermediate product to obtain the positive electrode active material includes: performing a first sintering treatment and a second sintering treatment on the intermediate product to obtain the positive electrode active material. The two sintering treatments are convenient for reducing defects in the positive electrode active material and are also conducive to increasing the compaction density of the positive electrode active material.

[0023] In a possible implementation, the temperature and time of the first sintering treatment and the second sintering treatment are the same, so as to simplify the preparation process of the positive electrode active material and reduce the preparation complexity of the positive electrode active material.

[0024] In a possible implementation, the sintering temperature T satisfies: 750°C ≤ T ≤ 800°C; and / or the sintering time t satisfies: 6h ≤ t ≤ 10h. In this way, the raw materials can react fully to generate the corresponding positive electrode active material.

[0025] In a possible implementation, the solvent includes nitric acid. In this way, nickel oxide, iron, tin oxide, lithium carbonate, etc. are easily dissolved in nitric acid to generate corresponding ions and generate intermediate products through reaction; and nitrate ions in nitric acid are easily removed, which can reduce the risk of introducing impurity ions into the positive electrode active material.

[0026] In a third aspect, a positive electrode plate is provided, comprising the positive electrode active material in the first aspect and any possible implementation thereof, and / or the positive electrode active material obtained by the preparation method in the second aspect and any possible implementation thereof.

[0027] In a fourth aspect, a battery cell is provided, comprising the positive electrode plate described in the third aspect.

[0028] In a fifth aspect, a battery is provided, comprising the battery cell described in the fourth aspect.

[0029] In a sixth aspect, an electrical device is provided, comprising the battery described in the fifth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0031] Figure 1 A schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application;

[0032] Figure 2A schematic diagram of a battery cell according to an embodiment of the present application;

[0033] Figure 3 A schematic diagram of a battery according to an embodiment of the present application;

[0034] Figure 4 A schematic diagram of an electrical device according to an embodiment of the present application;

[0035] Figure 5 Schematic diagram of XRD test results of positive electrode active materials of an embodiment of the present application and some comparative examples;

[0036] Figure 6 This is a SEM image of a pair of positive electrode active materials of this application;

[0037] Figure 7 This is a SEM image of a pair of positive electrode active materials of this application;

[0038] Figure 8 This is a SEM image of the positive electrode active material of one embodiment of the present application. DETAILED DESCRIPTION

[0039] The embodiments of the positive electrode active material and preparation method thereof, positive electrode sheet, battery cell, battery, and electrical device of the present application are specifically disclosed with appropriate reference to the drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of actually the same structure may be omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0040] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0043] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0044] Typically, a battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery cell, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, and at the same time to allow active ions to pass through. In some embodiments, the above-mentioned battery cell is also called a secondary battery, and the battery cell can be the smallest battery unit.

[0045] During the charging process of a lithium-ion battery, lithium ions are removed from the positive electrode active material, move and intercalate into the negative electrode material; during the discharging process, lithium ions are removed from the negative electrode material, move and intercalate into the positive electrode active material.

[0046] It should be understood that the "intercalation" process described in this application refers to the process in which lithium ions intercalate into the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the "removal" and "deintercalation" processes described in this application refer to the process in which lithium ions are removed from the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0047] The development of battery technology needs to consider multiple design factors simultaneously. For example, energy density, cycle performance, discharge capacity, charge-discharge rate, reliability, etc. A battery cell includes a positive electrode plate, and the performance of the positive electrode active material in the positive electrode plate is crucial for the capacity, cycle performance, and charge-discharge rate performance of the battery cell. As a lithium-containing phosphate, lithium iron phosphate is used as a positive electrode active material because of its low cost, strong reliability, and relatively excellent cycle performance. However, lithium iron phosphate has a low theoretical specific capacity and tap density, which is not conducive to improving the energy density of the battery cell. In some treatment methods, the energy density of the battery cell is increased by increasing the tap density and capacity utilization degree of lithium iron phosphate; in other treatment methods, the voltage platform of the positive electrode active material is increased by doping corresponding elements in lithium iron phosphate, thereby improving the energy density of the battery cell. However, which elements to dope to improve the energy density of the battery cell without affecting the cycle performance of the battery cell is a technical problem that亟待解决 (to be urgently solved).

[0048] In view of this, an embodiment of this application provides a positive electrode active material, which includes a lithium-containing phosphate doped with Sn element and Ni element. This positive electrode active material has a high voltage platform, which is beneficial to improving the energy density and cycle performance of the battery cell.

[0049] [Positive electrode active material]

[0050] An embodiment of this application provides a positive electrode active material, including: a lithium-containing phosphate, and the chemical formula of the lithium-containing phosphate is Li 1+a Fe 1-x-y-z Ni x Sn y M z PO4, where 0≤a≤0.2, 0<x<1, 0<y<1, 0≤z<1, x + y + z<1, and M includes at least one of transition metal elements.

[0051] The lithium-containing phosphate in the embodiment of the present application may be a material obtained by doping Ni and Sn into lithium iron phosphate, and the lithium-containing phosphate may have the same crystal structure as that of lithium iron phosphate.

[0052] The values ​​of x and y are both greater than 0, which means that Ni and Sn elements exist in the lithium-containing phosphate. z can be 0. When z is 0, the lithium-containing phosphate does not include the M element. x+y+z<1 means that the lithium-containing phosphate includes the Fe element.

[0053] a can be 0, 0.1, 0.2 or any value within the above range, x can be 0.01, 0.02, 0.05, 0.08 or any value within the above range, y can be 0.01, 0.02, 0.05, 0.08 or any value within the above range, and z can be 0, 0.01, 0.02, 0.05, 0.08 or any value within the above range.

[0054] M includes at least one transition metal element, for example, M includes at least one element such as Cr and Ti.

[0055] Ni 2+ , Fe 2+ The ionic radius of Ni 2+ , Fe 2+ The ionization energies of Ni 2+ It is easier to occupy Fe 2+ The position of the lithium iron phosphate is doped into the crystal lattice.

[0056] Ni 2+ After being doped with lithium iron phosphate, Ni-O bonds can be formed, which causes the Li-O bonds to become shorter, so that more energy is required for lithium ions to escape, the ionization energy of lithium ions increases, and the ionization potential of the positive electrode active material increases, thereby increasing the voltage platform of the positive electrode active material or the battery cell. The voltage platform of the positive electrode active material is related to the energy density of the battery cell. Generally speaking, the higher the voltage platform, the higher the energy density of the battery cell. Therefore, by doping Ni elements in lithium iron phosphate, the energy density of the battery cell can be improved.

[0057] Due to Li + and Ni 2+ The ionic radius of Fe is similar, and Li-Ni mixing is easy to occur during the preparation of positive electrode active materials and the charging and discharging process of battery cells. 2+ and Li + The ionic radius of Ni is also similar, which will further increase the risk of Li-Ni mixing on the basis of Li-Fe mixing. 2+ and Fe 2+After occupying the Li site (the Li site refers to the position of lithium ions in lithium iron phosphate), it will hinder the transmission of lithium ions, which is not conducive to the improvement of the performance of a single battery cell. For example, the transmission rate of lithium ions decreases, and the number of lithium ions that can be removed from the cathode active material becomes smaller. These may lead to a decline in the kinetic performance of a single battery cell and a smaller capacity that a single battery cell can exhibit.

[0058] Sn 2+ has an ionization energy close to that of Fe 2+ . The doping of Sn 2+ can reduce the unit cell parameters of lithium iron phosphate, so that the bond lengths of Ni-O, Li-O, and Fe-O become shorter, and Ni 2+ , Fe 2+ can be bound to their respective positions. The potential energy for Ni 2+ , Fe 2+ to dissolve out from the lattice of lithium-containing phosphate increases, so that the risk of Li-Ni mixing can be reduced. At the same time, it is also conducive to reducing the risk of Ni 2+ , Fe 2+ dissolving out. Therefore, by doping Sn 2+ in lithium-containing phosphate, the risk of Li-Ni mixing can be reduced, and at the same time, it is also conducive to improving the stability of lithium-containing phosphate and the cycle performance of a single battery cell.

[0059] An embodiment of the present application provides a cathode active material. The cathode active material includes lithium-containing phosphate, and the chemical formula of the lithium-containing phosphate is Li 1+a Fe 1-x-y-z Ni x Sn y M z PO4, and 0≤a≤0.2, 0<x<1, 0<y<1, 0≤z<1, x + y + z<1. By adding Ni elements and Sn elements to the lithium-containing phosphate, it is conducive to improving the voltage platform and stability of the cathode active material, thereby being conducive to improving the energy density and cycle performance of a single battery cell.

[0060] It should be noted that during the charge and discharge process of a single battery cell, the deintercalation and consumption of Li will occur, and the molar content of Li is different when the battery is discharged to different states. In the listing of the cathode active material in the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the cathode active material is applied to the battery system and undergoes charge and discharge cycles, the molar content of Li will change.

[0061] In the listing of the cathode active material in the present application, the molar content of O is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will show fluctuations. Similarly, the molar contents of P, Fe, Ni, Sn, and M are theoretical state values.

[0062] In some embodiments, 0.005 ≤ x ≤ 0.05. x can be 0.005, 0.01, 0.02, 0.03, 0.05, or any value within the above range.

[0063] x is greater than or equal to 0.005, so that the doping of nickel elements during the preparation process is facilitated, and the risk of increased doping difficulty caused by a small doping amount of nickel elements can be reduced; in addition, when x is greater than or equal to 0.005, the nickel element has a more appropriate doping amount, which is also beneficial to effectively improving the energy density of the battery cell.

[0064] When the doping amount of Ni is too high, the risk of generating nickel phosphide (such as Ni e P, 0 < e < 2.4) increases. By setting x ≤ 0.05, the Ni element in the lithium-containing phosphate has an appropriate content, thereby reducing the risk of generating Ni e P impurities, and thus reducing the risk of reducing the reversible capacity of the battery cell. In addition, when the Ni element has an appropriate content, the risk of generating LiNiPO4 due to excessive doping amount of Ni can also be reduced, thereby reducing the risk that the voltage platform of the positive electrode active material changes to the voltage platform of LiNiPO4 or the positive electrode active material has multiple voltage platforms.

[0065] Optionally, 0.01 ≤ x ≤ 0.03. In this way, the risk of generating impurities such as nickel phosphide can be further reduced.

[0066] In some embodiments, 0.002 ≤ y ≤ 0.03. y can be 0.002, 0.005, 0.01, 0.02, 0.03, or any value within the above range.

[0067] y is greater than or equal to 0.002, so that the doping of Sn elements during the preparation process is facilitated, and the risk of increased doping difficulty caused by a small doping amount of Sn elements can be reduced; in addition, when y is greater than or equal to 0.002, the Sn element has a more appropriate doping amount, which is beneficial to effectively improving the cycle performance of the battery cell.

[0068] When the doping amount of Sn is too high, the risk of generating a heterophase LiSnPO4 in the positive electrode active material increases. By setting y ≤ 0.03, the Sn element in the lithium-containing phosphate has an appropriate content, thereby reducing the risk of generating the heterophase LiSnPO4, and thus reducing the risk of deterioration of the kinetic performance and energy density of the battery cell.

[0069] Optionally, 0.005 ≤ y ≤ 0.02. In this way, the risk of generating the heterophase LiSnPO4 can be further reduced.

[0070] In some embodiments, Ni elements are uniformly doped in lithium iron phosphate. That is to say, Ni elements are uniformly distributed in lithium-containing phosphate. The uniform doping of Ni elements can be qualitatively and semi-quantitatively characterized by XRD and EDS, and the uniform doping of Ni elements is characterized by testing the distribution of Ni elements.

[0071] In some embodiments, 0≤z≤0.01. z can be 0.005, 0.01 or any value within the above range.

[0072] In some embodiments, 0<x + y + z≤0.03. x + y + z can be 0.01, 0.02, 0.03 or any value within the above range.

[0073] In the above embodiments, by setting the range of z and / or the range of x + y + z, the Ni elements, Sn elements, and M elements doped in the lithium-containing phosphate have appropriate contents, so that the Fe elements in the lithium-containing phosphate have relatively appropriate contents, which is conducive to making the lithium-containing phosphate have the same or substantially the same crystal structure as lithium iron phosphate.

[0074] In some embodiments, M includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Sr, Nb, V or Ti. By doping the corresponding M element in the lithium-containing phosphate, it is beneficial to improve the performance of the battery monomer such as ionic conductivity, reversible capacity, and kinetics.

[0075] In some embodiments, Ni elements occupy at least part of the Fe sites in the lithium-containing phosphate, and the Fe sites are the Fe in the lithium-containing phosphate 2+ positions.

[0076] Ni 2+ can occupy at least part of the Fe sites by solid solution substitution. On the one hand, it is beneficial to increase the electrode potential of the positive electrode active material, and then increase the voltage platform of the positive electrode active material; on the other hand, the lithium-containing phosphate doped with Ni elements has substantially the same crystal structure as lithium iron phosphate, which can reduce the risk of generating LiNiPO4, thereby reducing the risk that the electrolyte is difficult to work stably due to the too high voltage platform of LiNiPO4.

[0077] For example, for pure-phase LiNiPO4, its voltage platform is about 4.5V. At a voltage of 4.5V, the electrolyte is easily oxidized, and the cycle life of the battery monomer is poor, which is not conducive to the use of the battery monomer.

[0078] In some embodiments, Sn elements are located inside the unit cell of the lithium-containing phosphate. That is to say, Sn elements are doped into the unit cell of lithium iron phosphate, and Sn elements are not located at the grain boundaries.

[0079] The Sn element is located within the unit cell of the lithium-containing phosphate, which is beneficial to increasing the potential energy required for the dissolution of Ni 2+ and Fe 2+ Thereby, it is beneficial to improving the stability of the cathode active material and the cycle life of the battery cell. In addition, it is also beneficial to reducing the risk of generating the impurity phase LiSnPO4.

[0080] In some embodiments, based on the total mass of the cathode active material, the mass content A of Ni e P in the cathode active material satisfies: A < 0.1 wt%, 0 < e < 2.4. In this way, there is very little or almost no Ni e P impurity in the cathode active material, thereby reducing the influence of the Ni e P impurity on the reversible capacity of the battery cell.

[0081] Optionally, when x is less than or equal to 0.05, A is less than 0.1%; further, when x is less than or equal to 0.03, A is 0.

[0082] In some embodiments, the specific surface area S of the cathode active material satisfies: 9.5 m 2 / g ≤ S ≤ 14.56 m 2 / g. For example, S is 9.5 m 2 / g, 10 m 2 / g, 12 m 2 / g, 14.56 m 2 / g or any value within the above range. In this way, the specific surface area of the cathode active material is relatively large, which is beneficial to improving the rate performance of the battery cell.

[0083] In some embodiments, the volume average particle size Dv50 of the cathode active material satisfies: 0.61 μm ≤ Dv50 ≤ 1.80 μm. For example, Dv50 is 0.61 μm, 1 μm, 1.80 μm or any value within the above range. In this way, the particle size of the cathode active material is relatively small, which is beneficial to improving the rate performance of the battery cell.

[0084] In some embodiments, the cathode active material further includes a carbon material, and the carbon material is located on the outer surface of the lithium-containing phosphate and coats the lithium-containing phosphate.

[0085] The cathode active material may have a core-shell structure, with the core being the lithium-containing phosphate and the outer surface being a carbon coating layer of the carbon material, and the carbon coating layer coats the outer surface of the lithium-containing phosphate. In this way, the cathode active material has a lower powder resistivity and higher conductivity, which is beneficial to forming a complete conductive network between the particles of the cathode active material and inside the electrode sheet, beneficial to improving the long-term cycle life of the battery cell, and also beneficial to the battery cell to exhibit a higher capacity.

[0086] In some embodiments, based on the total mass of the positive electrode active material, the mass content B of the carbon material is 0.99wt% to 1.31wt%. For example, B is 0.99wt%, 1.2wt%, 1.31wt% or any value within the above range. Accordingly, the powder resistivity of the positive electrode active material can be less than or equal to 100Ω.cm.

[0087] In some embodiments, the positive electrode active material may include particles with a volume average particle size of 50 to 200 nm and 0.5 to 5 μm. In other words, the positive electrode active material includes positive electrode active materials with larger particle sizes and positive electrode active materials with smaller particle sizes. The combination of positive electrode active materials with larger particle sizes and smaller particle sizes is conducive to improving the compaction density of the positive electrode active material, thereby helping to improve the energy density of the battery cell.

[0088] In some embodiments, the powder compaction density of the positive electrode active material may be greater than 2.40 g / cc, wherein the compaction density is the density after being pressed under a pressure of 3T.

[0089] [Method for preparing positive electrode active material]

[0090] The present application provides a method for preparing a positive electrode active material. Figure 1 Schematic diagram of a method for preparing a positive electrode active material according to an embodiment of the present application. Figure 1 As shown, the preparation method 100 includes the following steps. The preparation method 100 can be used to prepare the positive electrode active material in any of the above embodiments.

[0091] Step 110, adding lithium carbonate, phosphoric acid, iron, nickel oxide, and tin oxide into a solvent to obtain an intermediate product.

[0092] In some embodiments, the solvent includes an acidic solution, such as a nitric acid solution. As an example, the nitric acid solution is a nitric acid solution with a concentration of 60%.

[0093] The above materials can be dissolved in a solvent (e.g., nitric acid solution), and after being fully dissolved, a solution containing Li, Fe, Ni, and Sn ions can be obtained. Afterwards, the solution is placed in a beaker, and the beaker is heated to decompose the ions (e.g., nitrate ions) in the solvent, and evaporate the water in the solution, and then a dry gel mixture is obtained. Among them, the dry gel mixture is a mixture of Li, Fe, Ni, and Sn elements.

[0094] As an example, the solvent may be removed during the heating process, thereby reducing the risk of introducing unwanted impurities into the intermediate product.

[0095] Optionally, glucose may be added in step 110. Glucose serves as a carbon source to facilitate subsequent preparation of a carbon coating layer on the surface of the lithium phosphate.

[0096] Step 120: sintering the intermediate product to obtain a positive electrode active material.

[0097] The intermediate product may be the obtained dry gel mixture. As an example, the dry gel mixture is crushed, and then the crushed product is placed in a graphite sagger and sintered at a certain temperature for a certain time in a roller kiln.

[0098] Optionally, in step 120 , the lithium-containing phosphate may be coated with a carbon material by a vapor phase chemical deposition (CVD) method to prepare a positive electrode active material including a carbon coating layer.

[0099] As an example, sintering is performed in an inert atmosphere, for example, nitrogen is introduced at a rate of 4 L / min, and this rate is maintained throughout the entire sintering process of heating, heat preservation, and cooling.

[0100] The positive electrode active material of the embodiment of the present application can be prepared by the method 100 , and the positive electrode active material has a higher energy density and better cycle performance.

[0101] In some embodiments, the intermediate product is subjected to a sintering treatment to obtain a positive electrode active material, including: performing a first sintering treatment and a second sintering treatment on the intermediate product to obtain the positive electrode active material.

[0102] As an example, the intermediate product is first subjected to a first sintering treatment, and then the product after the first sintering treatment is subjected to a second sintering treatment. Specifically, after the first sintering treatment, the product after the first sintering treatment is crushed and placed in a graphite crucible again for a second sintering treatment.

[0103] That is, the intermediate product is sintered twice to obtain the positive electrode active material.

[0104] The conditions of the first sintering process and the second sintering process (for example, sintering atmosphere, temperature, and time) may be the same or different.

[0105] Through the two sintering treatments, it is convenient to reduce the defects in the positive electrode active material, and it is also beneficial to improve the compaction density of the positive electrode active material.

[0106] In some embodiments, the temperature and time of the first sintering process and the second sintering process are the same. In this way, the preparation process of the positive electrode active material is simplified and the preparation complexity of the positive electrode active material is reduced.

[0107] As an example, the atmosphere of the first sintering process and the second sintering process is nitrogen, the sintering time is 10 hours, and the sintering temperature is 750°C.

[0108] In some embodiments, the sintering temperature T satisfies: 750° C. ≤ T ≤ 800° C., and / or the sintering time t satisfies: 6 h ≤ t ≤ 10 h, so as to facilitate sufficient reaction between the raw materials to generate the corresponding positive electrode active material.

[0109] The temperature T may be 750° C., 780° C., 800° C. or any value within the above range, and the time t may be 6 h, 8 h, 10 h or any value within the above range.

[0110] When the sintering temperature T is not less than 750°C, it is beneficial to improve the compaction density of the positive electrode active material; when the sintering temperature T does not exceed 800°C, the particles of the positive electrode active material have a suitable size, which is beneficial to reduce the risk of the positive electrode active material particles being too large.

[0111] In some embodiments, the solvent includes nitric acid. In this way, nickel oxide, iron, tin oxide, lithium carbonate, etc. are easily dissolved and uniformly mixed in the nitric acid solution; and the nitrate in the nitric acid is easy to remove (for example, the nitrate is decomposed by heat, so that it is easy to remove in the solution), which can reduce the risk of introducing impurity ions into the positive electrode active material.

[0112] [Positive electrode]

[0113] An embodiment of the present application provides a positive electrode plate, comprising the positive electrode active material in any of the above embodiments, and / or the positive electrode active material prepared by the preparation method in any of the above embodiments.

[0114] The positive electrode plate includes a positive electrode current collector and a positive electrode film layer arranged on the positive electrode current collector, and the positive electrode film layer includes a positive electrode active material.

[0115] The positive electrode current collector may be a metal foil or a composite current collector. For example, the positive electrode current collector may be an aluminum foil.

[0116] The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0117] The positive electrode film layer may also optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0118] The positive electrode film layer may also optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0119] [Negative electrode]

[0120] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on the negative electrode current collector.

[0121] The negative electrode current collector may be a metal foil or a composite current collector. The negative electrode current collector may be a copper foil. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0122] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0123] The negative electrode film layer may also optionally include a conductive agent, which may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0124] [Electrolytes]

[0125] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application embodiment has no specific restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0126] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0127] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorobisoxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0128] The solvent may include at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0129] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and may also include performance additives that can improve certain battery properties, such as improving battery overcharge performance, improving battery high temperature or low temperature performance, etc.

[0130] [Isolator]

[0131] The separator is used to separate the positive electrode sheet from the negative electrode sheet. The embodiment of the present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

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

[0133] The positive electrode sheet, the negative electrode sheet and the separator can be made into an electrode assembly through a winding process or a lamination process.

[0134] [Battery Cell]

[0135] An embodiment of the present application provides a battery cell, comprising the positive electrode plate in the above embodiment.

[0136] The embodiment of the present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. The battery cell may be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, etc.

[0137] Figure 2 FIG. 1 is a schematic diagram of a battery cell according to an embodiment of the present application. Figure 2 As shown, the battery cell 3 includes a shell 31 , an end cover assembly 32 and an electrode assembly 33 . The electrode assembly 33 is disposed in the shell 31 , and the end cover assembly 32 is used to cover the shell 31 .

[0138] The end cap assembly 32 includes an electrode terminal 322, such as Figure 2 As shown, the end cap assembly 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0139] The electrode assembly 33 includes an electrode assembly body 331 and a tab 332 extending from the electrode assembly body 331 . The electrode assembly 33 can be made of a positive electrode sheet, a negative electrode sheet and a separator by a winding process or a lamination process.

[0140] The battery cell 3 further includes a current collecting member 34, which is used to connect the electrode tab 332 of the electrode assembly 33 and the electrode terminal 322. Figure 3 As shown, the battery cell 3 includes two current collecting members 34 , one current collecting member 34 is used to connect the positive electrode tab and the positive electrode terminal, and the other current collecting member 34 is used to connect the negative electrode tab and the negative electrode terminal.

[0141] In some embodiments, battery cells may be assembled into a battery module. The number of battery cells contained in the battery module may be one or more. The specific number may be selected by those skilled in the art according to the application and capacity of the battery module.

[0142] [Battery]

[0143] An embodiment of the present application provides a battery, comprising the battery cell in the above embodiment. Figure 3 Schematic diagram of a battery according to an embodiment of the present application. Figure 3 As shown, the battery 5 may include a plurality of battery cells (not shown in the figure).

[0144] The battery cells 3 can directly form the battery 5 , or can first form a battery module, and then multiple battery modules form the battery 5 .

[0145] [Electrical devices]

[0146] An embodiment of the present application provides an electrical device, comprising the battery described in the above embodiment.

[0147] Figure 4 FIG. 1 is a schematic diagram of an electrical device according to an embodiment of the present application. Figure 4 As shown, the present application provides an electrical device 6, including the battery in the above embodiment.

[0148] Optionally, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc. The embodiments of the present application include but are not limited to these.

[0149] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0150] [Example]

[0151] Example 1

[0152] In Example 1, a positive electrode active material is provided. The positive electrode active material is a lithium-containing phosphate having a carbon coating layer. The chemical formula of the lithium-containing phosphate is Li 1.002 Fe 0.985 Ni 0.01 Sn 0.005 PO4, based on the total mass of the positive electrode active material, the mass content of the carbon coating layer is 1.15wt%.

[0153] In Example 1, the preparation method of the positive electrode active material is as follows:

[0154] (1) Li2CO3, phosphoric acid, glucose, Fe powder, NiO, and SnO are added into a nitric acid solution with a concentration of 60% according to a corresponding ratio (the ratio can be set according to the ratio of each element of the prepared lithium phosphate) and after being fully dissolved, a nitric acid solution containing Li, Fe, Ni, Sn elements and PO4 is obtained. 3- A uniform nitric acid solution;

[0155] (2) placing the above solution in a beaker and heating the beaker to evaporate the water and release heat by decomposing the nitrate, thereby accelerating the decomposition reaction of the nitrate. Finally, all the solution is evaporated to obtain a uniform dry gel mixture;

[0156] (3) The dry gel mixture is simply crushed and placed in a graphite sagger, and sintered at a constant temperature of 760° C. for 8 h in a roller kiln, and simultaneously subjected to CVD treatment to coat the surface of the lithium phosphate with a carbon coating layer; wherein the nitrogen gas is introduced at a rate of 4 L / min throughout the entire sintering process of heating, heat preservation, and cooling; the mass content of the carbon coating layer in the positive electrode active material after the first sintering is approximately 1.05-1.10%;

[0157] (4) The product of the primary sintering is crushed and placed back in a graphite crucible for secondary sintering, and CVD treatment is simultaneously performed to prepare a carbon coating layer. The sintering atmosphere conditions are consistent with those of the primary sintering. The mass content of the carbon coating layer of the positive electrode active material after the secondary sintering is approximately 1.15-1.20%. The product of the secondary sintering is crushed to obtain the positive electrode active material in the embodiment.

[0158] Embodiment 2-5

[0159] The difference between Examples 2-5 and Example 1 is that the doping amount of Ni element in the lithium-containing phosphate is different. x is 0.005, 0.02, 0.03, and 0.05 respectively.

[0160] Embodiment 6-9

[0161] The difference between Examples 6-9 and Example 1 is that the doping amount of Sn element in the lithium-containing phosphate is different. y is 0.002, 0.01, 0.02, and 0.03 respectively.

[0162] Examples 10-12

[0163] The difference between Example 10 and Example 1 is that the lithium-containing phosphate is doped with Ti and V. The doping amount of Ti is 0.002, and the doping amount of V is 0.0005. In the process of preparing the positive electrode active material, TiO2 and V2O5 are also added in step (1).

[0164] The difference between Example 11 and Example 1 is that the lithium-containing phosphate is doped with Ti element, wherein the doping amount of Ti element is 0.005. In the process of preparing the positive electrode active material, TiO2 is also added in step (1).

[0165] The difference between Example 12 and Example 1 is that the lithium-containing phosphate is doped with Mn element, wherein the doping amount of Mn element is 0.005. In the process of preparing the positive electrode active material, in step (1), Mn oxide is also added.

[0166] The preparation methods of the positive electrode active materials of Examples 2-12 can refer to the preparation method of the positive electrode active material of Example 1, and will not be described in detail here.

[0167] Examples 13-14

[0168] The difference between Example 13-14 and Example 1 is that the sintering temperatures are different, and the sintering temperatures are 720° C. and 820° C. respectively.

[0169] Comparative Example 1

[0170] In Comparative Example 1, the positive electrode active material is lithium iron phosphate with a carbon coating layer, and the positive electrode active material is not doped with Ni element and Sn element.

[0171] Comparative Example 2

[0172] The difference between Comparative Example 2 and Example 1 is that only Ni element is doped, and Sn element is not doped.

[0173] Comparative Example 3

[0174] The difference between Comparative Example 3 and Example 1 is that only Sn element is doped, and Ni element is not doped.

[0175] Table 1 Parameters of positive electrode active materials of Examples and Comparative Examples

[0176]

[0177] Table 2 Test results of embodiments and comparative examples

[0178]

[0179]

[0180] [Preparation of battery cells]

[0181] (1) Preparation of positive electrode sheets: A slurry is prepared with a mass ratio of positive electrode active material, conductive agent super-P and carbon nanotubes CNT, and binder PVDF of 95:1.5:0.5:3, and coated on a 13 μm aluminum foil. The positive electrode sheets are obtained after vacuum drying at 120°C, cold pressing, and cutting into strips.

[0182] (2) Preparation of negative electrode sheets: artificial graphite and hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 90:5:2:2:1, and the mixture is stirred thoroughly to prepare a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector copper foil, and then dried, cold pressed, and cut to obtain a negative electrode sheet.

[0183] (3) Isolation film: polyethylene film is used.

[0184] (4) Preparation of lithium-ion battery cells: stack and wind the above-mentioned positive electrode sheets, separators, and negative electrode sheets in order to obtain an electrode assembly; place the electrode assembly in an outer package, add an electrolyte solution whose electrolyte salt is lithium hexafluorophosphate, and obtain a lithium-ion battery cell after packaging, standing, forming, aging, and other processes.

[0185] [Powder compaction density test of positive electrode active material]

[0186] As an example, the compaction density of the powder of the positive electrode active material can be measured at a pressure of 3T using a UTM7305 compaction density analyzer produced by Sansi Zongheng Technology Co., Ltd.

[0187] Specifically, as an example, 1g of positive electrode active material is weighed and added to a cylindrical mold, and the cross-sectional area of ​​the circular hole of the mold is S. A pressure of 3T is applied to the powder in the mold, and the pressure is maintained for 30s, and the thickness of the powder is recorded as t. The powder compaction density of the positive electrode active material can be calculated by the following formula: ρ = m / (S×t), where ρ is the compaction density, m is the mass of the positive electrode active material, S is the cross-sectional area of ​​the circular hole of the mold, and t is the thickness of the powder.

[0188] [Test of discharge gram capacity of positive electrode active materials]

[0189] A button-type half-cell is prepared using the positive electrode active material, and the button-type half-cell is tested. (Specifically, a positive electrode sheet is prepared using the positive electrode active material, and a lithium sheet is used as a negative electrode sheet to prepare a button-type half-cell)

[0190] The button half-cell was placed in an oven at 25°C for 2 h, and then the charge and discharge test was performed.

[0191] The 0.1C charge and discharge process is as follows: 0.1C constant current charging to 3.65V, continue constant voltage charging until the charging current is less than 0.05C and then cut off; pause for 5 minutes; 0.1C constant current discharge to 2.0V, the discharge capacity of this step is the discharge gram capacity of the positive electrode active material.

[0192] [Testing of discharge capacity, voltage platform and energy density of battery cells]

[0193] A lithium-ion battery cell (secondary battery) is prepared using the positive electrode active material, and the lithium-ion battery cell is tested.

[0194] The lithium-ion battery cells were placed in a 25°C oven, left to stand for 2 hours, and then the charge and discharge tests were performed.

[0195] The charge and discharge process is as follows: 0.33C constant current charging to 3.65V, continue constant voltage charging until the charging current is less than 0.05C, then stop; pause for 30 minutes; 0.33C constant current discharge to 2.0V; pause for 30 minutes. The above is the charge and discharge of the battery once.

[0196] After repeating three times, take the last discharge capacity, which is the discharge gram capacity of the lithium-ion battery cell at 0.33C.

[0197] Voltage platform = third discharge energy / discharge capacity. Discharge energy and discharge capacity can be measured by a test device connected to a lithium-ion battery cell.

[0198] Cell mass energy density (Wh / kg) = energy of the third discharge / mass of the positive electrode active material in the battery.

[0199] [XRD test]

[0200] The XRD spectra of each positive electrode active material were tested using X-ray diffraction equipment.

[0201] [Battery cell cycle performance test]

[0202] The lithium-ion battery cells were placed in a 60°C oven, left to stand for 2 hours, and then subjected to charge and discharge tests.

[0203] A charge and discharge cycle process is as follows: 0.33C constant current charging to 3.65V, continue constant voltage charging until the charging current is less than 0.05C and then cut off; pause for 30 minutes; 0.33C constant current discharge to 2.0V; pause for 30 minutes. The above is a charge and discharge cycle of the battery, which is repeated continuously until the battery capacity decays to 80% of the initial value, and the number of cycles is recorded.

[0204] As shown in Examples 1-14 and Comparative Example 1, the positive electrode active material in the examples of the present application includes a lithium-containing phosphate, and the lithium-containing phosphate includes Ni and Sn elements, while the lithium-containing phosphate in Comparative Example 1 is lithium iron phosphate, and the lithium-containing phosphate in Comparative Example 1 does not include Ni and Sn elements. By doping Ni and Sn elements in lithium iron phosphate, the voltage platform of the positive electrode active material is improved, the energy density of the battery cell is improved, and the battery cell also has a higher cycle life.

[0205] As shown in Examples 1-14 and Comparative Examples 2-3, it is difficult to take into account both the energy density and cycle life of the battery cell by doping the Ni element alone or the Sn element alone.

[0206] As shown in Examples 1-5, when x is in the range of 0.005 to 0.05, the Ni element has a suitable doping amount, and the battery cell can have a higher energy density and a longer cycle life. Further, when x is in the range of 0.01 to 0.03, the generation of Ni can be further reduced while the battery cell has a higher energy density and a longer cycle life. e Risk of P impurities.

[0207] As shown in Examples 6-9, when y is in the range of 0.002 to 0.03, the Sn element has a suitable doping amount, and the battery cell can have a higher energy density and cycle life. Further, when y is in the range of 0.005 to 0.02, the risk of generating impure phase LiSnPO4 can be further reduced while the battery cell has a higher energy density and a longer cycle life.

[0208] Figure 5The following is a schematic diagram of the XRD test results of an embodiment and a comparative example of the present application. Figure 5 As shown, the XRD curves of Example 1 and Comparative Examples 1-2 are substantially the same, that is, in Example 1, no new phase appears in the lithium-containing phosphate, that is, the lithium-containing phosphate is a single phase and has the same or substantially the same lattice structure as lithium iron phosphate, which can also reflect that Ni does not appear in the positive electrode active material. e P impurities and impurity phase LiSnPO4; and it can also reflect that both Ni and Sn elements appear in the crystal cell containing lithium iron phosphate.

[0209] Figure 6 This is a SEM image of a pair of positive electrode active materials of this application. Figure 7 This is a SEM image of a pair of positive electrode active materials of this application. Figure 8 is a SEM image of the positive electrode active material of an embodiment of the present application. Figure 6 As shown, Figure 6 The SEM image of lithium iron phosphate without Ni and Sn elements is shown; Figure 7 As shown, Figure 7 The SEM image of the positive electrode active material doped with Ni is shown. It can be seen from the image that after doping with Ni, the grains are refined and the particle size of the particles of the positive electrode active material becomes smaller. Figure 8 As shown, after doping with Ni and Sn elements, the particle size of the positive electrode active material particles is smaller than that of the positive electrode active material of Comparative Example 1. In addition, in combination with Examples 1-12, the positive electrode active material of the embodiment of the present application has a smaller volume average particle size and a larger specific surface area than that of the comparative example.

[0210] As shown in Examples 10-11, elements such as Ti, V, and Mn may be doped into the lithium-containing phosphate, thereby further improving the kinetic properties of the positive electrode active material, for example, the discharge capacity in grams may be improved.

[0211] As shown in Example 13, when the sintering temperature is 720°C, the compaction density of the prepared positive electrode active material is relatively small; as shown in Example 14, when the sintering temperature is 820°C, the tendency of the lithium-containing phosphate crystals to grow increases, the particle size of the positive electrode active material particles tends to increase, and the cycle life of the battery cell is improved less. And after testing the positive electrode active materials of Examples 13 and 14 prepared into battery cells, it was found that the energy density of the battery cell was improved less. Therefore, in combination with Examples 1-12 and Examples 13-14, it can be seen that by setting the sintering temperature at 750°C to 800°C, specifically, it can be set at 760°C to 780°C, it is beneficial to obtain positive electrode active materials with higher compaction density, and battery cells with higher energy density and longer cycle life.

[0212] In the embodiment of the present application, the voltage platform corresponding to the positive electrode active material may be greater than 3.2V, and the voltage platform of the positive electrode active material in the comparative example may be about 3.1V. The voltage platform of the positive electrode active material in the embodiment is improved.

[0213] In addition, whether there is electrochemical dissolution of metal ions (such as nickel ions and ferrous ions) in the lithium-containing phosphate can be reflected by the test of cycle performance. By testing the cycle performance, it can be reflected whether the metal ions are electrochemically dissolved or how much they are electrochemically dissolved. Combined with the examples 1-12, the battery cell has a high cycle life, which can reflect that the Sn element can reduce the dissolution of metal ions in the positive electrode active material.

[0214] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A positive electrode active material, characterized in that: The positive electrode active material includes a lithium-containing phosphate, and the chemical formula of the lithium-containing phosphate is Li 1+a Fe 1-x-y-z Ni x Sn y M z PO4, where 0 ≤ a ≤ 0.2, 0 < x < 1, 0 < y < 1, 0 ≤ z < 1, x + y + z < 1, and M includes at least one of transition metal elements.

2. The positive electrode active material according to claim 1, characterized in that 0.005≤x≤0.05; optionally, 0.01≤x≤0.

03.

3. The positive electrode active material according to claim 1 or 2, characterized in that: 0.002≤y≤0.03; optionally, 0.005≤y≤0.

02.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that 0≤z≤0.01。 5. The positive electrode active material according to any one of claims 1 to 4, characterized in that 0 <x+y+z≤0.03。 6. The positive electrode active material according to any one of claims 1 to 5, characterized in that M includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Sr, Nb, V or Ti.

7. The positive electrode active material according to any one of claims 1 to 6, characterized in that The Ni element occupies at least part of the Fe site in the lithium-containing phosphate, and the Fe site is the Fe 2+ location.

8. The positive electrode active material according to any one of claims 1 to 7, characterized in that The Sn element is located in the unit cell of the lithium-containing phosphate.

9. The positive electrode active material according to any one of claims 1 to 8, characterized in that Based on the total mass of the positive electrode active material, the Ni in the positive electrode active material e P mass content A satisfies: A<0.1wt%, 0 <e<2.4。 10. The positive electrode active material according to any one of claims 1 to 9, characterized in that The specific surface area S of the positive electrode active material satisfies: 9.5 m 2 / g≤S≤14.56m 2 / g.

11. The positive electrode active material according to any one of claims 1 to 10, characterized in that The volume average particle size Dv50 of the positive electrode active material satisfies: 0.61 μm≤Dv50≤1.80 μm.

12. The positive electrode active material according to any one of claims 1 to 11, characterized in that The positive electrode active material further includes a carbon material, which is located on the outer surface of the lithium-containing phosphate and covers the lithium-containing phosphate.

13. The positive electrode active material according to claim 12, characterized in that: Based on the total mass of the positive electrode active material, the mass content B of the carbon material satisfies: 0.99 wt %≤B≤1.31 wt %.

14. A method for preparing a positive electrode active material according to any one of claims 1 to 13, characterized in that: include: adding lithium carbonate, phosphoric acid, iron, nickel oxide, and tin oxide into a solvent to obtain an intermediate product; The intermediate product is sintered to obtain the positive electrode active material.

15. The preparation method according to claim 14, characterized in that: The sintering treatment of the intermediate product to obtain the positive electrode active material comprises: The intermediate product is subjected to a first sintering process and a second sintering process to obtain the positive electrode active material.

16. The preparation method according to claim 15, characterized in that: The temperature and time of the first sintering process and the second sintering process are the same.

17. The preparation method according to any one of claims 14 to 16, characterized in that: The temperature T of the sintering treatment satisfies: 750° C. ≤ T ≤ 800° C., and / or the time t of the sintering treatment satisfies: 6h ≤ t ≤ 10h.

18. The preparation method according to any one of claims 14 to 17, characterized in that: The solvent includes nitric acid.

19. A positive electrode plate, characterized in that: include: A positive electrode active material according to any one of claims 1 to 13, and / or a positive electrode active material prepared by the preparation method according to any one of claims 14 to 18.

20. A battery cell, characterized in that: Comprising the positive electrode sheet as described in claim 19.

21. A battery, characterized in that: Comprising the battery cell as claimed in claim 20.

22. An electrical device, characterized in that: Comprising the battery of claim 21.

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