Positive electrode active material, method for manufacturing the same, positive electrode sheet, battery cell, battery, and electric device

Abstract

A positive electrode active material and a preparation method thereof, a positive electrode sheet, a battery monomer, a battery and a power utilization device, which belong to the technical field of batteries. The positive electrode active material comprises a lithium-containing phosphate, and a chemical formula of the lithium-containing phosphate is Li 1+a Fe 1‑x‑y‑z Ni x Sn y M z PO4, wherein 0<=a<=0.2, 0

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 sheet, a battery cell, a battery, and an electrical device. Background Art

[0002] With the increasing 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 sheet, 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 one possible implementation, 0.005 ≤ x ≤ 0.05. By setting x to satisfy this range, it facilitates nickel doping and ensures a suitable Ni content in the lithium phosphate, thereby reducing the risk of impurities such as nickel phosphides and thus mitigating the risk of reversible capacity reduction in the battery cell. Alternatively, 0.01 ≤ x ≤ 0.03. This further reduces the risk of impurities such as nickel phosphides.

[0009] In one possible implementation, 0.002 ≤ y ≤ 0.03. By setting y to satisfy this range, it facilitates tin doping and ensures a suitable Sn content in the lithium phosphate, thereby reducing the risk of generating impure LiSnPO4 phase and consequently mitigating the degradation of cell kinetic performance and energy density. Alternatively, 0.005 ≤ y ≤ 0.02. This further reduces the risk of generating impure LiSnPO4 phase.

[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, Sn and M elements doped in the lithium phosphate have appropriate contents, thereby the Fe element in the lithium phosphate has a relatively appropriate content, which is beneficial to make the lithium phosphate have the same or basically the same crystal structure as lithium iron phosphate.

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

[0014] In one possible implementation, Ni element occupies at least a portion of the Fe sites in the lithium-containing phosphate, said Fe sites being Fe in the lithium-containing phosphate. 2+ The position of Ni. 2+ At least some Fe sites can be occupied through solid solution substitution. On the one hand, this 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, lithium phosphates doped with Ni have a crystal structure that is basically the same as that of lithium iron phosphate, which can reduce the risk of LiNiPO4 formation. This can reduce the risk that the electrolyte will be difficult to operate 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+ , thus facilitating the improvement of the stability of the positive electrode active material and the cycle life of the battery cell; in addition, it is also beneficial for reducing 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, thus 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 positive electrode active material has a relatively large specific surface area, which is beneficial for 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 for 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 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 one possible implementation, the sintering treatment of 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 facilitate the reduction of defects in the positive electrode active material and also help to increase the compaction density of the positive electrode active material.

[0023] In one possible implementation, the temperature and time of the first sintering treatment and the second sintering treatment are the same. This simplifies the preparation process of the positive electrode active material and reduces its complexity.

[0024] In one possible implementation, the sintering temperature T satisfies: 750℃ ≤ T ≤ 800℃; and / or, the sintering time t satisfies: 6h ≤ t ≤ 10h. This facilitates sufficient reaction between the raw materials to generate the corresponding positive electrode active material.

[0025] In one possible implementation, the solvent includes nitric acid. This facilitates the dissolution of nickel oxide, iron, tin oxide, lithium carbonate, etc., in nitric acid, generating the corresponding ions and producing intermediate products through reaction; furthermore, nitrate ions in nitric acid are easily removed, reducing the risk of introducing impurities into the positive electrode active material.

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

[0027] Fourthly, a battery cell is provided, including the positive electrode sheet described in the third aspect.

[0028] Fifthly, 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. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced 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.

[0031] Figure 1 This is a schematic diagram of a method for preparing a positive electrode active material according to an embodiment of this application; Figure 2This is a schematic diagram of a battery cell according to an embodiment of this application; Figure 3 This is a schematic diagram of a battery according to an embodiment of this application; Figure 4 This is a schematic diagram of an electrical device according to an embodiment of this application; Figure 5 This is a schematic diagram of the XRD test results of a positive electrode active material of one embodiment and some comparative examples of this application; Figure 6 SEM images of a pair of proportional positive electrode active materials of this application; Figure 7 SEM images of a pair of proportional positive electrode active materials of this application; Figure 8 This is a SEM image of a positive electrode active material according to an embodiment of this application. Detailed Implementation

[0032] The embodiments of the positive electrode active material, its preparation method, positive electrode sheet, battery cell, battery, and power device of this application are disclosed in detail with appropriate reference to the accompanying drawings. 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 for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0033] 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.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During the charging and discharging process, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte, acting as a conductor for the active ions, lies between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing the passage of active ions. In some embodiments, this battery cell is also referred to as a secondary battery, and the battery cell can be the smallest possible battery unit.

[0038] During the charging process of a lithium-ion battery, lithium ions are released from the positive electrode active material, move and embed into the negative electrode material; while during the discharging process, lithium ions are released from the negative electrode material, move and embed into the positive electrode active material.

[0039] It should be understood that the “intercalation” process described in this application refers to the process in which lithium ions are intercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction, and the “deintercalation” and “deintercalation” processes described in this application refer to the process in which lithium ions are deintercalated in the positive electrode active material and the negative electrode material due to an electrochemical reaction.

[0040] The development of battery technology needs to consider various 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 the positive electrode active material because of its low cost, strong reliability, and relatively good 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 improving the tap density and capacity utilization 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 (needs to be urgently solved).

[0041] In view of this, the embodiments of the present application provide a positive electrode active material, which includes a lithium-containing phosphate doped with Sn elements and Ni elements. This positive electrode active material has a high voltage platform, which is conducive to improving the energy density and cycle performance of the battery cell.

[0042] [Positive electrode active material] The embodiments of the present application provide 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.

[0043] The lithium-containing phosphate in the embodiments of the present application can be a material obtained by doping Ni elements and Sn elements in lithium iron phosphate, and the lithium-containing phosphate can have the same crystal structure as lithium iron phosphate.

[0044] The values of x and y are both greater than 0, which means that in the lithium-containing phosphate, there are Ni elements and Sn elements. z can be 0. In the case where z is 0, the lithium-containing phosphate does not include M elements. x + y + z<1 means that the lithium-containing phosphate includes Fe elements.

[0045] 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.

[0046] M includes at least one transition metal element, such as Cr, Ti, etc.

[0047] Ni 2+ Fe 2+ The ionic radii are relatively close, and Ni 2+ Fe 2+ The ionization energies of Ni are relatively close, therefore 2+ It is easier to occupy Fe 2+ They are doped into the lattice of lithium iron phosphate at specific locations.

[0048] Ni 2+ Doping lithium iron phosphate (LFP) allows the formation of Ni-O bonds, which shortens the Li-O bonds. This results in more energy required for lithium ion extraction, increasing the ionization energy of lithium ions and the ionization potential of the cathode active material. Consequently, this raises the voltage plateau of the cathode active material or the battery cell. The voltage plateau of the cathode active material is related to the energy density of the battery cell; generally, a higher voltage plateau corresponds to a higher energy density. Therefore, doping lithium iron phosphate with Ni can improve the energy density of the battery cell.

[0049] Due to Li + and Ni 2+ The ionic radii of Fe and Ni are similar, making Li-Ni mixing likely to occur during the preparation of positive electrode active materials and the charge / discharge process of battery cells. If only Ni is doped, due to the similarity of Fe ionic radii, Li-Ni mixing is more likely to occur. 2+ and Li + The ionic radii are also similar, which will further increase the risk of Li-Ni mixing on the basis of Li-Fe mixing. 2+ and Fe 2+ Occupying a Li site (Li site refers to the position of lithium ions in lithium iron phosphate) will hinder the transport of lithium ions, which is not conducive to improving the performance of the battery cell. For example, the lithium ion transport rate will decrease and the number of lithium ions that can be extracted from the positive electrode active material will decrease. These may lead to a decrease in the kinetic performance of the battery cell and a smaller capacity that the battery cell can exert.

[0050] Sn 2+ The ionization energy of Fe 2+ Approaching, Sn 2+Doping can reduce the unit cell parameters of lithium iron phosphate, thereby shortening the bond lengths of Ni-O, Li-O, and Fe-O bonds, and Ni 2+ and Fe 2+ can be bound in their respective positions. The potential energy for Ni 2+ and Fe 2+ to dissolve out from the lattice of lithium-containing phosphate increases, thereby reducing the risk of Li-Ni mixing. At the same time, it is also beneficial to reduce the risk of Ni 2+ and Fe 2+ dissolving out. Therefore, by doping Sn 2+ in lithium-containing phosphate, the risk of Li-Ni mixing can be reduced. At the same time, it is also beneficial to improve the stability of lithium-containing phosphate and the cycling performance of battery cells.

[0051] An embodiment of the present application provides a positive electrode active material. The positive electrode 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 element and Sn element to lithium-containing phosphate, it is beneficial to improve the voltage platform and stability of the positive electrode active material, thereby improving the energy density and cycling performance of battery cells.

[0052] It should be noted that during the charge and discharge process of battery cells, the deintercalation and consumption of Li will occur, and the molar content of Li is different when the battery discharges to different states. In the listing of the positive electrode 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 positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li will change.

[0053] In the listing of the positive electrode 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.

[0054] 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.

[0055] x is greater than or equal to 0.005. In this way, it is convenient for the doping of nickel element in the preparation process, and the risk of increasing the doping difficulty due to the small doping amount of nickel element 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 improve the energy density of the battery cell.

[0056] If 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 less than or equal to 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, with an appropriate content of Ni element, 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 turns into the voltage platform of LiNiPO4 or the positive electrode active material has multiple voltage platforms.

[0057] Optionally, 0.01 ≤ x ≤ 0.03. In this way, the risk of generating impurities such as nickel phosphide can be further reduced.

[0058] 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.

[0059] y is greater than or equal to 0.002. In this way, it is convenient for the doping of Sn element in the preparation process, and the risk of increasing the doping difficulty due to the small doping amount of Sn element 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 improve the cycle performance of the battery cell.

[0060] If 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 less than or equal to 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 the decline of the kinetic performance and energy density of the battery cell.

[0061] Optionally, 0.005 ≤ y ≤ 0.02. In this way, the risk of generating the heterophase LiSnPO4 can be further reduced.

[0062] In some embodiments, the Ni element is uniformly doped in lithium iron phosphate, that is to say, the Ni element is uniformly distributed in the lithium-containing phosphate. The uniform doping of the Ni element can be qualitatively and semi-quantitatively characterized by XRD and EDS, and the uniform doping of the Ni element is characterized by testing the distribution of the Ni element.

[0063] In some embodiments, 0 ≤ z ≤ 0.01. z can be 0.005, 0.01, or any value within the above range.

[0064] 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.

[0065] In the above embodiments, 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 relatively appropriate content, which is beneficial to making the lithium-containing phosphate have the same or substantially the same crystal structure as lithium iron phosphate.

[0066] 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.

[0067] In some embodiments, the Ni element occupies at least part of the Fe site in the lithium-containing phosphate, and the Fe site is the Fe in the lithium-containing phosphate 2+ position.

[0068] Ni 2+ can occupy at least part of the Fe site by solid solution substitution. On the one hand, it is beneficial to increase the electrode potential of the positive electrode active material, and thus increase the voltage platform of the positive electrode active material; on the other hand, the lithium-containing phosphate doped with the Ni element 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.

[0069] 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.

[0070] In some embodiments, the Sn element is located inside the unit cell of the lithium-containing phosphate. It can also be said that the Sn element is doped into the unit cell of lithium iron phosphate, and the Sn element is not located at the grain boundary.

[0071] The Sn element being located inside the unit cell of the lithium-containing phosphate is beneficial to increasing the potential energy required for the dissolution of 2+ Ni 2+ and Fe, thereby being beneficial to improving the stability of the positive electrode active material and the cycle life of the battery monomer. In addition, it is also beneficial to reduce the risk of generating the impurity phase LiSnPO4.

[0072] In some embodiments, based on the total mass of the positive electrode active material, Ni e The mass content A of P satisfies: A < 0.1 wt%, 0 < e < 2.4. In this way, the Ni e P impurities are few or almost non-existent, thereby reducing the e influence of P impurities on the reversible capacity of the battery cell.

[0073] 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.

[0074] In some embodiments, the specific surface area S of the positive electrode 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 positive electrode active material is relatively large, which is beneficial to improving the rate performance of the battery cell.

[0075] In some embodiments, the volume average particle size Dv50 of the positive electrode 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 positive electrode active material is relatively small, which is beneficial to improving the rate performance of the battery cell.

[0076] In some embodiments, 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.

[0077] The positive electrode active material may have a core-shell structure, with the inner core being 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 positive electrode active material has a lower powder resistivity and higher conductivity, which is beneficial to forming a complete conductive network between the particles of the positive electrode 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.

[0078] In some embodiments, based on the total mass of the positive electrode active material, the mass content B of the carbon material is 0.99 wt% - 1.31 wt%. For example, B is 0.99 wt%, 1.2 wt%, 1.31 wt% or any value within the above range. Correspondingly, the powder resistivity of the positive electrode active material can be less than or equal to 100 Ω·cm.

[0079] In some embodiments, the positive electrode active material may include particles with a volume average particle size of 50-200 nm and 0.5-5 μm. That is, 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 large-diameter and small-diameter positive electrode active materials is beneficial to improving the compaction density of the positive electrode active material, thereby improving the energy density of the battery cell.

[0080] In some embodiments, the powder compaction density of the positive electrode active material can be greater than 2.40 g / cc, wherein the compaction density is the density after being pressed under a pressure of 3T.

[0081] [Preparation method of positive electrode active material] This application provides a method for preparing a positive electrode active material. Figure 1 This is a schematic diagram illustrating a method for preparing a positive electrode active material according to an embodiment of this application. For example, such as... Figure 1 As shown, the preparation method 100 includes the following steps, and the preparation method 100 can be used to prepare the positive electrode active material in any of the above embodiments.

[0082] Step 110: Lithium carbonate, phosphoric acid, iron, nickel oxide, and tin oxide are added to a solvent to obtain an intermediate product.

[0083] In some embodiments, the solvent includes an acidic solution, such as a nitric acid solution. As an example, the nitric acid solution is a 60% nitric acid solution.

[0084] The above materials can be dissolved in a solvent (e.g., nitric acid solution). After complete dissolution, a solution containing Li, Fe, Ni, and Sn ions can be obtained. The solution is then placed in a beaker and heated to decompose the ions in the solvent (e.g., nitrate ions) and evaporate the water in the solution, resulting in a dry gel mixture. This dry gel mixture is a mixture containing Li, Fe, Ni, and Sn elements.

[0085] As an example, the solvent can be removed during heating, thereby reducing the risk of introducing unwanted impurities into the intermediate product.

[0086] Optionally, glucose may also be added in step 110. Glucose serves as a carbon source to facilitate the subsequent preparation of a carbon coating layer on the lithium phosphate-containing surface.

[0087] Step 120: The intermediate product is sintered to obtain the positive electrode active material.

[0088] The intermediate product can be the resulting 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 constant temperature for a certain period of time in a roller kiln.

[0089] Optionally, in step 120, the lithium phosphate-coated carbon material can also be simultaneously coated by chemical vapor deposition (CVD) to prepare a positive electrode active material including a carbon coating layer.

[0090] As an example, sintering is carried out in an inert atmosphere. For instance, nitrogen is introduced at a rate of 4 L / min, and this rate is maintained throughout the entire sintering process, including heating, holding, and cooling.

[0091] The positive electrode active material of the present application embodiment can be prepared by method 100. The positive electrode active material has high energy density and good cycle performance.

[0092] In some embodiments, the intermediate product is subjected to 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 a positive electrode active material.

[0093] 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 back into a graphite sagger for a second sintering treatment.

[0094] In other words, the intermediate product undergoes two sintering processes to obtain the positive electrode active material.

[0095] The conditions for the first sintering treatment and the second sintering treatment (e.g., sintering atmosphere, temperature, time) can be the same or different.

[0096] The two sintering processes facilitate the reduction of defects in the positive electrode active material and also help to increase the compaction density of the positive electrode active material.

[0097] In some embodiments, the temperature and time of the first sintering treatment and the second sintering treatment are the same. This simplifies the preparation process of the positive electrode active material and reduces its complexity.

[0098] As an example, both the first and second sintering processes were performed in nitrogen atmosphere, with a sintering time of 10 hours and a sintering temperature of 750°C.

[0099] In some embodiments, the sintering temperature T satisfies: 750℃≤T≤800℃, and / or the sintering time t satisfies: 6h≤t≤10h, to facilitate sufficient reaction between raw materials to generate the corresponding positive electrode active material.

[0100] The temperature T can be 750℃, 780℃, 800℃ or any value within the above range, and the time t can be 6h, 8h, 10h or any value within the above range.

[0101] When the sintering temperature T is not less than 750℃, it is beneficial to increase the compaction density of the positive electrode active material; when the sintering temperature T does not exceed 800℃, 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.

[0102] In some embodiments, the solvent includes nitric acid. This facilitates the dissolution and uniform mixing of nickel oxide, iron, tin oxide, lithium carbonate, etc., in the nitric acid solution; and nitrate ions in the nitric acid are easily removed (e.g., nitrate ions decompose upon heating, thus facilitating their removal in the solution), reducing the risk of introducing impurities into the positive electrode active material.

[0103] [Positive electrode plate] This application provides a positive electrode sheet, including the positive electrode active material in any of the above embodiments, and / or the positive electrode active material prepared by the preparation method of any of the above embodiments.

[0104] The positive electrode includes a positive current collector and a positive electrode film layer disposed on the positive current collector, wherein the positive electrode film layer includes a positive active material.

[0105] The positive electrode current collector can be a metal foil or a composite current collector. For example, the positive electrode current collector can be an aluminum foil.

[0106] Composite current collectors may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0107] The positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0108] The positive electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] [Negative electrode plate] The negative electrode includes a negative current collector and a negative electrode film layer disposed on the negative current collector.

[0110] The negative electrode current collector can be a metal foil or a composite current collector. The negative electrode current collector can be copper foil. Composite current collectors can 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 polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0111] The negative electrode film layer includes a negative electrode active material. The negative electrode active material can be any negative electrode active material known in the art for use in batteries. 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, and 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, this application is not limited to these materials, and other conventional 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.

[0112] The negative electrode film may optionally include a conductive agent. The conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0113] [Electrolytes] 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.

[0114] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0115] The electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0116] Solvents may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0117] The electrolyte may also optionally include negative electrode film-forming additives, positive electrode film-forming additives, and performance additives that can improve certain battery performance, such as performance additives that improve battery overcharge performance, battery high temperature or low temperature performance, etc.

[0118] [Isolation Component] The separator is used to separate the positive electrode and the negative electrode. This application does not impose any particular limitation on the type of separator; any known porous membrane with good chemical and mechanical stability can be selected.

[0119] 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.

[0120] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0121] [Battery cell] This application provides a battery cell including the positive electrode sheet described in the above embodiments.

[0122] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. The battery cell can be a lithium-ion battery, a lithium-sulfur battery, a sodium-ion battery, a magnesium-ion battery, etc.

[0123] Figure 2 This is a schematic diagram of a battery cell according to an embodiment of this application. Figure 2 As shown, the battery cell 3 includes a housing 31, an end cap assembly 32, and an electrode assembly 33. The electrode assembly 33 is disposed in the housing 31, and the end cap assembly 32 is used to cover the housing 31.

[0124] End cap assembly 32 includes electrode terminals 322, for example, 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.

[0125] 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 from a positive electrode, a negative electrode and an insulating element by a winding process or a stacking process.

[0126] The battery cell 3 also includes a current collector 34, which is used to connect the tabs 332 and the electrode terminals 322 of the electrode assembly 33. For example, as Figure 3 As shown, the battery cell 3 includes two current collectors 34. One current collector 34 is used to connect the positive electrode tab and the positive electrode terminal, and the other current collector 34 is used to connect the negative electrode tab and the negative electrode terminal.

[0127] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0128] [Battery] This application provides a battery, including the battery cell described in the above embodiments. Figure 3 This is a schematic diagram of a battery according to an embodiment of this application. Figure 3 As shown, battery 5 may include multiple battery cells (not shown in the figure).

[0129] Battery cells 3 can be directly assembled into battery 5, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into battery 5.

[0130] [Electrical appliances] This application provides an electrical device, including the battery described in the above embodiments.

[0131] Figure 4 This is a schematic diagram of an electrical device according to an embodiment of this application. Figure 4 As shown, this application provides an electrical device 6, which includes the battery in the above embodiment.

[0132] Alternatively, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., as is the case in the embodiments of this application.

[0133] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0134] [Example] Example 1 In Example 1, a positive electrode active material is provided. The positive electrode active material is a lithium phosphate with a carbon coating layer, and the chemical formula of the lithium 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, has a carbon coating content of 1.15 wt%.

[0135] In Example 1, the preparation method of the positive electrode active material is as follows: (1) Add Li2CO3, phosphoric acid, glucose, Fe powder, NiO, and SnO to a 60% nitric acid solution in the appropriate proportions (the proportions can be set according to the proportions of the elements in the prepared lithium phosphate). After complete dissolution, a solution containing Li, Fe, Ni, Sn, and PO4 is obtained. 3- A homogeneous nitric acid solution; (2) Place the above solution in a beaker, heat the beaker, the water evaporates, the nitrate ions decompose and release heat, thereby accelerating the nitrate ion decomposition reaction, and finally the solution is completely evaporated to obtain a homogeneous dry gel mixture. (3) After simple crushing, the above dry gel mixture is placed in a graphite sagger and sintered at a constant temperature of 760°C for 8 hours in a roller kiln, while simultaneously performing CVD treatment to coat the lithium phosphate-containing surface with a carbon coating layer; wherein, the nitrogen gas flow rate is 4L / min and runs through the entire sintering process of heating, holding and cooling; the mass content of the carbon coating layer in the positive electrode active material after one sintering is approximately 1.05-1.10%; (4) The product of the first sintering is crushed and placed in a graphite saggar for a second sintering. CVD treatment is carried out simultaneously to prepare a carbon coating layer. The sintering atmosphere conditions are the same as those of the first sintering. After the second sintering, the mass content of the carbon coating layer of the positive electrode active material is about 1.15-1.20%. After crushing the product of the second sintering, the positive electrode active material in the example is obtained.

[0136] Examples 2-5 The difference between Examples 2-5 and Example 1 is that the amount of Ni doping in the lithium phosphate is different. The values ​​of x are 0.005, 0.02, 0.03, and 0.05, respectively.

[0137] Examples 6-9 The difference between Examples 6-9 and Example 1 is that the doping amount of Sn in the lithium phosphate is different. The doping amounts are 0.002, 0.01, 0.02, and 0.03, respectively.

[0138] Examples 10-12 The difference between Example 10 and Example 1 is that the lithium phosphate is doped with Ti and V elements. 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).

[0139] The difference between Example 11 and Example 1 is that the lithium phosphate is doped with Ti. The doping amount of Ti is 0.005. In the process of preparing the positive electrode active material, TiO2 is also added in step (1).

[0140] The difference between Example 12 and Example 1 is that the lithium phosphate is doped with Mn. The doping amount of Mn is 0.005. In the process of preparing the positive electrode active material, in step (1), an oxide of Mn is also added.

[0141] The preparation methods of the positive electrode active materials in Examples 2-12 can be found in the preparation method of the positive electrode active material in Example 1, and will not be repeated here.

[0142] Examples 13-14 The difference between Examples 13-14 and Example 1 is that the sintering temperatures are different, namely 720℃ and 820℃ respectively.

[0143] Comparative Example 1 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 and Sn elements.

[0144] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 is doped with only Ni element and not Sn element.

[0145] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 is doped with Sn only, and not with Ni.

[0146] Table 1. Parameters of the positive electrode active materials in the examples and comparative examples.

[0147] Table 2 Test results of the examples and comparative examples

[0148] [Preparation of battery cells] (1) Preparation of positive electrode sheet: A slurry was prepared by mixing positive active material, conductive agent super-P, carbon nanotubes (CNT), and binder PVDF in a mass ratio of 95:1.5:0.5:3. The slurry was coated on 13μm aluminum foil and then dried under vacuum at 120℃, cold-pressed, and cut into strips to obtain the positive electrode sheet.

[0149] (2) Preparation of negative electrode sheet: The negative electrode active material 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 in a mass ratio of 90:5:2:2:1 and mixed 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 the negative electrode sheet.

[0150] (3) Separation membrane: Polyethylene film is used.

[0151] (4) Preparation of lithium-ion battery cell: The above positive electrode, separator and negative electrode are stacked and wound in sequence to obtain electrode assembly; the electrode assembly is placed in outer packaging, and an electrolyte solution with lithium hexafluorophosphate as electrolyte salt is added. After encapsulation, standing, formation and aging, lithium-ion battery cell is obtained.

[0152] [Powder compaction density test of positive electrode active materials] As an example, the UTM7305 compaction density analyzer from Sansi Technology Co., Ltd. can be used to determine the powder compaction density of the positive electrode active material under a pressure of 3T.

[0153] Specifically, as an example, 1g of positive electrode active material is weighed and added to a cylindrical mold with a cross-sectional area of ​​S in the mold's circular hole. A pressure of 3T is applied to the powder inside the mold and held for 30s, and the powder thickness is recorded as t. The compacted density of the positive electrode active material can be calculated using the following formula: ρ=m / (S×t), where ρ is the compacted density, m is the mass of the positive electrode active material, S is the cross-sectional area of ​​the mold's circular hole, and t is the powder thickness.

[0154] [Testing the discharge specific capacity of positive electrode active materials] A coin cell was fabricated using a positive electrode active material, and the coin cell was then tested. (Specifically, a positive electrode was fabricated using the positive electrode active material, and a lithium sheet was used as the negative electrode to fabricate a coin cell.) The button cell was placed in a 25°C oven and left to stand for 2 hours before being charged and discharged.

[0155] The 0.1C charge-discharge process is as follows: charge with a constant current of 0.1C to 3.65V, continue constant voltage charging until the charging current is less than 0.05C and then stop; pause for 5 minutes; discharge with a constant current of 0.1C to 2.0V. The discharge capacity of this step is the discharge capacity of the positive electrode active material.

[0156] [Testing of discharge capacity, voltage plateau, and energy density of individual battery cells] Lithium-ion battery cells (secondary batteries) are prepared using positive electrode active materials, and the lithium-ion battery cells are tested.

[0157] The lithium-ion battery cells were placed in a 25°C oven and left to stand for 2 hours before being tested for charge and discharge.

[0158] One charge-discharge cycle is as follows: constant current charging at 0.33C to 3.65V, then constant voltage charging continues until the charging current is less than 0.05C, at which point the cycle is stopped; pause for 30 minutes; constant current discharging at 0.33C to 2.0V; pause for 30 minutes. This is one charge-discharge cycle of the battery.

[0159] After repeating this process three times, the discharge capacity of the last discharge is taken, which is the discharge capacity of a single lithium-ion battery cell at 0.33C.

[0160] Voltage plateau = Third discharge energy / Discharge capacity. Both discharge energy and discharge capacity can be measured using testing equipment connected to a single lithium-ion battery cell.

[0161] Cell mass energy density (Wh / kg) = Energy of the third discharge / Mass of positive electrode active material in the battery.

[0162] [XRD Testing] The XRD patterns of each positive electrode active material were tested using X-ray diffraction equipment.

[0163] [Cycle performance testing of individual battery cells] The lithium-ion battery cells were placed in a 60°C oven and left to stand for 2 hours before being tested for charge and discharge.

[0164] One charge-discharge cycle is as follows: Charge to 3.65V with a constant current of 0.33C, then continue charging with a constant voltage until the charging current is less than 0.05C, at which point the charging is stopped; pause for 30 minutes; discharge to 2.0V with a constant current of 0.33C; pause for 30 minutes. This constitutes one charge-discharge cycle of the battery. This process is repeated continuously until the battery capacity decreases to 80% of its initial value, and the number of cycles is recorded.

[0165] Referring to Examples 1-14 and Comparative Example 1, the positive electrode active material in the embodiments of this application includes a lithium-containing phosphate, which contains Ni and Sn elements. In contrast, the lithium-containing phosphate in Comparative Example 1 is lithium iron phosphate, which does not include Ni and Sn elements. By doping lithium iron phosphate with Ni and Sn elements, the voltage platform of the positive electrode active material is improved, the energy density of the battery cell is increased, and the battery cell also exhibits a higher cycle life.

[0166] As shown in Examples 1-14 and Comparative Examples 2-3, it is difficult to balance the energy density and cycle life of a single battery cell when doping with Ni or Sn alone.

[0167] As shown in Examples 1-5, when x is in the range of 0.005 to 0.05, a suitable doping amount of Ni can result in a single battery cell exhibiting high energy density and long cycle life. Furthermore, when x is in the range of 0.01 to 0.03, while maintaining high energy density and long cycle life in the single battery cell, the amount of Ni generated can be further reduced. e The risk of P impurities.

[0168] As shown in Examples 6-9, when y is in the range of 0.002 to 0.03, a suitable doping amount of Sn can result in a single battery cell with high energy density and cycle life. Furthermore, when y is in the range of 0.005 to 0.02, the risk of generating impure phase LiSnPO4 can be further reduced while maintaining high energy density and long cycle life in the single battery cell.

[0169] Figure 5 This is a schematic diagram of the XRD test results of an embodiment and a comparative example of this application. Combined with Embodiment 1 and Comparative Examples 1-2, and... Figure 5 As shown, the XRD curves of Example 1 and Comparative Examples 1-2 are basically the same. That is to say, in Example 1, no new phase appeared in the lithium phosphate, meaning that the lithium phosphate is a single phase with the same or basically the same crystal structure as lithium iron phosphate. This also reflects that Ni did not appear in the positive electrode active material. e P impurities and the impurity phase LiSnPO4; and it can also be seen that Ni and Sn elements are present in the unit cell containing lithium iron phosphate.

[0170] Figure 6 This is a SEM image of a pair of proportional positive electrode active materials in this application. Figure 7 This is a SEM image of a pair of proportional positive electrode active materials in this application. Figure 8 This is a SEM image of the positive electrode active material according to an embodiment of this application. Combined with Comparative Example 1 and... Figure 6 As shown,Figure 6 The following are SEM images of lithium iron phosphate without Ni and Sn doping; combined with Comparative Example 2 and... Figure 7 As shown, Figure 7 SEM images of the Ni-doped cathode active material are shown. The images show that Ni doping refines the grain size, resulting in smaller particle size in the cathode active material. (This is in conjunction with Example 1 and...) Figure 8 As shown, after doping with Ni and Sn, the particle size of the positive electrode active material is smaller than that of the positive electrode active material in Comparative Example 1. Furthermore, as shown in Examples 1-12, the positive electrode active material of this application has a smaller volume average particle size and a larger specific surface area compared to the comparative example.

[0171] As shown in Examples 10-11, elements such as Ti, V, and Mn can also be doped into lithium phosphate, which is beneficial to further improve the kinetic performance of the positive electrode active material, such as increasing the discharge specific capacity.

[0172] As shown in Example 13, the compaction density of the prepared positive electrode active material is relatively low when the sintering temperature is 720℃. As shown in Example 14, the growth trend of lithium phosphate crystals increases when the sintering temperature is 820℃, the particle size of the positive electrode active material tends to increase, and the improvement in cycle life of the battery cell is relatively small. Furthermore, after testing the battery cells prepared from the positive electrode active materials of Examples 13 and 14, it was found that the improvement in energy density of the battery cells was relatively small. Therefore, based on Examples 1-12 and Examples 13-14, it can be seen that setting the sintering temperature to 750℃~800℃, specifically 760℃~780℃, is beneficial for obtaining positive electrode active materials with higher compaction density, higher energy density, and longer cycle life in battery cells.

[0173] In the embodiments of this application, the voltage platform corresponding to the positive electrode active material can be greater than 3.2V, while the voltage platform of the positive electrode active material in the comparative example can be about 3.1V. The voltage platform of the positive electrode active material in the embodiments has been improved.

[0174] Furthermore, the presence of electrochemical dissolution of metal ions (such as nickel ions and ferrous ions) in lithium phosphate can be determined through cycle performance testing. Cycle performance testing can reflect whether or how much electrochemical dissolution of metal ions occurs. As shown in Examples 1-12, the battery cells exhibit high cycle life, indicating that Sn can reduce the dissolution of metal ions from the positive electrode active material.

[0175] 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 battery cell, characterized in that, include: A positive electrode, a negative electrode, and a separator membrane located between the positive and negative electrode, wherein, The positive electrode sheet includes a positive electrode active material, which includes a lithium phosphate. The lithium phosphate includes Fe, P, O, Ni, and Sn elements, wherein the Ni element occupies at least a portion of the Fe sites in the lithium phosphate, and the Fe sites are Fe atoms in the lithium phosphate. 2+ The location.

2. The battery cell according to claim 1, characterized in that, 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 the transition metal elements.

3. The battery cell according to claim 2, characterized in that, 0.005≤x≤0.05。 4. The battery cell according to claim 3, characterized in that, 0.01≤x≤0.03。 5. The battery cell according to any one of claims 2-4, characterized in that, 0.002≤y≤0.03。 6. The battery cell according to claim 5, characterized in that, 0.005≤y≤0.02。 7. The battery cell according to any one of claims 2-6, characterized in that, 0≤z≤0.01。 8. The battery cell according to any one of claims 2-7, characterized in that, 0 <x+y+z≤0.03。 9. The battery cell according to any one of claims 2-8, characterized in that, M includes at least one of Cu, Mn, Cr, Zn, Pb, Ca, Co, Sr, Nb, V, or Ti.

10. The battery cell according to any one of claims 1-9, characterized in that, The Sn element is located within the unit cell of the lithium phosphate.

11. The battery cell according to any one of claims 1-10, characterized in that, Based on the total mass of the positive electrode active material, the Ni in the positive electrode active material e The mass content of P, A, satisfies the following conditions: A < 0.1 wt%, 0 <e<2.4。 12. The battery cell according to any one of claims 1-11, characterized in that, The specific surface area S of the positive electrode active material satisfies: 9.5 m² 2 / g≤S≤14.56m 2 / g.

13. The battery cell according to any one of claims 1-12, characterized in that, The volume average particle size Dv50 of the positive electrode active material satisfies: 0.61μm≤Dv50≤1.80μm.

14. The battery cell according to any one of claims 1-13, characterized in that, The positive electrode active material also includes a carbon material, which is located on the outer surface of the lithium-containing phosphate and coats the lithium-containing phosphate.

15. The battery cell according to claim 14, characterized in that, Based on the total mass of the positive electrode active material, the mass content B of the carbon material satisfies: 0.99wt%≤B≤1.31wt%.

16. A method for preparing a battery cell according to any one of claims 1-15, characterized in that, include: Prepare a positive electrode active material to obtain the battery cell; The preparation of the positive electrode active material includes: Lithium carbonate, phosphoric acid, iron, nickel oxide, and tin oxide are added to a solvent to obtain an intermediate product; The intermediate product is sintered to obtain the positive electrode active material.

17. The method for preparing a battery cell according to claim 16, characterized in that, The sintering treatment of the intermediate product to obtain the positive electrode active material includes: The intermediate product is subjected to a first sintering treatment and a second sintering treatment to obtain the positive electrode active material.

18. The method for preparing a single battery cell according to claim 17, characterized in that, The temperature and time are the same for the first sintering treatment and the second sintering treatment.

19. The method for preparing a battery cell according to any one of claims 16-18, characterized in that, The sintering temperature T satisfies: 750℃≤T≤800℃, and / or the sintering time t satisfies: 6h≤t≤10h.

20. The method for preparing a battery cell according to any one of claims 16-19, characterized in that, The solvent includes nitric acid.

21. A battery, characterized in that, Includes the battery cell as described in any one of claims 1-15.

22. An electrical appliance, characterized in that, Includes the battery as described in claim 21.

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