Positive electrode active material, method for producing same, battery cell, and power storage device

Abstract

The application discloses a positive electrode active material, a preparation method of the positive electrode active material, a battery cell and an electric device. The positive electrode active material comprises a lithium-containing phosphate, and an X-ray diffraction pattern of the positive electrode active material tested under a full charge state satisfies: a (311) crystal face peak in a range of 35°-36°, a (011) crystal face peak in a range of 20°-21°, and a ratio of a peak intensity I 311 of the (311) crystal face peak to a peak intensity I 011 of the (011) crystal face peak satisfies I 311 / I 011 ≥0.008. The positive electrode active material provided by the application can improve the cycle performance of a battery.

Description

Technical Field

[0001] This application relates to a positive electrode active material and its preparation method, a battery cell, and an electrical device. Background Technology

[0002] In recent years, batteries have been widely used in energy storage power stations, for example, due to the increasing demand for peak-valley regulation of the power grid. Consequently, the requirements for the cycle life of batteries used in energy storage are also becoming increasingly stringent. However, achieving a longer cycle life remains a challenge in current battery development. Summary of the Invention

[0003] This application provides a positive electrode active material and its preparation method, a battery cell, and an electrical device, which can improve the cycle performance of the battery.

[0004] The first aspect of this application provides a positive electrode active material, the positive electrode active material comprising lithium phosphate, and the X-ray diffraction pattern of the positive electrode active material tested in a fully charged state satisfies the following: having a (311) crystal plane peak in the range of 35°-36°, having a (011) crystal plane peak in the range of 20°-21°, and the peak intensity I of the (311) crystal plane peak is... 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.008.

[0005] The positive electrode active material provided in this application contains some lithium-containing phosphate that has not been delithiated in the initial fully charged state. This portion of the undelithiated lithium-containing phosphate can be gradually activated during battery cycling, causing the active lithium to be gradually released. Therefore, the positive electrode active material provided in this application can act as a capacity-releasing agent, thereby enabling batteries using it to have a long cycle life.

[0006] In any embodiment, 0.009 ≤ I 311 / I 011 ≤0.037, optionally, 0.012≤I 311 / I 011 ≤0.024. This allows the battery to have both long cycle life, high energy density, and good kinetic performance.

[0007] In any embodiment, at least a portion of the surface of the lithium phosphate has a carbon coating layer.

[0008] In any embodiment, the weight content of the carbon coating layer is denoted as m, and the specific surface area of ​​the positive electrode active material, based on the total weight of the positive electrode active material, is denoted as A, in m³. 2 / g, 5.0≤A / (100×m)≤9.0, optionally, 6.4≤A / (100×m)≤8.2. This allows the battery to better combine long cycle life, high energy density, and good kinetic performance.

[0009] In any embodiment, 1.0% ≤ m ≤ 3.4%, and optionally, 1.2% ≤ m ≤ 2.0%. When the weight content m of the carbon coating layer is within the above range, it can better coat the lithium phosphate body, playing the role of over-coating the lithium phosphate body. This can hide part of the initial capacity of the positive electrode active material, thereby enabling the positive electrode active material to act as a capacity-releasing agent.

[0010] In any embodiment, A ≤ 18.5m 2 / g, optionally, A≤13.5m 2 / g. When the specific surface area of ​​the positive electrode active material is within the above range, it can also improve the processing performance of the positive electrode slurry and positive electrode sheet, and reduce the problems of slurry over-stickiness and coating cracking.

[0011] In any embodiment, the positive electrode active material is a single crystal structure or a near-single crystal structure.

[0012] In any embodiment, the volume distribution particle size Dv50 of the positive electrode active material is 0.6 μm-2.5 μm, and optionally 0.7 μm-2.3 μm. When the volume distribution particle size Dv50 of the positive electrode active material is within the above range, the positive electrode active material can have good ion transport performance, thereby enabling the battery to have good power performance. It can also improve the processing performance of the positive electrode slurry and positive electrode sheet, for example, reducing problems such as slurry over-adhesion and coating cracking.

[0013] In any embodiment, the powder resistivity of the positive electrode active material at 25°C is denoted as δ, where δ ≤ 20 Ω·cm, and optionally, δ ≤ 12.1 Ω·cm. When the powder resistivity of the positive electrode active material is within the above range, it can improve the electronic conductivity of lithium phosphate and reduce the hydrophilicity of lithium phosphate, thereby reducing water adsorption and further improving the cycle performance of the battery.

[0014] In any embodiment, the lithium-containing phosphate includes one or more of lithium iron phosphate and its doped and modified compounds. Optionally, the lithium-containing phosphate includes compounds with the molecular formula Li. m A x Fe 1-y B y P 1-z C z O 4-n D nThe material, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; m is selected from the range of 0.5 to 1.15, and optionally from the range of 0.95 to 1.05; x is selected from the range of 0 to 0.1, and optionally from the range of 0.001 to 0.005; y is selected from the range of 0 to 0.5, and optionally from the range of 0.001 to 0.1; z is selected from the range of 0 to 0.5, and optionally from the range of 0.001 to 0.1; n is selected from the range of 0 to 0.5, and optionally from the range of 0.001 to 0.1.

[0015] The second aspect of this application provides a method for preparing a positive electrode active material, comprising the following steps: providing a lithium phosphate precursor; grinding the lithium phosphate precursor with a carbon source; heating the ground material to a first temperature T1 at a first rate under a protective gas atmosphere and holding it at the first temperature T1 for a first time t1, then heating it to a second temperature T2 at a second rate and holding it at the second temperature T2 for a second time t2 to obtain a positive electrode active material, wherein the positive electrode active material comprises a lithium phosphate, and the X-ray diffraction pattern of the positive electrode active material tested in a fully charged state satisfies the following: having a (311) crystal plane peak in the range of 35°-36°, having a (011) crystal plane peak in the range of 20°-21°, and the peak intensity I of the (311) crystal plane peak is 1. 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.008.

[0016] In any embodiment, the first rate is less than or equal to 4°C / min, and can be selected as 1°C / min-4°C / min. This not only allows the positive electrode active material to act as a capacity-releasing agent, but also ensures that the positive electrode active material particles have a suitable primary particle size (here, primary particles are quasi-single-crystal primary particles), thereby giving the positive electrode active material good kinetic performance. Consequently, batteries using this positive electrode active material can possess long cycle life, good kinetic performance, and high energy conversion efficiency.

[0017] In any embodiment, the first temperature T1 is greater than or equal to 400°C, and can be selected as 400°C-600°C, or more preferably 450°C-550°C. By adjusting the first temperature T1 within the above range, the carbon source can be fully decomposed to form carbon, and the positive electrode active material particles can have a uniform primary particle size (here, the primary particle is a single-crystal-like primary particle). This allows the positive electrode active material to better function as a capacity-releasing agent, thereby enabling the battery using this positive electrode active material to have a long cycle life.

[0018] In any embodiment, the first time t1 is greater than or equal to 1 hour, and can be selected as 1 hour to 7 hours, or more preferably 3 hours to 5 hours. This not only allows the positive electrode active material to act as a capacity-releasing agent, but also allows the positive electrode active material particles to have a suitable primary particle size (here, primary particles are single-crystal-like primary particles), thereby enabling the positive electrode active material to have good kinetic performance. Consequently, the battery using this positive electrode active material can possess long cycle life, good kinetic performance, and high energy conversion efficiency.

[0019] In any embodiment, the second temperature T2 is greater than or equal to 720°C, and can be selected as 720°C-850°C, or more preferably 750°C-810°C. This allows the positive electrode active material particles to have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), which not only enables the positive electrode active material to have good kinetic performance but also allows it to act as a capacity-releasing agent. Consequently, the battery using this positive electrode active material can possess long cycle life, good kinetic performance, and high energy conversion efficiency.

[0020] In any embodiment, the second rate is 1°C / min-10°C / min, optionally 5°C / min-9°C / min. This allows the positive electrode active material particles to have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), which not only gives the positive electrode active material good kinetic performance but also allows it to act as a capacity-controlled release agent.

[0021] In any embodiment, the second time t2 is 5h-20h, and can be selected as 8h-15h. This allows the positive electrode active material particles to have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), which can give the positive electrode active material good kinetic performance and enable it to act as a capacity-controlled release agent.

[0022] In any embodiment, the carbon source includes a first carbon source comprising a water-soluble polymer. When the first carbon source comprises a water-soluble polymer, the water-soluble polymer can fully encapsulate the lithium phosphate precursor, thereby making the formed carbon coating layer more uniform and dense, which helps to conceal part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent.

[0023] In any embodiment, the weight content of the first carbon source is ≥50%, optionally 50%-70%, based on the total weight of the carbon source. This is beneficial for the battery to have both long cycle life, high energy density, and good kinetic performance.

[0024] In any embodiment, the water-soluble polymer includes one or more of polyethylene glycol, polyaniline, and their respective derivatives. When the water-soluble polymer is within the above range, it can improve the electronic conductivity of lithium phosphate and reduce the specific surface area of ​​the prepared positive electrode active material, thereby making the formed carbon coating layer more uniform and dense. This helps to conceal part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent.

[0025] In any embodiment, the carbon source further includes a second carbon source, which includes one or more of glucose, sucrose, lactose, and maltose.

[0026] In any embodiment, the weight content of the second carbon source is ≤50%, optionally 30%-50%, based on the total weight of the carbon source. This is beneficial for the battery to have both long cycle life, high energy density, and good kinetic performance, and also helps to reduce the raw material cost of the battery.

[0027] A third aspect of this application provides a battery cell including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application or the positive electrode active material prepared by the preparation method of the second aspect of this application.

[0028] The fourth aspect of this application provides an electrical device that includes a battery cell according to the third aspect of this application.

[0029] The electrical device of this application includes the battery cell provided in this application, and therefore has at least the same advantages as it. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0032] Figure 2 yes Figure 1 An exploded view of the implementation method of the battery cell.

[0033] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0034] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0035] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0036] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses the battery of this application as a power source.

[0037] Figure 7 The image shows the X-ray diffraction pattern of the positive electrode obtained by disassembling the battery prepared in Example 5 after it has been fully charged.

[0038] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0039] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material, its preparation method, battery cell, and power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0040] 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.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0043] 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 mention that the method may also include step (c) indicates 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.

[0044] Unless otherwise specified, in this application, the terms "first," "second," etc., are used to distinguish different objects, rather than to describe a specific order or primary / secondary relationship.

[0045] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0046] In the description of the embodiments of this application, unless otherwise specified, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0047] Unless otherwise stated, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0048] Unless otherwise stated, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in the embodiments of this application. Unless otherwise stated, the test temperature for each parameter is 25°C.

[0049] The battery mentioned in the embodiments of this application can be a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the battery mentioned in this application can include battery cells, battery modules, or battery packs.

[0050] A battery cell is the smallest unit that makes up a battery, and it can independently perform the functions of charging and discharging. A battery cell can be cylindrical, cuboid, or other shapes, etc., and the embodiments of this application are not limited in this respect. Figure 1 The example shown is a rectangular battery cell 5.

[0051] When there are multiple battery cells, they are connected in series, parallel, or mixed via a busbar. In some embodiments, the battery can be a battery module; when there are multiple battery cells, they are arranged and fixed to form a battery module. In some embodiments, the battery can be a battery pack, which includes a housing and battery cells, with the battery cells or battery modules housed within the housing. In some embodiments, the housing can be part of the vehicle's chassis structure. For example, a portion of the housing can be at least part of the vehicle's floor, or a portion of the housing can be at least part of the vehicle's crossbeams and longitudinal beams.

[0052] In some embodiments, the battery can be an energy storage device. Energy storage devices include energy storage containers, energy storage cabinets, etc.

[0053] A single battery cell generally includes an electrode assembly. The electrode assembly typically includes a positive electrode and a negative electrode. The electrode assembly can be a wound structure or a stacked structure, and the embodiments of this application are not limited in this regard.

[0054] The battery cell may also include an outer packaging, which can be used to encapsulate the electrode components and electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a flexible package, such as a pouch-type flexible package. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0055] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0056] In some embodiments, individual battery cells can be assembled into a battery module, and the number of individual battery cells contained in the battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0057] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0058] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0059] Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5 As shown, the battery pack 1 may include a housing and multiple battery modules 4 disposed within the housing. The housing includes an upper housing 2 and a lower housing 3. The upper housing 2 covers the lower housing 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the housing.

[0060] To improve battery cycle life, the commonly used strategy is to perform lithium replenishment. However, the large-scale industrialization of lithium replenishment technology requires technological advancements, and both positive and negative electrode lithium replenishment have low lithium utilization rates and increase costs.

[0061] Another common strategy is to add additives to the electrolyte. The principle behind these additives is usually to form a dense SEI film at the negative electrode or a dense CEI film at the positive electrode. However, this usually deteriorates the battery's kinetic performance, thereby reducing energy conversion efficiency, and has limited improvement on battery cycle life.

[0062] In view of this, the inventors have proposed a novel positive electrode active material that enables batteries using it to have a long cycle life.

[0063] The positive electrode active material provided in this application includes lithium phosphate, and the X-ray diffraction pattern of the positive electrode active material tested in a fully charged state satisfies the following: it has a (311) crystal plane peak in the range of 35°-36°, a (011) crystal plane peak in the range of 20°-21°, and the peak intensity of the (311) crystal plane peak is I. 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.008.

[0064] The X-ray diffraction pattern of the positive electrode active material under full charge can be obtained by performing a full charge test on a battery containing the positive electrode active material, then disassembling the positive electrode sheet from the fully charged battery, and testing it with an X-ray diffractometer.

[0065] When the positive electrode active material is in a fully charged state, the battery containing the positive electrode active material is in a fully charged state, while the positive electrode active material itself is in a delithiation state.

[0066] In X-ray diffraction analysis, a copper target can be used as the anode target, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range can be 15°-45°, and the scanning rate can be 2° / min.

[0067] The (311) crystal plane peak represents the diffraction peak of the lithium-containing phosphate that has not been delithiated, and the (011) crystal plane peak represents the diffraction peak of the lithium-containing phosphate that has been delithiated. The peak intensity I of the (311) crystal plane peak 311 Peak intensity I of (011) crystal plane peak 011 The ratio can be expressed as the ratio of the peak height of the (311) crystal plane peak to the peak height of the (011) crystal plane peak.

[0068] When performing a full-charge test on the positive electrode active material (i.e., the battery containing this positive electrode active material), it can be charged at a constant current rate of 1C to the upper limit cutoff voltage of the battery, and then charged at a constant voltage to a current of 0.05C. The test temperature is 25℃. When the positive electrode active material is lithium iron phosphate (LiFePO4) and its doped and modified compounds, the upper limit cutoff voltage can be 3.65V.

[0069] The X-ray diffraction pattern of the positive electrode active material provided in this application embodiment, tested under a fully charged state, has a (311) crystal plane peak and a (011) crystal plane peak, and the peak intensity of the (311) crystal plane peak is I 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.008. This indicates that some lithium-containing phosphates in the positive electrode active material remain undelithiated during the initial fully charged state. These undelithiated lithium-containing phosphates can gradually activate during battery cycling, causing the active lithium to gradually be released. Therefore, the positive electrode active material provided in this application embodiment can act as a capacity-releasing agent, thereby enabling batteries using it to have a long cycle life.

[0070] In some embodiments, 0.008 ≤ I 311 / I 011 ≤0.037. I 311 / I 011 When the value is greater than 0.037, the positive electrode active material will have more undelithiated lithium phosphate in the initial fully charged state, meaning that more initial capacity is hidden, which is beneficial to improving the cycle life of the battery. However, the initial capacity of the positive electrode active material will decrease, and the lithium-ion transport rate of the positive electrode active material will also decrease, which will affect the energy density and kinetic performance of the battery. By further adjusting the peak intensity I of the (311) crystal plane peak 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies 0.008 ≤ I 311 / I 011 A value of ≤0.037 is beneficial for batteries to have both long cycle life, high energy density, and good dynamic performance.

[0071] Alternatively, 0.009≤I 311 / I 011 ≤0.037, 0.009≤I 311 / I 011 ≤0.034, 0.012≤I 311 / I 011 ≤0.024, 0.012≤I 311 / I 011 ≤0.022, 0.012≤I 311 / I011 ≤0.021, 0.013≤I 311 / I 011 ≤0.020, 0.013≤I 311 / I 011 ≤0.018. This allows the battery to have both long cycle life, high energy density, and good kinetic performance.

[0072] In some embodiments, at least a portion of the surface of the lithium phosphate contains a carbon coating.

[0073] In some embodiments, the weight content of the carbon coating layer is denoted as m, based on the total weight of the positive electrode active material, and the specific surface area of ​​the positive electrode active material is denoted as A, in m³. 2 / g, 5.0≤A / (100×m)≤9.0.

[0074] A / (100×m) has the following meaning: when the weight content m of the carbon coating layer is 1.0% and the specific surface area A of the positive electrode active material is 5m², 2 When / g, A / (100×m)=5÷(100×1.0%)=5.

[0075] The carbon coating layer in the positive electrode active material provided in this application embodiment can provide a good conductive network, improve the electronic conductivity of lithium phosphate, and also play the role of over-coating the lithium phosphate body. This can hide part of the initial capacity of the positive electrode active material, thereby enabling the positive electrode active material to act as a capacity-releasing agent.

[0076] A / (100×m) reflects the density of the carbon coating layer. When A / (100×m) is small, the kinetic performance of the positive electrode active material deteriorates, and the internal resistance of the battery may be high. When A / (100×m) is large, the initial capacity of the positive electrode active material may be fully utilized during the initial full charge, thus making the capacity-releasing agent effect of the positive electrode active material less effective and its improvement on battery cycle performance insufficient. The inventors have found that by adjusting the weight content m of the carbon coating layer and the specific surface area A of the positive electrode active material to satisfy 5.0≤A / (100×m)≤9.0, the positive electrode active material can have both high initial capacity and good kinetic performance, and can also better act as a capacity-releasing agent. Therefore, batteries using this positive electrode active material can have long cycle life, high energy density, and good kinetic performance.

[0077] Optionally, 6.4≤A / (100×m)≤8.2, 7.1≤A / (100×m)≤8.2, and 7.2≤A / (100×m)≤8.0. This allows the battery to better combine long cycle life, high energy density, and good kinetic performance.

[0078] In some embodiments, the weight content m of the carbon coating layer satisfies 1.0% ≤ m ≤ 3.4%, and optionally, 1.2% ≤ m ≤ 2.0%. When the weight content m of the carbon coating layer is within the above range, it can better coat the lithium phosphate body, playing the role of over-coating the lithium phosphate body. This can hide part of the initial capacity of the positive electrode active material, thereby enabling the positive electrode active material to act as a capacity-releasing agent.

[0079] The weight content m of the carbon coating can be tested using a carbon-sulfur analyzer, and the testing standard can be found in GB / T20123-2006.

[0080] In some embodiments, the positive electrode active material has a single crystal structure or a single crystal-like structure.

[0081] In this application, the term "quasi-single crystal" refers to particles formed by the aggregation of a small number of primary particles (e.g., no more than 10 primary particles).

[0082] The carbon coating of a near-single-crystal structure cathode active material includes both the carbon coating layer located on the overall outer surface of the lithium phosphate-containing material and the carbon coating layer located on the surface of the primary particles that make up the near-single-crystal particles. Therefore, the weight content m of the carbon coating layer refers to the total weight content of the carbon coating layer at different locations in the cathode active material.

[0083] In some embodiments, the specific surface area A of the positive electrode active material satisfies A ≤ 18.5 m². 2 / g, optionally, A≤13.5m 2 / g, 5m 2 / g≤A≤13.5m 2 / g, 7.6m 2 / g≤A≤13.5m 2 / g, 8.8m 2 / g≤A≤13.5m 2 / g, 9.0m 2 / g≤A≤13.1m 2 / g. When the specific surface area of ​​the positive electrode active material is within the above range, it can also improve the processing performance of the positive electrode slurry and positive electrode sheet, and reduce the problems of slurry over-stickiness and coating cracking.

[0084] The specific surface area of ​​the positive electrode active material is a well-known concept in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017, and calculated using the BET (Brunauer Emmett Teller) method. The testing instrument can be the Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, USA.

[0085] In some embodiments, the volumetric particle size Dv50 of the positive electrode active material can be 0.6 μm-2.5 μm, optionally 0.7 μm-2.3 μm, or 1.0 μm-2.0 μm. When the volumetric particle size Dv50 of the positive electrode active material is within the above range, the positive electrode active material can have good ion transport performance, thereby enabling the battery to have good power performance. It can also improve the processing performance of the positive electrode slurry and positive electrode sheet, for example, reducing problems such as slurry over-viscosity and coating cracking.

[0086] The Dv50 of a positive electrode active material has a well-known meaning in the art and can be determined using instruments and methods known in the art. For example, it can be conveniently determined using a laser particle size analyzer (such as the Malvern Mastersizer 3000) in accordance with GB / T 19077-2016. The physical definition of Dv50 is the particle size corresponding to a cumulative volume distribution percentage of 50% for the material.

[0087] In some embodiments, the powder resistivity of the positive electrode active material at 25°C is denoted as δ, where δ ≤ 20 Ω·cm, and optionally, δ ≤ 12.1 Ω·cm, 1.2 Ω·cm ≤ δ ≤ 12.1 Ω·cm, 3.9 Ω·cm ≤ δ ≤ 12.1 Ω·cm, 5.5 Ω·cm ≤ δ ≤ 11.1 Ω·cm, 5.5 Ω·cm ≤ δ ≤ 10.0 Ω·cm, and 5.5 Ω·cm ≤ δ ≤ 9.1 Ω·cm. When the powder resistivity of the positive electrode active material is within the above range, the electronic conductivity of the lithium phosphate can be improved, and the hydrophilicity of the lithium phosphate can be reduced, thus reducing water adsorption and further improving the cycle performance of the battery.

[0088] The resistivity of the positive electrode active material powder has a well-known meaning in the art and can be measured using instruments and methods known in the art. For example, it can be tested according to GB / T 32993-2016. The test temperature is 25℃.

[0089] In some embodiments, the lithium phosphate may have an olivine structure.

[0090] In some embodiments, lithium-containing phosphates include one or more of lithium iron phosphate (LiFePO4) and its doped and modified compounds.

[0091] In some embodiments, lithium phosphates may include those with the molecular formula Li m A x Fe 1-y B y P 1-z C z O 4-n D nThe material, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; m is selected from the range of 0.5 to 1.15, and optionally from the range of 0.95 to 1.05; x is selected from the range of 0 to 0.1, and optionally from the range of 0.001 to 0.005; y is selected from the range of 0 to 0.5, and optionally from the range of 0.001 to 0.1; z is selected from the range of 0 to 0.5, and optionally from the range of 0.001 to 0.1; n is selected from the range of 0 to 0.5, and optionally from the range of 0.001 to 0.1. The values ​​of m, x, y, z, and n must ensure that the lithium phosphate is electrically neutral.

[0092] During the charging and discharging process, lithium (Li) undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of lithium phosphates in this application, the molar Li content refers to the initial molar content of the lithium phosphate. When the positive electrode active material is used in a battery system, the molar Li content typically changes after charge-discharge cycles.

[0093] [Preparation Method]

[0094] This application also provides a method for preparing the above-mentioned positive electrode active material.

[0095] The method includes the following steps: providing a lithium phosphate precursor; grinding the lithium phosphate precursor with a carbon source; heating the ground material to a first temperature T1 at a first rate under a protective gas atmosphere and holding it at the first temperature T1 for a first time t1, then heating it to a second temperature T2 at a second rate and holding it at the second temperature T2 for a second time t2 to obtain a positive electrode active material. The positive electrode active material includes a lithium phosphate, and the X-ray diffraction pattern of the positive electrode active material tested in a fully charged state satisfies the following: having a (311) crystal plane peak in the range of 35°-36°, having a (011) crystal plane peak in the range of 20°-21°, and the peak intensity I of the (311) crystal plane peak is... 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.008.

[0096] In some embodiments, the first rate is less than or equal to 4 °C / min. By adjusting the first rate within the above range, a dense and uniform carbon coating layer can be formed, thereby concealing part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent, and thus enabling the battery using the positive electrode active material to have a long cycle life.

[0097] When the initial charge rate exceeds 4°C / min, the density and uniformity of the carbon coating layer are poor, resulting in sufficient contact between the lithium phosphate and the electrolyte in the initial state. At this time, the X-ray diffraction pattern of the positive electrode active material under full charge does not have a (311) crystal plane peak in the range of 35°-36°, and the initial capacity of the positive electrode active material can be fully utilized. Therefore, the positive electrode active material is difficult to act as a capacity release agent, and thus it is difficult to enable the battery using the positive electrode active material to have a long cycle life.

[0098] In some embodiments, the first rate can be 1℃ / min-4℃ / min, optionally 1.5℃ / min-3.5℃ / min, 1.5℃ / min-3℃ / min, or 1.5℃ / min-2.5℃ / min. By further adjusting the first rate within the above range, not only can the positive electrode active material act as a capacity-releasing agent, but the positive electrode active material particles can also have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), thereby enabling the positive electrode active material to have good kinetic performance. Consequently, the battery using this positive electrode active material can possess both long cycle life, good kinetic performance, and high energy conversion efficiency.

[0099] In some embodiments, the first temperature T1 is greater than or equal to 400°C. By adjusting the first temperature T1 within the above range, the carbon source can be fully decomposed to form carbon.

[0100] In some embodiments, the first temperature T1 can be 400℃-600℃, or optionally 450℃-550℃. By adjusting the first temperature T1 within the above range, the carbon source can be fully decomposed to form carbon, and the positive electrode active material particles can have a uniform primary particle size (here, the primary particle is a single-crystal-like primary particle). This allows the positive electrode active material to better function as a capacity-releasing agent, thereby enabling the battery using this positive electrode active material to have a long cycle life.

[0101] In some embodiments, the first time t1 is greater than or equal to 1 hour. By adjusting the first time t1 within the above range, the positive electrode active material particles can have a suitable and uniform primary particle size (here, the primary particle is a single crystal-like primary particle). This can hide part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent, thereby enabling the battery using this positive electrode active material to have a long cycle life.

[0102] When the time interval t1 is less than 1 hour or is 0, the size of the primary particles forming the positive electrode active material particles is too small. This results in the initial capacity of the prepared positive electrode active material not being fully utilized, and the X-ray diffraction pattern of the positive electrode active material under full charge does not have a (311) crystal plane peak in the range of 35°-36°. Therefore, the positive electrode active material is difficult to act as a capacity release agent, and thus it is difficult to enable the battery using the positive electrode active material to have a long cycle life.

[0103] In some embodiments, the first time t1 can be 1h-7h, and optionally 3h-5h. By further adjusting the first time t1 within the above range, not only can the positive electrode active material act as a capacity-releasing agent, but the positive electrode active material particles can also have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), thereby enabling the positive electrode active material to have good kinetic performance. Consequently, the battery using this positive electrode active material can have a long cycle life, good kinetic performance, and high energy conversion efficiency.

[0104] In some embodiments, the second temperature T2 is greater than or equal to 720°C. By adjusting the second temperature T2 within the above range, the positive electrode active material particles can have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), thereby hiding part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent, and thus enabling the battery using this positive electrode active material to have a long cycle life.

[0105] When the second temperature T2 is less than 720℃, the size of the primary particles forming the positive electrode active material is too small. This results in the initial capacity of the prepared positive electrode active material not being fully utilized, and the X-ray diffraction pattern of the positive electrode active material under full charge does not have a (311) crystal plane peak in the 35°-36° range. Therefore, the positive electrode active material is difficult to act as a capacity-releasing agent, thus making it difficult for batteries using positive electrode active materials to have a long cycle life. At the same time, when the second temperature T2 is less than 720℃, the graphitization degree of the carbon coating layer formed on the lithium phosphate surface will also be relatively small, and the electronic conductivity will also be relatively poor, which will further reduce the kinetic performance and energy conversion efficiency of the positive electrode active material and the battery.

[0106] The second temperature T2 should not be too high. A higher T2 results in larger primary particles (here, primary particles are quasi-single-crystal particles) forming the positive electrode active material particles, which reduces the kinetic performance of both the positive electrode active material and the battery. In some embodiments, the second temperature T2 can be 720℃-850℃, preferably 750℃-810℃. By further adjusting the second temperature T2 within the above range, the positive electrode active material particles can have a suitable primary particle size (here, primary particles are quasi-single-crystal particles), which allows the positive electrode active material to have good kinetic performance and also to act as a capacity-releasing agent. This allows the battery using this positive electrode active material to possess long cycle life, good kinetic performance, and high energy conversion efficiency.

[0107] In some embodiments, the second rate can be 1°C / min-10°C / min, and optionally 5°C / min-9°C / min. This allows the positive electrode active material particles to have a suitable primary particle size (here, the primary particle is a single-crystal-like primary particle), which not only enables the positive electrode active material to have good kinetic performance, but also allows the positive electrode active material to act as a capacity-controlled release agent.

[0108] In some embodiments, the first rate can be 1℃ / min-4℃ / min, and the second rate can be 5℃ / min-9℃ / min.

[0109] In some embodiments, the second time t2 can be 5h-20h, and can be selected as 8h-15h. This allows the positive electrode active material particles to have a suitable primary particle size (here, the primary particle is a single crystal-like primary particle), which can give the positive electrode active material good kinetic performance and enable it to act as a capacity-controlled release agent.

[0110] In some embodiments, the carbon source includes a first carbon source comprising a water-soluble polymer. When the first carbon source comprises a water-soluble polymer, the water-soluble polymer can adequately encapsulate the lithium phosphate precursor, thereby making the formed carbon coating layer more uniform and dense, which helps to conceal part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent.

[0111] In some embodiments, the water-soluble polymer may include one or more of polyethylene glycol, polyaniline, and their respective derivatives. A derivative generally refers to a product derived from which hydrogen atoms or groups of atoms in a compound are replaced by other atoms or groups of atoms.

[0112] When water-soluble polymers are within the above range, they can improve the electronic conductivity of lithium phosphate and reduce the specific surface area of ​​the prepared positive electrode active material. This makes the carbon coating layer more uniform and dense, which helps to hide part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-releasing agent.

[0113] In some embodiments, the weight content of the first carbon source can be ≥50%, based on the total weight of the carbon source. When the weight content of the first carbon source is within the above range, the resulting carbon coating layer can be more uniform and dense, thereby helping to conceal part of the initial capacity of the positive electrode active material, allowing the positive electrode active material to act as a capacity-controlled release agent.

[0114] When the weight content of the first carbon source is less than 50%, the density of the carbon coating layer is poor, resulting in sufficient contact between the lithium phosphate and the electrolyte in the initial state. At this time, the X-ray diffraction pattern of the positive electrode active material under full charge does not have the (311) crystal plane peak in the range of 35°-36°, and the initial capacity of the positive electrode active material can be fully utilized. Therefore, the positive electrode active material is difficult to act as a capacity release agent, and thus it is difficult to enable the battery using the positive electrode active material to have a long cycle life.

[0115] In some embodiments, the weight content of the first carbon source can be 50%-70%, based on the total weight of the carbon source. When the weight content of the first carbon source is large, more of the initial capacity of the positive electrode active material is hidden in the initial fully charged state, thereby improving the cycle life of the battery. However, the initial capacity of the positive electrode active material will decrease; at the same time, the lithium-ion transport rate of the positive electrode active material will also decrease, thereby affecting the energy density and kinetic performance of the battery. By further adjusting the weight content of the first carbon source within the above range, it is beneficial for the battery to have both long cycle life, high energy density, and good kinetic performance.

[0116] In some embodiments, the carbon source may further include a second carbon source, which may include one or more of glucose, sucrose, lactose, and maltose.

[0117] In some embodiments, the weight content of the second carbon source may be ≤50%, optionally 30%-50%, based on the total weight of the carbon source.

[0118] By further adjusting the weight content of the second carbon source within the above range, it is beneficial for the battery to have both long cycle life, high energy density and good kinetic performance, and also to reduce the raw material cost of the battery.

[0119] The amount of carbon source added can be calculated based on the residual carbon value of the carbon source (corresponding to the weight of the carbon coating layer in the positive electrode active material). In some embodiments, the weight content m of the carbon coating layer (i.e., the weight content of the residual carbon of the carbon source) satisfies 1.0% ≤ m ≤ 3.4%, and optionally, 1.2% ≤ m ≤ 2.0%.

[0120] In some embodiments, the precursor of lithium phosphate can be a mixture of various raw materials required for the preparation of lithium phosphate, such as lithium source, metal source (e.g., iron source), phosphorus source, and optional sources of various doping elements (e.g., A, B, C, D).

[0121] The lithium source may include one or more of lithium hydroxide, lithium carbonate, lithium phosphate, lithium oxalate, and lithium acetate.

[0122] The metal source may include one or more of the following: oxides, hydroxides, halides, phosphates, oxalates, sulfates, carbonates, and nitrates of a metal element.

[0123] Phosphorus sources may include one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, and iron phosphate.

[0124] The dopant source can include various compounds containing dopant elements.

[0125] In some embodiments, iron phosphate (FePO4) can be used as both the iron and phosphorus source.

[0126] In some embodiments, a solvent, such as one or more mixtures of water, ethanol, and propanol, may be added during the step of grinding the lithium phosphate precursor with the carbon source.

[0127] In some embodiments, after grinding the lithium phosphate precursor and the carbon source, spray drying can be performed. Then, the spray-dried powder can be heated to a first temperature T1 at a first rate and held at the first temperature T1 for a first time t1. Then, it can be heated to a second temperature T2 at a second rate and held at the second temperature T2 for a second time t2 to obtain the positive electrode active material.

[0128] In some embodiments, the protective gas may include one or more of nitrogen, argon, and helium.

[0129] In some embodiments, the obtained positive electrode active material may also be subjected to a crushing process. The crushing process may be airflow crushing.

[0130] In some embodiments, the method includes the following steps: providing a lithium phosphate precursor; grinding the lithium phosphate precursor with a carbon source, the carbon source including a first carbon source, the first carbon source including one or more of polyethylene glycol, polyaniline, and their respective derivatives, the first carbon source having a weight content ≥50% based on the total weight of the carbon source; heating the ground material to 400℃-600℃ at a rate of 1℃ / min-4℃ / min under a protective gas atmosphere and holding it at this temperature for 1h-7h, then heating it to 720℃-850℃ at a rate of 5℃ / min-9℃ / min and holding it at this temperature for 5h-20h to obtain a positive electrode active material. This allows batteries using this positive electrode active material to possess long cycle life, good kinetic performance, high energy density, and high energy conversion efficiency.

[0131] The method provided in this application embodiment can be used to prepare the positive electrode active material provided in this application embodiment. Other parameters of the prepared positive electrode active material can be referred to the positive electrode active material as above, and will not be repeated here.

[0132] [Positive electrode plate]

[0133] The positive electrode provided in this application includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive electrode active material as described above or a positive electrode active material prepared by the method described above.

[0134] The positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0135] In some embodiments, the positive electrode film layer may also include other positive electrode active materials besides the positive electrode active materials described above or the positive electrode active materials prepared by the methods described above, such as lithium transition metal oxides, etc., which are not limited in this application.

[0136] In some embodiments, the positive electrode film layer may optionally include a positive electrode conductive agent. This application does not impose any particular limitation on the type of positive electrode conductive agent. In some embodiments, as examples, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the positive electrode film layer may optionally include a positive electrode binder. This application does not impose any particular limitation on the type of positive electrode binder. In some embodiments, as examples, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0138] In some embodiments, the positive current collector may be a metal foil or a composite current collector. An example of a metal foil is aluminum foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. An example of a metal material may be one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. An example of a polymer substrate may be one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0139] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is usually formed by dispersing positive electrode active materials, positive electrode binders, and positive electrode conductive agents in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0140] [Negative electrode plate]

[0141] A single battery cell includes a negative electrode plate.

[0142] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0143] The negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0144] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0145] In some embodiments, the negative electrode active material may be a material known in the art. As an example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more 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 may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0146] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. As an example, the binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0147] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0148] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC)).

[0149] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, negative electrode conductive agent, negative electrode binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0150] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet may also include a protective layer covering the surface of the negative electrode film layer.

[0151] [Electrolytes]

[0152] The battery cell also includes an electrolyte. The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte may include one or more of solid electrolytes, gel electrolytes, and liquid electrolytes (i.e., electrolyte solutions).

[0153] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0154] The type of electrolyte salt is not specifically limited and can be selected according to actual needs. In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0155] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0156] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.

[0157] [Isolation membrane]

[0158] The battery cell may also include a separator. The separator can be disposed between the positive electrode and the negative electrode, mainly to prevent internal short circuits. 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.

[0159] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0160] Methods for preparing battery cells are well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a battery cell. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with the aforementioned electrolyte. After vacuum sealing, settling, and formation processes, a battery cell is obtained. Multiple battery cells can further be connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0161] This application also provides an electrical device, which includes the battery provided in this application embodiment. The battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, tablets, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0162] Electrical devices can choose the type of battery according to their usage needs, such as individual battery cells, battery modules, or battery packs.

[0163] Figure 6 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0164] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0165] Example

[0166] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0167] Example 1

[0168] (1) Preparation of positive electrode active material

[0169] FePO4, Li2CO3, glucose and polyethylene glycol were mixed evenly, a small amount of water was added, and the mixture was ground and then spray-dried. The spray-dried powder was placed in a sintering furnace and heated from 25°C to 500°C (first temperature T1) at a rate of 2°C / min under a nitrogen atmosphere and held at that temperature for 3 hours (first time t1). Then, the temperature was increased to 780°C (second temperature T2) at a rate of 5°C / min and held at that temperature for 10 hours (second time t2). After the process was completed, the mixture was cooled and broken up by airflow to obtain the positive electrode active material, namely carbon-coated LiFePO4.

[0170] The carbon source is a mixture of glucose and polyethylene glycol in a mass ratio of 5:5. The amount of carbon source added is such that the weight content of residual carbon in the carbon source (i.e., the weight content m of the carbon coating layer) is 1.29%, based on the total weight of the prepared positive electrode active material.

[0171] (2) Battery manufacturing

[0172] The above-mentioned positive electrode active material was mixed evenly with carbon black SP and polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone solvent system at a weight ratio of 92:2.5:5.5. The mixture was then coated onto aluminum foil, dried, and cold-pressed to obtain the positive electrode sheet.

[0173] The negative electrode active materials graphite, acetylene black, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) are mixed evenly in deionized water at a weight ratio of 95:2:2:1, coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet.

[0174] Ethyl carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried LiPF6 was dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0175] Using a porous polyethylene (PE) polymer film as the separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the battery assembly. The battery assembly is placed in an outer package, injected with electrolyte, and sealed. After formation and other processes, the battery is obtained.

[0176] Examples 2-14 and Comparative Examples 1-5

[0177] The battery preparation method is similar to that in Example 1, except that the preparation parameters of the positive electrode active material are different, as shown in Table 1. In Table 1, m represents the weight percentage of the carbon coating layer (residual carbon from the carbon source) based on the total weight of the prepared positive electrode active material; a first time t1 of 0 indicates that no heat preservation was performed at the first temperature.

[0178] Performance testing

[0179] (1) X-ray diffraction analysis of positive electrode active materials

[0180] The battery prepared above was charged at 25°C with a constant current of 1C to 3.65V, and then charged with a constant voltage to a current of 0.05C, at which point the battery was in a fully charged state. The positive electrode was then removed from the fully charged battery and tested using an X-ray diffractometer. The fully charged state of the positive electrode active material corresponds to the fully charged state of the battery, while the positive electrode active material itself is in a delithiation state.

[0181] In X-ray diffraction analysis, a copper target is used as the anode target, and CuKα rays are used as the radiation source. The wavelength of the rays is... The scanning 2θ angle range is 15°–45°, and the scanning rate is 2° / min. The testing instrument can be a Bruker D8 Discover X-ray diffractometer.

[0182] In the obtained X-ray diffraction pattern, there is a (311) crystal plane peak (LiFePO4 phase) in the range of 35°-36° and a (011) crystal plane peak (FePO4 phase) in the range of 20°-21°. 311 / I 011 This represents the ratio of the peak height of the (311) crystal plane peak to the peak height of the (011) crystal plane peak.

[0183] (2) Battery cycle performance test

[0184] At 25°C, the prepared battery was left to stand for 30 minutes before the following test was performed. The battery was charged to 3.65V at a constant power of 0.5P; after standing for 10 minutes, the battery was discharged to 2.5V at a constant power of 0.5P. The above steps were repeated until the battery's discharge capacity decreased to 90% of the initial discharge capacity, and the number of battery cycles was recorded.

[0185] (3) Initial DC internal resistance test of the battery

[0186] At 25°C, the battery prepared above was charged at a constant current of 0.5C to 3.65V, and then charged at a constant voltage to a current of 0.05C. The battery was then discharged at a constant current of 0.5C for 60 minutes to adjust the battery to 50% SOC, and the voltage of the battery at this time was recorded as U1. The battery was then discharged at a constant current of 1C for 30 seconds, and the voltage at the end of the discharge was recorded as U2 using a 0.1-second sampling time. The initial DC internal resistance DCR of the battery at 50% SOC is represented by the discharge DCR, where DCR = (U1 - U2) / 1C.

[0187] Table 2 shows the test results of the above embodiments and comparative examples.

[0188] In Table 2, A represents the specific surface area of ​​the prepared positive electrode active material, in m². 2 / g; δ represents the powder resistivity of the prepared positive electrode active material at 25°C, in Ω·cm. The specific surface area and powder resistivity of the positive electrode active material at 25°C can be tested according to the test methods given in the instruction manual.

[0189] Table 1

[0190]

[0191] Table 2

[0192]

[0193] Based on the test results in Tables 1 and 2, it can be seen that the X-ray diffraction patterns of the positive electrode active materials prepared in Comparative Examples 1 to 5 under full charge do not have the (311) crystal plane peak. At this time, the positive electrode active materials also do not have the capacity release effect, and the cycle life of the batteries using this positive electrode active material is relatively short.

[0194] Based on the test results in Tables 1 and 2, it can also be seen that by adjusting the peak intensity I of the (311) crystal plane peak in the X-ray diffraction pattern of the positive electrode active material under full charge, the peak intensity I can be adjusted. 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 A value ≥0.008 can give the battery a long cycle life.

[0195] Figure 7 This is the X-ray diffraction pattern of the positive electrode obtained by disassembling the battery prepared in Example 5 after it has been fully charged. From Figure 7 It can be seen that the X-ray diffraction pattern of the positive electrode active material under full charge state has a (311) crystal plane peak, and the peak intensity I of the (311) crystal plane peak is... 311Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.008 indicates that some lithium iron phosphate in the prepared positive electrode active material has not been delithiated. This undelithiated lithium iron phosphate can be gradually activated during battery cycling, and active lithium can be gradually released. This allows the positive electrode active material to act as a capacity release agent, thereby enabling the battery using it to have a long cycle life.

[0196] Based on the test results in Tables 1 and 2, it can also be seen that by adjusting the peak intensity I of the (311) crystal plane peak in the X-ray diffraction pattern of the positive electrode active material under full charge, the peak intensity I can be adjusted. 311 Peak intensity I of (011) crystal plane peak 011 The ratio further satisfies 0.012 ≤ I 311 / I 011 A value of ≤0.024 can also enable the battery to have a longer cycle life while maintaining low internal resistance and good dynamic performance.

[0197] 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 positive electrode active material, characterized in that, The positive electrode active material includes lithium phosphate, and the X-ray diffraction pattern of the positive electrode active material tested in a fully charged state satisfies the following: it has a (311) crystal plane peak in the range of 35°-36°, a (011) crystal plane peak in the range of 20°-21°, and the peak intensity of the (311) crystal plane peak is I. 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.

008.

2. The positive electrode active material according to claim 1, characterized in that, 0.009≤I 311 / I 011 ≤0.037。 3. The positive electrode active material according to claim 2, characterized in that, 0.012≤I 311 / I 011 ≤0.024。 4. The positive electrode active material according to any one of claims 1-3, characterized in that, At least a portion of the surface of the lithium phosphate has a carbon coating layer.

5. The positive electrode active material according to claim 4, characterized in that, The weight content of the carbon coating layer is denoted as m, and the specific surface area of ​​the positive electrode active material, based on the total weight of the positive electrode active material, is denoted as A, with units of m³. 2 / g, 5.0≤A / (100×m)≤9.

0.

6. The positive electrode active material according to claim 5, characterized in that, 6.4≤A / (100×m)≤8.

2.

7. The positive electrode active material according to any one of claims 4-6, characterized in that, 1.0% ≤ m ≤ 3.4%; and / or, A≤18.5m 2 / g。 8. The positive electrode active material according to claim 7, characterized in that, 1.2% ≤ m ≤ 2.0%; and / or, A≤13.5m 2 / g。 9. The positive electrode active material according to any one of claims 1-8, characterized in that, The positive electrode active material has a single crystal structure or a near-single crystal structure.

10. The positive electrode active material according to any one of claims 1-9, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 0.6 μm-2.5 μm; and / or, The resistivity of the positive electrode active material at 25°C is denoted as δ, where δ ≤ 20 Ω·cm.

11. The positive electrode active material according to claim 10, characterized in that, The volume distribution particle size Dv50 of the positive electrode active material is 0.7 μm-2.3 μm; and / or, The resistivity of the positive electrode active material at 25°C is denoted as δ, where δ ≤ 12.1 Ω·cm.

12. The positive electrode active material according to any one of claims 1-11, characterized in that, The lithium-containing phosphate includes one or more of lithium iron phosphate and its doped and modified compounds.

13. The positive electrode active material according to claim 12, characterized in that, The lithium-containing phosphate includes those with the molecular formula Li. m A x Fe 1-y B y P 1-z C z O 4-n D n The material, A includes one or more elements selected from Zn, Al, Na, K, and Mg; B includes one or more elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; m is selected from the range of 0.5 to 1.15; x is selected from the range of 0 to 0.1; y is selected from the range of 0 to 0.5; z is selected from the range of 0 to 0.5; n is selected from the range of 0 to 0.

5.

14. The positive electrode active material according to claim 13, characterized in that, m is selected from the range of 0.95 to 1.

05.

15. The positive electrode active material according to claim 13, characterized in that, x is selected from the range of 0.001 to 0.

005.

16. The positive electrode active material according to claim 13, characterized in that, y is selected from the range of 0.001 to 0.

1.

17. The positive electrode active material according to claim 13, characterized in that, z is selected from the range of 0.001 to 0.

1.

18. The positive electrode active material according to claim 13, characterized in that, n is selected from the range of 0.001 to 0.

1.

19. A method for preparing a positive electrode active material, characterized in that, Includes the following steps: Provide lithium phosphate precursors; The lithium phosphate precursor was ground with a carbon source; The ground material is heated to a first temperature T1 at a first rate under a protective gas atmosphere and held at the first temperature T1 for a first time t1. Then, it is heated to a second temperature T2 at a second rate and held at the second temperature T2 for a second time t2 to obtain the positive electrode active material. The positive electrode active material includes lithium phosphate, and the X-ray diffraction pattern of the positive electrode active material tested in a fully charged state satisfies the following: it has a (311) crystal plane peak in the range of 35°-36°, and a (011) crystal plane peak in the range of 20°-21°, and the peak intensity of the (311) crystal plane peak is I. 311 Peak intensity I of (011) crystal plane peak 011 The ratio satisfies I 311 / I 011 ≥0.

008.

20. The preparation method according to claim 19, characterized in that, The first rate is less than or equal to 4 °C / min.

21. The preparation method according to claim 20, characterized in that, The first rate is 1℃ / min-4℃ / min.

22. The preparation method according to any one of claims 19-21, characterized in that, The first temperature T1 is greater than or equal to 400℃.

23. The preparation method according to claim 22, characterized in that, The first temperature T1 is 400℃-600℃.

24. The preparation method according to claim 23, characterized in that, The first temperature T1 is 450℃-550℃.

25. The preparation method according to any one of claims 19-24, characterized in that, The first time t1 is greater than or equal to 1 hour.

26. The preparation method according to claim 25, characterized in that, The first time t1 is 1h-7h.

27. The preparation method according to claim 26, characterized in that, The first time t1 is 3h-5h.

28. The preparation method according to any one of claims 19-27, characterized in that, The second temperature T2 is greater than or equal to 720℃.

29. The preparation method according to claim 28, characterized in that, The second temperature T2 is 720℃-850℃.

30. The preparation method according to claim 29, characterized in that, The second temperature T2 is 750℃-810℃.

31. The preparation method according to any one of claims 19-30, characterized in that, The second rate is 1℃ / min-10℃ / min; and / or, The second time t2 is 5h-20h.

32. The preparation method according to claim 31, characterized in that, The second rate is 5°C / min - 9°C / min; and / or, The second time t2 is 8h-15h.

33. The preparation method according to any one of claims 19-32, characterized in that, The carbon source includes a first carbon source, which includes a water-soluble polymer.

34. The preparation method according to claim 33, characterized in that, The first carbon source has a weight content of ≥50%, based on the total weight of the carbon source.

35. The preparation method according to claim 34, characterized in that, The first carbon source has a weight content of 50%-70%, based on the total weight of the carbon source.

36. The preparation method according to any one of claims 33-35, characterized in that, The water-soluble polymer includes one or more of polyethylene glycol, polyaniline, and their respective derivatives.

37. The preparation method according to any one of claims 33-36, characterized in that, The carbon source also includes a second carbon source, which includes one or more of glucose, sucrose, lactose, and maltose.

38. The preparation method according to claim 37, characterized in that, The second carbon source has a weight content of ≤50%, based on the total weight of the carbon source.

39. The preparation method according to claim 38, characterized in that, The second carbon source has a weight content of 30%-50%, based on the total weight of the carbon source.

40. A battery cell, comprising a positive electrode sheet, said positive electrode sheet comprising a positive current collector and a positive electrode film layer disposed on at least one surface of said positive current collector, characterized in that, The positive electrode film layer comprises the positive electrode active material according to any one of claims 1-18 or the positive electrode active material prepared by the preparation method according to any one of claims 19-39.

41. An electrical appliance, characterized in that, Includes the battery cell as described in claim 40.

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