Battery cells, battery cell preparation methods and electrical devices

Abstract

This application provides a battery cell, a method for preparing the battery cell, and an electrical device. The battery cell includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes a positive electrode active material, which includes a lithium phosphate material. The iron dissolution rate of the positive electrode active material is 0 mg / L–10 mg / L, and the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06. The battery cell of this application exhibits good cycle stability and good specific capacity. The method for preparing the positive electrode active material of this application simplifies the preparation process, reduces production costs, and lowers the iron dissolution rate of the positive electrode active material.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a battery cell, a method for preparing the battery cell, and an electrical device thereof. Background Technology

[0002] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the increasing application of rechargeable batteries, higher requirements have been placed on their cycle performance and service life.

[0003] Lithium iron phosphate (LFP) materials have advantages such as high safety and play an important role in the application of rechargeable batteries. However, the preparation process of LFP is complex and expensive, and the prepared LFP cannot simultaneously achieve good cycle stability and specific capacity. Summary of the Invention

[0004] This application was made in view of the aforementioned issues and aims to at least solve one of the technical problems existing in the prior art. Therefore, this application provides a battery cell, a method for manufacturing the battery cell, and an electrical device.

[0005] The first aspect of this application provides a battery cell, which includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes a positive electrode active material, which includes a lithium phosphate material. The iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06.

[0006] The iron dissolution rate of the positive electrode active material is within the above-mentioned range, which reduces the content of iron ions dissolved from the positive electrode active material during battery charging and discharging. This reduces the risk of iron ions precipitating at the negative electrode to form iron dendrites and dendrites piercing the solid electrolyte interphase (SEI) film, thus improving the battery's cycle stability. The molar ratio of lithium to iron in the positive electrode active material is also within the above-mentioned range, which helps to improve the specific capacity and lithium-ion diffusion coefficient of the positive electrode active material. In summary, the battery cell of this application embodiment exhibits excellent cycle stability while also achieving good specific capacity.

[0007] In any embodiment, the iron dissolution rate of the positive electrode active material is 0 mg / L-5 mg / L.

[0008] The iron dissolution rate of the positive electrode active material is within the above range, which is beneficial to further improve the cycle stability of the battery.

[0009] In any embodiment, based on the total mass of the positive electrode active material, the mass content of sulfur in the positive electrode active material is 0ppm-50ppm.

[0010] The sulfur content of the positive electrode active material is within the above range, which helps to reduce the content of sulfur impurities dissolved in the electrolyte, reduce the degree of side reactions of sulfur impurities, and thus further improve the cycle stability of the secondary battery in this application embodiment.

[0011] In any embodiment, the Dv90 of the positive electrode active material is 2μm-5μm.

[0012] The fact that the Dv90 of the positive electrode active material is within the above range indicates that the proportion of large-diameter active material particles in the positive electrode active material is low. This is beneficial to shortening the diffusion distance of lithium ions in the positive electrode active material for extraction / intercalation, thereby improving the lithium ion diffusion coefficient of the positive electrode active material and improving the rate performance of the battery.

[0013] In any embodiment, the Dv99 of the positive electrode active material is 4μm-8μm.

[0014] The fact that the Dv99 of the positive electrode active material is within the above range indicates that the proportion of large-diameter active material particles in the positive electrode active material is low. This is beneficial to further shorten the diffusion distance of lithium ions in the positive electrode active material for extraction / intercalation, thereby further improving the lithium ion diffusion coefficient of the positive electrode active material and contributing to the further improvement of battery rate performance.

[0015] In any embodiment, the specific capacity of the positive electrode active material at a discharge rate of 0.33C is 145mAh / g-152mAh / g.

[0016] Having a specific capacity of positive electrode active material within the above range is beneficial for improving the energy density of the battery.

[0017] In any embodiment, the lithium-ion diffusion coefficient of the positive electrode active material is 3 × 10⁻⁶. -14 cm 2 / s-8×10 - 14 cm 2 / s.

[0018] When the lithium-ion diffusion coefficient of the positive electrode active material is within the above range, it is beneficial to further improve the rate performance of the battery.

[0019] In any embodiment, the lithium phosphate comprises a component having the following general formula:

[0020] Li m Fe x P y O j Qq ,

[0021] Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0022] In any embodiment, the molar ratio of lithium to iron in the positive electrode active material is 1.01-1.06; and / or

[0023] The molar ratio of iron to phosphorus in the positive electrode active material is 0.96-1, and optionally, it is 0.96-0.98.

[0024] Within the aforementioned ranges, the molar ratios of lithium to iron and iron to phosphorus in the cathode active material are beneficial for further reducing impurities, further decreasing iron dissolution, and further improving the specific capacity and cycle stability of the cathode active material. Furthermore, suitable molar ratios of lithium to iron and iron to phosphorus are also beneficial for further improving the lithium-ion diffusion coefficient of the cathode active material.

[0025] A second aspect of this application provides a method for preparing a battery cell, comprising at least the following steps:

[0026] Preparation of positive electrode active material: Raw materials including a first lithium source, an iron source, and a phosphorus source are mixed with a solvent to obtain a slurry; the slurry is treated to obtain a precursor material; the precursor material is sintered to obtain the positive electrode active material, wherein the positive electrode active material includes a lithium phosphate material, the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06, and the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L;

[0027] The battery cell is prepared using the positive electrode active material.

[0028] Compared to the solid-phase method for preparing positive electrode active materials, the preparation method of this application obtains positive electrode active materials through a one-step liquid-phase co-precipitation method, which eliminates the need for complex precursor preparation processes and high-temperature and high-pressure reaction conditions, thereby reducing the production cost of lithium iron phosphate materials.

[0029] The preparation method of this application embodiment controls the molar ratio of lithium to iron in the positive electrode active material within the above-mentioned range, resulting in excellent specific capacity of the positive electrode active material. This also facilitates the formation of pure-phase lithium iron phosphate during the sintering process, thereby reducing the iron dissolution rate of the positive electrode active material. Furthermore, the liquid-phase co-precipitation method used in this application embodiment achieves atomic-level uniform distribution of iron, phosphorus, and lithium elements in the positive electrode active material, which enhances the binding of phosphate ions to iron ions, further reducing the iron dissolution rate and ensuring that the iron dissolution rate of the positive electrode active material meets the above-mentioned range. The secondary battery exhibits excellent cycle stability while maintaining good specific capacity.

[0030] In any embodiment, the first lithium source comprises lithium sulfate.

[0031] Lithium sulfate has advantages such as abundant sources, low cost, and good water solubility, making it suitable for the preparation method of this application embodiment. This helps to reduce raw material costs, thereby further reducing the production cost of lithium iron phosphate materials.

[0032] In any embodiment, the molar ratio of lithium in the first lithium source to iron in the iron source is greater than 1 and less than or equal to 1.06. Optionally, the molar ratio of lithium in the first lithium source to iron in the iron source is 1.01-1.06.

[0033] In any embodiment, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is 0.96-1, and optionally, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is 0.96-0.98.

[0034] When the molar ratio of lithium in the first lithium source to iron in the iron source, and the molar ratio of iron in the iron source to phosphorus in the phosphorus source, are within the above-mentioned ranges, it is beneficial to form pure-phase lithium iron phosphate during sintering, further reducing the iron dissolution rate of the prepared cathode active material, and thus further improving the specific capacity and cycle stability of the cathode active material. Furthermore, suitable molar ratios of lithium to iron and iron to phosphorus are also beneficial to further improving the lithium-ion diffusion coefficient of the cathode active material.

[0035] In any embodiment, the preparation of the positive electrode active material includes at least the following steps:

[0036] The raw materials, including the first lithium source, the iron source, and the phosphorus source, are mixed with the solvent to obtain the slurry; a pH adjuster is added until the pH of the slurry is greater than or equal to 7 to obtain the second slurry; the second slurry is separated to obtain the precursor material; and the precursor material is sintered to obtain the positive electrode active material.

[0037] Adjusting the pH of the slurry to be greater than or equal to 7 by adding a pH adjuster is beneficial for further precipitation of lithium ions in the slurry. This ensures that the molar ratio of lithium to iron in the precursor material is within a suitable range, for example, a molar ratio of 1.01-1.06. This facilitates the formation of a purer phase of lithium iron phosphate during sintering, thereby ensuring that the iron dissolution rate of the prepared cathode active material is within a suitable range, further balancing excellent specific capacity and cycle stability.

[0038] In any embodiment, the pH adjuster includes one or more of ammonium carbonate and ammonium bicarbonate.

[0039] The above-mentioned pH adjusters are compatible with the preparation method of this application.

[0040] In any embodiment, the preparation of the positive electrode active material further includes: separating the second slurry to obtain a solid material; adding a carbon source to the solid material and grinding it to obtain the precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0041] The precursor material includes a carbon source, and the surface of the positive electrode active material prepared by sintering is uniformly coated with a highly conductive carbon layer, which is beneficial to improving the conductivity of the positive electrode active material. Furthermore, carbon can act as a reducing agent to reduce Fe... 3+ Reduced to Fe 2+ This will help to further improve the specific capacity of the positive electrode active material.

[0042] In any embodiment, the carbon source has a mass content of 1%-5% based on the mass of the solid material.

[0043] By controlling the amount of carbon source added within a suitable range, the carbon coating thickness on the surface of the prepared positive electrode active material is appropriate, which is beneficial to further improve the conductivity and specific capacity of the positive electrode active material.

[0044] In any embodiment, the preparation of the positive electrode active material includes at least the following steps: mixing raw materials including the first lithium source, the iron source, and the phosphorus source with the solvent to obtain the slurry; separating the slurry to obtain a first solid material; washing the first solid material and sintering the first solid material after washing to obtain a second solid material; adding a second lithium source to the second solid material and grinding it to obtain the precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0045] The preparation method of this application, through washing and precipitation separation, effectively removes impurity ions such as sulfate introduced by the first lithium source from the first solid material, reducing the impurity content dissolved into the electrolyte, thereby reducing the degree of side reactions and further improving the cycle performance of the secondary battery. However, washing dissolves lithium in the first solid material, resulting in an excessively low molar ratio of lithium to iron in the second solid material. If directly used for sintering to prepare the positive electrode active material, this would increase the iron dissolution rate of the positive electrode active material, for example, greater than 10 mg / L, and reduce its specific capacity. Therefore, the preparation method of this application further incorporates a second lithium source into the second solid material, thereby ensuring that the molar ratio of lithium to iron in the precursor material used for sintering to prepare the positive electrode active material is within a suitable range. This facilitates the formation of a purer phase of lithium iron phosphate during sintering, keeping the iron dissolution rate of the positive electrode active material within a suitable range. The resulting positive electrode active material exhibits good cycle stability and excellent specific capacity. In summary, the above preparation method reduces the production cost of lithium iron phosphate. Meanwhile, the obtained positive electrode active material has a lower iron dissolution rate and a further reduced impurity ion content, which is beneficial to further improve the cycle performance of the positive electrode active material of this application while taking into account the specific capacity.

[0046] In any embodiment, based on the total mass of the positive electrode active material, the mass content of sulfur in the positive electrode active material is 0ppm-50ppm.

[0047] When lithium sulfate is used as the first lithium source, the first solid material obtained after washing and precipitation separation can effectively remove sulfate ions from the first solid, so that the mass content of sulfur in the positive electrode active material is within the above range, which is beneficial to further improve the cycle performance of the positive electrode active material of this application.

[0048] In any embodiment, the first solid material is washed 3-5 times.

[0049] Controlling the number of washes within the above range helps to remove impurities to the greatest extent while dissolving as little lithium as possible in the first solid material. This helps to further reduce the cost of subsequent lithium replenishment and balance the specific capacity and cycle stability of the secondary battery.

[0050] In any embodiment, the second lithium source includes one or more of lithium carbonate and lithium hydroxide.

[0051] In any embodiment, the temperature at which the first solid material is sintered is 300°C-400°C; and / or

[0052] The sintering time for the first solid material is 3-5 hours.

[0053] Controlling the temperature and time for sintering the first solid material within the aforementioned range facilitates the removal of moisture from the first solid material, transforming it into a second solid material containing an iron phosphate phase. By testing the iron-lithium ratio of the second solid material, it is easier to calculate the amount of the second lithium source that needs to be added. Furthermore, the aforementioned sintering temperature and time facilitate the uniform mixing of the sintered second solid material and the second lithium source to obtain a precursor material, thereby improving the efficiency of subsequent sintering of the precursor material.

[0054] In any embodiment, the preparation of the positive electrode active material further includes: adding the second lithium source and carbon source to the second solid material, grinding it to obtain the precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0055] The precursor material includes a carbon source, and the surface of the positive electrode active material prepared by sintering is uniformly coated with a highly conductive carbon layer, which is beneficial to improving the conductivity of the positive electrode active material. Furthermore, carbon can act as a reducing agent to reduce Fe... 3+ Reduced to Fe 2+ This will help to further improve the specific capacity of the positive electrode active material.

[0056] In any embodiment, the carbon source has a mass content of 1%-5% based on the mass of the second solid material.

[0057] By controlling the amount of carbon source added within a suitable range, the carbon coating thickness on the surface of the prepared positive electrode active material is appropriate, which is beneficial to further improve the conductivity and specific capacity of the positive electrode active material.

[0058] In any embodiment, the temperature for sintering the precursor material is 650°C-750°C; and / or

[0059] The sintering time for the precursor material is 5-15 hours.

[0060] Controlling the temperature and time of the sintering precursor within the above-mentioned range is beneficial to improving the conversion rate of the precursor material to the lithium iron phosphate phase, further reducing the iron dissolution rate of the cathode active material, and increasing the specific capacity of the cathode active material. Furthermore, the above-mentioned sintering temperature and time are conducive to the reaction of the added carbon source and ferric ions to ferrous ions, and make the surface of the sintered cathode active material have a uniform carbon coating layer, thereby further improving the specific capacity and cycle stability of the cathode active material.

[0061] In any embodiment, the iron source includes one or more of ferrous sulfate and ferric sulfate; and / or

[0062] The phosphorus source includes one or more of ammonium dihydrogen phosphate, phosphoric acid, and diammonium hydrogen phosphate.

[0063] A third aspect of this application provides an electrical device comprising a battery cell according to the first aspect of this application or a battery cell prepared according to the preparation method of the second aspect of this application. Attached Figure Description

[0064] Figure 1 This is a scanning electron microscope image of the positive electrode active material prepared according to one embodiment of this application;

[0065] Figure 2 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0066] Figure 3 yes Figure 2 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0067] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application;

[0068] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0069] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown;

[0070] Figure 7 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0071] Explanation of reference numerals in the attached figures:

[0072] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0073] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the battery cell, the method for preparing the battery cell, and the electrical device thereof. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially 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.

[0074] 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.

[0075] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0076] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0077] 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.

[0078] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0079] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0080] Lithium iron phosphate (LFP) boasts advantages such as high safety, making it a research hotspot in the field of cathode active materials for rechargeable batteries. However, the preparation process of LFP materials is complex and the production cost is high, and the prepared LFP materials often exhibit poor cycle performance or low specific capacity. Therefore, balancing the cycle performance and specific capacity of LFP materials with / or reducing their preparation cost is an urgent problem to be solved in the field of cathode active materials.

[0081] [Battery cell]

[0082] Based on this, this application provides a battery cell, which includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film disposed on at least one side of the positive current collector. The positive electrode film includes a positive electrode active material, which includes a lithium phosphate material. The iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06.

[0083] In some implementations, the iron dissolution rate is the iron dissolution rate of the positive electrode active material in its initial state or the iron dissolution rate of the positive electrode active material obtained after disassembling the battery.

[0084] In this paper, the iron dissolution rate of the positive electrode active material can be measured using methods and equipment known in the art. For example, the positive electrode is removed from the battery, the active material film is peeled off, dissolved in N-methylpyrrolidone (NMP) solvent, filtered, and thoroughly washed with NMP to remove the binder; then dried to obtain powder for subsequent characterization tests. A certain mass of 5g of powder is weighed and added to 100mL of 0.008mol / L hydrochloric acid to obtain a dispersion solution with a positive electrode active material concentration of 0.05g / mL. The solution is stirred at 25°C for 30min, then allowed to stand in a 25°C water bath for 2h. After filtration, the iron ion concentration in the filtrate is tested, for example using inductively coupled plasma atomic emission spectrometry (ICP), with the test method referring to national standards EPA 6010D-2018 and JY / T 0567-2020.

[0085] In some embodiments, the iron dissolution rate of the positive electrode active material can be 0 mg / L, 3 mg / L, 5 mg / L, 6 mg / L, 8 mg / L, 10 mg / L, or any range of two of the above iron dissolution rates, or other unlisted values ​​within such range.

[0086] In this paper, the molar ratio of lithium to iron in the positive electrode active material can be measured using methods and equipment known in the art. For example, the active material film layer of the positive electrode sheet is peeled off, dissolved in NMP solvent, filtered, and thoroughly washed with NMP to remove the binder; it is then dried to obtain powder for subsequent characterization tests. A certain mass (e.g., 0.5 g) of powder is weighed and added to a certain volume (e.g., 10 mL) of aqua regia for microwave digestion for a certain time (e.g., 20 min). Subsequently, a certain volume (e.g., 1 mL) of the sample is measured and diluted to a suitable volume (e.g., 100 mL) for later use. The Li and Fe elemental contents in the above sample are tested according to the national standard EPA6010D-2018JY / T 0567-2020 inductively coupled plasma atomic emission spectrometry, and the Li / Fe molar ratio in the positive electrode active material is calculated.

[0087] In some embodiments, the molar ratio of lithium to iron in the positive electrode active material can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, or any range of two of the above molar ratios, or other unlisted values ​​within that range.

[0088] The iron dissolution rate of the positive electrode active material is within the above-mentioned range, which reduces the content of iron ions dissolved from the positive electrode active material during battery charging and discharging. This reduces the risk of iron ions precipitating at the negative electrode to form iron dendrites and dendrites piercing the solid electrolyte interphase (SEI) film, thus improving the battery's cycle stability. The molar ratio of lithium to iron in the positive electrode active material is also within the above-mentioned range, which helps to improve the specific capacity and lithium-ion diffusion coefficient of the positive electrode active material. In summary, the battery cell of this application embodiment exhibits excellent cycle stability while also achieving good specific capacity.

[0089] In some implementations, the iron dissolution rate of the positive electrode active material is 0 mg / L-5 mg / L.

[0090] The iron dissolution rate of the positive electrode active material is within the above range, which is beneficial to further improve the cycle stability of the battery.

[0091] In some implementations, the sulfur content in the positive electrode active material is 0 ppm to 50 ppm based on the total mass of the positive electrode active material.

[0092] In some embodiments, based on the total mass of the positive electrode active material, the mass content of sulfur in the positive electrode active material can be 0 ppm, 5 ppm, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, or a range consisting of any two of the above-mentioned sulfur mass contents, or other unlisted values ​​within the range of the composition.

[0093] In this paper, based on the total mass of the positive electrode active material, the mass content of sulfur in the positive electrode active material can be measured using methods and equipment known in the art. For example, the positive electrode is removed from the battery, the active material film is peeled off, dissolved in NMP solvent, filtered, and thoroughly washed with NMP to remove the binder; it is then dried to obtain powder for subsequent characterization testing. A certain mass (e.g., 0.5 g) of powder is weighed, and a certain volume (e.g., 10 mL) of aqua regia is added for microwave digestion for a certain time (e.g., 20 min). Subsequently, a certain volume (e.g., 1 mL) of the sample is measured and diluted to a suitable volume (e.g., 100 mL) for later use. The sulfur content in the above sample is tested according to the national standard EPA 6010D-2018JY / T 0567-2020 inductively coupled plasma atomic emission spectrometry, and the mass content of sulfur in the positive electrode active material is finally calculated.

[0094] The sulfur content of the positive electrode active material is within the above range, which helps to reduce the content of sulfur impurities dissolved in the electrolyte, reduce the degree of side reactions of sulfur impurities, and thus further improve the cycle stability of the secondary battery in this application embodiment.

[0095] In some implementations, the Dv90 of the positive electrode active material is 2μm-5μm.

[0096] In this paper, the term "Dv90" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 90%.

[0097] In some embodiments, the Dv90 of the positive electrode active material can be 2μm, 3μm, 4μm, 5μm, or any range of two of the above Dv90s, or other unlisted values ​​within such range.

[0098] In this paper, the Dv90 of the positive electrode active material can be measured using methods and equipment known in the art. For example, an appropriate amount of the positive electrode active material to be tested is taken and determined using a laser particle size analyzer according to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0099] The fact that the Dv90 of the positive electrode active material is within the above range indicates that the proportion of large-diameter active material particles in the positive electrode active material is low. This is beneficial to shortening the diffusion distance of lithium ions in the positive electrode active material for extraction / intercalation, thereby improving the lithium ion diffusion coefficient of the positive electrode active material and improving the rate performance of the battery.

[0100] In some implementations, the Dv99 of the positive electrode active material is 4μm-8μm.

[0101] In this paper, the term "Dv99" refers to the particle size at which the cumulative volumetric size distribution percentage in the particle reaches 99%.

[0102] In some embodiments, the Dv99 of the positive electrode active material can be 4μm, 5μm, 6μm, 7μm, 8μm, or any range of two of the above Dv99, or other unlisted values ​​within the range of such range.

[0103] In this paper, the Dv99 of the positive electrode active material can be measured using methods and equipment known in the art. For example, an appropriate amount of the positive electrode active material to be tested is taken, and the Dv99 is determined using a laser particle size analyzer according to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0104] The fact that the Dv99 of the positive electrode active material is within the above range indicates that the proportion of large-diameter active material particles in the positive electrode active material is low. This is beneficial to further shorten the diffusion distance of lithium ions in the positive electrode active material for extraction / intercalation, thereby further improving the lithium ion diffusion coefficient of the positive electrode active material and contributing to the further improvement of battery rate performance.

[0105] In some embodiments, the specific capacity of the positive electrode active material at a discharge rate of 0.33C is 145mAh / g-152mAh / g.

[0106] In some embodiments, the specific capacity of the positive electrode active material at a discharge rate of 0.33C can be 145mAh / g, 146mAh / g, 147mAh / g, 148mAh / g, 149mAh / g, 150mAh / g, 151mAh / g, 152mAh / g, or any range of two of the above specific capacities, or other unlisted values ​​within such range.

[0107] In this paper, the specific capacity of the positive electrode active material at a discharge rate of 0.33C can be measured using methods and equipment known in the art. For example, at 25°C, a fresh battery cell is charged at a constant current of 0.33C to 3.8V, then charged at a constant voltage of 3.8V until the cutoff current is 0.05C. After a 5-minute pause, the cell is discharged at a constant current of the corresponding rate (e.g., 0.33C), with a discharge cutoff voltage of 2V. This process is repeated three times consecutively. The capacity obtained from the third charge / discharge is taken as the cell's test capacity. Combined with the mass of the positive electrode active material, the specific capacity of the positive electrode active material at a discharge rate of 0.33C can be calculated.

[0108] Having a specific capacity of positive electrode active material within the above range is beneficial for improving the energy density of the battery.

[0109] In some embodiments, the lithium-ion diffusion coefficient of the positive electrode active material is 3 × 10⁻⁶. -14 cm 2 / s-8×10 - 14 cm 2 / s.

[0110] In this paper, the term "lithium-ion diffusion coefficient" refers to the diffusion mass transfer rate of lithium ions under the action of a unit concentration gradient, and is an important indicator characterizing the speed of lithium-ion diffusion.

[0111] In some embodiments, the lithium-ion diffusion coefficient of the positive electrode active material can be 3 × 10⁻⁶. -14 cm 2 / s, 4×10 -14 cm 2 / s, 5×10 -14 cm 2 / s, 6×10 -14 cm 2 / s, 7×10 -14 cm 2 / s, 8×10 -14 cm 2 / s or any of the two lithium-ion diffusion coefficients mentioned above, or any other unlisted value within that range.

[0112] In this paper, the lithium-ion diffusion coefficient of the positive electrode active material can be measured using methods and equipment known in the art. For example, the cell capacity is adjusted to 50% SOC, continuously discharged at a 1C rate for 30 seconds, with a relaxation time of 2 minutes, and the result is obtained according to the formula... The lithium-ion diffusion coefficient at 50% SOC is calculated and is then used as the lithium-ion diffusion coefficient of the positive electrode active material.

[0113] When the lithium-ion diffusion coefficient of the positive electrode active material is within the above range, it is beneficial to further improve the rate performance of the battery.

[0114] In some embodiments, the lithium phosphate comprises a component having the following general formula:

[0115] Li m Fe x P y O j Q q ,

[0116] Wherein, Q includes one or more of Al, Na, K, Mg, Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, V, Ti, B, S, Si, N, F, Cl, and Br, with 0.8≤m≤1.15, 0.9≤x≤1, 0.95≤y≤1, 3.5≤j≤4, and 0≤q≤0.1.

[0117] When used herein, "lithium phosphates include components having the following general formula" is not limited to substances represented by the general molecular formula, but also includes other substances formed by further appropriate modifications based on the general molecular formula, which are not limited herein. The use of "general formula" is for ease of description only and is not intended to limit this application. It is understood that new materials or substances obtained by appropriate modifications based on the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modifications refer to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0118] In some implementations, m can be 0.8, 0.85, 0.9, 0.95, 0.98, 1.00, 1.03, 1.05, 1.08, 1.10, 1.13, 1.15, or a range consisting of any two of the above m, or a value within the range.

[0119] In some implementations, x can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.0, or a range consisting of any two of the above x, or a value within the range.

[0120] In some implementations, y can be 0.95, 0.98, 1.0, or a range of any two of the above y values, or a value within that range.

[0121] In some implementations, j can be 3.5, 3.6, 3.7, 3.8, 3.9, 4, or a range consisting of any two z values, or a value within that range.

[0122] In some implementations, q can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or a range of any two of the above q, or a value within that range.

[0123] In some embodiments, the modifying element Q can exist in the lithium phosphate material as a dopant element, or in the coating layer of the lithium phosphate material as a coating element.

[0124] In some embodiments, the molar ratio of lithium to iron in the positive electrode active material is 1.01-1.06.

[0125] In some embodiments, the molar ratio of iron to phosphorus in the positive electrode active material is 0.96-1.

[0126] In some embodiments, the molar ratio of iron to phosphorus in the positive electrode active material is 0.96-0.98.

[0127] In this paper, the molar ratio of iron to phosphorus in the cathode active material can be measured using methods and equipment known in the art. For example, the test method for the molar ratio of lithium to iron in the cathode active material can be referred to above.

[0128] In some embodiments, the molar ratio of iron to phosphorus in the positive electrode active material can be 0.96, 0.97, 0.98, 0.99, 1, or a range of any two of the above molar ratios, or other unlisted values ​​within the range of the above ratios.

[0129] Within the aforementioned ranges, the molar ratios of lithium to iron and iron to phosphorus in the cathode active material are beneficial for further reducing impurities and iron dissolution rates, thereby improving the specific capacity and cycle stability of the secondary battery. Furthermore, suitable molar ratios of lithium to iron and iron to phosphorus also contribute to increasing the lithium-ion diffusion coefficient of the cathode active material.

[0130] [Preparation methods for battery cells]

[0131] This application also provides a method for preparing a battery cell, comprising at least the following steps:

[0132] Preparation of positive electrode active material: Raw materials including a first lithium source, an iron source, and a phosphorus source are mixed with a solvent to obtain a slurry; the slurry is processed to obtain a precursor material; the precursor material is sintered to obtain a positive electrode active material, wherein the positive electrode active material includes a lithium phosphate material, the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06, and the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L;

[0133] Battery cells are prepared using positive electrode active materials.

[0134] In some embodiments, the iron dissolution rate of the positive electrode active material can be 0 mg / L, 3 mg / L, 5 mg / L, 6 mg / L, 8 mg / L, 10 mg / L, or any range of two of the above iron dissolution rates, or other unlisted values ​​within such range.

[0135] In some embodiments, the molar ratio of lithium to iron in the positive electrode active material can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, or any range of two of the above molar ratios, or other unlisted values ​​within that range.

[0136] Compared to the solid-phase method for preparing positive electrode active materials, the preparation method of this application obtains positive electrode active materials through a one-step liquid-phase co-precipitation method, which eliminates the need for complex precursor preparation processes and high-temperature and high-pressure reaction conditions, thereby reducing the production cost of lithium iron phosphate materials.

[0137] The preparation method of this application embodiment controls the molar ratio of lithium to iron in the positive electrode active material within the above-mentioned range, thereby enabling the positive electrode active material to have excellent specific capacity and facilitating the formation of pure-phase lithium iron phosphate during the sintering preparation process, thus reducing the iron dissolution rate of the positive electrode active material. The iron, phosphorus, and lithium elements in the positive electrode active material prepared by the liquid-phase co-precipitation method used in this application embodiment are uniformly distributed at the atomic level, which is beneficial to enhancing the binding of phosphate ions to iron ions, thereby further reducing the iron dissolution rate of the positive electrode active material. This ensures that the iron dissolution rate of the positive electrode active material meets the above-mentioned range, resulting in excellent cycle stability and good specific capacity.

[0138] In some implementations, the first lithium source includes lithium sulfate.

[0139] Lithium sulfate has advantages such as abundant sources, low cost, and good water solubility, making it suitable for the preparation method of this application embodiment. This helps to reduce raw material costs, thereby further reducing the production cost of lithium iron phosphate materials.

[0140] In some embodiments, the molar ratio of lithium in the first lithium source to iron in the iron source is greater than 1 and less than or equal to 1.06. Optionally, the molar ratio of lithium in the first lithium source to iron in the iron source is 1.01-1.06.

[0141] In some embodiments, the molar ratio of lithium in the first lithium source to iron in the iron source can be 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, or any range of two of the above molar ratios, or other unlisted values ​​within the range.

[0142] In some implementations, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is 0.96-1.

[0143] In some implementations, the molar ratio of iron in the iron source to phosphorus in the phosphorus source is 0.96-0.98.

[0144] In some embodiments, the molar ratio of iron in the iron source to phosphorus in the phosphorus source can be 0.96, 0.97, 0.98, 0.99, 1, or a range of any two of the above molar ratios, or other unlisted values ​​within that range.

[0145] When the molar ratio of lithium in the first lithium source to iron in the iron source, and the molar ratio of iron in the iron source to phosphorus in the phosphorus source, are within the above-mentioned ranges, it is beneficial to form pure-phase lithium iron phosphate during sintering, further reducing the iron dissolution rate of the prepared cathode active material, and thus further improving the specific capacity and cycle stability of the cathode active material. Furthermore, suitable molar ratios of lithium to iron and iron to phosphorus are also beneficial to further improving the lithium-ion diffusion coefficient of the cathode active material.

[0146] In some embodiments, the preparation of the positive electrode active material includes at least the following steps: mixing raw materials including a first lithium source, an iron source, and a phosphorus source with a solvent to obtain a slurry; adding a pH adjuster until the pH of the slurry is greater than or equal to 7 to obtain a second slurry; separating the second slurry to obtain a precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0147] In some implementations, a pH adjuster is added to bring the slurry pH to a value greater than or equal to 7 and less than or equal to 14.

[0148] In some embodiments, a pH adjuster is added to bring the slurry pH to 7, 8, 9, 10, 11, 12, 13, 14, or a range of any two of the above pH values, or other unlisted values ​​within that range.

[0149] Adjusting the pH of the slurry to be greater than or equal to 7 by adding a pH adjuster is beneficial for further precipitation of lithium ions in the slurry. This ensures that the molar ratio of lithium to iron in the precursor material is within a suitable range, for example, a molar ratio of 1.01-1.06. This facilitates the formation of a purer phase of lithium iron phosphate during sintering, thereby ensuring that the iron dissolution rate of the prepared cathode active material is within a suitable range, further balancing excellent specific capacity and cycle stability.

[0150] In some implementations, the pH adjuster includes one or more of ammonium carbonate and ammonium bicarbonate.

[0151] The above-mentioned pH adjusters are compatible with the preparation method of this application.

[0152] In some embodiments, the preparation of the positive electrode active material further includes: separating the second slurry to obtain a solid material; adding a carbon source to the solid material and grinding it to obtain a precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0153] The precursor material includes a carbon source, and the surface of the positive electrode active material prepared by sintering is uniformly coated with a highly conductive carbon layer, which is beneficial to improving the conductivity of the positive electrode active material. Furthermore, carbon can act as a reducing agent to reduce Fe... 3+ Reduced to Fe 2+ This will help to further improve the specific capacity of the positive electrode active material.

[0154] In some implementations, the carbon source content is 1%-5% by mass of the solid material.

[0155] In some embodiments, the mass content of the carbon source, based on the mass of the solid material, can be 1%, 2%, 3%, 4%, 5%, or a range consisting of the mass contents of any two of the above carbon sources, or other unlisted values ​​within the range of such components.

[0156] By controlling the amount of carbon source added within a suitable range, the carbon coating thickness on the surface of the prepared positive electrode active material is appropriate, which is beneficial to further improve the conductivity and specific capacity of the positive electrode active material.

[0157] In some implementations, the carbon source includes one or more of glucose, toner, sucrose, and polyethylene glycol.

[0158] In some embodiments, the preparation method further includes: separating the second slurry to obtain a solid material; adding a carbon source and additives to the solid material, grinding it to obtain a precursor material; and sintering the precursor material to obtain a positive electrode active material.

[0159] In some embodiments, the additives include one or more of zirconium oxide, titanium dioxide, aluminum oxide, and magnesium oxide.

[0160] The precursor material includes additives, so that the sintered positive electrode active material contains modified elements, which is beneficial to further improve the cycle stability of the positive electrode active material.

[0161] In some embodiments, the mass content of the additive is 500ppm-5000ppm based on the mass of the solid material.

[0162] In some embodiments, the mass content of the additive, based on the mass of the solid material, can be 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, or a range consisting of the mass contents of any two of the above additives, or other unlisted values ​​within the range of the composition.

[0163] Controlling the amount of additives added within a suitable range is beneficial to further improve the specific capacity and cycle stability of the positive electrode active material.

[0164] In some embodiments, the preparation of the positive electrode active material includes at least the following steps: mixing raw materials including a first lithium source, an iron source, and a phosphorus source with a solvent to obtain a slurry; adding a pH adjuster until the pH of the slurry is greater than or equal to 7 to obtain a second slurry; separating the second slurry to obtain a solid material; adding a carbon source and additives to the solid material, grinding it to obtain a precursor material; and sintering the precursor material to obtain the positive electrode active material, wherein the first lithium source includes lithium sulfate, the positive electrode active material includes a lithium phosphate material, the molar ratio of lithium to iron in the positive electrode active material is 1.01-1.06, and the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L.

[0165] The above preparation method uses inexpensive water-soluble lithium sulfate as the lithium source and prepares the positive electrode active material through a one-step liquid-phase co-precipitation method, reducing the cost of lithium iron phosphate materials and the iron dissolution rate of the positive electrode active material, which is beneficial to improving the cycle stability of secondary batteries. Adjusting the pH of the slurry to be greater than or equal to 7 by adding a pH adjuster facilitates further precipitation of lithium ions in the slurry, ensuring that the molar ratio of lithium to iron in the precursor material is within a suitable range. This promotes the formation of a purer phase of lithium iron phosphate during sintering, thus keeping the iron dissolution rate of the positive electrode active material within a suitable range. The resulting positive electrode active material exhibits excellent cycle stability while also maintaining good specific capacity. Furthermore, adding a carbon source and additives to the solid material and grinding it to obtain the precursor material further enhances the specific capacity and cycle stability of the positive electrode active material. In summary, the above preparation method shortens the preparation steps of lithium iron phosphate, reduces its production cost, and produces a positive electrode active material with a low iron dissolution rate. The positive electrode active material of the embodiments of this application exhibits excellent cycle stability while also maintaining good specific capacity.

[0166] In some embodiments, the preparation of the positive electrode active material includes at least the following steps: mixing raw materials including a first lithium source, an iron source, and a phosphorus source with a solvent to obtain a slurry; separating the slurry to obtain a first solid material; washing the first solid material and sintering the washed first solid material to obtain a second solid material; adding a second lithium source to the second solid material and grinding it to obtain a precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0167] The preparation method of this application, through washing and precipitation separation, effectively removes impurity ions such as sulfate introduced by the first lithium source from the first solid material, reducing the impurity content dissolved into the electrolyte, thereby reducing the degree of side reactions and further improving the cycle performance of the secondary battery. However, washing dissolves lithium in the first solid material, resulting in an excessively low molar ratio of lithium to iron in the second solid material. If directly used for sintering to prepare the positive electrode active material, this would increase the iron dissolution rate of the positive electrode active material, for example, greater than 10 mg / L, and reduce its specific capacity. Therefore, the preparation method of this application further incorporates a second lithium source into the second solid material, thereby ensuring that the molar ratio of lithium to iron in the precursor material used for sintering to prepare the positive electrode active material is within a suitable range. This facilitates the formation of a purer phase of lithium iron phosphate during sintering, ensuring that the iron dissolution rate of the positive electrode active material is within a suitable range. The resulting positive electrode active material exhibits superior cycle stability and excellent specific capacity. In summary, the above preparation method reduces the production cost of lithium iron phosphate. Meanwhile, the obtained positive electrode active material has a lower iron dissolution rate and a further reduced impurity ion content, which is beneficial to further improve the cycle stability of the positive electrode active material of this application while taking into account the specific capacity.

[0168] In some embodiments, the mass content of sulfur in the positive electrode active material is 0 ppm to 50 ppm, based on the total mass of the positive electrode active material.

[0169] When lithium sulfate is used as the first lithium source, the first solid material obtained after washing and precipitation separation can effectively remove sulfate ions from the first solid, so that the mass content of sulfur in the positive electrode active material is within the above range, which is beneficial to further improve the cycle performance of the positive electrode active material of this application.

[0170] In some implementations, the first solid material is washed 3-5 times.

[0171] In some embodiments, the number of times the first solid material is washed can be 3, 4, 5, or a range consisting of any two of the above washing times.

[0172] Controlling the number of washes within the above range helps to remove impurities to the greatest extent while dissolving as little lithium as possible in the first solid material. This helps to further reduce the cost of subsequent lithium replenishment and balance the specific capacity and cycle stability of the secondary battery.

[0173] In some implementations, the second lithium source includes one or more of lithium carbonate and lithium hydroxide.

[0174] In some embodiments, the temperature for sintering the first solid material is 300°C-400°C.

[0175] In some embodiments, the sintering time for the first solid material is 3-5 hours.

[0176] In some embodiments, the temperature for sintering the first solid material can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, or a range of any two of the above temperatures, or other unlisted values ​​within the range.

[0177] In some embodiments, the sintering time for the first solid material can be 3h, 4h, 5h, or a range of any two of the above times, or other unlisted values ​​within that range.

[0178] Controlling the temperature and time for sintering the first solid material within the aforementioned range facilitates the removal of moisture from the first solid material, transforming it into a second solid material containing an iron phosphate phase. By testing the iron-lithium ratio of the second solid material, it is easier to calculate the amount of the second lithium source that needs to be added. Furthermore, the aforementioned sintering temperature and time facilitate the uniform mixing of the sintered second solid material and the second lithium source to obtain a precursor material, thereby improving the efficiency of subsequent sintering of the precursor material.

[0179] In some embodiments, the preparation of the positive electrode active material further includes: adding a second lithium source and a carbon source to the second solid material, grinding it to obtain a precursor material; and sintering the precursor material to obtain the positive electrode active material.

[0180] The precursor material includes a carbon source, and the surface of the positive electrode active material prepared by sintering is uniformly coated with a highly conductive carbon layer, which is beneficial to improving the conductivity of the positive electrode active material. Furthermore, carbon can act as a reducing agent to reduce Fe... 3+ Reduced to Fe 2+ This will help to further improve the specific capacity of the positive electrode active material.

[0181] In some embodiments, the carbon source content is 1%-5% by mass of the second solid material.

[0182] In some embodiments, the mass content of the carbon source, based on the mass of the second solid material, can be 1%, 2%, 3%, 4%, 5%, or a range consisting of the mass contents of any two of the aforementioned carbon sources, or other unlisted values ​​within that range.

[0183] By controlling the amount of carbon source added within a suitable range, the carbon coating thickness on the surface of the prepared positive electrode active material is appropriate, which is beneficial to further improve the conductivity and specific capacity of the positive electrode active material.

[0184] In some embodiments, the carbon source includes one or more of glucose, toner, sucrose, and polyethylene glycol.

[0185] In some embodiments, the preparation method further includes: adding a second lithium source, a carbon source, and additives to a second solid material, grinding it to obtain a precursor material; and sintering the precursor material to obtain a positive electrode active material.

[0186] In some embodiments, the additives include one or more of zirconium oxide, titanium dioxide, aluminum oxide, and magnesium oxide.

[0187] The precursor material includes additives, so that the sintered positive electrode active material contains modified elements, which is beneficial to further improve the cycle stability of the positive electrode active material.

[0188] In some embodiments, the mass content of the additive is 500ppm-5000ppm based on the mass of the second solid material.

[0189] In some embodiments, the mass content of the additive, based on the mass of the second solid material, can be 500 ppm, 1000 ppm, 1500 ppm, 2000 ppm, 2500 ppm, 3000 ppm, 3500 ppm, 4000 ppm, 4500 ppm, 5000 ppm, or a range consisting of the mass contents of any two of the above additives, or other unlisted values ​​within the range of the composition.

[0190] Controlling the amount of additives added within a suitable range is beneficial to further improve the specific capacity and cycle stability of the positive electrode active material.

[0191] In some embodiments, the preparation of the positive electrode active material includes at least the following steps: mixing raw materials including a first lithium source, an iron source, and a phosphorus source with a solvent to obtain a slurry; separating the slurry to obtain a first solid material; washing the first solid material and sintering the washed first solid material to obtain a second solid material; adding a second lithium source, a carbon source, and additives to the second solid material, grinding it, and obtaining a precursor material; sintering the precursor material to obtain the positive electrode active material; wherein the first lithium source includes lithium sulfate, the positive electrode active material includes a lithium phosphate material, the molar ratio of lithium to iron in the positive electrode active material is 1.01-1.06, the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the mass content of sulfur in the positive electrode active material is 0 ppm-50 ppm based on the total mass of the positive electrode active material.

[0192] The above preparation method uses inexpensive water-soluble lithium sulfate as the lithium source and prepares the positive electrode active material through a one-step liquid-phase co-precipitation method, reducing the cost of lithium iron phosphate materials and the iron dissolution rate of the positive electrode active material, which is beneficial to improving the cycle stability of the secondary battery. Furthermore, the first solid material obtained after washing and precipitation separation can effectively remove impurity ions such as sulfate introduced by the inexpensive lithium sulfate raw material, further improving the cycle stability of the secondary battery. By adding a second lithium source, carbon source, and additives to the second solid material, the molar ratio of lithium to iron in the precursor material used for sintering to prepare the positive electrode active material is kept within a suitable range. The sintered positive electrode active material includes modified elements, and its surface is uniformly coated with a highly conductive carbon layer, further ensuring that the iron dissolution rate of the positive electrode active material is within a suitable range. The prepared positive electrode active material exhibits superior cycle stability while also possessing excellent specific capacity. In summary, the above preparation method uses an inexpensive lithium source and reduces the production cost of lithium iron phosphate. Meanwhile, the obtained positive electrode active material has a lower iron dissolution rate and a further reduced sulfur content, which is beneficial to further improve the cycle stability of the positive electrode active material of this application while taking into account the specific capacity.

[0193] In some embodiments, the temperature for sintering the precursor material is 650°C-750°C.

[0194] In some implementations, the sintering time for the precursor material is 5-15 hours.

[0195] In some embodiments, the temperature for sintering the precursor material can be 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, or a range of any two of the above temperatures, or other unlisted values ​​within the range.

[0196] In some embodiments, the sintering time for the precursor material can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or a range of any two of the above times, or other unlisted values ​​within the range.

[0197] Controlling the temperature and time of the sintering precursor within the above-mentioned range is beneficial to improving the conversion rate of the precursor material to the lithium iron phosphate phase, further reducing the iron dissolution rate of the cathode active material, and increasing the specific capacity of the cathode active material. Furthermore, the above-mentioned sintering temperature and time are conducive to the reaction of the added carbon source and ferric ions to ferrous ions, and make the surface of the sintered cathode active material have a uniform carbon coating layer, thereby further improving the specific capacity and cycle stability of the cathode active material.

[0198] In some implementations, the iron source includes one or more of ferrous sulfate and ferric sulfate.

[0199] In some embodiments, the phosphorus source includes one or more of ammonium dihydrogen phosphate, phosphoric acid, and diammonium hydrogen phosphate.

[0200] [Positive electrode plate]

[0201] This application provides a 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 includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material includes the positive electrode active material of any embodiment of this application or the positive electrode active material prepared by the preparation method of any embodiment of this application.

[0202] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0203] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer 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 (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0204] In some embodiments, 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.

[0205] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0206] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0207] [Negative electrode plate]

[0208] 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.

[0209] As an example, 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.

[0210] 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 (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0211] In some embodiments, the negative electrode active material may be a 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 be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from 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.

[0212] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0213] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0214] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0215] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, 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 then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0216] [Electrolytes]

[0217] The electrolyte acts as a conductor of ions between the positive and negative electrode plates. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, solid, or gel-like.

[0218] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0219] In some embodiments, the electrolyte salt may be selected from 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.

[0220] In some embodiments, the solvent may be selected from 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.

[0221] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0222] [Isolation membrane]

[0223] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0224] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0225] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0226] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0227] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0228] 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. For example, Figure 2 The example shown is a square-structured battery cell 5.

[0229] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0230] In some implementations, 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.

[0231] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 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.

[0232] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0233] 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 one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0234] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0235] In addition, this application also provides a battery device, including the battery cell provided in the first aspect of this application, wherein the battery device includes at least one of a battery module, a battery pack, and an energy storage battery.

[0236] In addition, this application also provides an electrical device, which includes the battery cell provided in the first aspect of this application. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0237] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0238] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0239] Another example 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.

[0240] Example

[0241] 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.

[0242] Preparation method

[0243] Example 1

[0244] 1) Preparation of positive electrode active materials

[0245] (1) Add 1 mol / L FeSO4 solution and 1 mol / L Li2SO4 solution to a stirred tank and mix evenly. The reactor is protected by nitrogen gas. The molar ratio of Li / Fe is controlled to be 1.03. Then add ammonium dihydrogen phosphate and control the molar ratio of Fe / P to be 0.97. After sand milling and stirring for 30 min, a slurry is obtained.

[0246] (2) Add ammonium carbonate until the pH of the slurry is greater than or equal to 7, and wait for complete precipitation to obtain the second slurry;

[0247] (3) Centrifuge and filter the second slurry to obtain a solid material. Add 4 wt% of glucose and polyethylene glycol mixture to the solid material. The mass ratio of glucose to polyethylene glycol is 1:1. Use water as a medium to sand mill and disperse evenly. Spray dry to obtain the precursor material.

[0248] (4) The precursor material was loaded into a crucible and sintered at 700°C for 10 hours. Nitrogen gas was introduced for protection during the sintering process. The sintered material was then rolled, air-jet crushed, and sieved to finally obtain the lithium iron phosphate cathode active material. The Dv90 of the cathode active material was 2.78 μm, and the Dv99 of the cathode active material was 5.61 μm.

[0249] 2) Preparation of positive electrode sheet

[0250] The prepared lithium iron phosphate positive electrode active material, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1:2, and then N-methylpyrrolidone solvent was added. After thorough stirring and mixing, a positive electrode slurry was prepared.

[0251] The positive electrode slurry was prepared at 20 mg / cm³ 2 The single-sided weight coating is applied to one side of the positive electrode current collector aluminum foil, and then dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0252] 3) Preparation of negative electrode sheet

[0253] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC) and solvent water are uniformly mixed in a weight ratio of 97:1:1:1:100 to obtain the negative electrode slurry.

[0254] The negative electrode slurry was prepared at a concentration of 10 mg / cm³. 2 The single-sided weight coating is applied to both sides of the negative electrode current collector copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0255] 4) Preparation of electrolyte

[0256] At 25°C, ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0257] 5) Separating membrane

[0258] A polyethylene film with a thickness of 10 μm was used as the separator.

[0259] 6) Preparation of secondary batteries

[0260] The above-mentioned positive electrode, separator, and negative electrode are stacked in sequence to obtain a stacked cell; the cell is placed in an outer packaging, the electrolyte prepared above is added, and after processes such as encapsulation, standing, formation, and aging, the secondary battery of Example 1 is obtained.

[0261] The preparation method of the secondary battery in Example 2 is basically similar to that in Example 1, except that the preparation of the positive electrode active material is different, specifically the molar ratio of Li / Fe in step (1).

[0262] The preparation methods of the secondary batteries in Examples 3-4 are basically similar to those in Example 1, except that the preparation of the positive electrode active material is different, specifically the Fe / P molar ratio in step (1).

[0263] The secondary battery in Example 5 is prepared in a basically similar manner to that in Example 1, except for the preparation of the positive electrode active material, which is shown below:

[0264] (1) Add 1 mol / L FeSO4 solution and 1 mol / L Li2SO4 solution to a stirred tank and mix evenly. The reactor is protected by nitrogen gas. The molar ratio of Li / Fe is controlled at 1.03. Then add ammonium dihydrogen phosphate and control the molar ratio of Fe / P at 0.97. After stirring for 30 min, the precipitation is complete and a slurry is obtained.

[0265] (2) The slurry was filtered to obtain the first solid material. The first solid material was washed three times with pure water, dried after washing, and sintered at 350℃ for 5 hours in a nitrogen atmosphere to obtain the second solid material.

[0266] (3) Lithium carbonate is added to the second solid material. The mass of lithium carbonate added is such that the molar ratio of lithium to iron in the positive electrode active material is controlled to be 1.03. A mixture of glucose and polyethylene glycol is added. The mass ratio of glucose to polyethylene glycol is 1:1. The amount added is 4 wt% of the mass of the second solid material. The mixture is dispersed evenly by sand milling with water as the medium and spray-dried to obtain the precursor material.

[0267] (4) The precursor material was loaded into a crucible and sintered at 700°C for 10 hours. Nitrogen gas was introduced for protection during the sintering process. The sintered material was then rolled, air-jet crushed, and sieved to finally obtain the lithium iron phosphate cathode active material. The Dv90 of the cathode active material was 3.76 μm and the Dv99 of the cathode active material was 7.01 μm.

[0268] The secondary batteries in Examples 6-7 are basically similar to those in Example 5 in terms of preparation method, except that the preparation of the positive electrode active material is different, specifically in the different molar ratio of Li / Fe in step (3).

[0269] The secondary battery of Comparative Example 1 is prepared in a basically similar manner to that of Example 1, except for the preparation of the positive electrode active material. The preparation method of the positive electrode active material of Comparative Example 1 is as follows:

[0270] (1) Add 1 mol / L FeSO4 solution and 1 mol / L H3PO4 solution to a stirred tank and mix evenly. Add hydrogen peroxide and sodium hydroxide to adjust the pH to neutral and control the Fe / P molar ratio to 1. After the precipitation is complete, centrifuge and filter. Wash the solid with water three times, dry it and sinter it at 300℃ for later use.

[0271] (2) The solid in step (1) is mixed evenly with lithium carbonate by sand milling, the Li / Fe ratio is controlled to be 1.03, 4 wt% of glucose and polyethylene glycol mixture is added, and water is used as a medium to disperse evenly by sand milling. After spray drying, powder material is obtained.

[0272] (3) The powder material from step (2) is loaded into a crucible and sintered at 700°C for 10 hours, with nitrogen gas introduced for protection during the sintering process. The sintered material is then crushed and sieved to obtain the target lithium iron phosphate cathode material.

[0273] The preparation method of the secondary battery in Comparative Example 2 is basically similar to that in Example 1. The difference lies in the preparation of the positive electrode active material. Specifically, the preparation process of the positive electrode active material in Comparative Example 2 does not include step (2) adding ammonium carbonate until the pH of the slurry is greater than or equal to 7, waiting for complete precipitation, and obtaining the second slurry. After step (1) is completed, step (3) is performed directly.

[0274] The preparation method of the secondary battery in Comparative Example 3 is basically similar to that in Example 5. The difference lies in the preparation of the positive electrode active material. Specifically, the preparation process of the positive electrode active material in Comparative Example 3 does not include the operation of supplementing the second lithium source lithium carbonate in step (3). In step (3), a mixture of glucose and ethylene glycol is directly added to the second solid material for subsequent operations.

[0275] II. Performance Testing

[0276] (1) Test of iron dissolution rate in positive electrode active material

[0277] The positive electrode was removed from the battery, and the active material film was peeled off. The film was dissolved in N-methylpyrrolidone (NMP) solvent, filtered, and thoroughly washed with NMP to remove the binder. The powder was then dried for subsequent characterization tests. 5g of powder was weighed and added to 100mL of 0.008mol / L hydrochloric acid. The mixture was stirred at 25℃ for 30min, then allowed to stand in a 25℃ water bath for 2h. After filtration, the filtrate was obtained, and the iron ion concentration in the filtrate was tested. Inductively coupled plasma atomic emission spectrometry (ICP) was used to determine the iron ion concentration in the filtrate, following the national standards EPA 6010D-2018 and JY / T 0567-2020.

[0278] (2) Testing of the mass content of each element in the positive electrode active material

[0279] The positive electrode was removed from the battery, and the active material film was peeled off. The film was dissolved and filtered using NMP solvent, then thoroughly washed with NMP to remove the binder. After drying, a powder was obtained for subsequent characterization testing. 0.5 g of the powder was weighed, added to 10 mL of aqua regia, and microwaved for 20 min. Then, 1 mL of the sample was diluted to 100 mL for later use. The sulfur content in the sample was determined according to the national standard EPA 6010D-2018JY / T 0567-2020 inductively coupled plasma atomic emission spectrometry (ICP-AES), and the mass content of sulfur in the positive electrode active material was finally calculated.

[0280] The contents of Li, Fe, and P elements in the above samples were tested according to the national standard EPA 6010D-2018JY / T 0567-2020 inductively coupled plasma atomic emission spectrometry, and the molar ratios of Li / Fe and Fe / P in the positive electrode active material were calculated.

[0281] (3) Testing of Dv90 and Dv99 of positive electrode active material

[0282] The volume distribution particle sizes Dv90 and Dv99 of the positive electrode active material can be determined using a laser particle size analyzer, referring to GB / T19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0283] (4) Specific capacity test at a discharge rate of 0.33C

[0284] At 25℃, a fresh battery cell is charged at a constant current rate of 0.33C to 3.8V, then charged at 3.8V until the cutoff current is 0.05C. After a 5-minute pause, it is discharged at a constant current rate of 0.33C, with a discharge cutoff voltage of 2V. This charging and discharging process is repeated three times. The capacity from the third charge is taken as the cell's test energy. Combined with the mass of the positive electrode active material, the specific capacity of the positive electrode active material at a 0.33C discharge rate can be calculated.

[0285] (5) Lithium-ion diffusion coefficient test

[0286] Adjust the cell capacity to 50% SOC, discharge continuously at 1C rate for 30 seconds, with a relaxation time of 2 minutes, according to the formula. The diffusion coefficient of lithium ions at 50% SOC was calculated.

[0287] (6) Capacity retention test

[0288] The test procedure is as follows: At 25℃, charge the battery with a constant current of 1C to 3.8V, then charge it with a constant voltage of 3.8V to a current of 0.05C, let it rest for 5 minutes, and then discharge it with 1C to 2.0V. The resulting discharge capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery, and record the discharge capacity Cn of the battery after the nth cycle. Then, the battery capacity retention rate after each cycle is Pn = (Cn / C0) × 100%. The battery capacity retention rate after 500 cycles can be used to reflect the difference in cycle performance.

[0289] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0290] Secondary batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in Tables 1 and 2 below.

[0291] Table 1

[0292]

[0293] Table 2

[0294]

[0295] As shown in Tables 1 and 2, Examples 1-7 provide a single battery cell. The single battery cell includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one side of the positive current collector. The positive electrode film layer includes a positive electrode active material, which includes a lithium phosphate material. The iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06.

[0296] As can be seen from the comparison between Examples 1-7 and Comparative Examples 1-3, the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06. The positive electrode active material of this application has excellent cycle stability and also has good specific capacity.

[0297] As can be seen from the comparison between Examples 1-3, 5-7 and Example 4, the iron dissolution rate of the positive electrode active material is 0 mg / L-5 mg / L, and the cycle stability of the battery is further improved.

[0298] As can be seen from the comparison between Examples 5-7 and Examples 1-4, the mass content of sulfur in the positive electrode active material is 0ppm-50ppm, which further improves the cycle stability of the battery.

[0299] As can be seen from Examples 1-7 and Comparative Example 1, the Dv90 of the positive electrode active material is 2μm-5μm and / or the Dv99 is 4μm-8μm, thus improving the lithium-ion diffusion coefficient of the positive electrode active material.

[0300] As can be seen from the comparison between Examples 1-7 and Comparative Examples 2-3, when the molar ratio of lithium to iron in the positive electrode active material is greater than 1, less than or equal to 1.06, and / or the molar ratio of iron to phosphorus in the positive electrode active material is 0.96-1, the iron dissolution rate of the positive electrode active material is further reduced and the specific capacity is further improved.

[0301] As can be seen from the comparison between Examples 1-3 and Example 4, when the molar ratio of iron to phosphorus in the positive electrode active material is 0.96-0.98, the cycle stability of the battery is further improved.

[0302] The preparation method of the positive electrode active material in Examples 1-7 includes the following steps: mixing raw materials including a first lithium source, an iron source, and a phosphorus source with a solvent to obtain a slurry; processing the slurry to obtain a precursor material; sintering the precursor material to obtain the positive electrode active material, wherein the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06, and the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L.

[0303] A comparison of Examples 1-7 and Comparative Example 1 shows that, compared to Comparative Example 1 which uses a solid-state method to prepare the positive electrode active material, the preparation methods of Examples 1-7 shorten the process and use lithium sulfate as the lithium source, which helps to reduce the preparation cost of the positive electrode active material. Furthermore, the liquid-phase co-precipitation method used in Examples 1-7 helps to reduce the iron dissolution rate of the positive electrode active material, reduce the Dv90 and Dv99 of the positive electrode active material, and improve the lithium-ion diffusion coefficient of the positive electrode active material, thereby improving the cycle stability of the battery.

[0304] As can be seen from the comparison between Examples 1-7 and Comparative Examples 2-3, the preparation method of Examples 1-7 results in a molar ratio of lithium to iron in the positive electrode active material that is greater than 1 and less than or equal to 1.06. The iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the battery has excellent cycle stability. At the same time, it is beneficial to further improve the specific capacity of the positive electrode active material.

[0305] As can be seen from the comparison between Examples 1-4 and Comparative Example 2, the preparation method of Examples 1-4, by adding a pH adjuster in step (2) to make the pH of the slurry greater than or equal to 7, is beneficial to keep the molar ratio of lithium to iron in the positive electrode active material within a suitable range, such as greater than 1 and less than or equal to 1.06, thereby further reducing the iron ion dissolution rate of the positive electrode active material, and taking into account the specific capacity while ensuring good cycle stability of the battery.

[0306] As can be seen from the comparison between Examples 5-7 and Comparative Example 3, the preparation method of Examples 5-7, by supplementing the second lithium source in step (3), is conducive to keeping the molar ratio of lithium to iron in the positive electrode active material within a suitable range, such as greater than 1 and less than or equal to 1.06, thereby further reducing the iron ion dissolution rate of the positive electrode active material, and taking into account the specific capacity while ensuring good cycle stability of the battery.

[0307] As can be seen from the comparison between Examples 1-4 and Examples 5-7, the preparation method of Examples 5-7, through the washing process to remove sulfur impurities and the supplementation of a second lithium source, results in a sulfur content of 0ppm-50ppm in the positive electrode active material based on the total mass of the positive electrode active material, thereby further improving the cycle stability of the battery.

[0308] 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 method for producing a battery cell, characterized by, The preparation method comprises at least the following steps: Preparation of the positive electrode active material: Mixing raw materials including a first lithium source, an iron source and a phosphorus source with a solvent to obtain a slurry; Treating the slurry to obtain a precursor material; Sintering the precursor material to obtain the positive electrode active material, The treatment of the slurry comprises: adding a pH regulator to the slurry to make the pH of the slurry greater than or equal to 7 to obtain a second slurry, and separating the second slurry to obtain the precursor material; or separating the slurry to obtain a first solid material, washing the first solid material, and sintering the first solid material after washing to obtain a second solid material, and adding a second lithium source to the second solid material to obtain the precursor material after grinding; The first lithium source includes lithium sulfate, the positive electrode active material includes a lithium phosphate material, the molar ratio of lithium to iron in the positive electrode active material is greater than 1 and less than or equal to 1.06, the iron dissolution rate of the positive electrode active material is 0 mg / L-10 mg / L, and the mass content of sulfur in the positive electrode active material is 0 ppm-50 ppm based on the total mass of the positive electrode active material; the lithium-ion diffusion coefficient of the positive electrode active material is 3 × 10⁻⁶. -14 cm 2 / s-8×10 -14 cm 2 / s; The positive electrode active material is used to prepare the battery cell.

2. The production method according to claim 1, characterized by, The molar ratio of lithium in the first lithium source to iron in the iron source is greater than 1 and less than or equal to 1.

06.

3. The preparation method according to claim 2, characterized in that, The molar ratio of lithium in the first lithium source to iron in the iron source is 1.01-1.

06.

4. The method of claim 1, wherein, The molar ratio of iron in the iron source to phosphorus in the phosphorus source is 0.96-1.

5. The production method according to claim 4, characterized by, The molar ratio of iron in the iron source to phosphorus in the phosphorus source is 0.96-0.

98.

6. The production method according to any one of claims 1 to 5, characterized by, The pH regulator comprises one or more of ammonium carbonate and ammonium bicarbonate.

7. The production method according to any one of claims 1 to 5, characterized by, The preparation of the positive electrode active material further comprises: separating the second slurry to obtain a solid material; adding a carbon source to the solid material to obtain the precursor material after grinding; sintering the precursor material to obtain the positive electrode active material.

8. The production method according to claim 7, characterized by, The mass content of the carbon source is 1%-5% based on the mass of the solid material.

9. The production method according to any one of claims 1 to 5, characterized by, The first solid material is washed for 3-5 times.

10. The production method according to any one of claims 1 to 5, characterized by, The second lithium source comprises one or more of lithium carbonate and lithium hydroxide.

11. The preparation method of any one of claims 1-5, wherein: the sintering temperature of the first solid material is 300-400°C; and / or the sintering time of the first solid material is 3-5 hours.

12. The production method according to any one of claims 1 to 5, characterized by, The preparation of the positive electrode active material further comprises: adding the second lithium source and a carbon source to the second solid material to obtain the precursor material after grinding; sintering the precursor material to obtain the positive electrode active material.

13. The method of claim 12, wherein, The mass content of the carbon source is 1%-5% based on the mass of the second solid material.

14. The preparation method of any one of claims 1-5, wherein: the sintering temperature of the precursor material is 650-750°C; and / or the sintering time of the precursor material is 5-15 hours.

15. The preparation method of any one of claims 1-5, wherein: the iron source comprises one or more of ferrous sulfate and iron sulfate; and / or the phosphorus source comprises one or more of ammonium dihydrogen phosphate, phosphoric acid and diammonium hydrogen phosphate.

16. A battery cell, characterized by The battery cell is obtained according to the preparation method of any one of claims 1-15.

17. An electrical device, comprising: The electrical device comprises the battery cell obtained according to the preparation method of any one of claims 1-15 or the battery cell of claim 16.

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