Positive electrode active material, method of preparing the same, positive electrode sheet comprising the same, secondary battery, and electric device

Abstract

The application provides a positive electrode active material, which is Na x R y (PO4) z (P2O7) k and C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W and Pb; wherein the water content of the positive electrode active material is not higher than 1600 ppm. The application also provides a preparation method of the positive electrode active material, and a positive electrode sheet, a secondary battery and an electric device comprising the material. The positive electrode active material has a low water content, which can effectively improve or avoid the processability of the positive electrode active material, and make the positive electrode sheet and the secondary battery comprising the material have a higher charge-discharge specific capacity and a higher first-cycle coulombic efficiency.

Description

Technical Field

[0001] This application relates to the field of sodium battery technology, and more particularly to a positive electrode active material, as well as a positive electrode sheet containing the positive electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] Rechargeable batteries are an ideal choice for energy storage technology. Although lithium-ion rechargeable batteries have achieved great success in various applications, the relative scarcity and high cost of lithium resources have led to increased attention on sodium, which has similar performance to lithium but is more abundant and readily available. Sodium-ion rechargeable batteries are considered a strong candidate for future energy storage systems. However, the high water content in sodium-ion cathode active materials in current technologies may affect the electrochemical performance, energy density, and safety performance of the electrode and battery.

[0003] In view of the above problems, there is a need to provide a sodium phosphate-based positive electrode active material with low water content, which can effectively improve or even avoid the problem of the positive electrode active material being related to water content during slurry processing, thereby enabling the battery positive electrode sheet and secondary battery to have higher charge and discharge specific capacity and first-cycle coulombic efficiency. Summary of the Invention

[0004] To achieve the above objectives, this application provides a positive electrode active material, as well as a positive electrode sheet, a secondary battery, and an electrical device comprising the same.

[0005] A first aspect of this application provides a positive electrode active material, wherein the positive electrode active material is Na. x R y (PO4) z (P2O7) k The complex with C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; wherein the water content of the positive electrode active material is not higher than 1600 ppm. The low water content of the positive electrode active material in this application embodiment can effectively improve or avoid the problem of slurry instability (e.g., gelation) of the positive electrode active material, thereby significantly improving its processability and giving the positive electrode sheet higher charge-discharge specific capacity and higher first-cycle coulombic efficiency.

[0006] In any embodiment, the water content is not higher than 1400 ppm, optionally not higher than 1200 ppm, optionally not higher than 1000 ppm, optionally not higher than 900 ppm, optionally not lower than 50 ppm, more optionally not lower than 70 ppm, and even more optionally 200-800 ppm. Positive electrode active materials with the above-mentioned water content range are more cost-effective while ensuring the aforementioned advantageous properties.

[0007] In any embodiment, the chemical composition of the positive electrode active material satisfies at least one of the following conditions:

[0008] (1) 3 ≤ x ≤ 5;

[0009] (2) 2 ≤ y ≤ 4;

[0010] (3) 1.5 ≤ z ≤ 2;

[0011] (4) 1≤k≤1.5;

[0012] (5) R is Fe.

[0013] Such positive electrode active materials have high energy density.

[0014] A second aspect of this application provides a method for preparing a positive electrode active material, wherein the positive electrode active material is Na. x R y (PO4) z (P2O7) k A complex with C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; wherein the water content of the positive electrode active material is not higher than 1600 ppm; the method includes the following steps:

[0015] a) Preparation of precursor material: Prepare a mixed slurry comprising an R-source compound, a sodium-source compound, a phosphorus-source compound, and a carbon-source compound, and dry the mixed slurry to obtain the precursor material;

[0016] b) Sintering the precursor material in a sintering atmosphere to obtain the positive electrode active material, wherein the ratio between the volumetric value of the sintering atmosphere and the weight value of the precursor material is 0.85-3.42 m³. 3 / kg, with an optional range of 1.70-3.42m 3 / kg, or more preferably 2.27-3.42m 3 / kg.

[0017] The positive electrode active material prepared by the above method has a low water content, good processability, and endows the positive electrode sheet and battery containing the material with high charge-discharge specific capacity and high first-cycle coulombic efficiency.

[0018] In any embodiment, in step b), the heating rate is 0.5-5 °C / min, optionally 2-5 °C / min. Such a heating rate helps to obtain a positive electrode active material with low water content.

[0019] In any embodiment, in step b), the sintering atmosphere includes nitrogen and / or argon.

[0020] In any embodiment, in step b), the nitrogen flow rate is 2-10 L / min, optionally 5-10 L / min; and / or the sintering time is about 10-30 hours, optionally about 18-23 hours.

[0021] Using the above conditions in step b) can further benefit the preparation of a positive electrode active material with a lower water content.

[0022] In any implementation, the method of this application further includes the following steps:

[0023] c) Crush the positive electrode active material, wherein the crushing is carried out at an ambient humidity of no more than 10%, optionally between 2% and 10%. Controlling the ambient humidity of the material during the crushing step is beneficial to ensure that the crushed positive electrode active material has a water content comparable to, or even lower than, that at the discharge stage.

[0024] In any implementation, the method of this application further includes the following steps:

[0025] d) Dry the positive electrode active material. The drying step can further reduce the moisture content of the material.

[0026] A third aspect of this application also provides a positive electrode sheet, comprising the positive electrode active material of the first aspect or the positive electrode active material obtained by the method of the second aspect of this application.

[0027] A fourth aspect of this application also provides a secondary battery, including the positive electrode sheet of the third aspect of this application.

[0028] The fifth aspect of this application also provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0029] This application provides a low-water-content sodium phosphate positive electrode active material, which can effectively improve the processability of the positive electrode active material (e.g., slurry gel), thereby enabling the battery positive electrode sheet to have a higher charge and discharge specific capacity. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0031] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0032] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0033] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0034] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0035] Figure 6 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.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0038] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the positive electrode active material and its preparation method, positive electrode sheet, secondary battery, and power application device according to the present application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter of the claims.

[0039] 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] 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.

[0043] 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.

[0044] 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).

[0045] Rechargeable batteries are one of the ideal choices for energy storage technology. Although lithium-ion rechargeable batteries have achieved great success in a variety of applications, the relative scarcity and high cost of lithium resources have led people to turn their attention to sodium, which has similar performance to lithium but is more abundant and readily available. Sodium-ion rechargeable batteries are also considered one of the strong candidates for future energy storage systems.

[0046] Various positive electrode active materials for sodium-ion batteries have been reported, among which sodium phosphate is considered the most promising positive electrode active material for sodium-ion secondary batteries due to its combination of advantages including low cost, environmental friendliness, high theoretical capacity, high average operating voltage, and low volume expansion. However, existing technologies show that these materials have a relatively high water content. In the preparation of non-aqueous slurries, the water content of the material is even more sensitive; even a very small amount of water can cause the slurry to gel, making coating difficult and further affecting the electrochemical performance and energy density of the electrode and the battery. In addition, the increased water content of the positive electrode active material makes it easier for sodium to be released from the bulk phase of the material, resulting in residual alkali on the material surface, such as sodium bicarbonate, sodium hydroxide, and sodium ions. This reduces the kinetic performance of the electrode material during charge and discharge, causing battery gas expansion during cycling.

[0047] Although drying is generally used in the art to reduce the moisture content of materials in order to improve the above-mentioned problems, the ability of drying to reduce water content is very limited and cannot meet the requirements.

[0048] In view of the above problems, this application provides a sodium phosphate positive electrode active material with low water content and a method for preparing the sodium phosphate positive electrode active material with low water content, which can effectively improve or even avoid the gelation problem of positive electrode active material during processing, thereby enabling the battery positive electrode sheet to have a higher charge and discharge specific capacity.

[0049] Positive electrode active materials and their preparation methods

[0050] One aspect of this application is a positive electrode active material, wherein the positive electrode active material is Na. x R y (PO4) z (P2O7) kThe complex with C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; wherein the water content of the positive electrode active material is not higher than 1600 ppm.

[0051] Not wanting to be confined to any theory, the positive electrode active material in this application embodiment has a low water content, which can effectively improve or avoid the problem of unstable slurry (e.g., gel) of the positive electrode active material, thereby significantly improving its processability and enabling the positive electrode sheet to have a higher charge-discharge specific capacity and a higher first-cycle coulombic efficiency.

[0052] In this article, "gel problem" refers to a situation where the slurry is jelly-like and lacks fluidity, thus making it impossible to coat properly.

[0053] Although drying the positive electrode active material before slurry preparation can reduce its moisture content to some extent, it still cannot meet the requirements for low moisture content in the art. However, the positive electrode active material in the embodiments of this application can have a lower moisture content, improving the processability of the slurry, thereby improving the performance of the electrode and the battery, such as charge / discharge specific capacity and first-cycle coulombic efficiency.

[0054] In this article, "moisture content" refers to the amount of water contained in a unit mass of positive electrode active material. The moisture content was determined according to GB / T11133-2015 (Determination of water content in petroleum products, lubricating oils and additives by Karl Fischer coulometric titration).

[0055] In this document, positive electrode active material refers to a material having the aforementioned chemical composition, and it may be in different states, including, for example, a discharge state, a pulverized state, and a dried state. Correspondingly, the moisture content of the positive electrode active material includes discharge moisture content, pulverized moisture content, and dried moisture content. The discharge state is defined as the positive electrode active material after sintering (optionally pre-sieved), at which point the moisture content of the material is the discharge moisture content. The pulverized state is defined as the powder obtained by pulverizing the material in the discharge state, at which point the moisture content of the material is the pulverized moisture content. The dried state is defined as the product obtained by drying the aforementioned powder, at which point the moisture content of the material is the dried moisture content.

[0056] In some embodiments, the Na x R y (PO4) z (P2O7) k The complex with C is Na with carbon coating. x R y (PO4) z (P2O7) k, where x, y, z, k and R are as defined above.

[0057] In some embodiments, the water content of the positive electrode active material is not higher than 1400 ppm, optionally not higher than 1200 ppm, optionally not higher than 1100 ppm, optionally not higher than 1000 ppm, optionally not higher than 950 ppm, optionally not higher than 900 ppm, optionally not higher than 850 ppm, optionally not higher than 800 ppm, optionally not higher than 750 ppm, optionally not higher than 700 ppm, optionally not higher than 650 ppm. In some embodiments, optionally, the water content of the positive electrode active material is not lower than 50 ppm, optionally not lower than 70 ppm, optionally not lower than 200 ppm, optionally not lower than 300 ppm, optionally not lower than 350 ppm, optionally not lower than 400 ppm, optionally not lower than 450 ppm, optionally not lower than 500 ppm, optionally not lower than 550 ppm. In some embodiments, the water content of the positive electrode active material is 200-800 ppm. While lower water content is desirable for cathode active materials, cathode active materials within the aforementioned water content range are more cost-effective while ensuring favorable material performance.

[0058] In some embodiments, the chemical composition of the positive electrode active material satisfies at least one of the following conditions:

[0059] (1) 3≤x≤5, the possible value is 4;

[0060] (2) 2≤y≤4, the possible value is 3;

[0061] (3) 1.5≤z≤2, the land can be 2;

[0062] (4) 1≤k≤1.5, the land can be 1;

[0063] (5) R is Fe.

[0064] Such positive electrode active materials have high energy density.

[0065] Another aspect of this application provides a method for preparing the above-described positive electrode active material, the method comprising the following steps:

[0066] a) Preparation of precursor material: Prepare a mixed slurry comprising an R-source compound, a sodium-source compound, a phosphorus-source compound, and a carbon-source compound, and dry the mixed slurry to obtain the precursor material;

[0067] b) Sintering: The precursor material is sintered in a sintering atmosphere to obtain the positive electrode active material, wherein the ratio between the gas flow rate of the sintering atmosphere and the weight of the precursor material is 0.85-3.42m.3 / kg, with an optional range of 1.70-3.42m 3 / kg, or more preferably 2.27-3.42m 3 / kg.

[0068] The positive electrode active material prepared by the above method has a low water content, good processability, and imparts high charge-discharge specific capacity and high first-cycle coulombic efficiency to the positive electrode sheet and battery containing this material. Not wishing to be confined to any theory, the method of this application embodiment effectively reduces the water content (especially the output water content) of the positive electrode active material by controlling the sintering step. Low output water content is beneficial for maintaining or even further reducing the water content of the positive electrode active material during possible further processing (such as crushing and / or drying). Specifically, by controlling the ratio between the gas flow rate of the sintering atmosphere (in cubic meters) and the weight of the precursor material (in kilograms) within the above-mentioned range, a low water content in the positive electrode active material is achieved.

[0069] The moisture content of the positive electrode active material obtained through the above steps is not higher than 1400 ppm, optionally not higher than 1200 ppm, optionally not higher than 1100 ppm, optionally not higher than 1000 ppm, optionally not higher than 950 ppm, optionally not higher than 900 ppm, optionally not higher than 850 ppm, optionally not higher than 800 ppm, optionally not higher than 750 ppm, optionally not higher than 700 ppm, optionally not higher than 700 ppm, optionally not higher than 650 ppm. In some embodiments, optionally, the moisture content of the positive electrode active material is not lower than 50 ppm, optionally not lower than 70 ppm, optionally not lower than 200 ppm, optionally not lower than 300 ppm, optionally not lower than 350 ppm, optionally not lower than 400 ppm, optionally not lower than 450 ppm, optionally not lower than 500 ppm, optionally not lower than 550 ppm. In some embodiments, the moisture content of the positive electrode active material is 200-800 ppm.

[0070] In this article, "ventilation volume" refers to the total volume of sintering atmosphere gas introduced into the sintering equipment during the sintering time; that is, the ventilation volume (unit: m³). 3 = Flow rate of sintering atmosphere gas * sintering time. For example, when the sintering atmosphere is nitrogen, the nitrogen flow rate (unit: m³) is... 3 = Nitrogen flow rate (L / min) * sintering time (h) * 0.06. With the same amount of nitrogen, a longer sintering time corresponds to a smaller nitrogen flow rate; a shorter sintering time corresponds to a larger nitrogen flow rate.

[0071] In this article, "sintering time" refers to the sum of the heating time, holding time, and cooling time in the sintering process.

[0072] In some embodiments, in step a), the mixed slurry can be prepared, for example, by adding an R source compound, a sodium source compound, and a phosphorus source compound to a solvent to form a slurry; and then adding a carbon source compound to the slurry to obtain the mixed slurry.

[0073] In some embodiments, in step a), the solvent may be, for example, water (optionally, deionized water) or ethanol.

[0074] In some embodiments, in step a), the slurry and the mixed slurry may be prepared by one or more methods such as grinding and solvent dispersion.

[0075] In some embodiments, in step a), the grinding can be performed in a manner conventional in the art, for example, the grinding can be ball milling, sand milling, vibratory milling, or tumbling milling. The grinding can be performed using equipment conventional in the art (e.g., ball mill, sand mill, vibratory mill, or tumbling mill).

[0076] In some embodiments, the R source compound can be any compound in the art capable of providing the R element. When the R element is Fe, the R source compound can be, for example, at least one of ferrous oxalate, ferric nitrate, ferric citrate, and ammonium ferric citrate.

[0077] In some embodiments, the sodium source compound can be any compound in the art capable of providing sodium. Such a compound can be, for example, at least one of sodium pyrophosphate, sodium acetate, sodium nitrate, sodium carbonate, sodium bicarbonate, sodium dihydrogen phosphate, and disodium hydrogen phosphate.

[0078] In some embodiments, the phosphorus source compound can be any compound in the art capable of providing phosphorus. Such a compound can be, for example, at least one of ammonium dihydrogen phosphate, phosphoric acid, diammonium hydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium pyrophosphate, and sodium dihydrogen phosphate.

[0079] In some embodiments, the carbon source compound is any compound in the art capable of providing carbon. Such a compound may be, for example, at least one selected from oxalic acid, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, soluble starch, ascorbic acid, sucrose, and glucose. The carbon source compound helps to improve the electrical conductivity of the material.

[0080] In some embodiments, in step a), the average particle size D of the solids contained in the mixed slurry obtained after grinding is... v 50 can be 0.1-0.8 micrometers. This particle size range is beneficial for the material to react more fully during the sintering process.

[0081] In this article, "average particle size D" v "50" means the particle size corresponding to 50% of the particles in the volume distribution. The average particle size can be detected using conventional methods in the art, such as laser particle size analyzer.

[0082] In some embodiments, in step a), the drying is performed by at least one of the following methods: forced-air drying, vacuum drying, freeze drying, and spray drying.

[0083] In some embodiments, in step b), the sintering atmosphere includes nitrogen and / or argon; optionally, the sintering atmosphere also includes hydrogen. In some embodiments, the sintering atmosphere is nitrogen. Generally, sintering atmospheres are classified as inert atmospheres or reducing atmospheres. In this document, a sintering atmosphere of nitrogen and / or argon is an inert sintering atmosphere; while a sintering atmosphere of a nitrogen-hydrogen mixture or an argon-hydrogen mixture is a reducing atmosphere. In some embodiments, in step b), the sintering atmosphere is nitrogen.

[0084] In some embodiments, in step b), the sintering atmosphere has an oxygen content of less than 100 ppm, optionally between 30 and 50 ppm. Controlling the oxygen content within this range is beneficial for reducing side reactions and improving the conductivity of the material. The sintering atmosphere is introduced after the system (e.g., within a sintering furnace) has been evacuated; the oxygen content is the amount of oxygen remaining in the system after evacuation.

[0085] In some embodiments, in step b), the nitrogen flow rate is 2-10 L / min, optionally 5-10 L / min.

[0086] In some embodiments, in step b), the sintering time is about 10-30 hours, optionally about 18-23 hours.

[0087] Without being bound by any theory, using sintering time and / or nitrogen flow rate within the respective ranges mentioned above can further benefit the obtained positive electrode active material having a lower moisture content (especially the discharge moisture content).

[0088] In some embodiments, the heating rate in step b) is 0.5-5 °C / min. In some embodiments, optionally, the heating rate is 2-5 °C / min. Not wishing to be bound by any theory, such a heating rate ensures a complete reaction while allowing the water produced in the reaction to be discharged in a timely manner, thus contributing to obtaining a positive electrode active material with low water content (especially in the discharge).

[0089] In some embodiments, in step b), the sintering is carried out by at least one of the following devices: tube furnace, vacuum box furnace, explosion-proof box furnace, pusher kiln, roller kiln, bell kiln, and rotary kiln.

[0090] In some embodiments, the sintering in step b) includes a low-temperature sintering stage and a high-temperature sintering stage. The low-temperature sintering can be performed at a temperature of 300-350°C for 3-5 hours. The high-temperature sintering can be performed at a temperature of 500-550°C for 7-11 hours, optionally about 10 hours. Here, the holding time as described above means the sum of the low-temperature sintering holding time and the high-temperature sintering holding time. The heating time as described above means the sum of the time required for the temperature to rise from the initial temperature (e.g., ambient temperature or room temperature (25°C)) to the low-temperature sintering temperature and from the low-temperature sintering temperature to the high-temperature sintering temperature.

[0091] In some embodiments, the method further includes the following steps:

[0092] c) Crush the positive electrode active material, wherein the crushing is carried out at an ambient humidity of no more than 10%, optionally between 2% and 10%. It is not desirable to be bound by any theory; controlling the ambient humidity of the material during the crushing step is beneficial to ensure that the crushed positive electrode active material has a water content comparable to, or even lower than, that of the discharged material.

[0093] The water content of the pulverized positive electrode active material is not higher than 1500 ppm, optionally not higher than 1200 ppm, optionally not higher than 1100 ppm, optionally not higher than 1000 ppm, optionally not higher than 950 ppm, optionally not higher than 900 ppm, optionally not higher than 850 ppm, optionally not higher than 800 ppm, optionally not higher than 750 ppm, optionally not higher than 700 ppm, optionally not higher than 700 ppm, optionally not higher than 700 ppm, optionally not lower than 700 ppm, optionally not lower than 400 ppm, optionally not lower than 450 ppm. In some embodiments, the water content of the pulverized positive electrode active material is 200-800 ppm.

[0094] In some embodiments, the method further includes the following steps:

[0095] d) Dry the positive electrode active material.

[0096] The drying step in this application can be performed using conventional drying methods in the art, such as vacuum drying. The drying temperature is 100℃-200℃, optionally 110℃-150℃. The drying time is 12h-36h.

[0097] The moisture content of the dried positive electrode active material is not higher than 1200 ppm, optionally not higher than 1150 ppm, optionally not higher than 1000 ppm, optionally not higher than 900 ppm, optionally not higher than 850 ppm, optionally not higher than 800 ppm, optionally not higher than 750 ppm, and optionally not higher than 700 ppm. In some embodiments, the moisture content of the dried positive electrode active material is not lower than 50 ppm, optionally not lower than 70 ppm, optionally not lower than 200 ppm, and optionally not lower than 250 ppm. In some embodiments, the moisture content of the dried positive electrode active material is 200-800 ppm.

[0098] One aspect of this application also provides a positive electrode active material prepared as described above.

[0099] Positive electrode plate, secondary battery and electrical device

[0100] Another aspect of this application provides a positive electrode sheet, which includes the positive electrode active material of this application or the positive electrode active material obtained by the method of this application.

[0101] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, wherein the positive electrode film layer includes the positive electrode active material of the present application embodiments.

[0102] 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.

[0103] 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.).

[0104] 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.

[0105] 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.

[0106] 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.

[0107] Another aspect of this application provides a secondary battery.

[0108] In this article, secondary batteries include battery cells, battery modules, and battery packs.

[0109] Another aspect of this application provides an electrical device, including a secondary battery according to embodiments of this application.

[0110] The battery cells, battery modules, battery packs, and power devices of the present application will be described below with appropriate reference to the accompanying drawings.

[0111] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0112] [Negative electrode plate]

[0113] 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.

[0114] 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.

[0115] 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.).

[0116] 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.

[0117] 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).

[0118] 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.

[0119] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0120] 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.

[0121] [Electrolytes]

[0122] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0123] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0124] In some embodiments, the electrolyte salt may be selected from sodium hexafluorophosphate (NaPF6), sodium hexafluoroborate (NaBF4), NaN(SO2F)2 (abbreviated as NaFSI), NaClO4, NaAsF6, NaB(C2O4)2 (abbreviated as NaBOB), NaBF2(C2O4) (abbreviated as NaDFOB), NaN(SO2R) F )2 and NaN(SO2F)(SO2R F One or more of the following: R; wherein, R F Representing C b F 2b+1 b is an integer in the range of 1-10, which can be optionally an integer in the range of 1-3. More optionally, R F It can be -CF3, -C2F5, or -CF2CF2CF3.

[0125] 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.

[0126] 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.

[0127] [Isolation membrane]

[0128] 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.

[0129] 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.

[0130] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0131] [Outer Packaging]

[0132] In some implementations, a battery cell may include an outer packaging for encapsulating a positive electrode, a negative electrode, and an electrolyte. As an example, the positive electrode, negative electrode, and separator may be stacked or wound to form a stacked or wound battery cell, with the cell encapsulated within the outer packaging; the electrolyte is immersed in the cell. The number of cells in a battery cell can be one or more, adjustable as needed.

[0133] In one embodiment, this application provides an electrode assembly. In some embodiments, the positive electrode, negative electrode, and separator are fabricated into the electrode assembly using a winding process or a stacking process. An outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0134] In some embodiments, the outer packaging of the battery cell can be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS). 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. 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 1 The example shown is a square-structured battery cell 5.

[0135] In some implementations, refer to Figure 2 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 the battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0136] In some implementations, individual battery cells can be assembled into battery modules or battery packs. The number of battery cells contained in a battery module or battery pack 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 or battery pack.

[0137] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0138] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0139] In some embodiments, the battery cells or the aforementioned battery modules can be assembled into a battery pack. The number of battery cells or battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0140] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The 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.

[0141] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in 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.

[0142] As the electrical device, a single battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0143] Figure 6This 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 the secondary battery for this device, a battery pack or battery module can be used.

[0144] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0145] Example

[0146] 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.

[0147] Example 1

[0148] 1. Preparation of a composite material of Na4Fe3(PO4)2P2O7 and C as the positive electrode active material

[0149] a) Preparation of precursor materials:

[0150] According to the atomic molar ratio of Na, Fe, and P in the chemical formula Na4Fe3(PO4)2P2O7, 1.164 kg of sodium pyrophosphate decahydrate (Na4P2O7.10H2O), 1.367 kg of ferrous oxalate dihydrate (FeC2O4.2H2O), and 0.6 kg of ammonium dihydrogen phosphate (NH4H2PO4) were added to 6 L of water and ground together. Then, 0.117 kg of glucose was added as a carbon source compound, and the mixture was stirred and milled to obtain a slurry. The slurry was then spray-dried to obtain the precursor material.

[0151] b) Sintering:

[0152] 4 kg of precursor material was placed in a sintering furnace. The furnace was evacuated to maintain an oxygen content of 30-50 ppm. The sintering atmosphere was nitrogen, with a nitrogen flow rate of 5.14 L / min. The precursor material was first heated from room temperature (25 °C) to 300 °C at a rate of 2 °C / min and calcined at 300 °C for 4 hours. Then, the temperature was increased to 550 °C at a rate of 2 °C / min and calcined at 550 °C for 10 hours. Finally, the temperature was decreased to 100 °C at a rate of 2 °C / min to obtain the product. X-ray diffraction (XRD) analysis and infrared carbon-sulfur analysis confirmed that the product was the desired positive electrode active material, a composite of Na₄Fe₃(PO₄)₂P₂O₇ and C (carbon-coated Na₄Fe₃(PO₄)₂P₂O₇). The nitrogen flow rate during sintering was 6.825 m³ / min. 3 The ratio of its weight (in kg) to that of the precursor is 1.70625. The material is transferred to a drying room for preliminary crushing and sieving. At this time, the positive electrode active material is in the discharge state. The moisture content of the discharge is measured and recorded in Table 1.

[0153] c) Crushing:

[0154] The sintered positive electrode active material (i.e., the positive electrode active material in the discharge state) was subjected to airflow pulverization under an ambient humidity of less than 10% to obtain positive electrode active material powder (pulverized state). The moisture content after pulverization was measured and recorded in Table 1.

[0155] d) Drying:

[0156] The positive electrode active material powder was placed in a drying oven and dried at 120℃ for 24 hours to obtain the dried positive electrode active material powder (dry state). The moisture content of the positive electrode active material (i.e., the moisture content after drying) was measured and recorded in Table 1.

[0157] 2. Preparation of the positive electrode sheet

[0158] Polyvinylidene fluoride binder was fully dissolved in N-methylpyrrolidone, and then carbon black conductive agent and the dried positive electrode active material powder were added to form a uniformly dispersed positive electrode slurry with a weight ratio of positive electrode active material powder, carbon black conductive agent, and binder of 7:2:1. The positive electrode slurry was then uniformly coated onto the surface of aluminum foil (aluminum foil thickness 13μm, loading 43.42mg / 1540.25mm). 2 Then, the electrode is transferred to a vacuum drying oven for complete drying. The resulting electrode is then rolled and punched to obtain the positive electrode.

[0159] 3. Preparation of negative electrode sheet

[0160] Carbon nanotube material, sodium carboxymethyl cellulose binder, and deionized water were mixed in a weight ratio of 4:1.6:94.4 to form a homogeneous slurry. The slurry was then coated onto the surface of a copper foil (copper foil thickness 8 μm, loading 2 mg / 1540.25 mm). 2 Then, it is transferred to a vacuum drying oven for complete drying, and then punched to obtain the negative electrode sheet.

[0161] 4. Preparation of electrolyte

[0162] Sodium hexafluorophosphate (NaPF6) was dissolved in the organic solvent ethylene glycol dimethyl ether (DME) in an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm) and stirred until homogeneous to obtain an electrolyte with a sodium salt concentration of 0.5 mol / L.

[0163] 5. Separating membrane

[0164] Polypropylene film is used as the separator.

[0165] 6. Preparation of secondary batteries

[0166] Stack the positive electrode, separator, and negative electrode in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Add 0.5g of the electrolyte to assemble the stacked battery.

[0167] 7. Moisture content test

[0168] The test was conducted according to GB / T11133-2015 (Determination of water content in petroleum products, lubricating oils and additives by Karl Fischer coulometric titration).

[0169] 8. Charge and discharge specific capacity and first-cycle coulombic efficiency test

[0170] The secondary battery prepared above was charged at 25°C with a constant current of 1 / 3C to 3.75V, and then charged at a constant voltage of 3.75V until the current dropped to 0.05C. The specific capacity of the first charge cycle (C) was measured. c1 Then, discharge to 1.5V with a constant current of 1 / 3C, and measure the first discharge specific capacity (C). d1 The first-cycle coulombic efficiency of the secondary battery is calculated using the following formula:

[0171]

[0172] Example 2-18

[0173] Except for the amount of nitrogen introduced (keeping the sintering time constant, the amount of nitrogen is changed by changing the nitrogen flow rate) and the ratio of nitrogen to the precursor sintering weight or the heating rate, the other steps in Examples 2-18 are the same as in Example 1 (see Table 1 below for details).

[0174] Comparative Examples 1 and 2

[0175] Comparative Example 1 is basically the same as Example 1, except that the ratio of nitrogen to precursor weight is changed.

[0176] The sintering and drying conditions and test results in the above embodiments and comparative examples are shown in Table 1 below.

[0177]

[0178]

[0179] As shown in Table 1, in the embodiments, when the precursor weight and heating rate are the same, the larger the ratio within the above range, the lower the water content (or the better the performance). Compared with Comparative Examples 1-2, the embodiments of this application (where the ratio between the volumetric value of the sintering atmosphere and the weight value of the precursor material is 0.85-3.42m) 3 A cathode active material with lower water content was obtained within the range of / kg, and the water content of the cathode active materials in the embodiments of this application is all below 1600ppm.

[0180] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A positive electrode active material, wherein the positive electrode active material is Na x R y (PO4) z (P2O7) k A complex with C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; wherein the water content of the positive electrode active material is not higher than 1600 ppm.

2. The positive electrode active material according to claim 1, wherein the water content is not higher than 1400 ppm.

3. The positive electrode active material according to claim 2, wherein the water content is not higher than 1200 ppm.

4. The positive electrode active material according to claim 3, wherein the water content is not higher than 1000 ppm.

5. The positive electrode active material according to claim 4, wherein the water content is not higher than 900 ppm.

6. The positive electrode active material according to claim 1, wherein the water content is not less than 50 ppm.

7. The positive electrode active material according to claim 6, wherein the water content is not less than 70 ppm.

8. The positive electrode active material according to claim 1, wherein the water content is 200-800 ppm.

9. The positive electrode active material according to any one of claims 1 to 8, wherein the chemical composition of the positive electrode active material satisfies at least one of the following conditions: （1）3≤x≤5； （2）2≤y≤4； （3）1.5≤z≤2； （4）1≤k≤1.5； (5) R is Fe.

10. A method for preparing a positive electrode active material, wherein the positive electrode active material is Na x R y (PO4) z (P2O7) k A complex with C, wherein 1≤x≤7, 1≤y≤4, 1≤z≤2, 1≤k≤4, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb; wherein the water content of the positive electrode active material is not higher than 1600 ppm; the method includes the following steps: a) Preparation of precursor material: Prepare a mixed slurry comprising an R-source compound, a sodium-source compound, a phosphorus-source compound, and a carbon-source compound, and dry the mixed slurry to obtain the precursor material; b) Sintering the precursor material in a sintering atmosphere to obtain the positive electrode active material, wherein the ratio between the volumetric value of the sintering atmosphere and the weight value of the precursor material is 0.85-3.42 m³. 3 / kg.

11. The method of claim 10, wherein in step b), the ratio between the volumetric value of the sintering atmosphere and the weight value of the precursor material is 1.70-3.42 m³. 3 / kg.

12. The method according to claim 11, wherein in step b), the ratio between the volumetric value of the sintering atmosphere and the weight value of the precursor material is 2.27-3.42 m³. 3 / kg.

13. The method according to claim 10, wherein in step b), the heating rate is 0.5-5 °C / min.

14. The method according to claim 13, wherein in step b), the heating rate is 2-5 °C / min.

15. The method according to any one of claims 10 to 14, wherein in step b), the sintering atmosphere comprises nitrogen and / or argon.

16. The method according to claim 15, wherein in step b), the nitrogen flow rate is 2-10.5 L / min; and / or the sintering time is 10-30 hours.

17. The method of claim 16, wherein in step b), the nitrogen flow rate is 5-10.5 L / min.

18. The method according to claim 16 or 17, wherein in step b), the sintering time is 18-23 hours.

19. The method according to any one of claims 10 to 14, further comprising the step of: c) Crush the positive electrode active material, wherein the crushing is carried out under an ambient humidity of no more than 10%.

20. The method according to claim 19, wherein in step c), the pulverization is carried out at an ambient humidity of 2% to 10%.

21. The method according to any one of claims 10 to 14, further comprising the step of: d) Dry the positive electrode active material.

22. A positive electrode sheet, comprising the positive electrode active material according to any one of claims 1 to 9 or the positive electrode active material obtained by the method according to any one of claims 10 to 21.

23. A secondary battery comprising the positive electrode sheet as described in claim 22.

24. An electrical device comprising the secondary battery of claim 23.

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