Battery cell, battery device, and electric device

Abstract

The application provides a battery monomer, a battery device and a power utilization device, the battery monomer comprising a carbon-coated lithium iron phosphate material. By regulating the relative proportion of the specific surface area of different micro-morphology carbon structures in the surface layer of the carbon-coated lithium iron phosphate material, specifically, the carbon-coated lithium iron phosphate material has a carbon-coated factor η, and when the η satisfies 0.81<=η<=0.95, the lithium iron phosphate material has high-quality carbon coating, which is beneficial to the capacity development of the lithium iron phosphate material and significantly improves the efficiency of the pole piece dehydration, and the battery monomer prepared has excellent energy density, cycle performance and excellent processing performance.

Description

[0001] This application is a divisional application of patent application 202180083427.0 filed on August 23, 2021, entitled “Carbon-coated lithium iron phosphate positive electrode active material, preparation method thereof, positive electrode sheet containing the same and lithium-ion battery”. Technical Field

[0002] This application relates to the field of electrochemistry, and more particularly to a battery cell, a battery device, and an electrical device. Background Technology

[0003] With the rapid development of the new energy field, lithium-ion batteries are widely used in various large-scale power devices, energy storage systems and various consumer products due to their excellent electrochemical performance, no memory effect and low environmental pollution, especially in the field of new energy vehicles such as pure electric vehicles and hybrid electric vehicles.

[0004] Among the commonly used positive electrode active materials for lithium-ion batteries, lithium iron phosphate (LFP) is one of the most widely used positive electrode active materials in industrialized lithium-ion batteries. However, because the specific capacity of LFP is lower than that of ternary materials, recent research has focused primarily on improving the capacity of LFP. However, focusing solely on improving the capacity performance of LFP inevitably leads to a loss in other battery properties, such as cycle performance and processing performance.

[0005] Therefore, the goal is to design a lithium-ion battery that combines high energy density, high cycle performance, and excellent processing performance. Summary of the Invention

[0006] In view of the problems existing in the background technology, the purpose of this application is to provide a carbon-coated lithium iron phosphate cathode active material, which has high capacity utilization, high compaction density, and easy dehydration of the electrode, so that lithium-ion batteries have excellent energy density, cycle performance and excellent processing performance, and can significantly improve battery production efficiency and reduce battery production cost.

[0007] The first aspect of this application provides a carbon-coated lithium iron phosphate cathode active material, the cathode active material comprising a lithium iron phosphate substrate and a carbon coating layer located on the surface of the substrate, the lithium iron phosphate substrate having the general structural formula LiFe. 1-a M a PO4, wherein M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti, and 0 ≤ a ≤ 0.01; the carbon coating factor of the carbon-coated lithium iron phosphate material. Wherein, BET1 is the specific surface area of ​​the carbon-coated lithium iron phosphate with mesopores and macropores, BET2 is the total specific surface area of ​​the carbon-coated lithium iron phosphate, and η satisfies 0.81≤η≤0.95.

[0008] In any implementation, η can be selected as 0.85≤η≤0.93, and more preferably as 0.88≤η≤0.92.

[0009] In any implementation, the numerical range of BET1 is 5.5~9.5m. 2 / g, wherein the value of BET2 ranges from 6.0 to 11.5m. 2 / g.

[0010] In any embodiment, the ratio H / D of the thickness H of the carbon coating layer to the average particle size D of the carbon-coated lithium iron phosphate is 0.01 to 0.04.

[0011] In any embodiment, the carbon component in the carbon coating layer accounts for 0.7% to 1.3% of the total mass of the lithium iron phosphate cathode active material, which can be selected as 0.9% to 1.3%, or more preferably 0.9% to 1.1%.

[0012] In any embodiment, the volume average particle size Dv50 of the carbon-coated lithium iron phosphate satisfies 840 nm ≤ Dv50 ≤ 3570 nm, and can be optionally 1170 nm ≤ Dv50 ≤ 1820 nm.

[0013] In any embodiment, the compacted density of the carbon-coated lithium iron phosphate powder is not less than 2.4 g / cm³. 3 2.5 g / cm³ is an optional value. 3 Alternatively, a 2.6 g / cm³ option can be selected. 3 .

[0014] In any embodiment, the degree of graphitization of the carbon-coated lithium iron phosphate is 0.15~0.32, and can be selected as 0.19~0.26.

[0015] In any embodiment, the resistivity of the carbon-coated lithium iron phosphate powder does not exceed 60 Ω·m, is optionally not more than 30 Ω·m, and more preferably not more than 20 Ω·m.

[0016] A second aspect of this application provides a method for preparing the positive electrode active material described in the first aspect of this application, the method comprising the following steps:

[0017] Provide lithium iron phosphate substrate;

[0018] The positive electrode active material is obtained by carbon coating the lithium iron phosphate substrate, wherein the positive electrode active material comprises a lithium iron phosphate substrate and a carbon coating layer located on the surface of the substrate, and the lithium iron phosphate substrate has a general structure LiFe 1-a M aPO4, wherein M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti, and 0 ≤ a ≤ 0.01; the carbon coating factor of the carbon-coated lithium iron phosphate material. Wherein, BET1 is the specific surface area of ​​the carbon-coated lithium iron phosphate with mesopores and macropores, BET2 is the total specific surface area of ​​the carbon-coated lithium iron phosphate, and η satisfies 0.81≤η≤0.95.

[0019] In any embodiment, the method for preparing the positive electrode active material includes the following steps:

[0020] (1) Provide a lithium iron phosphate substrate, wherein raw materials of Fe source, Li source, M source and / or P source and reagents as reducing agent and carbon source are mixed, and the resulting mixture is treated at high temperature under an inert atmosphere to obtain a lithium iron phosphate substrate.

[0021] (2) Carbon coating is performed on the lithium iron phosphate substrate, wherein the lithium iron phosphate substrate is treated at high temperature under an inert atmosphere and carbon source is sprayed at the same time, and carbon-coated lithium iron phosphate material is obtained by chemical vapor deposition.

[0022] The Fe source can be one or more selected from FeSO4, FePO4, FeCl2, FeC2O4, and Fe2O3.

[0023] The Li source can be one or more selected from Li2CO3, LiH2PO4, and Li3PO4.

[0024] The P source can be one or more selected from NH4H2PO4 and H3PO4. The M source contains elements selected from Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, or Ti.

[0025] In step (1), the reagent used as a reducing agent and carbon source can be one or more selected from C2H2, CH4, glucose, polyethylene glycol, sucrose, starch, H2, and CO. Optionally, the amount of the reagent used as a reducing agent and carbon source accounts for 4% to 8% of the total mass of the raw materials, optionally 6%.

[0026] In step (2), the carbon source can be materials such as acetone.

[0027] The processing temperature in step (1) or (2) can vary over a wide range, for example, 500~800℃.

[0028] A third aspect of this application provides a positive electrode sheet for a lithium-ion battery, comprising a positive current collector and a positive active material disposed on at least one surface of the positive current collector, wherein the positive active material is the positive active material described in the first aspect of this application or a positive active material prepared by the method described in the second aspect of this application.

[0029] In any embodiment, the saturated water content of the positive electrode sheet at 25°C and 45% relative humidity does not exceed 500 ppm.

[0030] The fourth aspect of this application provides a lithium-ion battery, the lithium-ion battery including a positive electrode and a negative electrode, the positive electrode including a positive current collector and a positive active material disposed on at least one surface of the positive current collector, the positive active material being the positive active material described in the first aspect of this application or a positive active material prepared by the method described in the second aspect of this application, the positive electrode having a saturated water content of no more than 500 ppm at 25°C and 45% relative humidity.

[0031] In any embodiment, the compaction density of the positive electrode sheet is not less than 2.35 g / cm³. 3 The compaction density of the negative electrode sheet is not less than 1.6 g / cm³. 3 The negative electrode active material in the negative electrode sheet is graphite coated with amorphous carbon.

[0032] This application provides a battery module, including the lithium-ion battery of the fourth aspect of this application. The battery module can be fabricated using methods known in the prior art for fabricating battery modules.

[0033] A sixth aspect of this application provides a battery pack, including a lithium-ion battery according to the fourth aspect of this application or a battery module according to the fifth aspect of this application. The battery pack can be manufactured using methods known in the prior art for manufacturing battery packs.

[0034] A seventh aspect of this application provides an electrical device, including a lithium-ion battery according to a fourth aspect of this application, a battery module according to a fifth aspect of this application, or a battery pack according to a fifth aspect of this application, wherein the lithium-ion battery, the battery module, or the battery pack serves as a power source for the electrical device or an energy storage unit for the electrical device. The electrical device can be manufactured using methods known in the prior art for manufacturing electrical devices.

[0035] [Beneficial Effects]

[0036] This application obtains its cathode active material by controlling the relative proportion of the specific surface area of ​​carbon structures with different microstructures in the surface layer of carbon-coated lithium iron phosphate material. The carbon-coated lithium iron phosphate material of this application has a carbon coating factor η, and when η satisfies 0.81≤η≤0.95, the carbon-coated lithium iron phosphate exhibits high-quality carbon coating, significantly improving the process bottleneck of electrode dehydration. The resulting lithium-ion battery possesses excellent energy density, cycle performance, and processing performance.

[0037] The battery module, battery pack, and power device of this application include the lithium-ion battery provided in this application, and therefore have at least the same advantages as the lithium-ion battery. Attached Figure Description

[0038] Figure 1 These are TEM images of the carbon-coated lithium iron phosphate cathode active material according to an embodiment of this application at different magnifications.

[0039] Figure 2 This is a schematic diagram of a lithium-ion battery according to one embodiment of this application.

[0040] Figure 3 yes Figure 2 An exploded view of a lithium-ion battery according to an embodiment of this application is shown.

[0041] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0042] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0043] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0044] Figure 7 This is a schematic diagram of an electrical device according to one embodiment of this application.

[0045] Figure 8 This is a graph showing the graphitization degree test results of the carbon-coated lithium iron phosphate cathode active material according to one embodiment of this application.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1. Battery pack;

[0048] 2. Upper box;

[0049] 3. Lower box;

[0050] 4. Battery module;

[0051] 5. Lithium-ion batteries;

[0052] 51. Shell;

[0053] 52. Electrode assembly.

[0054] 53. Cover plate. Detailed Implementation

[0055] The following detailed description, with reference to the accompanying drawings, specifically discloses the carbon-coated lithium iron phosphate positive electrode active material of this application, its preparation method, the positive electrode sheet containing it, the lithium-ion battery, the battery module, the battery pack, and the power supply device. 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 this application and are not intended to limit the subject matter of the claims.

[0056] For the sake of brevity, this application specifically discloses several numerical ranges, which can be combined to form corresponding implementation schemes. Any lower limit can be combined with any upper limit to form the range of this application; and any lower limit can be combined with other lower limits to form the range of this application. Similarly, any upper limit can be combined with any other upper limit to form the range of this application. Furthermore, each individually disclosed point or single value can itself serve as a lower limit or upper limit and can be combined with any other point or single value or with other lower limits or upper limits to form the range of this application.

[0057] Unless otherwise stated, the terms used in this application have the common meanings understood by those skilled in the art. In this application, unless otherwise stated, "above" and "below" include the number itself; for example, "more than one of a and b" means at least one of a and b, such as a, b, or a and b. Similarly, "one or more" means including at least one. In the description herein, unless otherwise stated, the term "or" is inclusive, that is, the phrase "A or (or) B" means "A, B, or both A and B".

[0058] It should be noted that the term "carbon coating layer" refers to the portion coated on the lithium iron phosphate substrate. This portion may, but does not necessarily, completely cover the lithium iron phosphate substrate. The use of "carbon coating layer" is for ease of description only and is not intended to limit this application. Similarly, the term "thickness of the carbon coating layer" refers to the maximum thickness of the portion coated on the lithium iron phosphate substrate.

[0059] Through research on lithium iron phosphate cathode active materials, the inventors of this application discovered that the low electronic and ionic conductivity of pure-phase lithium iron phosphate cathode active materials (carbon-free) deteriorates the capacity utilization of lithium iron phosphate cathode active materials, resulting in a significant difference in energy density between lithium-ion batteries using lithium iron phosphate as the cathode active material and ternary lithium-ion batteries.

[0060] To address the poor electronic and ionic conductivity of lithium iron phosphate cathode active materials, carbon coating and nano-sizing treatments can be applied. However, the inventors of this application have discovered that both carbon coating and nano-sizing treatments inevitably degrade other aspects of battery performance, particularly cycle performance and processing performance.

[0061] In particular, the inventors discovered during practical operation that different carbon coating processes lead to different microscopic pore structures in the positive electrode active material for carbon-coated lithium iron phosphate materials. These include microporous structures (network structures with pores smaller than 2 nm), mesoporous structures (network structures with pores between 2 nm and 50 nm), macroporous structures (network structures with pores larger than 50 nm), and other structures without obvious pores, such as layered carbon structures. Extensive experiments revealed that for carbon-coated lithium iron phosphate materials, the unreasonable combination of various pore structures on the surface not only has no significant effect on improving the electronic and ionic conductivity of the lithium iron phosphate positive electrode active material, but also significantly increases the difficulty of dehydration of the electrode sheets made from it. Even after prolonged dehydration treatment, the dehydration rate of the electrode sheets made from it does not meet the requirements for battery preparation. In particular, when the coating thickness of the positive electrode active material layer is increased to increase the battery energy density, the dehydration rate of the electrode sheets becomes even more difficult to achieve the required level.

[0062] In particular, the inventors also discovered during actual operation that nano-sizing also exacerbates the difficulty of electrode dehydration, thereby deteriorating battery cycle performance. Furthermore, nano-sizing reduces the powder compaction density of the lithium iron phosphate cathode active material, thus significantly reducing its contribution to energy density through improved electronic and ionic conductivity.

[0063] Excessive water content in the electrode sheet can lead to problems such as easy shedding of the positive electrode film and instability in structure and chemical properties, ultimately affecting the battery's cycle performance. On the other hand, it also increases the risk of defective products during battery manufacturing, which not only increases costs but also seriously affects battery production efficiency.

[0064] In summary, the goal is to develop a positive electrode active material that combines high capacity, high compaction density, and easy dehydration of the electrode sheets, thereby designing a lithium-ion battery with high energy density, high cycle performance, and excellent processing performance.

[0065] Through extensive experiments and research, the inventors of this application have discovered a technical solution that enables lithium iron phosphate cathode active materials to achieve both high capacity utilization, high compaction density, and easy dehydration of the electrode sheets. This solution enables lithium-ion batteries to possess excellent energy density, cycle performance, and processing performance, and can significantly improve battery production efficiency and reduce battery production costs.

[0066] [Carbon-coated lithium iron phosphate cathode active material]

[0067] This application provides a carbon-coated lithium iron phosphate cathode active material, comprising a lithium iron phosphate substrate and a carbon coating layer on the surface of the substrate, wherein the lithium iron phosphate substrate has the general structural formula LiFe. 1-a M a PO4, wherein M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti, and 0 ≤ a ≤ 0.01.

[0068] The carbon coating factor of the carbon-coated lithium iron phosphate material Wherein, BET1 is the specific surface area of ​​the carbon-coated lithium iron phosphate with mesopores and macropores, BET2 is the total specific surface area of ​​the carbon-coated lithium iron phosphate, and η satisfies 0.81≤η≤0.95.

[0069] The substrate has a general structure LiFe 1-a M a PO4, where M is selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr, Nb, and Ti, and 0 ≤ a ≤ 0.01. Doping with element M is beneficial to improving the structural stability of lithium iron phosphate substrate and preventing the structural collapse of lithium iron phosphate cathode active material after several charge-discharge cycles.

[0070] Carbon coating can improve electronic and ionic conductivity, thereby increasing battery energy density. However, as a porous structure composed of carbon, the carbon coating significantly increases the overall specific surface energy of the lithium iron phosphate cathode active material, thus significantly increasing its water absorption capacity. Through extensive experimental verification, the inventors of this application have discovered that when the carbon-coated lithium iron phosphate material meets certain conditions… When η ≤ 0.95, the carbon-coated lithium iron phosphate, while achieving high capacity, also possesses a reasonable specific surface energy. This significantly reduces the overall specific surface energy of the electrode made from the carbon-coated lithium iron phosphate cathode active material, thereby significantly improving the electrode dehydration efficiency and overcoming the bottleneck of electrode dehydration. Therefore, batteries made from carbon-coated lithium iron phosphate cathode active material with η ≤ 0.95 exhibit excellent energy density, cycle performance, and processing performance.

[0071] In this application, the carbon coating factor η actually characterizes the relative proportion of the specific surface area contributed by different microstructures of pores in the carbon-coated lithium iron phosphate material. It reflects the proportion of the specific surface area of ​​microporous structures that contribute significantly to surface energy to the specific surface area contributed by all channels, and its magnitude reflects the effectiveness of the lithium iron phosphate carbon layer coating. Through extensive experimental research and long-term experience in preparing cathode materials, the inventors discovered that when 0.81≤η≤0.95, a dense and efficient carbon coating layer can significantly improve the capacity of the lithium iron phosphate cathode active material while significantly reducing its surface energy. This results in lithium-ion batteries with excellent energy density, as well as significantly improved cycle performance and processing performance.

[0072] Through extensive experimental research, the inventors discovered that when the carbon coating factor η is in the range of 0.85≤η≤0.93, the relative proportion of pores with different microstructures in the surface layer is within a more reasonable range. Lithium iron phosphate has high-quality carbon coating, which is conducive to the capacity utilization of lithium iron phosphate cathode active material, significantly reduces the water absorption of the electrode, and the prepared lithium-ion battery has excellent energy density, cycle performance and excellent processing performance.

[0073] In some implementations, optionally, the range of η is 0.88≤η≤0.92, resulting in better electrochemical and processing performance of the lithium-ion battery.

[0074] In summary, this application obtained the carbon-coated lithium iron phosphate cathode active material by controlling the relative proportion of the specific surface area of ​​carbon structures with different microstructures in the surface layer of the carbon-coated lithium iron phosphate material. When the carbon coating factor η of the carbon-coated lithium iron phosphate material of this application satisfies 0.81≤η≤0.95, the lithium iron phosphate material has high-quality carbon coating, which is beneficial to significantly improve the dehydration efficiency of the electrode. The lithium-ion battery prepared has excellent energy density, cycle performance, and processing performance. See Table 1 for details.

[0075] Optionally, the value of η can be 0.811, 0.836, 0.862, 0.894, 0.915, 0.922, 0.928, 0.939, or its value can be a range of values ​​composed of any two of the above points.

[0076] In some implementations, optionally, the numerical range of BET1 is 5.5~9.5 m. 2 / g, the value range of BET2 is 6.0~11.5 m 2 / g, at this point the relative proportion of different microscopic carbon structures in the surface layer is within a more reasonable range, the electrode is less likely to absorb water, and it is more conducive to improving the battery energy density and cycle performance.

[0077] Optionally, BET1 can be 9.08, 8.86, 7.05, 6.68, 6.93, 6.46, 5.95, or 5.82, or its value can be a range of any two of the above values. BET2 can be 11.2, 10.6, 8.19, 7.48, 7.16, 7.01, 6.40, or 6.20, or its value can be a range of any two of the above values.

[0078] In some embodiments, optionally, in the positive electrode active material of this application, the ratio H / D of the thickness H of the carbon coating layer to the average particle size D of the carbon-coated lithium iron phosphate is 0.01 to 0.04.

[0079] When the ratio of the carbon coating thickness to the average particle size of the carbon-coated lithium iron phosphate is 0.01 to 0.04, the integrity of the carbon coating on the surface of the lithium iron phosphate material and its electronic conductivity are good, resulting in high electronic conductivity. Simultaneously, because the ratio of the carbon coating thickness to the overall particle size is within a reasonable range, the lithium iron phosphate material also exhibits high powder compaction density, thus leading to better energy density and cycle performance in lithium-ion batteries. A reasonable carbon coating thickness also reduces the dehydration difficulty of electrodes made from lithium iron phosphate material, which is beneficial for improving processing performance.

[0080] In some embodiments, the carbon component may optionally account for 0.7% to 1.3% of the total mass of the carbon-coated lithium iron phosphate, or more preferably 0.9% to 1.3%, or even more preferably 0.8% to 1.1%.

[0081] If the carbon content is too low, the integrity of the carbon coating layer on the surface of the lithium iron phosphate material is poor, resulting in poor material kinetics and a low energy density of the battery. Conversely, if the carbon content is too high, it hinders the growth of individual particles during sintering, causing the lithium iron phosphate material to tend to form secondary particles composed of numerous small particles. Furthermore, the carbon component does not contribute to the battery capacity, similarly resulting in a low energy density of the lithium-ion battery. In this application, based on the total mass of the carbon-coated lithium iron phosphate, the carbon content satisfies 0.7% ≤ C ≤ 1.3%; optionally, it is 0.9% ≤ C ≤ 1.3%; more preferably, it is 0.8% ≤ C ≤ 1.1%. See Table 2 for details.

[0082] Optionally, based on the total mass of carbon-coated lithium iron phosphate, the content of the carbon component can be 0.70%, 0.82%, 0.95%, 1.12%, 1.3%, or a range of values ​​consisting of any two of the above points.

[0083] In some embodiments, optionally, the volume average particle size Dv50 of the carbon-coated lithium iron phosphate of this application satisfies 840 nm ≤ Dv50 ≤ 3570 nm, and optionally 1170 nm ≤ Dv50 ≤ 1820 nm.

[0084] The inventors of this application discovered that nano-sizing can be used to address the poor electronic and ionic conductivity of lithium iron phosphate cathode active materials. However, extensive practical experience has shown that nano-sizing also increases the surface energy of the lithium iron phosphate cathode active material, increasing the electrode's water absorption capacity and leading to dehydration difficulties, ultimately deteriorating battery cycle performance and processing performance. Furthermore, nano-sizing reduces the powder compaction density of the lithium iron phosphate cathode active material, thus significantly diminishing the energy density contribution from improved electronic and ionic conductivity.

[0085] Experiments revealed that, within the range of 0.81 ≤ η ≤ 0.95, when the carbon-coated lithium iron phosphate further satisfies a volume average particle size of 840 nm ≤ Dv50 ≤ 3570 nm (optionally 1170 nm ≤ Dv50 ≤ 1820 nm), the powder compaction density of the carbon-coated lithium iron phosphate can reach a maximum of 2.64 g / cm³. 3 The electrode compaction density can reach up to 2.64 g / cm³. 3 In this application, as the volume average particle size Dv50 increases, both the powder compaction density and the electrode compaction density show a decreasing trend, resulting in a gradual decrease in battery energy density. However, as Dv50 increases, the electrode dehydration efficiency improves, correspondingly improving the cycle performance of the lithium-ion battery. See Table 4 for details.

[0086] Optionally, Dv50 can be 840, 1170, 1430, 1820, 3520, or its value can be a range of values ​​composed of any two of the above points.

[0087] In some embodiments, optionally, the degree of graphitization of the carbon-coated lithium iron phosphate in this application is 0.15~0.32. When the carbon coating factor of the carbon-coated lithium iron phosphate material in this application is 0.81≤η≤0.95 and the degree of graphitization of the carbon-coated lithium iron phosphate is 0.15~0.32, it is not only beneficial to the capacity of the lithium iron phosphate material, but also beneficial to improving the powder resistivity of the lithium iron phosphate material and increasing the battery energy density. See Table 5 for details.

[0088] The "graphitization degree" of carbon-coated lithium iron phosphate refers to the degree of graphitization of the carbon components, reflecting the integrity of the graphite crystal structure in the carbon-coated lithium iron phosphate of this application, especially in the carbon coating layer, that is, the regularity of the arrangement of carbon atoms in the graphite structure.

[0089] Optionally, the degree of graphitization can be 0.155, 0.197, 0.255, 0.245, 0.312, or a range of values ​​consisting of any two of the above points.

[0090] In some embodiments, the lithium iron phosphate substrate is doped with carbon, optionally 0.1% to 0.5% carbon, based on the mass of the lithium iron phosphate substrate.

[0091] In some embodiments, optionally, the resistivity of the carbon-coated lithium iron phosphate powder of this application is not more than 60 Ω·m, optionally not more than 30 Ω·m, and more preferably not more than 20 Ω·m.

[0092] In some embodiments, optionally, the positive electrode active material of this application, in addition to the carbon-coated lithium iron phosphate, also includes other conventional positive electrode active materials in the art, such as other lithium phosphates with olivine structures, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials can also be used. These positive electrode active materials can be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of other lithium phosphates with olivine structures may include, but are not limited to, at least one of lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0093] [Positive electrode plate]

[0094] This application provides a positive electrode sheet, including a positive current collector and a positive active material disposed on at least one surface of the positive current collector, wherein the positive active material is carbon-coated lithium iron phosphate according to one aspect of this application.

[0095] The lithium-ion battery of this application includes a positive electrode and a negative electrode. The positive electrode includes the carbon-coated lithium iron phosphate positive electrode active material described above in this application. The saturated water content of the positive electrode at 25°C and 45% relative humidity does not exceed 500 ppm. In the prior art, the electrode made from conventionally carbon-coated lithium iron phosphate positive electrode active material can have a saturated water content of up to 1000 ppm at 25°C and 45% relative humidity, which is significantly higher than the water absorption of the electrode made from the carbon-coated lithium iron phosphate positive electrode active material of this application.

[0096] In some embodiments, optionally, the compaction density of the positive electrode sheet of this application can be as high as 2.65 g / cm³. 3 The compaction density of the negative electrode sheet is not less than 1.6 g / cm³. 3 The negative electrode active material in the negative electrode sheet is graphite coated with amorphous carbon.

[0097] In this application, to complement the high-capacity lithium iron phosphate cathode active material of this application, a capacity of not less than 350 mAh / g and an electrode compaction density of not less than 1.6 g / cm³ are provided. 3 The graphite anode has an amorphous carbon coating on its surface, which provides lithium-ion intercalation capability and a high charging window that are compatible with the cathode of this application.

[0098] In some embodiments, optionally, the carbon-coated lithium iron phosphate positive electrode active material accounts for 90%-98% of the total mass of the positive electrode film layer of the positive electrode sheet of this application. The carbon-coated lithium iron phosphate positive electrode active material of this application, due to the specific surface area contributed by the carbon structure with reasonable different microstructures, can bond a larger amount of lithium iron phosphate positive electrode active material with the same binder content. When the positive electrode film layer contains 2% PVDF, the coating amount is ≥300 mg / mm². 2 The mass production coating speed can reach 60 m / min, which significantly improves the processing efficiency in actual operation and also significantly improves the battery energy density.

[0099] The positive electrode includes a positive current collector and a positive electrode material disposed on at least one surface of the positive current collector. As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode material is disposed on either or both of the two opposite surfaces of the positive current collector.

[0100] In the lithium-ion battery of this application, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), 1,3-propanesulfonate lactone (PS), polyethylene (PE), etc.), but this application is not limited to these materials.

[0101] The cathode material may optionally include a conductive agent. However, there is no specific limitation on the type of conductive agent, and those skilled in the art can select it according to actual needs. As an example, the conductive agent used in the cathode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0102] In this application, the positive electrode sheet can be prepared according to methods known in the art. As an example, the positive active material, conductive agent and binder of this application can be dispersed in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet is obtained.

[0103] [Negative electrode sheet] 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.

[0104] 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.

[0105] Optionally, in some embodiments, the compaction density of the positive electrode sheet of this application is not less than 2.35 g / cm³. 3 The negative electrode sheet has a compaction density of not less than 1.6 g / cm³. 3 The negative electrode active material in the negative electrode sheet is graphite coated with amorphous carbon.

[0106] In this application, in order to complement the high-capacity lithium iron phosphate cathode active material, a method is provided that provides a capacity of not less than 350 mAh / g and an electrode compaction density of not less than 1.6 g / cm³. 3 The graphite anode has an amorphous carbon coating on its surface, which provides lithium-ion intercalation capability and a high charging window that are compatible with the cathode of this application.

[0107] In the lithium-ion battery of this application, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.), but this application is not limited to these materials.

[0108] In the negative electrode sheet of this application, the negative electrode film layer typically comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is usually formed by coating and drying a negative electrode slurry. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0109] As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0110] In the negative electrode sheet of this application, the negative electrode film layer, in addition to including the negative electrode active material, may optionally include other commonly used negative electrode active materials. Examples of other commonly used negative electrode active materials include artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0111] [Electrolytes]

[0112] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0113] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0114] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0115] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0116] 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 additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0117] In some embodiments, optionally, the electrolyte of this application has a conductivity of not less than 13 mS / cm, in order to be used in conjunction with the positive electrode and negative electrode of this application.

[0118] [Isolation membrane]

[0119] Lithium-ion batteries using electrolytes, and some lithium-ion batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, serving a separating function. 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. In some embodiments, the separator material can be selected from one or more of glass fiber, non-woven 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.

[0120] [Lithium-ion battery]

[0121] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process, wherein the positive electrode includes the carbon-coated lithium iron phosphate of this application.

[0122] In some embodiments, the lithium-ion battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0123] In some implementations, the outer packaging of a lithium-ion battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a lithium-ion battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0124] This application does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured lithium-ion battery 5.

[0125] 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. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 via 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 lithium-ion battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific needs.

[0126] [Battery Module]

[0127] In some implementations, lithium-ion batteries can be assembled into battery modules, and the number of lithium-ion batteries contained in a battery module 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 module.

[0128] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple lithium-ion batteries 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 lithium-ion batteries 5 can be fixed in place using fasteners.

[0129] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple lithium-ion batteries 5 are housed.

[0130] [Battery Pack]

[0131] 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 selected by those skilled in the art based on the application and capacity of the battery pack.

[0132] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 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.

[0133] [Electrical appliances]

[0134] In addition, this application also provides an electrical device, which includes one or more of the lithium-ion battery, battery module, or battery pack provided in this application. The lithium-ion battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, 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.

[0135] As the electrical device, a lithium-ion battery, battery module, or battery pack can be selected according to its usage requirements.

[0136] Figure 7 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density lithium-ion batteries, a battery pack or battery module can be used.

[0137] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0138] Example

[0139] 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 the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products commonly used in the art and available commercially. Unless otherwise specified, the content of each component in the embodiments of this application is by mass.

[0140] Example

[0141] Example 1-1

[0142] Preparation of carbon-coated lithium iron phosphate as a positive electrode active material

[0143] Preparation of Lithium Iron Phosphate (LiFePO4): Using iron phosphate, lithium carbonate, and titanium dioxide as raw materials, and according to a stoichiometric ratio of FePO4:Li2CO3:TiO2 = 0.996:0.498:0.004, iron phosphate, lithium carbonate, and titanium dioxide were mixed. Glucose and polyethylene glycol (mass ratio of glucose to polyethylene glycol 1:1, carbon source accounting for 6% of the total raw material mass) were added as carbon source and reducing agent. Then, water was added as a solvent for wet grinding to obtain a mixed slurry. The slurry was spray-dried, and the dried product was then sintered in a roller furnace at 500℃ in the absence of air for 20 hours. After natural cooling to a material temperature <80℃, the material was discharged to obtain calcined material. The calcined material was crushed, sieved, and demagnetized to obtain the lithium iron phosphate (LiFePO4) substrate. 0.998 Ti 0.002 PO4, which is doped with about 0.3% carbon.

[0144] Carbon coating: The above-mentioned substrate was placed in a roller furnace and sintered under a nitrogen atmosphere, while a carbon source acetone solution was sprayed into the sintering furnace. The sintering was carried out at a constant temperature of 770°C for 10 hours. After the material cooled naturally to a temperature <80°C, it was discharged. After further pulverization using an air jet mill, the carbon-coated lithium iron phosphate of Example 1-1 was obtained.

[0145]

Positive Electrode

[0146] The carbon-coated lithium iron phosphate cathode active material, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black were mixed at a mass ratio of 96.5:2.0:1.5, and then N-methylpyrrolidone (NMP) solvent was added to form a uniform cathode slurry. This slurry was then coated onto a carbon-coated aluminum foil with a thickness of 13 μm and a coating density of 26 mg / cm³. 2 After drying, cold pressing, and slitting, the positive electrode sheet of Example 1-1 of this application is obtained.

[0147] [Negative electrode plate]

[0148] The negative electrode active material graphite, the thickener sodium carboxymethyl cellulose, the binder styrene-butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 97:1:1:1, and deionized water was added. The mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a copper foil with a thickness of 8 μm. After drying, the negative electrode sheet was obtained by cold pressing and slitting. The negative electrode sheet of Example 1-1 of this application was obtained.

[0149] Electrolyte

[0150] Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a mass ratio of 30:70 and completely dissolved. LiPF6 was then added, followed by vinylene carbonate (VC) and fluoroethylene carbonate (FEC). After mixing thoroughly, an electrolyte with a LiPF6 concentration of 1 mol / L and a mass content of 3% each of vinylene carbonate (VC) and fluoroethylene carbonate (FEC) was obtained.

[0151]

Isolation Film

[0152] A 12 μm thick polypropylene separator membrane was selected.

[0153] [Preparation of Lithium-ion Batteries]

[0154] The electrode sheets are baked in a 110°C high-temperature oven for 7 hours to remove moisture. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. After being wound into a square bare cell, it is placed in an aluminum-plastic film, injected with the corresponding non-aqueous electrolyte, and sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, the lithium-ion battery of Example 1-1 of this application is obtained.

[0155] Examples 1-2

[0156] Except for the isothermal sintering temperature of 780°C in the "carbon coating" step, the other steps are the same as in Example 1-1.

[0157] Examples 1-3

[0158] Except for the "carbon coating" step, the other steps are the same as in Example 1-1.

[0159] The "carbon coating" steps of Examples 1-3 are as follows: The lithium iron phosphate substrates of Examples 1-3 are placed in a roller furnace under a nitrogen atmosphere for sintering, while simultaneously spraying acetone solution. Sintering is carried out at a constant temperature of 550°C for 10 hours. After the material naturally cools to a temperature <80°C, it is discharged, crushed, and sieved. The material is then placed back into the roller furnace and sprayed with acetone solution again, and sintered at a constant temperature of 770°C for 10 hours. After the material naturally cools to a temperature <80°C, it is discharged. The product from the second sintering is then subjected to airflow pulverization to obtain the carbon-coated lithium iron phosphate of Examples 1-3.

[0160] Examples 1-4

[0161] Except for the second isothermal sintering temperature of 780°C in the "carbon coating" step, the other steps are the same as in Examples 1-3.

[0162] Examples 1-5

[0163] Except for the second isothermal sintering temperature of 790°C in the "carbon coating" step, the other steps are the same as in Examples 1-3.

[0164] Examples 1-6

[0165] Except for the first isothermal sintering temperature of 600°C and the second isothermal sintering temperature of 770°C in the "carbon coating" step, the other steps are the same as in Examples 1-3.

[0166] Examples 1-7

[0167] Except for the second isothermal sintering temperature of 780°C in the "carbon coating" step, the other steps are the same as in Examples 1-6.

[0168] Examples 1-8

[0169] Except for the second isothermal sintering temperature of 790°C in the "carbon coating" step, the other steps are the same as in Examples 1-6.

[0170] Comparative Example 1

[0171] Except for the isothermal sintering temperature of 750°C in the "carbon coating" step, the other steps are the same as in Example 1-1.

[0172] Comparative Example 2

[0173] Conventional sintering: Using iron phosphate, lithium carbonate, and titanium dioxide as raw materials, according to the stoichiometric ratio of FePO4:Li2CO3:TiO2=0.996:0.498:0.004, iron phosphate, lithium carbonate, and titanium dioxide are mixed, and glucose and polyethylene glycol (mass ratio of glucose to polyethylene glycol is 1:1, and the amount of carbon source accounts for 6% of the total mass of raw materials) are added as carbon sources. Then, water is added as a solvent and wet grinding is performed to obtain a mixed slurry. The obtained slurry is spray-dried, and then the dried product is placed in a roller furnace and sintered at 750℃ in the absence of air for 10 hours. After natural cooling to the material temperature <80℃, the material is discharged to obtain calcined material. The calcined material is crushed, sieved, and demagnetized to obtain lithium iron phosphate of Comparative Example 2.

[0174] Comparative Example 3

[0175] Except for the first isothermal sintering temperature of 650°C and the second isothermal sintering temperature of 830°C in the "carbon coating" step, the other steps are the same as in Examples 1-6.

[0176] Example 2-1

[0177] Except for the step of reducing the carbon source feed to 4% of the total raw material mass in the "substrate preparation" step and the step of isothermal sintering at 800℃ for 13 hours in the "carbon coating" step, the other steps are the same as in Examples 1-1. The substrate is doped with approximately 0.15% carbon.

[0178] Example 2-2

[0179] Except for the step of reducing the amount of carbon source to 5% of the total mass of raw materials in the "substrate preparation" step, and the step of setting the first isothermal sintering temperature to 600°C and the second isothermal sintering temperature to 800°C in the "carbon coating" step, the other steps are the same as in Examples 1-3.

[0180] Example 2-3

[0181] Except for the "Preparation of Substrate" step where the carbon source feed amount is 6% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 600℃ and the second isothermal sintering temperature is 780℃, the other steps are the same as in Examples 2-2.

[0182] Examples 2-4

[0183] Except for the step of "preparation of substrate" where the amount of carbon source is increased to 7% of the total mass of raw materials, and the step of "carbon coating" where the first isothermal sintering temperature is 550°C and the second isothermal sintering temperature is 800°C, the other steps are the same as in Examples 2-3.

[0184] Examples 2-5

[0185] Except for the step of "preparation of substrate" where the amount of carbon source is increased to 8% of the total mass of raw materials, and the step of "carbon coating" where the first isothermal sintering temperature is 550°C and the second isothermal sintering temperature is 780°C, the other steps are the same as in Examples 2-4.

[0186] Comparative Example 4

[0187] Except for the step of “Preparation of Substrate”, in which the amount of carbon source is reduced to 3% of the total mass of raw materials, the constant temperature sintering temperature is 830°C, and the constant temperature sintering time is 15h, the other steps are the same as in Example 2-1.

[0188] Comparative Example 5

[0189] Except for the step of "preparation of substrate" where the amount of carbon source is increased to 10% of the total mass of raw materials, and the step of "carbon coating" where the first isothermal sintering temperature is 550°C and the second isothermal sintering temperature is 770°C, the other steps are the same as in Examples 2-5.

[0190] Comparative Example 6

[0191] Except for the step of "preparation of substrate", in which the amount of carbon source added is increased to 15% of the total mass of raw materials, the other steps are the same as those in Comparative Example 5.

[0192] Example 3-1

[0193] Except for the "Preparation of Substrate" step where the amount of carbon source added is 5% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 620℃ (isothermal sintering time is 12h) and the second isothermal sintering temperature is 820℃ (isothermal sintering time is 12h), the other steps are the same as in Examples 2-5.

[0194] Example 3-2

[0195] Except for the "Preparation of Substrate" step where the amount of carbon source is 6% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 600℃ (isothermal sintering time is 10h) and the second isothermal sintering temperature is 780℃ (isothermal sintering time is 10h), the other steps are the same as in Example 3-1.

[0196] Example 3-3

[0197] Except for the "Preparation of Substrate" step where the carbon source feed amount is 8% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 600℃ (isothermal sintering time is 10h) and the second isothermal sintering temperature is 780℃ (isothermal sintering time is 10h), the other steps are the same as in Examples 3-2.

[0198] Comparative Example 7

[0199] Except for the "Preparation of Substrate" step where the amount of carbon source added is 3% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 650℃ (isothermal sintering time is 10h) and the second isothermal sintering temperature is 830℃ (isothermal sintering time is 12h), the other steps are the same as in Example 3-1.

[0200] Comparative Example 8

[0201] Except for the "Preparation of Substrate" step where the amount of carbon source added is 12% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 600℃ (isothermal sintering time is 10h) and the second isothermal sintering temperature is 780℃ (isothermal sintering time is 10h), the other steps are the same as those in Comparative Example 7.

[0202] Example 4-1

[0203] Except for the first isothermal sintering temperature of 550℃ (isothermal sintering time of 10h) and the second isothermal sintering temperature of 790℃ (isothermal sintering time of 15h) in the "carbon coating" step, the other steps are the same as in Examples 2-3. The volume average particle size Dv50 of the carbon-coated lithium iron phosphate cathode active material finally obtained in Example 4-1 is 530 nm.

[0204] Examples 4-2 to 4-7

[0205] The volume average particle sizes (Dv50) of the carbon-coated lithium iron phosphate cathode active materials obtained were 840 nm, 1170 nm, 1430 nm, 1820 nm, 3520 nm, and 5070 nm, respectively. By adjusting the classification frequency of the air jet mill, lithium iron phosphate cathode active materials with different Dv50s were obtained.

[0206] Comparative Example 9

[0207] The sintering process is the same as in Example 1-1, except that the constant temperature sintering temperature is 750℃.

[0208] Example 5-1

[0209] Except for the "Preparation of Substrate" step where the carbon source feed amount is 8% of the total mass of raw materials and the "Carbon Coating" step where the isothermal sintering temperature is 750℃ (isothermal sintering time is 10h), the other steps are the same as in Examples 1-1.

[0210] Example 5-2

[0211] Except for the "Preparation of Substrate" step where the amount of carbon source is 6% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 550℃ (isothermal sintering time is 10h) and the second isothermal sintering temperature is 790℃ (isothermal sintering time is 10h), the other steps are the same as in Examples 2-2.

[0212] Example 5-3

[0213] Except for the "Preparation of Substrate" step where the amount of carbon source added is 5% of the total mass of raw materials, and the "Carbon Coating" step where the first isothermal sintering temperature is 600℃ (isothermal sintering time is 10h) and the second isothermal sintering temperature is 830℃ (isothermal sintering time is 14h), the other steps are the same as in Examples 5-3.

[0214] Comparative Example 10

[0215] The "substrate preparation" step is the same as in Comparative Example 7, except for the "carbon coating" step. The specific "carbon coating" steps are as follows:

[0216] The lithium iron phosphate substrate of Comparative Example 10 was sintered in a roller furnace under a nitrogen atmosphere while simultaneously spraying with acetone solution. Sintering was carried out at a constant temperature of 600℃ for 10 hours. After the material naturally cooled to <80℃, it was discharged, crushed, and sieved. The material was then placed back into the roller furnace and sprayed with acetone solution again, sintering at a constant temperature of 650℃ for 10 hours. After the material naturally cooled to <80℃, it was discharged, crushed, and sieved. The material was then placed back into the roller furnace and sprayed with acetone solution a third time, sintering at a constant temperature of 830℃ for 10 hours. After the material naturally cooled to <80℃, it was discharged. The product from the third sintering was then subjected to air jet milling to obtain the lithium iron phosphate cathode active material of Comparative Example 10.

[0217] For details regarding the specific surface area, volume average particle size Dv50, carbon content, electrode dehydration efficiency, powder compaction density, electrode dehydration efficiency, battery energy density, and battery cycle retention rate of the lithium iron phosphate cathode active materials in the above embodiments and comparative examples, please refer to Tables 1 to 5.

[0218] [Testing of Relevant Parameters for Lithium Iron Phosphate Cathode Active Materials]

[0219] 1. Average particle size D

[0220] The X-ray powder diffractometer used in this application is the X'pert PRO from the United States. The detailed testing procedure for the average particle size D is as follows:

[0221] 1) Measurement of the measured width Bm of the sample under test. The instrument scanning rate was set to 2 degrees / minute to obtain the XRD pattern of the sample under test. The Bm of each diffraction peak was obtained by subtracting the Cu Kα2 background using JADE software.

[0222] 2) Instrument widening Bs measurement.

[0223] Using a standard sample of the same material as the sample to be tested and with a grain size of 5-20 μm, the XRD pattern of the standard sample was measured under the same experimental conditions as the sample to be tested, and Bs was obtained from the pattern.

[0224] 3) Calculation of half-height and width B. B = Bm - Bs. (Note: If the calculated unit of B is degrees, it needs to be converted to radians.)

[0225] 4) Calculation of average particle size D. Using the Scherrer formula D = Kλ / Bcosθ, where K is 0.89, θ is the diffraction angle, and λ = 0.154056 nm, substituting B, we can obtain the grain thickness D' of the normal direction of the crystal plane represented by a single diffraction peak. Calculate D' for multiple diffraction peaks separately, and take the average value to obtain the average particle size D.

[0226] 2. Scanning Electron Microscope (SEM)

[0227] All lithium iron phosphate cathode active materials of the examples and comparative examples were tested using a ZEISS Sigma 300 scanning electron microscope, and then tested according to standard JY / T010-1996 to observe the morphology of the samples.

[0228] It should be noted that the lithium iron phosphate substrate in this application is not necessarily perfectly spherical; it may also be irregular, consisting of primary particles. It should also be noted that the carbon-coated lithium iron phosphate cathode active material obtained in this application is not necessarily spherical; it may also be irregular.

[0229] 3. Transmission Electron Microscope (TEM)

[0230] All lithium iron phosphate cathode active materials of the examples and comparative examples were tested using a JEOL2010 transmission electron microscope. The testing standard was GB / T 34002-2017.

[0231] 4. Powder compaction density

[0232] Weigh 1g of lithium iron phosphate cathode active material from each of the examples and comparative examples, and add it to a cylindrical mold with a cross-sectional area of ​​S in the circular hole. Apply a pressure of 3t to the powder inside the mold and hold the pressure for 30s, recording the powder thickness as t. The compacted density ρ of the lithium iron phosphate cathode active material corresponding to each of the examples and comparative examples can be calculated using the following formula: ρ = m / (S × t).

[0233] 5. Electrode compaction density

[0234] The electrode sheets from the examples and comparative examples were cut into 1000mm long films. The electrode sheets were then rolled under pressure. Due to the ductility of the aluminum foil, the film length was reduced to 1006mm. A 1540.25mm diameter was then punched into the film. 2 Small circular pieces were prepared, and their weight (M) and thickness (L) were measured. Pure aluminum foil was then punched to a size of 1540.25 mm. 2 The small circular pieces are weighed, and the mass M0 of the empty aluminum foil is measured. The compaction density of the positive electrode sheet corresponding to each of the embodiments and comparative examples can be calculated by the following formula:

[0235] PD = (M-M0) / 1.54025 / 2 / L.

[0236] 6. Carbon content test

[0237] In all the above embodiments and comparative examples, the carbon content of the positive electrode active material was tested by infrared absorption method after combustion in a high-frequency induction furnace. The specific testing process was based on the standard GB / T 20123-2006 / ISO 15350:2000 "Determination of total carbon and sulfur content in iron and steel - Infrared absorption method after combustion in a high-frequency induction furnace". The carbon and sulfur content was conveniently determined using a carbon and sulfur analyzer, such as the Dekai HCS infrared carbon and sulfur analyzer.

[0238] 7. Specific surface area test

[0239] The specific surface area parameters of the examples and comparative examples were tested using a 3Flex specific surface area analyzer from Micron Technology, Inc. In this application, the specific surface area BET2 of the pore structure with a pore size of 0.5 nm to 100 nm was obtained by fitting using the T-Plot method, reflecting the total surface area of ​​micropores, mesopores, and macropores in the lithium iron phosphate material; BET1 is the specific surface area of ​​mesopores and macropores with a pore size of 2.0 nm to 100 nm obtained using the T-Plot method.

[0240] 8. Powder resistivity

[0241] The powder resistivity of the positive electrode active materials in all the above embodiments and comparative examples was tested using a powder resistivity tester (ST2722) in accordance with standard GB / T 30835-2014.

[0242] 9. Electrode dehydration efficiency

[0243] The lithium iron phosphate positive electrode active material, polyvinylidene fluoride (PVDF) binder, and acetylene black conductive agent of the examples and comparative examples were mixed at a mass ratio of 96.5:2.0:1.5, and an appropriate amount of N-methylpyrrolidone (NMP) solvent was added. The mixture was stirred thoroughly to form a uniform positive electrode slurry. This slurry was then coated onto a carbon-coated aluminum foil with a positive electrode current collector thickness of 13 μm and a coating density of 26 mg / cm². 2 The electrodes were then dried, cold-pressed, and slit for later use to obtain positive electrode sheets. The electrode dish was placed in a 50% water content environment and allowed to absorb water for 24 hours until near saturation. Using a die-cutting machine, small round sheets with a diameter of 1.4 cm were cut into small pieces of approximately 0.5 cm × 0.5 cm and placed in a moisture meter to test their water content, which was A ppm. The remaining electrode sheets were then placed in a vacuum oven, sealed in plastic bags to prevent moisture absorption, and dried at 110℃ for 7 hours. Small round sheets were then cut into pieces and their water content was tested, which was B ppm. The material dehydration rate W = (AB) / 420 ppm / min.

[0244] 10. Volume average particle size Dv50

[0245] In a particle group, 50% of the particles have a diameter greater than a certain value D, and another 50% of the particles have a diameter less than this value D. This value D is the median particle size.

[0246] Equipment Model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer; Reference Standard Procedure: GB / T19077-2016 / ISO 13320:2009; Specific Test Procedure: Take an appropriate amount of lithium iron phosphate cathode active material from the examples and comparative examples, add 20 ml of deionized water (the sample concentration should be 8-12% light-blocking), and simultaneously ultrasonically disperse for 5 min (53 kHz / 120 W) to ensure complete dispersion. Then, measure the particle size of the samples from the examples and comparative examples according to GB / T19077-2016 / ISO 13320:2009. Particle size volume distribution and particle size number distribution are plotted based on the test data. From this distribution, it is found that 50% of the particles in the total volume have a diameter greater than a certain D value, and another 50% of the particles in the total volume have a diameter less than this D value. This D value is the median particle size.

[0247] 11. Degree of graphitization

[0248] The degree of graphitization was characterized using Raman spectroscopy. The Raman spectrometer used was a new generation high-resolution Raman spectrometer from HORIBA JobinYvon, France, model LabRAM HR Evolution, with a light source wavelength of 532 nm. Spectra within the range of 750-2000 cm⁻¹ were extracted, and after background subtraction, they were fitted using the following Gaussian function. Ai, vi, and wi represent the peak intensity, peak position, and peak width, respectively. The two peaks corresponding to the carbon coating layer can be fitted using four peaks, such as... Figure 8 As shown, the corresponding peak intensities are denoted as D2, D1, D3 and G, respectively, and the degree of graphitization is G / (D3+G).

[0249] .

[0250] [Battery Performance Test]

[0251] 1. Energy density testing method

[0252] All lithium-ion batteries from the examples and comparative examples were placed in a 25°C oven and left to stand for 2 hours before undergoing charge-discharge tests. A single charge-discharge cycle was as follows: constant current charging at 1C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; a 5-minute pause; constant current discharging at 1C to 2.0V; a 5-minute pause. This constitutes one charge-discharge cycle of the battery. Cell mass energy density (Wh / kg) = energy from the third discharge / mass of lithium iron phosphate active material in the battery.

[0253] 2. Cyclic performance test

[0254] All lithium-ion batteries from the examples and comparative examples were placed in a 60°C oven and left to stand for 2 hours before undergoing charge-discharge tests. One charge-discharge cycle was as follows: constant current charging at 1C to 3.65V, followed by constant voltage charging until the charging current was less than 0.05C; pause for 5 minutes; constant current discharging at 1C to 2.5V; pause for 5 minutes. This constituted one charge-discharge cycle of the battery, which was repeated continuously until the battery capacity decreased to 80% of its initial value, and the number of cycles was recorded.

[0255] Table 1: Relevant parameters of lithium-ion batteries in the examples and comparative examples

[0256]

[0257] Table 2: Relevant parameters of lithium-ion batteries in the examples and comparative examples

[0258]

[0259] Table 3: Relevant parameters of lithium-ion batteries in the examples and comparative examples

[0260]

[0261] Table 4: Relevant parameters of lithium-ion batteries in the examples and comparative examples

[0262]

[0263] Table 5: Relevant parameters of lithium-ion batteries in the examples and comparative examples

[0264]

[0265] According to Table 1, comparing S1-1 to S1-8 and D1 to D3, when η is between 0.81 and 0.95 (S1-1 to S1-8), the corresponding electrode dehydration rate is significantly better than that of D1 to D3, and the corresponding lithium-ion battery also has excellent cycle capacity retention and high energy density. Furthermore, when η is between 0.82 and 0.93 (S1-2 to S1-7), the corresponding electrode dehydration rate is even better, and the corresponding lithium-ion battery also has better cycle performance and energy density. Even further, when η is between 0.88 and 0.92 (S1-4 to S1-6), the corresponding electrode dehydration rate is even better, and the corresponding lithium-ion battery also has better cycle performance and energy density, resulting in excellent overall performance. However, the comparative examples D1 to D3 cannot simultaneously achieve good electrode dehydration rate, high cycle capacity retention, and high energy density.

[0266] According to Table 2, comparing S2-1 to S2-5 and D4 to D6, when 0.81 ≤ η ≤ 0.95 and the carbon content is between 0.82% and 1.3%, the lithium-ion battery exhibits good electrode dehydration rate, excellent cycle capacity retention, and high energy density. Furthermore, when the carbon content is between 0.9% and 1.3%, the electrode dehydration rate is even better, and the cycle performance and energy density of the lithium-ion battery are also superior. Even further, when the carbon content is between 0.9% and 1.1%, the electrode dehydration rate is even better, and the cycle performance and energy density of the lithium-ion battery are also superior, resulting in even better overall performance. However, D4 to D6 cannot simultaneously possess good electrode dehydration rate, high cycle capacity retention, and high energy density.

[0267] According to Table 3, comparing S3-1 to S3-3 and D7 to D8, when 0.81 ≤ η ≤ 0.95 and H / D is between 0.01 and 0.04, lithium-ion batteries exhibit a good electrode dehydration rate, excellent cycle capacity retention, and high energy density. However, D7 to D8 batteries cannot simultaneously achieve a good electrode dehydration rate, high cycle capacity retention, and high energy density.

[0268] According to Table 4, comparing S4-1 to S4-7, when 0.81≤η≤0.95 and 530 nm≤Dv50≤5070 nm, the lithium-ion battery has good electrode dehydration rate, excellent cycle capacity retention rate and high energy density. Furthermore, when 1170 nm≤Dv50≤1820 nm, the electrode dehydration rate is even better, and the cycle performance and energy density of the lithium-ion battery are also better, resulting in a more superior overall performance of the lithium-ion battery.

[0269] According to Table 5, comparing S5-1 to S5-3 and D9 to D10, when the graphitization degree of the positive electrode active material is between 0.15 and 0.32, the lithium-ion battery exhibits good electrode dehydration rate, excellent cycle capacity retention, and high energy density. Furthermore, when the graphitization degree of the carbon coating layer is between 0.19 and 0.26, the electrode dehydration rate is even better, and the cycle performance and energy density of the lithium-ion battery are also superior, resulting in better overall performance. However, comparative examples D9 to D10 cannot simultaneously achieve good electrode dehydration rate, high cycle capacity retention, and high energy density.

[0270] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely illustrative, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, include: A housing, the housing including a bottom plate and side plates connected to the bottom plate, the bottom plate and the side plates forming a receiving cavity; One or more electrode assemblies, the electrode assemblies being disposed within the receiving cavity; An electrolyte, which is immersed in the electrode assembly; The electrode assembly includes a positive electrode and a negative electrode stacked together; the positive electrode includes a positive current collector and a positive film layer located on at least one side surface of the positive current collector; The positive electrode film layer includes a carbon-coated lithium iron phosphate material, which includes a lithium iron phosphate substrate and a carbon coating layer located on the surface of the substrate. The carbon coating factor of the carbon-coated lithium iron phosphate material Where BET1 is the specific surface area of ​​the mesopore and macropore structures of the carbon-coated lithium iron phosphate material, BET2 is the total specific surface area of ​​the carbon-coated lithium iron phosphate material, and η satisfies 0.81≤η≤0.

95.

2. The battery cell according to claim 1, characterized in that, η is 0.85≤η≤0.

93.

3. The battery cell according to claim 2, characterized in that, 0.88≤η≤0.

92.

4. The battery cell according to claim 1, characterized in that, The numerical range of BET1 is 5.5~9.5m. 2 / g, the value range of BET2 is 6.0~11.5m 2 / g.

5. The battery cell according to claim 1, characterized in that, The carbon component accounts for 0.7% to 1.3% of the total mass of the carbon-coated lithium iron phosphate.

6. The battery cell according to claim 5, characterized in that, The carbon component accounts for 0.9% to 1.3% of the total mass of the carbon-coated lithium iron phosphate.

7. The battery cell according to claim 6, characterized in that, The carbon component accounts for 0.9% to 1.1% of the total mass of the carbon-coated lithium iron phosphate.

8. The battery cell according to claim 1, characterized in that, The ratio H / D of the thickness H of the carbon coating layer to the average particle size D of the carbon-coated lithium iron phosphate is 0.01~0.

04.

9. The battery cell according to claim 1, characterized in that, The volume average particle size Dv50 of the carbon-coated lithium iron phosphate satisfies 840 nm ≤ Dv50 ≤ 3570 nm.

10. The battery cell according to claim 9, characterized in that, 1170 nm≤Dv50≤1820 nm.

11. The battery cell according to claim 1, characterized in that, The compacted density of the carbon-coated lithium iron phosphate powder is not less than 2.4 g / cm³. 3 .

12. The battery cell according to claim 11, characterized in that, The compacted density of the carbon-coated lithium iron phosphate powder is 2.5 g / cm³. 3 .

13. The battery cell according to claim 12, characterized in that, The carbon-coated lithium iron phosphate powder has a compacted density of 2.6 g / cm³. 3 .

14. The battery cell according to claim 1, characterized in that, The degree of graphitization of the carbon-coated lithium iron phosphate is 0.15~0.

32.

15. The battery cell according to claim 14, characterized in that, The degree of graphitization of the carbon-coated lithium iron phosphate is 0.19~0.

26.

16. The battery cell according to claim 1, characterized in that, The resistivity of the carbon-coated lithium iron phosphate powder does not exceed 60 Ω·m.

17. The battery cell according to claim 16, characterized in that, The resistivity of the carbon-coated lithium iron phosphate powder does not exceed 30 Ω·m.

18. The battery cell according to claim 17, characterized in that, The resistivity of the carbon-coated lithium iron phosphate powder does not exceed 20 Ω·m.

19. The battery cell according to claim 1, characterized in that, The lithium iron phosphate substrate is doped with carbon.

20. The battery cell according to claim 19, characterized in that, The lithium iron phosphate substrate is doped with 0.1% to 0.5% carbon, based on the mass of the lithium iron phosphate substrate.

21. The battery cell according to claim 1, characterized in that, The positive electrode sheet has a saturated water content of no more than 500 ppm at 25°C and 45% relative humidity.

22. The battery cell according to claim 1, characterized in that, The compaction density of the positive electrode sheet is not less than 2.35 g / cm³. 3 The negative electrode sheet has a compaction density of not less than 1.6 g / cm³. 3 The negative electrode active material in the negative electrode sheet includes amorphous carbon-coated graphite.

23. The battery cell according to claim 1, characterized in that, The positive electrode sheet has a compaction density of 2.35 g / cm³. 3 Up to 2.65 g / cm 3 .

24. The battery cell according to claim 1, characterized in that, The positive electrode film layer includes a binder, and based on the total mass of the positive electrode film layer, the binder has a mass percentage content of 2%, and the single-sided coating weight of the positive electrode film layer is ≥300 mg / mm². 2 .

25. The battery cell according to claim 1, characterized in that, The capacity of the battery cell is no less than 350mAh / g.

26. The battery cell according to claim 1, characterized in that, The battery cell includes a cover plate, and the housing has an opening communicating with the receiving cavity. The cover plate cooperates with the opening to close the receiving cavity.

27. The battery cell according to claim 1, characterized in that, The electrolyte comprises an electrolyte salt and a solvent, wherein the solvent comprises one or more of carbonates, carboxylic esters, and solvent sulfones.

28. The battery cell according to claim 1, characterized in that, The conductivity of the electrolyte is not less than 13 mS / cm.

29. A battery device, characterized in that, Includes the battery cell according to any one of claims 1 to 28.

30. An electrical device, characterized in that, Includes the battery cell described in any one of claims 1 to 28, or the battery device described in claim 29.

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