Lithium iron phosphate material, positive electrode, lithium ion battery and electric equipment

Abstract

The invention discloses a lithium iron phosphate material, a positive electrode, a lithium ion battery and electric equipment, relates to the technical field of lithium ion batteries, and aims to solve the safety problem caused when the lithium ion battery loads more active substances. The lithium iron phosphate material meets the following relational expression: 9 < = 100 * carbon content * specific surface area * (D90-D10) / D50 < = 100; d10 > = 0.3 [mu] m; the value range of D50 is 0.3 [mu] m to 1 [mu] m; d90 < = 2.5 [mu] m; the carbon content represents the ratio of the mass of carbon in the lithium iron phosphate material to the mass of the lithium iron phosphate material, and the value range of the carbon content is 0.01-0.015; the value range of the specific surface area is 10m < 2 > / g to 15m < 2 > / g.

Description

Technical Field

[0001] This application relates to the technical field of lithium-ion batteries, and particularly to lithium iron phosphate materials, positive electrodes, lithium-ion batteries, and electrical equipment. Background Art

[0002] At present, there are increasing requirements for the mass and / or volume energy density of lithium-ion batteries. Through reasonable design, loading more active materials on the same-sized electrode can improve the energy density. However, loading more active materials will bring battery safety problems. That is to say, the increase in active materials will make the internal reaction of the lithium-ion battery more intense, possibly generating higher heat and greater stress, increasing the risk of thermal runaway and short circuit of the lithium-ion battery; it may also cause greater volume changes during the charge and discharge process of the lithium-ion battery, thereby affecting the cycle life and stability of the lithium-ion battery. Summary of the Invention

[0003] The purpose of this application is to provide a lithium iron phosphate material, a positive electrode, a lithium-ion battery, and an electrical equipment, aiming to solve the safety problems brought about when the lithium-ion battery loads more active materials.

[0004] To achieve the above purpose, this application adopts the following technical solutions:

[0005] In the first aspect, this application provides a lithium iron phosphate material. This lithium iron phosphate material satisfies the following relational expression:

[0006] 9 ≤ 100 × carbon content × specific surface area × (D90 - D10) / D50 ≤ 100;

[0007] wherein, D10 ≥ 0.3 μm; the value range of D50 is 0.3 μm to 1 μm; D90 ≤ 2.5 μm; the carbon content represents the ratio of the mass of carbon in the lithium iron phosphate material to the mass of the lithium iron phosphate material, and the value range of the carbon content is 0.01 to 0.015; the value range of the specific surface area is 10 m 2 / g to 15 m 2 / g.

[0008] The lithium iron phosphate material provided by the embodiments of this application adjusts the particle size distribution of the lithium iron phosphate material of D90, D50, and D10, making the particle size of the lithium iron phosphate material particles more uniform, which helps to optimize the filling density inside the battery, reduce voids, thereby improving the energy density of the lithium-ion battery. At the same time, it reduces the resistance non-uniformity of the electrode, optimizes the stacking density and conductivity of the electrode, helps to reduce heat and stress concentration during the charge and discharge process of the battery, and maintains the structural stability of the electrode.

[0009] Further, by adjusting the combined range among the carbon content, specific surface area, and the average particle diameter size distribution of the lithium iron phosphate material, the above relationship can ensure that the electrode has appropriate conductivity and resistance distribution, while optimizing the performance of the lithium iron phosphate material, enabling the lithium iron phosphate material to have high conductivity and small internal resistance, and ensuring that the lithium iron phosphate material has high energy density while reducing heat and stress concentration during the charge and discharge process of the battery, improving the cycle stability and consistency of the battery, and making the lithium-ion battery have good safety performance.

[0010] In some embodiments, the lithium iron phosphate material satisfies the following relationship:

[0011] 9 ≤ 100 × carbon content × specific surface area × (D90 - D10) / D50 ≤ 25;

[0012] Wherein, D10 ≥ 0.3 μm; the value range of D50 is 0.3 μm to 1 μm; D90 ≤ 2.5 μm; the carbon content represents the ratio of the mass of carbon in the lithium iron phosphate material to the mass of the lithium iron phosphate material, and the value range of the carbon content is 0.012 to 0.014; the value range of the specific surface area is 11 m 2 / g to 13 m 2 / g.

[0013] In some embodiments, D99 is less than or equal to 3 μm.

[0014] In a second aspect, the present application provides a positive electrode. The positive electrode includes: a first current collector, a functional coating, and a positive electrode active material layer. The functional coating is located between the first current collector and the positive electrode active material layer.

[0015] Wherein, the material of the functional coating includes the lithium iron phosphate material as described in any one of the above embodiments.

[0016] It can be understood that for the positive electrode provided in the above embodiments of the present application, the beneficial effects that can be achieved can refer to the beneficial effects of the lithium iron phosphate material in the above text, which will not be elaborated here.

[0017] In some embodiments, the thickness range of the functional coating is 4 μm to 15 μm.

[0018] In some embodiments, the thickness range of the functional coating is 6 μm to 10 μm.

[0019] In some embodiments, the material of the functional coating includes: 2 wt% to 10 wt% of a binder, 0.5 wt% to 4 wt% of a conductive agent, 20 wt% to 80 wt% of boehmite, and 6 wt% to 77.5 wt% of a lithium iron phosphate material.

[0020] In some embodiments, the thickness range of the positive electrode active material layer is 65 μm to 120 μm.

[0021] In some embodiments, the in-plane resistivity between the first current collector and the functional coating is less than or equal to 4000 Ω·cm.

[0022] In some embodiments, the peel strength between the first current collector and the functional coating is greater than or equal to 80 gf / cm.

[0023] In a third aspect, the present application provides a lithium-ion battery. The lithium-ion battery includes: a negative electrode and a positive electrode as described in any one of the above embodiments. The negative electrode is disposed opposite to the positive electrode.

[0024] It can be understood that for the lithium-ion battery provided by the above embodiments of the present application, the beneficial effects that can be achieved can refer to the beneficial effects of the lithium iron phosphate material in the above text, which will not be elaborated here.

[0025] In some embodiments, the negative electrode includes: a second current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on one side of the second current collector. Wherein, the thickness range of the negative electrode active material layer is 85 μm to 160 μm.

[0026] In a fourth aspect, the present application provides an electrical device. The electrical device includes a lithium-ion battery as described in any one of the above embodiments.

[0027] It can be understood that for the electrical device provided by the above embodiments of the present application, the beneficial effects that can be achieved can refer to the beneficial effects of the lithium iron phosphate material in the above text, which will not be elaborated here. Detailed Description of the Embodiments

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0029] The terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0030] In the embodiments of the present application, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, article or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of additional identical elements in the process, article or device comprising such element.

[0031] In the embodiments of the present application, words such as "exemplary" or "for example" are used to mean as an example, illustration or explanation. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or advantageous than other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0032] In the description of this specification, specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner.

[0033] An electrical device refers to a device that converts electrical energy into other forms of energy (such as mechanical energy, thermal energy, light energy, etc.) or performs a specific function.

[0034] In some examples, electrical devices include portable electronic devices, transportation vehicles, energy storage systems, industrial devices, etc.

[0035] Exemplarily, the portable electronic device can be a mobile phone, computer, digital camera, game console, smart watch, fitness tracker, etc., without limitation here.

[0036] Exemplarily, the transportation vehicle can be an electric vehicle, hybrid vehicle, electric bicycle, electric scooter, and driverless vehicle, etc., without limitation here.

[0037] Exemplarily, the energy storage system can be a home and commercial energy storage system, an energy storage backup system for solar and wind power generation stations, etc., without limitation here.

[0038] Exemplarily, the industrial device can be a robot, drone, power tool, medical device, etc., without limitation here.

[0039] The embodiments of the present application provide an electrical device. The electrical device includes a lithium-ion battery. The lithium-ion battery is a key component for energy storage and supply of the electrical device, capable of storing electrical energy and providing power to the electrical device when needed.

[0040] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, smart grids, etc. due to their advantages such as high energy density, long cycle life, and no memory effect.

[0041] Embodiments of the present application provide a lithium-ion battery. The lithium-ion battery includes: a negative electrode and a positive electrode. The negative electrode is disposed opposite to the positive electrode.

[0042] In a lithium-ion battery, the negative electrode is the receiving end of lithium ions. During the charging process, lithium ions migrate from the positive electrode through the electrolyte to the negative electrode and are embedded in the negative electrode material, realizing the storage of electrical energy.

[0043] Exemplarily, the negative electrode material includes negative electrode active material graphite, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC), etc.

[0044] The negative electrode and the positive electrode are isolated by an electrolyte and a separator to prevent internal short circuit of the lithium-ion battery. The electrolyte is the medium for ion transport in the lithium-ion battery and is usually composed of an organic solvent and a lithium salt. The separator serves to isolate the positive and negative electrodes and prevent internal short circuit of the battery.

[0045] Exemplarily, the separator includes a polyethylene (PE) separator.

[0046] In some examples, in addition to the organic solvent and the lithium salt, the electrolyte further includes an additive, which can improve the performance of the battery.

[0047] Exemplarily, the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP).

[0048] Exemplarily, the lithium salt includes lithium hexafluorophosphate (LiPF 6 )

[0049] Exemplarily, the additive includes at least one of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,3,6-hexanetricarbonitrile, and adiponitrile (ADN).

[0050] The positive electrode is the providing end of lithium ions in the lithium-ion battery. During the discharging process, lithium ions are released from the positive electrode material, migrate through the electrolyte to the negative electrode, and are embedded in the negative electrode material, releasing the stored electrical energy.

[0051] Exemplarily, the positive electrode material includes positive electrode active material lithium cobalt oxide (LiCoO 2 ), conductive agent carbon nanotubes (CNT), and binder polyvinylidene fluoride, etc.

[0052] The positive electrode active material on the positive electrode can store and release lithium ions. The more the loading amount of the positive electrode active material, the greater the current density inside the lithium ion battery. A larger current density can improve the energy density of the lithium ion battery; that is, loading more active material on the same-sized electrode can increase the energy density.

[0053] However, loading more active material will make the internal reaction of the lithium ion battery more intense, which may generate more heat and thermal stress, and may trigger thermal runaway and cause volume changes in the active material, affecting the cycle stability of the lithium ion battery, and even damaging the structure of the lithium ion battery, resulting in battery short circuit or performance degradation.

[0054] Based on this, an embodiment of the present application provides a lithium iron phosphate material. This lithium iron phosphate material satisfies the following relationship:

[0055] 9 ≤ 100 × carbon content × specific surface area × (D90 - D10) / D50 ≤ 100;

[0056] Wherein, D10 ≥ 0.3 μm; the value range of D50 is 0.3 μm to 1 μm; D90 ≤ 2.5 μm; the carbon content represents the ratio of the mass of carbon in the lithium iron phosphate material to the mass of the lithium iron phosphate material, and the value range of the carbon content is 0.01 to 0.015; the value range of the specific surface area is 10 m 2 / g to 15 m 2 / g.

[0057] Here, D10 represents the particle size corresponding to the cumulative particle size distribution number reaching 10% in the lithium iron phosphate material particles; D50 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 50% in the lithium iron phosphate material particles; D90 represents the particle size corresponding to the cumulative particle size distribution percentage reaching 90% in the lithium iron phosphate material particles.

[0058] The carbon coated on the lithium iron phosphate can improve the conductivity of the material and ensure the conductivity of the lithium ion battery.

[0059] The specific surface area can provide active sites, which is beneficial to the diffusion and insertion / extraction process of lithium ions.

[0060] By adjusting the D90, D50 and D10 distributions, the particle sizes of the lithium iron phosphate material particles are made more uniform, which helps to optimize the packing density inside the lithium ion battery, reduce voids, thereby improving the energy density of the lithium ion battery. At the same time, it reduces the resistance non-uniformity of the electrode, optimizes the packing density and conductivity of the electrode, helps to reduce the heat and stress concentration during the charge and discharge process of the lithium ion battery, and maintains the structural stability of the electrode.

[0061] Furthermore, by adjusting the combination range among the carbon content, specific surface area, and the average particle diameter distribution of the lithium iron phosphate material, the above relationship can ensure that the electrode has appropriate conductivity and resistance distribution. Meanwhile, the performance of the lithium iron phosphate material is optimized, enabling the lithium iron phosphate material to have high conductivity and low internal resistance. On the premise of ensuring high energy density of the lithium iron phosphate material, heat and stress concentration during the charge and discharge process of the battery are reduced, the cycle stability and consistency of the battery are improved, and the lithium-ion battery has good safety performance.

[0062] In some embodiments, the lithium iron phosphate material satisfies the following relationship:

[0063] 9 ≤ 100 × carbon content × specific surface area × (D90 - D10) / D50 ≤ 25;

[0064] Wherein, D10 ≥ 0.3 μm; the value range of D50 is 0.3 μm to 1 μm; D90 ≤ 2.5 μm; the carbon content represents the ratio of the mass of carbon in the lithium iron phosphate material to the mass of the lithium iron phosphate material, and the value range of the carbon content is 0.012 to 0.014; the value range of the specific surface area is 11 m 2 / g to 13 m 2 / g.

[0065] It can be understood that by further adjusting the combination range of the carbon content, specific surface area, and particle size distribution, the electrode can be ensured to have appropriate conductivity and resistance distribution. Meanwhile, the performance of the lithium iron phosphate material is optimized. Further, on the premise that the lithium iron phosphate material has high conductivity and low internal resistance, that is, while ensuring high energy density of the lithium iron phosphate material, heat and stress concentration during the charge and discharge process of the lithium-ion battery are reduced, the cycle stability and consistency of the lithium-ion battery are improved, and the safety performance of the lithium-ion battery is improved.

[0066] In some embodiments, D99 is less than or equal to 3 μm.

[0067] Here, D99 represents the particle size corresponding to the cumulative particle size distribution percentage of 99% in the lithium iron phosphate material particles.

[0068] Exemplarily, D99 in the lithium iron phosphate material can be 0.3 μm, 1 μm, 1.5 μm, 2.5 μm, 3 μm, etc., and there is no limitation here.

[0069] It can be understood that setting D99 within the range of less than or equal to 3 μm can make the distribution of the lithium iron phosphate material particles on the electrode of the lithium-ion battery more uniform, contribute to reducing heat and stress concentration during the charge and discharge process of the lithium-ion battery, and improve the cycle stability and safety performance of the lithium-ion battery.

[0070] The above is the description of the lithium iron phosphate material. The following describes the application of the lithium iron phosphate material in the positive electrode.

[0071] An embodiment of the present application provides a positive electrode. The positive electrode includes: a first current collector, a functional coating, and a positive electrode active material layer. The functional coating is located between the first current collector and the positive electrode active material layer. Among them, the material of the functional coating includes the lithium iron phosphate material described in any one of the above embodiments.

[0072] The first current collector serves as the conductive substrate of the positive electrode, bears the positive electrode active material layer, and helps collect and conduct current. The selection of the first current collector requires it to have good electrical conductivity, mechanical strength, and good adhesion to the positive electrode active material.

[0073] In some examples, the first current collector can be a metal foil.

[0074] Exemplarily, the first current collector can be an aluminum foil.

[0075] The positive electrode active material layer is the core component of the positive electrode of the lithium-ion battery. The active material that can reversibly embed and extract lithium ions can directly affect the energy density, cycle stability, and safety performance of the lithium-ion battery.

[0076] First, the functional coating can improve the interfacial bonding force between the positive electrode active material layer and the first current collector, and prevent the shedding and peeling of the positive electrode active material during the charge and discharge cycle of the lithium-ion battery. Second, by adjusting the composition and structure of the functional coating and using the lithium iron phosphate material described in any one of the above embodiments, the heat and stress concentration during the charge and discharge process of the lithium-ion battery can be reduced, and the cycle stability and safety performance of the lithium-ion battery can be improved.

[0077] In some embodiments, the thickness range of the functional coating is 4 μm to 15 μm.

[0078] Exemplarily, the functional coating can be 4 μm, 8 μm, 10 μm, 12 μm, or 15 μm, etc., and there is no limitation here.

[0079] It can be understood that through the above settings, while the interfacial bonding force between the functional coating and the first current collector is relatively high, when the thickness of the functional coating is small, it cannot improve the safety performance of the lithium-ion battery, and when the thickness of the functional coating is large, the positive electrode drops materials, so as to improve the cycle stability and consistency of the lithium-ion battery and improve the safety performance of the lithium-ion battery.

[0080] In some embodiments, the thickness range of the functional coating is 6 μm to 10 μm.

[0081] Exemplarily, the functional coating can be 6μm, 7μm, 8μm, 9μm or 10μm, etc., without limitation here.

[0082] Through the above settings, the interfacial bonding force between the functional coating and the first current collector can be further improved, the cycle stability and consistency of the lithium-ion battery can be improved, and the safety performance of the lithium-ion battery can be improved.

[0083] In some embodiments, the materials of the functional coating include: 2wt% - 10wt% of binder, 0.5wt% - 4wt% of conductive agent, 20wt% - 80wt% of boehmite and 6wt% - 77.5wt% of lithium iron phosphate material.

[0084] Exemplarily, the binder can be 2wt%, 4wt%, 6wt%, 8wt% or 10wt%, etc., without limitation here.

[0085] Exemplarily, the conductive agent can be 0.5wt%, 1wt%, 2wt%, 3wt% or 4wt%, etc., without limitation here.

[0086] Exemplarily, the boehmite can be 20wt%, 40wt%, 60wt%, 70wt% or 80wt%, etc., without limitation here.

[0087] Exemplarily, the lithium iron phosphate material can be 6wt%, 20wt%, 40wt%, 60wt% or 77.5wt%, etc., without limitation here.

[0088] The 2wt% - 10wt% binder can bond the particles of boehmite, conductive agent and lithium iron phosphate together, preventing shedding or delamination during the charge and discharge process of the battery.

[0089] The 0.5wt% - 4wt% conductive agent plays a role in improving the conductivity of the functional coating in the functional coating, which helps to reduce the internal resistance of the lithium-ion battery and improve the charge and discharge performance and power density of the lithium-ion battery.

[0090] The 20wt% - 80wt% has excellent heat resistance, chemical stability and mechanical strength, which can effectively improve the stability and puncture resistance of the lithium-ion battery in a high-temperature environment, and can improve the safety performance and cycle stability of the lithium-ion battery.

[0091] The 6wt% - 77.5wt% lithium iron phosphate material can improve the cycle stability and consistency of the lithium-ion battery, and improve the safety performance of the lithium-ion battery.

[0092] Through the settings of the above components, the functional coating can have good conductivity and bonding properties, and can also improve the safety performance of the lithium-ion battery.

[0093] In some embodiments, the thickness of the positive electrode active material layer ranges from 65 μm to 120 μm.

[0094] Exemplarily, the thickness of the positive electrode active material layer can be 65 μm, 80 μm, 95 μm, 105 μm, 120 μm, etc., and there is no limitation here.

[0095] More preferably, the thickness of the positive electrode active material layer ranges from 80 μm to 100 μm.

[0096] Through the above settings, when the thickness of the positive electrode active material layer is relatively thin (e.g., less than 65 μm), it is difficult to improve the energy density of the lithium-ion battery, and when the thickness of the positive electrode active material layer is relatively thick (e.g., greater than 100 μm), the resistance to lithium-ion transfer is too large, and the performance of the lithium-ion battery will deteriorate. The situation can be reduced, making the lithium-ion transfer in the positive electrode active material layer smooth and improving the energy density of the lithium-ion battery.

[0097] In some embodiments, the in-plane resistivity of the electrode between the first current collector and the functional coating is less than or equal to 4000 Ω·cm.

[0098] Exemplarily, the in-plane resistivity of the electrode between the first current collector and the functional coating can be 4000 Ω·cm, 3500 Ω·cm, 3000 Ω·cm, 2500 Ω·cm, 2000 Ω·cm, etc., and there is no limitation here.

[0099] More preferably, the in-plane resistivity of the electrode between the first current collector and the functional coating is less than or equal to 2000 Ω·cm.

[0100] The above settings illustrate that the in-plane resistivity between the first current collector and the functional coating is relatively low, making the electron transfer ability between the first current collector and the functional coating relatively strong, which helps to achieve efficient current transfer during the charge and discharge process of the lithium-ion battery, thereby improving the performance of the lithium-ion battery. Also, the relatively low in-plane resistivity of the electrode indicates that less heat is generated during the charge and discharge process of the lithium-ion battery, improving the safety performance of the lithium-ion battery.

[0101] In some embodiments, the peel strength between the first current collector and the functional coating is greater than or equal to 80 gf / cm.

[0102] Exemplarily, the peel strength between the first current collector and the functional coating can be 80 gf / cm, 90 gf / cm, 100 gf / cm, 110 gf / cm, 120 gf / cm, etc., and there is no limitation here.

[0103] More preferably, the peel strength between the first current collector and the functional coating is greater than or equal to 120 gf / cm.

[0104] The above settings illustrate that the peel strength between the first current collector and the functional coating is relatively high, resulting in a strong adhesion force between the functional coating and the first current collector. This helps to ensure that during the use of the lithium-ion battery, the functional coating is not easily detached or peeled off from the first current collector, thereby maintaining the integrity and stability of the lithium-ion battery structure. Moreover, the tight bonding between the first current collector and the functional coating helps to prevent internal short circuits and heat accumulation in the lithium-ion battery, improving the safety performance of the lithium-ion battery.

[0105] In some embodiments, the negative electrode includes: a second current collector and a negative electrode active material layer. The negative electrode active material layer is disposed on one side of the second current collector. Among them, the thickness range of the negative electrode active material layer is 85 μm to 160 μm.

[0106] Exemplarily, the thickness of the negative electrode active material layer can be 85 μm, 100 μm, 120 μm, 140 μm, 160 μm, etc., and there is no limitation here.

[0107] More preferably, the thickness range of the negative electrode active material layer is 100 μm to 140 μm.

[0108] The second current collector conducts the current generated in the negative electrode active material layer and transfers it to the external circuit.

[0109] In some examples, the second current collector can be a metal foil.

[0110] Exemplarily, the second current collector can be a copper foil.

[0111] The negative electrode active material layer is the main region where electrochemical reactions occur in the negative electrode of the lithium-ion battery, responsible for storing and releasing lithium ions.

[0112] By setting the thickness range of the negative electrode active material layer to be 85 μm to 160 μm, when the thickness is relatively thin (e.g., less than 85 μm), it may reduce the capacity and cycle life of the negative electrode. If the thickness is relatively thick (e.g., greater than 160 μm), it may increase the internal resistance and polarization phenomenon of the lithium-ion battery, affecting the performance of the lithium-ion battery. This can be avoided, enabling the negative electrode to match the energy density of the positive electrode while maintaining a high energy density, thereby improving the performance of the lithium-ion battery.

[0113] The following further describes the lithium iron phosphate material in detail through specific examples as illustrations.

[0114] Example 1

[0115] Example 1 provides a lithium-ion battery, and the preparation method of this lithium-ion battery is as follows:

[0116] Step 1: In an argon atmosphere glove box with a water content < 1 ppm and an oxygen content < 1 ppm, uniformly mix ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) solvents, then add fluoroethylene carbonate (FEC), 1,3 - propane sultone (PS), 1,3,6 - hexanetricarbonitrile, and adiponitrile (ADN) and mix them evenly. Finally, add LiPF 6 to form an electrolyte solution.

[0117] Step 2: Prepare a functional coating slurry by mixing PVDF binder, conductive agent, boehmite, and lithium iron phosphate materials. Then evenly coat the functional coating slurry on the positive current collector aluminum foil and dry it at 85 °C to form a functional coating with a thickness of 8 μm. Among the lithium iron phosphate materials, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 10.

[0118] Step 3: Mix the positive electrode active material lithium cobalt oxide (LiCoO 2 )、conductive agent carbon nanotubes (CNT), and binder polyvinylidene fluoride in a mass ratio of 95:2:3 and mix them evenly. Then add N - methylpyrrolidone (NMP) and stir them into a uniform positive electrode slurry under a vacuum mixer. Then evenly coat the positive electrode slurry on the functional coating, dry it at 85 °C, and after cold pressing, slitting, and die cutting, dry it under vacuum conditions at 85 °C for 4 h to form a positive electrode sheet with a positive electrode active material layer thickness of 90 μm.

[0119] Step 4: Thoroughly stir and mix the negative electrode active material graphite, binder styrene - butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) in a mass ratio of 95:2:3 in a deionized water solvent to form a uniform negative electrode slurry. Coat the negative electrode slurry on the negative current collector copper foil to form a negative electrode active material layer, and after drying, cold pressing, slitting, and die cutting, form a negative electrode sheet.

[0120] Step 5: Prepare a polyethylene (PE) separator.

[0121] Step 6: Stack the positive electrode sheet, separator, and negative electrode sheet in sequence, with the separator between the positive electrode sheet and the negative electrode sheet to play a role in isolation. Then wind them up and place them in an outer packaging foil. Inject the electrolyte solution from Step 1 into the dried battery, and after processes such as vacuum packaging, standing, forming, and shaping, form a lithium - ion battery.

[0122] Example 2

[0123] Example 2 provides a lithium - ion battery. The preparation method of this lithium - ion battery is the same as that of Example 1, except that in the lithium iron phosphate material of Step 2, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 15.

[0124] Example 3

[0125] Example 3 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in step 2, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 25.

[0126] Example 4

[0127] Example 4 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in step 2, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 30.

[0128] Example 5

[0129] Example 5 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in step 2, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 50.

[0130] Example 6

[0131] Example 6 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in step 2, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 100.

[0132] Example 7

[0133] Example 7 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in step 2, the thickness of the functional layer is 20 μm.

[0134] Example 8

[0135] Example 8 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in step 3, the thickness of the positive electrode active material layer is 120 μm.

[0136] Comparative Example 1

[0137] Comparative Example 1 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in step 2, 100 × carbon content × specific surface area × (D90 - D10) / D50 = 5.

[0138] Comparative Example 2

[0139] Comparative Example 2 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in Step 2, 100×carbon content×specific surface area×(D90 - D10) / D50 = 120.

[0140] Comparative Example 3

[0141] Comparative Example 3 provides a lithium-ion battery. The preparation method of this lithium-ion battery is the same as that of Example 1, except that in the lithium iron phosphate material in Step 2, 100×carbon content×specific surface area×(D90 - D10) / D50 = 200.

[0142] Comparative Example 4

[0143] Comparative Example 4 provides a lithium-ion battery. The preparation method of this lithium-ion battery is as follows:

[0144] Step 1: In an argon atmosphere glove box with water content < 1 ppm and oxygen content < 1 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) solvents are uniformly mixed, then fluoroethylene carbonate (FEC), 1,3 - propane sultone (PS), 1,3,6 - hexanetricarbonitrile, and adiponitrile (ADN) are added and mixed evenly. Finally, LiPF 6 is added to form an electrolyte solution.

[0145] Step 2: The positive electrode active material lithium cobalt oxide (LiCoO 2 )、conductive agent carbon nanotubes (CNT), and binder polyvinylidene fluoride are mixed evenly according to a mass ratio of 95:2:3. Then N - methylpyrrolidone (NMP) is added, and the mixture is stirred into a uniform positive electrode paste with a vacuum stirrer. Then the positive electrode paste is uniformly coated on the functional coating, dried at 85°C, cold-pressed, slit, and cut into pieces, and then dried under vacuum conditions at 85°C for 4 h to form a positive electrode sheet with a positive electrode active material layer thickness of 90 μm.

[0146] Step 3: The negative electrode active material graphite, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose are fully stirred and mixed in deionized water solvent according to a mass ratio of 95:2:3 to form a uniform negative electrode paste. The negative electrode paste is coated on the negative electrode current collector copper foil to form a negative electrode active material layer. After drying, cold-pressing, slitting, and cutting into pieces, a negative electrode sheet is formed.

[0147] Step 4: Prepare a polyethylene (PE) separator.

[0148] Step 5: Stack the positive electrode sheet, the separator, and the negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, then wind them up and place them in the outer packaging foil, inject the electrolyte in step 1 into the dried battery, and form a lithium-ion battery after vacuum packaging, standing, formation, shaping and other processes.

[0149] Performance Testing

[0150] The lithium ion batteries of the embodiment and the comparative example were tested as follows, and the results are shown in Table 1.

[0151] (1) High temperature cycle test

[0152] The lithium-ion batteries of the embodiment and comparative example were charged to 4.5V at a constant current of 1C at a high temperature of 45°C, then charged to a current of 0.05C at a constant voltage of 4.5V, left for 5 minutes, and then discharged to 3.0V at a constant current of 1C, left for 5 minutes. This was considered a cycle. The capacity retention rate and thickness expansion rate of 600 high-temperature cycles were recorded.

[0153] (2) Normal temperature cycle test

[0154] After the lithium ion batteries of the embodiment and the comparative example were left at room temperature for 2 hours, they were charged to 4.5V at a constant current rate of 0.5C, then charged to a current of 0.05C at a constant voltage rate at 4.5V, left for 5 minutes, and then discharged to 3.0V at a constant current rate of 0.5C, left for 5 minutes. This was considered a cycle. The capacity retention rate and thickness expansion rate of 1000 cycles were recorded.

[0155] (3) Rate performance test

[0156] The lithium ion batteries of the embodiment and the comparative example were discharged to 3.0V at an ambient temperature of 25°C and left for 5 minutes; they were charged to 4.5V at 0.2C constant current and constant voltage, cut off at 0.025C, left for 5 minutes, and then discharged to 3.0V at 0.2C, and the discharge capacity was recorded as the 0.2C room temperature capacity; they were charged to the full charge voltage at 0.2C constant current and constant voltage, cut off at 0.025C, left for 5 minutes, and then discharged to 3.0V at 1.0 / 1.5C, and the discharge capacity and capacity retention rate were recorded each time.

[0157] (4) Bending and unfolding test

[0158] The lithium-ion batteries of the embodiment and the comparative example were fixed on a bracket, and the jig was lowered at a speed of 1 mm / S to press the battery to the target deformation amount for a positive displacement withstand voltage test, and the surface temperature of the battery cell was recorded and the experimental phenomenon was observed. After the bent battery cell was placed at room temperature for 48 hours, the battery cell was placed on a flat jig, and the surface temperature of the battery cell was tested when the battery cell returned to a flat state and the experimental phenomenon was observed.

[0159] (5) Acupuncture test

[0160] Fix the lithium-ion batteries of the examples and comparative examples on the bracket, and use a steel needle with a diameter of 3 mm to completely pierce the center of the battery cell at a speed of 15 mm / s. Keep the piercing state, record the temperature of the battery cell, and observe the experimental phenomena.

[0161] Table 1 Results of the resistivity of the vertical resistivity of the electrode sheet between the first current collector and the functional coating and the peel strength between the first current collector and the functional coating in the examples and comparative examples

[0162] Vertical resistivity / Ω·cm Peeling strength / gf / cm Example 1 1200 120 Example 2 1500 120 Example 3 1700 120 Example 4 3500 100 Example 5 3800 95 Example 6 4500 85 Example 7 4500 120 Example 8 1500 120 Comparative Example 1 4500 200 Comparative Example 2 5000 70 Comparative Example 3 6000 50 Comparative Example 4 / /

[0163] As can be seen from Table 1, the vertical resistivity of the electrode sheet between the first current collector and the functional coating in the examples of the present application is less than that between the first current collector and the functional coating in the comparative examples, indicating that when the lithium iron phosphate material satisfies 9 ≤ 100 × carbon content × specific surface area × (D90 - D10) / D50 ≤ 100, the vertical resistivity between the first current collector and the functional coating is relatively low, resulting in a strong electron transfer ability between the first current collector and the functional coating, which helps to achieve efficient current transmission during the charge and discharge process of the battery, thereby improving the performance of the battery; the heat generated during the charge and discharge process of the lithium-ion battery is less, improving the safety performance of the lithium-ion battery.

[0164] At the same time, the peel strength between the first current collector and the functional coating in the examples of the present application is greater than or equal to 80 gf / cm, indicating that the peel strength between the first current collector and the functional coating in the examples of the present application is relatively high, resulting in a strong adhesion force between the functional coating and the first current collector, which helps to ensure that during the use of the lithium-ion battery, the functional coating is not easily detached or peeled off from the first current collector, thereby maintaining the integrity and stability of the structure of the lithium-ion battery. In addition, the tight combination between the first current collector and the functional coating helps to prevent internal short circuit and heat accumulation in the lithium-ion battery, improving the safety performance of the lithium-ion battery.

[0165] Table 2 Lithium-ion battery test results

[0166]

[0167] As can be seen from Table 2, the retention rate expansion rate of the normal temperature cycle, the retention rate and expansion rate of the high temperature cycle, the 1C retention rate and the 1.5C retention rate of the lithium-ion battery of Comparative Example 1 and the lithium-ion battery of Comparative Example 4 are not much different, but the bending temperature, unfolding temperature and puncture temperature of the lithium-ion battery of Example 1 are significantly less than those of the lithium-ion battery of Comparative Example 4, indicating that when the functional coating is added to the lithium-ion battery of Example 1 of the present application, the safety performance of the lithium-ion battery can be significantly improved.

[0168] The retention rate and expansion rate of the normal temperature cycle, the retention rate and expansion rate of the high temperature cycle, the 1C retention rate and the 1.5C retention rate of the lithium-ion batteries of Examples 1 to 8 are all greater than those of the lithium-ion batteries of Comparative Examples 1 to 3, indicating that the lithium-ion batteries of Examples 1 to 8 of the present application have excellent normal temperature cycle capacity retention rate, high temperature cycle capacity retention rate and rate performance. This is because when the lithium iron phosphate material in the functional coating satisfies the following relationship: 9 ≤ 100 × carbon content × specific surface area × (D90 - D10) / D50 ≤ 100, it can ensure that the lithium iron phosphate material has a high energy density while enabling the lithium-ion battery to have good safety performance.

[0169] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A lithium iron phosphate material, characterized in that: The materials satisfy the following relationship: 9≤100×carbon content×specific surface area×(D90-D10) / D50≤100; Among them, D10 ≥ 0.3 μm; D50 ranges from 0.3 μm to 1 μm; D90 ≤ 2.5 μm; carbon content means: the ratio of the mass of carbon in lithium iron phosphate material to the mass of lithium iron phosphate material, the carbon content ranges from 0.01 to 0.015; the specific surface area ranges from 10m 2 / g~15m 2 / g.

2. The lithium iron phosphate material according to claim 1, characterized in that ,, the material satisfies the following relationship: 10≤100×carbon content×specific surface area×(D90-D10) / D50≤25; Among them, D10 ≥ 0.3μm; D50 ranges from 0.3μm to 1μm; D90 ≤ 2.5μm; carbon content means: the ratio of the mass of carbon in lithium iron phosphate material to the mass of lithium iron phosphate material, the carbon content ranges from 0.012 to 0.014; the specific surface area ranges from 11m 2 / g~13m 2 / g.

3. The lithium iron phosphate material according to claim 1 or 2, characterized in that: D99 is less than or equal to 3μm.

4. A positive electrode, characterized in that include: a first current collector, a functional coating layer, and a positive electrode active material layer; The functional coating is located between the first current collector and the positive electrode active material layer; Wherein, the material of the functional coating comprises the lithium iron phosphate material as claimed in any one of claims 1 to 3.

5. The positive electrode according to claim 4, characterized in that The thickness of the functional coating is in the range of 4 μm to 15 μm.

6. The positive electrode according to claim 5, characterized in that The thickness of the functional coating is in the range of 6 μm to 10 μm.

7. The positive electrode according to claim 4, characterized in that The materials of the functional coating include: 2wt% to 10wt% of a binder, 0.5wt% to 4wt% of a conductive agent, 20wt% to 80wt% of boehmite and 6wt% to 77.5wt% of the lithium iron phosphate material.

8. The positive electrode according to claim 4, characterized in that The thickness of the positive electrode active material layer is in the range of 65 μm to 120 μm.

9. The positive electrode according to claim 4, characterized in that The vertical resistivity of the pole piece between the first current collector and the functional coating is less than or equal to 4000Ω·cm.

10. The positive electrode according to claim 4, characterized in that The peel strength between the first current collector and the functional coating layer is greater than or equal to 80 gf / cm.

11. A lithium ion battery, characterized in that: include: The positive electrode according to any one of claims 4 to 10; The negative electrode is arranged opposite to the positive electrode.

12. The lithium ion battery according to claim 11, characterized in that: The negative electrode comprises: Second episode fluid; A negative electrode active material layer is disposed on one side of the second current collector; Wherein, the thickness of the negative electrode active material layer is in the range of 85 μm to 160 μm.

13. An electrical equipment, characterized in that: include: A lithium ion battery as claimed in claim 11 or 12.

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