A positive electrode material, a preparation method thereof, an electrochemical device, and an electronic device
By creating gaps on the surface of secondary particles and filling them with carbon nanotubes and solid electrolytes, the rate and cycle performance issues of ternary cathode materials were solved, achieving efficient fast charging and improved stability of the materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- DEEPAL AUTOMOBILE TECH CO LTD
- Filing Date
- 2023-06-28
- Publication Date
- 2026-07-07
AI Technical Summary
Existing ternary cathode materials have poor rate performance and cycle performance, especially due to structural instability caused by easy cracking of the coating layer during high-temperature solid-phase synthesis.
By creating gaps on the surface of secondary particles and filling them with carbon nanotubes and solid electrolytes, a conductive network is formed, which blocks the contact between the liquid electrolyte and the active material and provides ion transport channels.
It improves the rate performance and cycle performance of the cathode material, enhances the ion insertion/extraction efficiency during fast charging, and strengthens the structural stability of the material.
Smart Images
Figure CN116706022B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrochemical energy storage technology, specifically to a cathode material, its preparation method, an electrochemical device, and an electronic device. Background Technology
[0002] Lithium-ion batteries possess advantages such as high operating voltage, no memory effect, small size, light weight, high energy density, low self-discharge, long cycle life, and no pollution, making them an ideal new energy source. They are widely used in electronic products such as new energy vehicles, smartphones, laptops, and intelligent robots. In recent years, with the rapid development of new energy vehicles, people have paid increasing attention to their range and charging capabilities, namely, the high energy density and fast-charging performance of batteries. Currently, the fast-charging time for mainstream new energy vehicles on the market is in the range of 20-60 minutes, while the charging time for gasoline vehicles is usually within 5 minutes. Shortening the fast-charging time of new energy vehicles has become one of the main research directions in the field.
[0003] Currently, nickel-cobalt-manganese ternary materials are commonly used as high-energy-density battery cells. To further improve the performance of these materials, they are typically doped and / or surface-coated. For example, patent document CN108199013A describes a method of combining ternary materials with carbon materials through multiple ball milling processes to form carbon-coated ternary materials. However, the uncoated portions of the carbon-coated ternary materials obtained by this method exhibit poor conductivity, leading to poor rate performance and cycle performance of the cathode material. Patent document CN109192975A describes adding a ternary precursor wet material A and a lithium source to a carbon source solution, followed by freeze-drying to obtain ternary precursor material B. Ternary precursor material B is then sintered to obtain a carbon-coated ternary cathode material. The ternary precursor wet material A is obtained by reacting a mixture of a ternary mixed salt solution, a precipitant solution, a complexing agent solution, and an anionic surfactant solution. This method simultaneously carbonizes both the surface and the interior, thereby improving high-rate stability and high-voltage cycling stability, while also enhancing structural stability and internal electronic conductivity. However, the inner and outer coating layers of the carbon-coated ternary cathode material prepared by this method crack due to volume changes caused by particle recrystallization during the high-temperature solid-state synthesis process of the ternary material, resulting in poor cycle performance of the cathode material. Summary of the Invention
[0004] One objective of this invention is to provide a cathode material to solve the technical problem of poor rate performance and cycle performance of ternary cathode materials in the prior art; a second objective is to provide a method for preparing the cathode material as described above; a third objective is to provide an electrochemical device; and a fourth objective is to provide an electronic device.
[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0006] In one embodiment of this application, a positive electrode material is provided, the positive electrode material comprising secondary particles formed by a plurality of primary particles and a coating layer covering the outer surface of the secondary particles, the primary particles comprising a single-crystal ternary material, the secondary particles having slits, the slits being filled with carbon nanotubes and a solid electrolyte.
[0007] In some embodiments, the mass ratio of carbon nanotubes to secondary particles in the cathode material is <1:100.
[0008] In some embodiments, the coating layer comprises carbon nanotubes and a solid electrolyte.
[0009] In some embodiments, the secondary particles comprise a nickel-cobalt-manganese ternary material.
[0010] In some embodiments, the solid electrolyte includes at least one of lithium zirconium chloride, lithium indium chloride, lithium bismuth chloride, and lithium yttrium chloride.
[0011] In some embodiments, a portion of the carbon nanotubes filling the gap extends to the outside of the secondary particles.
[0012] In some embodiments, carbon nanotubes and solid electrolytes are embedded in the gaps between the primary particles.
[0013] In some embodiments, this application also provides a method for preparing the cathode material as described above, the method comprising:
[0014] S1. The precursor of the polycrystalline ternary material is mixed with a lithium source and then calcined in an oxygen atmosphere to obtain the polycrystalline ternary material.
[0015] S2. The polycrystalline ternary material is placed in a high temperature and high humidity environment for treatment, and then mixed with a catalyst and a first organic solvent for a solvothermal reaction, followed by washing and vacuum drying; the temperature of the high temperature and high humidity environment is 60-100℃, and the relative humidity is 50%-70%;
[0016] S3. The vacuum-dried solid obtained in step S2 is mixed with lithium chloride, a second organic solvent and a chloride metal salt, and then subjected to a solvothermal reaction. After filtration, it is calcined in a protective gas atmosphere to obtain the cathode material.
[0017] In some embodiments, in step S2, the temperature of the solvothermal reaction is 300-600°C, and the duration of the solvothermal reaction is 2-24 hours.
[0018] In some embodiments, in step S3, the temperature of the solvothermal reaction is 120-200°C, and the duration of the solvothermal reaction is 6-12 hours.
[0019] In some embodiments, this application also provides an electrochemical device, the electrochemical device including a positive electrode, the positive electrode including the positive electrode material as described above or the positive electrode material prepared according to the preparation method described above.
[0020] In some embodiments, this application also provides an electronic device comprising the electrochemical device described above.
[0021] The beneficial effects of this invention are:
[0022] This application pre-opens gaps in secondary particles and fills these gaps with carbon nanotubes and a solid electrolyte. This exposes the potentially fractured parts of the ternary cathode material in advance, and the carbon nanotubes filling the gaps provide a conductive network, thereby improving the rate performance and cycle performance of the cathode material. The solid electrolyte, to a certain extent, blocks the contact between the liquid electrolyte and the ternary active material, thus improving the cycle performance of the cathode material. At the same time, the solid electrolyte also provides ion transport channels, facilitating ion insertion / extraction during the fast charging process of the polycrystalline ternary material, thereby improving the rate performance of the cathode material.
[0023] The cathode material of this invention can also be used in dry mixing processes, further solving the problem of poor dispersion of conductive agents in dry mixing. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the structure of the cathode material of the present invention;
[0025] Figure 2 The image shown is a scanning electron microscope (SEM) image of the surface of the cracked polycrystalline ternary material A in Example 1.
[0026] Figure 3 This is a cross-sectional scanning electron microscope (SEM) image of polycrystalline ternary material A in Example 1;
[0027] Figure 4 This is a scanning electron microscope (SEM) image of carbon nanotubes grown in the gaps of polycrystalline ternary material B in Example 1.
[0028] Figure 5 The image shown is a transmission electron microscope (TEM) image of the solid electrolyte coating layer of the cathode material prepared in Example 1.
[0029] Figure 6 The graph shows the test results for capacity retention during rate discharge. Detailed Implementation
[0030] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.
[0031] To achieve the above objectives, the technical solution adopted by the present invention is as follows:
[0032] like Figure 1 As shown, this application provides a cathode material, which includes secondary particles formed by a plurality of primary particles and a coating layer (i.e., a solid electrolyte coating layer) covering the outer surface of the secondary particles. The primary particles include a single-crystal ternary material, and the secondary particles have slits filled with carbon nanotubes and solid electrolyte.
[0033] In this application, the secondary particles are polycrystalline ternary materials formed from a number of primary particles.
[0034] This application pre-opens gaps in secondary particles and fills these gaps with carbon nanotubes and a solid electrolyte. This exposes the potentially fractured portions of the ternary cathode material (i.e., the cathode material) in advance. The carbon nanotubes filling the gaps provide a conductive network, thereby improving the rate performance and cycle performance of the cathode material. The solid electrolyte, to a certain extent, blocks the contact between the liquid electrolyte and the ternary active material, thus improving the cycle performance of the cathode material. At the same time, the solid electrolyte also provides ion transport channels, facilitating ion insertion / extraction during the fast charging process of the polycrystalline ternary material, thereby improving the rate performance of the cathode material.
[0035] It should be understood that, in this application, primary particles refer to unagglomerated particles, and secondary particles refer to agglomerated particles.
[0036] In some embodiments, the mass ratio of carbon nanotubes to secondary particles in the cathode material is <1:100.
[0037] In this application, the mass ratio of carbon nanotubes to secondary particles refers to the mass ratio of carbon nanotubes to secondary particles in the gaps that are not filled with carbon nanotubes and solid electrolytes.
[0038] In some embodiments, the coating layer includes carbon nanotubes and a solid electrolyte.
[0039] In this application, by coating the outer surface of secondary particles with a coating layer, and setting the coating layer to include carbon nanotubes and solid electrolyte, the contact between liquid electrolyte and ternary active material (i.e., single-crystal ternary material) can be blocked, thereby improving the cycle performance of the cathode material. At the same time, the solid electrolyte can also provide ion transport channels, which facilitates ion deintercalation and deintercalation of ternary active material during fast charging, thereby improving the rate performance of cathode material.
[0040] It should be understood that in this application, carbon nanotubes can be single-walled carbon nanotubes, multi-walled carbon nanotubes, or a mixture of both. The following embodiments only illustrate the specific case of multi-walled carbon nanotubes as carbon nanotubes; those skilled in the art can also choose other methods to prepare single-walled carbon nanotubes, and thus prepare cathode materials.
[0041] In some embodiments, the secondary particles include nickel-cobalt-manganese ternary materials, such as lithium nickel cobalt-manganese oxide.
[0042] In some embodiments, the D50 particle size of the secondary particles is 5-10 μm.
[0043] In some embodiments, the solid electrolyte includes at least one of lithium zirconium chloride, lithium indium chloride, lithium bismuth chloride, and lithium yttrium chloride.
[0044] In some embodiments, a portion of the carbon nanotubes filling the gaps extend to the outside of the secondary particles.
[0045] In this application, some of the carbon nanotubes filling the gaps extend to the outside of the secondary particles, and together with the carbon nanotubes in the gaps, they can form a linear conductive network between the internal and external particles of the positive electrode, thereby improving the rate performance and cycle performance of the positive electrode material.
[0046] In some embodiments, carbon nanotubes and solid electrolytes are embedded in the gaps between primary particles.
[0047] In some embodiments, the thickness of the coating layer and the thickness of the solid electrolyte layer at the interface within the gap are both <100 nm.
[0048] In some embodiments, this application also provides a method for preparing the cathode material as described above, comprising:
[0049] S1. The precursor of the polycrystalline ternary material is mixed with a lithium source and then calcined in an oxygen atmosphere to obtain the polycrystalline ternary material.
[0050] S2. The polycrystalline ternary material is placed in a high temperature and high humidity environment for treatment, and then mixed with a catalyst and a first organic solvent for a solvothermal reaction, followed by washing and vacuum drying; the temperature of the high temperature and high humidity environment is 60-100℃, and the relative humidity is 50%-70%;
[0051] S3. The vacuum-dried solid obtained in step S2 is mixed with lithium chloride, a second organic solvent and a chloride metal salt and subjected to a solvothermal reaction. Then it is filtered and calcined in a protective gas atmosphere to obtain the cathode material.
[0052] In some embodiments, in step S1, the precursor of the polycrystalline ternary material may include substances such as nickel-cobalt-manganese hydroxide.
[0053] In some embodiments, in step S1, the ratio of the precursor of the polycrystalline ternary material to the lithium source is such that the molar ratio of the total transition metal in the precursor of the polycrystalline ternary material to the lithium in the lithium source is 1:1-1.2, preferably 1:1-1.1.
[0054] In some embodiments, the lithium source may include at least one of lithium hydroxide, lithium carbonate, lithium fluoride, lithium oxide, and lithium acetate.
[0055] In some embodiments, in step S1, the calcination temperature is 700-900℃, preferably 720-900℃; the calcination time is 8-12h, preferably 8.5-12h.
[0056] In some embodiments, in step S2, the polycrystalline ternary material is placed in a high temperature and high humidity environment for 12-24 hours, preferably 15-24 hours.
[0057] In some embodiments, in step S2, the catalyst includes at least one of Mg, K, Al, Ni, Zn, Fe, La2O3, and LaNi5.
[0058] In some embodiments, in step S2, the particle size of the catalyst is 20-100 nm.
[0059] In some embodiments, in step S2, the mass ratio of the catalyst to the polycrystalline ternary material treated in a high-temperature and high-humidity environment is 0.01-0.5:100, preferably 0.02-0.5:100.
[0060] In some embodiments, in step S2, the volume ratio of the polycrystalline ternary material treated in a high-temperature and high-humidity environment to the first organic solvent is 0.1-0.5:1, preferably 0.12-0.5:1.
[0061] In some embodiments, in step S2, the first organic solvent includes at least one selected from ethylenediamine, diethylamine, triethylamine, methanol, ethanol, toluene, xylene, and hexachlorobenzene.
[0062] In some embodiments, in step S2, the temperature of the solvothermal reaction is 300-600°C, preferably 350-600°C; and the duration of the solvothermal reaction is 2-24 hours, preferably 3-24 hours.
[0063] In some embodiments, in step S2, the temperature of vacuum drying is 80-120°C, preferably 90-120°C; the duration of vacuum drying is 4-12 hours, preferably 5-12 hours.
[0064] In some embodiments, in step S3, the mass ratio of lithium chloride to the vacuum-dried solid obtained in step S2 is 0.01-0.1:100, preferably 0.02-0.1:100.
[0065] In some embodiments, in step S3, the volume ratio of the vacuum-dried solid obtained in step S2 to the second organic solvent is 0.1-0.3:1, preferably 0.12-0.3:1.
[0066] In some embodiments, in step S3, the second organic solvent includes at least one of ethylenediamine, diethylamine, triethylamine, methanol, ethanol, toluene, xylene, and hexachlorobenzene.
[0067] In some embodiments, in step S3, the protective gas may be at least one of nitrogen, argon, helium, and xenon.
[0068] In some embodiments, in step S3, the temperature of the solvothermal reaction is 120-200°C, preferably 130-200°C; and the duration of the solvothermal reaction is 6-12 hours, preferably 8-24 hours.
[0069] In some embodiments, in step S3, the calcination temperature is 200-400℃, preferably 210-400℃; the calcination time is 2-8h, preferably 3-8h.
[0070] In some embodiments, this application also provides an electrochemical device comprising a positive electrode, the positive electrode comprising the positive electrode material as described above or the positive electrode material prepared according to the preparation method described above.
[0071] It should be noted that, in this invention, the electrode assembly of the electrochemical device includes a positive electrode, a negative electrode, and a diaphragm (if necessary) disposed between the positive electrode and the negative electrode. The electrochemical device is obtained by arranging the positive electrode and the negative electrode relative to each other through the diaphragm (if necessary) and adding an electrolyte.
[0072] Regarding the diaphragm, the diaphragm can be made of at least one of the following: polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, and aramid.
[0073] In some embodiments, a porous layer may also be provided on the surface of the diaphragm, the porous layer being disposed on at least one surface of the substrate of the diaphragm, and the porous layer may include inorganic particles and a binder.
[0074] It should be understood that, in this invention, the diaphragm is not a necessary component of the electrochemical device. For example, in certain types of electrochemical devices (such as structures where the positive and negative electrodes do not directly contact each other), a diaphragm may not be necessary.
[0075] In some embodiments, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.
[0076] In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be at least one of a gel electrolyte, a solid electrolyte, or an electrolyte solution.
[0077] Taking lithium-ion secondary batteries as an example, the electrolyte includes a lithium source and a solvent. Examples of lithium sources include at least one of the following: LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.
[0078] Regarding solvents, examples include at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.
[0079] In the case of carbonate compounds, examples include at least one of chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, and other organic solvents.
[0080] Regarding chain carbonate compounds, examples include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (MEC). Cyclic carbonate compounds include at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), and vinyl ethylene carbonate (VEC).
[0081] In the case of fluorocarbonate compounds, examples include at least one of the following: fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.
[0082] As far as carboxylic acid ester compounds are concerned, carboxylic acid ester compounds may include at least one of the following: methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, and methyl formate.
[0083] In terms of ether compounds, examples include at least one of dibutyl ether, tetraethylene dimethyl ether, diethylene dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.
[0084] Other organic solvents include, for example, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.
[0085] In some embodiments, taking a lithium-ion secondary battery as an example, the electrochemical device can be prepared by sequentially winding or stacking a positive electrode, a separator, and a negative electrode into an electrode assembly, then encapsulating it in an aluminum-plastic film, adding an electrolyte, forming, and encapsulating, thus assembling a lithium-ion secondary battery.
[0086] It should be noted that the electrochemical device in this invention is not particularly limited and can be made into paper-type batteries, button-type batteries, coin-type batteries, stacked batteries, cylindrical batteries, square batteries, etc.
[0087] In some embodiments, this application also provides an electronic device that includes the electrochemical device described above.
[0088] It should be noted that the electronic device in this invention is not particularly limited and can be any electronic device known in the prior art.
[0089] In some embodiments, electronic devices may include, for example, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, capacitors, and other materials.
[0090] The following specific examples illustrate the present invention in detail. It should also be understood that the following examples are only for specific illustrative purposes and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values in the examples below.
[0091] It should be understood that the following examples only illustrate specific scenarios where lithium hydroxide is used as the lithium source, Al, La2O3, and LaNi5 are used as catalysts, ethylenediamine and hexachlorobenzene are used as the first organic solvent, and ethanol is used as the second organic solvent. Those skilled in the art can also choose other lithium sources besides lithium hydroxide, such as lithium carbonate, lithium fluoride, lithium oxide, and lithium acetate; other catalysts besides Al, La2O3, and LaNi5, such as Mg, Al, Ni, Zn, and Fe; other first organic solvents besides ethylenediamine and hexachlorobenzene, such as diethylamine, triethylamine, methanol, ethanol, toluene, and xylene; and other second organic solvents besides ethanol, such as ethylenediamine, diethylamine, triethylamine, methanol, toluene, xylene, and hexachlorobenzene.
[0092] Example 1
[0093] This embodiment provides a positive electrode material, which is prepared according to the following steps:
[0094] S1. 50g of NCM811 ternary material precursor (i.e., Ni) with a particle size of 6μm was added. 0.8 Co 0.1 Mn 0.1 (OH)2) and 45g of lithium hydroxide were added to a high-speed mixer and mixed evenly. The mixed material was calcined at 750℃ in an oxygen atmosphere for 10h to obtain polycrystalline ternary material A.
[0095] S2. Polycrystalline ternary material A was placed in a constant temperature and humidity chamber with a relative humidity of 60% and a temperature of 70℃ for 12 hours. Polycrystalline ternary material A cracked along the grain boundaries of the primary particles to expose the crystal plane.
[0096] The surface and fissures of the cracked polycrystalline ternary material A were scanned using a scanning electron microscope, and the results are as follows: Figure 2 and Figure 3 As shown, where, Figure 2 This is a scanning electron microscope (SEM) image of the surface of the cracked polycrystalline ternary material A. Figure 3 Scanning electron microscope image of the crack in polycrystalline ternary material A;
[0097] The cracked polycrystalline ternary material A was cut open along the fissure, and the surface of the cut surface was analyzed using a scanning electron microscope. The results are as follows: Figure 4 As shown;
[0098] 60g of cracked polycrystalline ternary material A, 0.2g of aluminum powder with a particle size of 20nm and 500g of ethylenediamine were placed in a tetrafluoroethylene reactor and stirred evenly. The mixture was then placed in a resistance furnace at 450℃ for solvothermal reaction for 24h. The solid product after reaction was washed three times with deionized water and dried under vacuum at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes grown on it.
[0099] S3. Place 50g of vacuum-dried solid (i.e., polycrystalline ternary material B), 0.3g of lithium chloride, 1.649g of zirconium chloride, and 200g of anhydrous ethanol into a tetrafluoroethylene reactor and stir for 5 minutes. Then, place it in a resistance furnace at 180℃ for a solvothermal reaction for 8 hours. After filtration, calcine the obtained solid at 300℃ under a nitrogen atmosphere for 4 hours to obtain the cathode material.
[0100] The cross-section of the cathode material prepared in this embodiment was scanned using a scanning electron microscope, and the results are as follows: Figure 5 As shown.
[0101] Example 2
[0102] The difference between this embodiment and Embodiment 1 is that:
[0103] S2. Polycrystalline ternary material A was placed in a constant temperature and humidity chamber with a relative humidity of 60% and a temperature of 70℃ for 12 hours. Polycrystalline ternary material A cracked along the grain boundaries of the primary particles to expose the crystal plane.
[0104] 60g of cracked polycrystalline ternary material A, 0.2g of La2O3 and 300g of hexachlorobenzene were placed in a tetrafluoroethylene reactor and stirred evenly. The mixture was then placed in a resistance furnace at 600℃ for a solvothermal reaction for 20h. The solid product after the reaction was washed three times with deionized water and dried under vacuum at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes.
[0105] Example 3
[0106] The difference between this embodiment and Embodiment 1 is that:
[0107] S2. Polycrystalline ternary material A was placed in a constant temperature and humidity chamber with a relative humidity of 60% and a temperature of 70℃ for 12 hours. Polycrystalline ternary material A cracked along the grain boundaries of the primary particles to expose the crystal plane.
[0108] 60g of cracked polycrystalline ternary material A, 0.2g of LaNi5 and 300g of hexachlorobenzene were placed in a tetrafluoroethylene reactor and stirred evenly. The mixture was then placed in a resistance furnace at 600℃ for solvothermal reaction for 20h. The solid product after reaction was washed three times with deionized water and dried under vacuum at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes.
[0109] Example 4
[0110] The difference between this embodiment and Embodiment 1 is that:
[0111] S3. Place 60g of vacuum-dried solid (i.e., polycrystalline ternary material B), 0.3g of lithium chloride, 1.5653g of indium chloride, and 200g of anhydrous ethanol into a tetrafluoroethylene reactor and stir for 5 minutes. Then, place it in a resistance furnace at 180℃ for a solvothermal reaction for 8 hours. After filtration, calcine the obtained solid at 300℃ under a nitrogen atmosphere for 4 hours to obtain the cathode material.
[0112] Example 5
[0113] The difference between this embodiment and Embodiment 1 is that:
[0114] S3. Place 60g of vacuum-dried solid (i.e., polycrystalline ternary material B), 0.25g of lithium chloride, 0.6872g of citric acid, 0.5758g of yttrium chloride, and 200g of anhydrous ethanol into a tetrafluoroethylene reactor and stir for 5 minutes. Then, place it in a resistance furnace at 160℃ for a solvothermal reaction for 8 hours. After filtration, calcine the obtained solid at 300℃ under a nitrogen atmosphere for 4 hours to obtain the cathode material.
[0115] Comparative Example 1
[0116] This comparative example provides a cathode material, which is prepared according to the following steps:
[0117] 50g of NCM811 ternary material precursor (i.e., Ni) with a particle size of 6μm was used. 0.8 Co 0.1 Mn 0.1 (OH)2) and 45g of lithium hydroxide are added together in a high-speed mixer and mixed evenly. Then the mixed material is calcined at 750℃ in an oxygen atmosphere for 10h to obtain the positive electrode material.
[0118] Comparative Example 2
[0119] The difference between this comparative example and Example 1 is that:
[0120] S2. 60g of polycrystalline ternary material A, 0.5g of aluminum powder with a particle size of 20nm and 500g of ethylenediamine were placed in a tetrafluoroethylene reactor and stirred evenly. The mixture was then placed in a resistance furnace at 450℃ for solvothermal reaction for 24h. The solid product after reaction was washed three times with deionized water and vacuum dried at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes grown on it. This comparative example was not treated in a high temperature and high humidity environment.
[0121] Comparative Example 3
[0122] The difference between this comparative example and Example 1 is that:
[0123] S2. Polycrystalline ternary material A was placed in a constant temperature and humidity chamber with a relative humidity of 60% and a temperature of 70℃ for 12 hours. Polycrystalline ternary material A cracked along the grain boundaries of the primary particles to expose the crystal plane.
[0124] 60g of cracked polycrystalline ternary material A, 0.5g of aluminum powder with a particle size of 20nm and 500g of ethylenediamine were placed in a tetrafluoroethylene reactor and stirred evenly. The mixture was then placed in a resistance furnace at 220℃ for a solvothermal reaction for 24h. The solid product after the reaction was washed three times with deionized water and dried under vacuum at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes grown on it. That is, the temperature of the solvothermal reaction in step S2 of this comparative example is different.
[0125] Comparative Example 4
[0126] The difference between this comparative example and Example 1 is that:
[0127] S2. Polycrystalline ternary material A was placed in a constant temperature and humidity chamber with a relative humidity of 60% and a temperature of 70℃ for 12 hours. Polycrystalline ternary material A cracked along the grain boundaries of the primary particles to expose the crystal plane.
[0128] 60g of cracked polycrystalline ternary material A, 1g of aluminum powder with a particle size of 20nm and 500g of ethylenediamine were placed in a tetrafluoroethylene reactor and stirred evenly. The mixture was then placed in a resistance furnace at 450℃ for a solvothermal reaction for 24h. The solid product after the reaction was washed three times with deionized water and dried under vacuum at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes grown on it. This comparative example shows that the amount of carbon nanotubes obtained was increased by increasing the amount of aluminum powder catalyst.
[0129] Comparative Example 5
[0130] The difference between this comparative example and Example 1 is that:
[0131] S2. Polycrystalline ternary material A was placed in a constant temperature and humidity chamber with a relative humidity of 60% and a temperature of 70℃ for 12 hours. Polycrystalline ternary material A cracked along the grain boundaries of the primary particles to expose the crystal plane.
[0132] 60g of cracked polycrystalline ternary material A, 0.6g of acetylene black, and 200g of anhydrous ethanol were placed in a tetrafluoroethylene reactor and stirred until homogeneous. The mixture was then placed in a resistance furnace at 260℃ for a solvothermal reaction for 12h. The solid product after the reaction was washed three times with deionized water and then vacuum dried at 100℃ for 10h to obtain polycrystalline ternary material B with multi-walled carbon nanotubes grown on it. In this comparative example, the conductive carbon black prepared with acetylene black as the carbon source was used to replace the carbon nanotubes prepared in Example 1.
[0133] Performance testing
[0134] The cycle performance and rate performance of the cathode materials prepared in Examples 1-5 and Comparative Examples 1-5 were tested respectively. The specific steps are as follows:
[0135] The positive electrode materials prepared in Examples 1-5 and Comparative Examples 1-5 were added to N-methylpyrrolidone (NMP) solvent at a mass ratio of 90:5:5 with conductive carbon black (SP) and polyvinylidene fluoride (PVDF). After being stirred evenly with a centrifugal mixer, the mixture was uniformly coated onto an aluminum foil with a thickness of 13 μm and dried in an 80°C forced-air drying oven for 5 h. Then, it was rolled at a compaction density of 3 g / cc, manually punched, and then dried in a 120°C vacuum drying oven for 12 h to obtain the positive electrode sheet.
[0136] The electrolyte preparation steps are as follows: Prepare the electrolyte according to the volume ratio of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) of 3:3:4, the concentration of LiPF6 of 1.2 mol / L, the concentration of vinylene carbonate (VC) of 1 wt%, and the concentration of vinyl sulfate (DTD) of 1 wt%.
[0137] A PE base film with a thickness of 9μm was used as the separator;
[0138] The positive electrode, negative electrode, and separator are assembled into a coin cell. The specific steps are as follows: stack the positive electrode shell, positive electrode, separator, lithium sheet, stainless steel sheet, spring sheet, and negative electrode shell in concentric circles in the order of positive electrode shell, positive electrode, separator, and negative electrode shell. Before installing the separator and negative electrode shell, add 30μL of electrolyte to each of them, and then seal them with a coin cell sealing machine.
[0139] After the assembled coin cells were left to stand for 12 hours, they were charged and discharged three times at 0.1C within the range of 2.8-4.3V. The ratio of the initial 0.1C discharge capacity to the initial 0.1C charge capacity is the first efficiency. Similarly, the ratio of the initial 0.1C discharge capacity to the net content of active material loaded on the electrode of this coin cell is the specific capacity. Discharge tests were then conducted at 0.33C charging, and at rates of 0.33C, 0.5C, 1C, 2C, 5C, and 10C, with three charge-discharge cycles at each rate. The ratio of the discharge capacity at each discharge rate to the 0.33C discharge capacity is the discharge capacity retention rate. A 1C cycle was performed 100 times at a 1C charge-discharge rate, and the discharge capacity at the 1st and 100th cycles was recorded. The ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle is the cycle retention rate. The results are shown in Table 1 and [Table data would be inserted here]. Figure 6 As shown.
[0140] Table 1 Test Results
[0141]
[0142] As shown in Table 1, compared with Comparative Example 1 (uncoated with carbon nanotubes and solid electrolyte), the rate performance (i.e., capacity retention vs. 0.1C) and cycle performance, especially the high-rate performance (capacity retention vs. 0.1C (2C), capacity retention vs. 0.1C (5C), and capacity retention vs. 0.1C (10C)) of the cathode materials prepared in Examples 1-6 (coated with carbon nanotubes and solid electrolyte) are significantly improved. This result demonstrates that the present invention can improve the rate performance and cycle performance of cathode materials by coating the secondary particles with carbon nanotubes and solid electrolyte.
[0143] As shown in Table 1, compared with Comparative Example 2 (not subjected to high temperature and humidity treatment), the high rate performance (capacity retention rate vs. 0.1C (5C) and capacity retention rate vs. 0.1C (10C)) and 100-cycle retention rate of the cathode material prepared in Example 1 (subjected to high temperature and humidity treatment) are significantly improved. This result indicates that the present invention pre-opens gaps in the secondary particles by using a high temperature and humidity environment, and fills these gaps with carbon nanotubes and a solid electrolyte. This exposes the potentially fractured parts of the ternary cathode material in advance, and the carbon nanotubes filling the gaps provide a conductive network, thereby improving the rate performance and cycle performance of the cathode material. Furthermore, the solid electrolyte, to a certain extent, blocks the contact between the liquid electrolyte and the ternary active material, thus improving the cycle performance of the cathode material. Simultaneously, the solid electrolyte also provides ion transport channels, facilitating ion insertion / extraction during the fast charging process of the polycrystalline ternary material, thereby improving the rate performance of the cathode material.
[0144] As shown in Table 1, compared with Comparative Example 3 (where the solvothermal reaction temperature was not within a specific range), the capacity retention rate vs. 0.1C (10C) and 100-cycle retention rate of the cathode material prepared in Example 1 (where the solvothermal reaction temperature was within a specific range) were significantly increased. This result demonstrates that by controlling the solvothermal reaction temperature within a specific range, the present invention can improve the rate performance and cycle performance of electrochemical devices assembled from cathode materials.
[0145] As shown in Table 2, compared with Comparative Example 4 (where the carbon nanotube content was not within a specific range), the 100-cycle cycle retention rate of the cathode material prepared in Example 1 (where the carbon nanotube content was within a specific range) was significantly increased. This result demonstrates that by controlling the carbon nanotube content within a specific range, the present invention can improve the cycle performance of electrochemical devices assembled from cathode materials.
[0146] As shown in Table 2, compared with Comparative Example 5 (using conductive carbon black instead of carbon nanotubes), the high-rate performance (capacity retention vs. 0.1C (2C), capacity retention vs. 0.1C (5C), and capacity retention vs. 0.1C (10C)) and cycle performance of the cathode material prepared in Example 1 (using carbon nanotubes) are significantly improved. This result indicates that by employing carbon nanotubes, the present invention can provide more electron transport channels, shorten the conduction path between internal particles and other external particles, and thus improve the rate performance and cycle performance of the electrochemical device assembled from the cathode material.
[0147] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.
Claims
1. A method for preparing a positive electrode material, characterized in that, The positive electrode material includes secondary particles formed from a plurality of primary particles and a coating layer covering the outer surface of the secondary particles. The primary particles include a single-crystal ternary material. The secondary particles have slits filled with carbon nanotubes and a solid electrolyte. The preparation method includes: S1. The precursor of the polycrystalline ternary material is mixed with a lithium source and then calcined in an oxygen atmosphere to obtain the polycrystalline ternary material. S2. The polycrystalline ternary material is placed in a high-temperature and high-humidity environment for treatment, then mixed with a catalyst and a first organic solvent for a solvothermal reaction, followed by washing and vacuum drying; the temperature of the high-temperature and high-humidity environment is 60-100℃, and the relative humidity is 50%-70%; S3. The vacuum-dried solid obtained in step S2 is mixed with lithium chloride, a second organic solvent and a chloride metal salt, and then subjected to a solvothermal reaction. After filtration, it is calcined in a protective gas atmosphere to obtain the cathode material.
2. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the solvothermal reaction is 300-600℃, and the duration of the solvothermal reaction is 2-24h.
3. The preparation method according to claim 1, characterized in that, In step S3, the temperature of the solvothermal reaction is 120-200℃, and the duration of the solvothermal reaction is 6-12h.
4. The preparation method according to claim 1, characterized in that, In the cathode material, the mass ratio of carbon nanotubes to secondary particles is <1:
100.
5. The preparation method according to claim 1, characterized in that, The coating layer comprises carbon nanotubes and a solid electrolyte.
6. The preparation method according to claim 1, characterized in that, The secondary particles include nickel-cobalt-manganese ternary materials.
7. The preparation method according to claim 1, characterized in that, The solid electrolyte includes at least one of lithium zirconium chloride, lithium indium chloride, lithium bismuth chloride, and lithium yttrium chloride.
8. The preparation method according to claim 1, characterized in that, The carbon nanotubes filling the gap extend to the outside of the secondary particles.
9. The preparation method according to claim 1, characterized in that, Carbon nanotubes and solid electrolytes are embedded in the gaps between the primary particles.
10. An electrochemical device, characterized in that, The electrochemical device includes a positive electrode, which comprises a positive electrode material prepared by the preparation method according to any one of claims 1-9.
11. An electronic device, characterized in that, The electronic device includes the electrochemical device as described in claim 10.