A non-polar active material capable of being charged and discharged cyclically, a preparation method, a non-polar pole piece and a secondary battery

Abstract

The present invention belongs to the technical field of battery materials and provides a non-polar active material that can be charged and discharged cyclically, a preparation method, a non-polar pole piece, and a secondary battery. The method comprises the following steps: adding oxalic acid and a manganese source to a mixed solvent to obtain a precursor solution, performing a hydrothermal reaction to obtain a first precursor; uniformly mixing the first precursor, a lithium source, and a titanium source, and then calcining the mixture to obtain titanium-doped lithium manganate powder; mixing a carbon source, a boron source, and a solvent to obtain a coating precursor solution; mixing the titanium-doped lithium manganate powder, the coating precursor solution, and a pore-forming agent, and then spray-drying the mixture to obtain a second precursor; uniformly mixing tetraethyl orthosilicate and an ethanol aqueous solution to obtain a mixed solution; dispersing the coated lithium manganate powder in the mixed solution to obtain a reaction solution; heating in a water bath and dropwise adding ammonia water to obtain composite coated lithium manganate powder; and dispersing oxidized MXene nanosheets and the composite coated lithium manganate powder in a CTAB solution to form a dispersion, which is then filtered, washed, and dried to obtain the non-polar active material.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a non-polar active material that can be charged and discharged cyclically, a preparation method, a non-polar pole piece and a secondary battery. Background Art

[0002] In recent years, rapid advances in electronic technology have enabled portable electronic devices to become smaller, lighter, thinner, and more multifunctional. Consequently, there is a strong demand for smaller, lighter, thinner, and more reliable batteries, which serve as power sources for these devices. To meet these demands, multilayer lithium-ion secondary batteries have been proposed, featuring alternating layers of positive and negative electrodes interposed with solid electrolyte layers. By stacking battery cells tens of microns thick to form a multilayer lithium-ion secondary battery, the battery can be easily made smaller, lighter, and thinner.

[0003] Generally speaking, the active materials that constitute the positive electrode layer differ from those that constitute the negative electrode layer. Specifically, the positive electrode active material is selected to have a higher redox potential, while the negative electrode active material is selected to have a lower redox potential. In a battery with this structure, charging occurs by applying a positive voltage to the positive electrode terminal, with the negative electrode terminal serving as the reference voltage. During discharge, a positive voltage is output from the positive electrode terminal. Generally, the positive electrode active material functions solely as a positive electrode material, while the negative electrode active material functions solely as a negative electrode material. Applying a reverse voltage to a secondary battery will prevent normal charging and discharging. Furthermore, applying a reverse voltage to secondary batteries is strictly prohibited, especially when using a liquid electrolyte. Otherwise, the electrode metal dissolves into the electrolyte, the precipitated metal pierces the separator, and the detached metal floats in the liquid electrolyte. This can lead to internal short circuits and heat generation, potentially damaging the battery. Furthermore, the secondary battery will not be able to resume normal function upon recharging.

[0004] Therefore, for current secondary batteries, the charging regulations of the positive and negative poles must be strictly followed, and special attention must be paid to the installation direction of the positive and negative poles of the secondary battery when in use. In order to prevent the secondary battery from failing to work or even short-circuiting due to the reverse installation of the positive and negative poles, it is urgent to design a secondary battery that does not require identification of the installation direction and the positive and negative poles can be installed at will. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a non-polar active material, a preparation method, a non-polar electrode and a secondary battery that can be charged and discharged in a cyclical manner. The non-polar active material prepared by the present invention can be used as both a positive electrode active material and a negative electrode active material. When the non-polar active material provided by the present invention is used as a battery material for a secondary battery, there is no need to deliberately distinguish the installation direction of the positive and negative electrodes of the secondary battery, which can prevent the secondary battery from failing to work or even short-circuiting due to the reverse installation of the positive and negative electrodes, thereby improving the convenience of use of the secondary battery.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing a non-polar active material that can be charged and discharged and recycled, the preparation method comprising:

[0008] (I) adding oxalic acid and a manganese source to a mixed solvent, mixing and stirring until the oxalic acid and the manganese source are completely dissolved in the mixed solvent to obtain a precursor solution, transferring the precursor solution to a hydrothermal kettle for a hydrothermal reaction, filtering the reaction product after the reaction to obtain a filter cake, and drying, crushing and grinding the filter cake in sequence to obtain a first precursor; mixing the first precursor, a lithium source and a titanium source uniformly, placing the mixture in a tube furnace, heating to a first temperature and maintaining the temperature, performing a first calcination, then continuously heating to a second temperature and maintaining the temperature, performing a second calcination, and cooling the mixture to room temperature in the furnace after the second calcination to obtain titanium-doped lithium manganate powder;

[0009] (II) uniformly mixing a carbon source, a boron source, and a solvent to obtain a coating precursor solution, spray-drying the titanium-doped lithium manganate powder, the coating precursor solution, and a pore-forming agent, and then subjecting the mixture to a second precursor, subjecting the second precursor to a high-temperature carbonization treatment under an inert atmosphere to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder; uniformly mixing ethyl orthosilicate with an ethanol aqueous solution to obtain a mixed solution, dispersing the coated lithium manganate powder in the mixed solution to obtain a reaction solution, heating the reaction solution in a water bath while dropwise adding ammonia water to in situ grow nano-silica on the boron-doped porous carbon layer, and then filtering and drying to obtain a composite coated lithium manganate powder;

[0010] (III) dissolving a fluoride salt in an acid solution to obtain an intercalation solution, adding titanium aluminum carbide to the intercalation solution, and mixing uniformly to obtain a precursor solution. The precursor solution is stirred and heated to obtain a MXene suspension. The MXene suspension is subjected to ultrasonic exfoliation and high-speed centrifugation in sequence. The supernatant after centrifugation is freeze-dried to obtain MXene nanosheets. The MXene nanosheets are heat-treated in an oxygen-containing atmosphere to obtain oxidized MXene nanosheets. The oxidized MXene nanosheets and the composite-coated lithium manganate powder are dispersed in a cetyltrimethylammonium bromide solution to form a dispersion. The dispersion is filtered, washed, and dried to obtain the non-polar active substance.

[0011] The non-polar active material prepared by the present invention can be used as both a positive electrode active material and a negative electrode active material. When the non-polar active material provided by the present invention is used as a battery material for a secondary battery, there is no need to deliberately distinguish the installation direction of the positive and negative electrodes of the secondary battery. This can prevent the secondary battery from failing to work or even short-circuiting due to the reverse installation of the positive and negative electrodes, thereby improving the convenience of use of the secondary battery.

[0012] The cycle performance of spinel-type lithium manganese oxide is poor, which is caused by the dissolution of trivalent manganese, Jan-Taylor distortion and decomposition of the electrolyte. Among them, the dissolution of trivalent manganese and Jan-Taylor distortion mainly occur at the end of discharge. At this time, trivalent manganese ions are enriched on the surface of lithium manganese oxide. Therefore, the present invention uses oxalic acid as a precipitant and adopts a co-precipitation process to prepare a spinel-type lithium manganese oxide with a one-dimensional rod-like structure. This structure can effectively shorten the solid-phase diffusion path, reduce the enrichment of lithium ions on the surface, and also reduce the enrichment of trivalent manganese. At the same time, in the process of preparing lithium manganese oxide, titanium ions are doped to partially replace the trivalent manganese ions on 16d. By reducing the number of trivalent manganese ions and increasing the average valence of manganese, the Jan-Taylor effect can be weakened and the dissolution of trivalent manganese can be reduced. At the same time, the Mn-O bond can be strengthened, making the structure of lithium manganese oxide more stable, thereby improving the cycle performance of the non-polar active material. In addition, the manganese on the surface of lithium manganate has unpaired single electrons, so there are a large number of catalytic active sites. These active sites reduce the compatibility of lithium manganate and the electrolyte and accelerate the dissolution of manganese. Therefore, the present invention coats the surface of the titanium-doped lithium manganate powder with a boron-doped porous carbon layer. The boron-doped porous carbon layer not only provides an ion migration tunnel and accelerates the migration speed of lithium ions, but also prevents direct contact between the titanium-doped lithium manganate powder and the electrolyte, effectively avoiding the occurrence of electrolyte decomposition.

[0013] The present invention conducts a coprecipitation reaction in a mixed solvent system consisting of polyethylene glycol and deionized water. Utilizing the good dispersibility of the mixed solvent and using oxalic acid as a precipitant, the reaction produces a uniform, monodispersed, one-dimensional rod-shaped precursor, manganese oxalate. Subsequently, after a first calcination and a second calcination, a spinel-type titanium-doped lithium manganate powder with a well-maintained one-dimensional rod-shaped structure is obtained. The titanium-doped lithium manganate powder with a one-dimensional rod-shaped structure can maintain a consistent charge and discharge state during the charge and discharge process. Furthermore, the one-dimensional rod-shaped structure can shorten the diffusion path of lithium ions, effectively buffering the structural strain caused by the insertion and removal of lithium ions, improving the material's cyclic stability, and exhibiting excellent cycling performance under high-rate discharge conditions.

[0014] Under high current charge and discharge conditions, spinel lithium manganese oxide is prone to electrode polarization on the surface of the material, causing a decrease in discharge capacity. The more severe the electrode polarization, the worse the cycle stability. On the other hand, under high current charge and discharge conditions, the surface of the material is easily corroded by the electrolyte, resulting in a reduction in active substances and a decrease in capacity. The present invention combines bulk doping with surface coating to synthesize composite coated lithium manganate powder in two steps. First, titanium-doped lithium manganate powder is synthesized by a solid-phase method. Bulk doping allows titanium ions to enter the lattice of lithium manganate, effectively suppressing the Jahn-Teller effect and achieving the effect of stabilizing the spinel-type lithium manganate framework structure. Subsequently, a composite coated lithium manganate powder with a boron-doped porous carbon layer is prepared by spray drying and high-temperature carbonization. Surface coating reduces the direct contact between the titanium-doped lithium manganate powder and the electrolyte to reduce the dissolution of manganese. At the same time, the boron-doped porous carbon layer coated on the surface of the titanium-doped lithium manganate powder has a rich pore structure, provides an ion migration tunnel, accelerates the migration speed of lithium ions, and can quickly complete the deintercalation and embedding of lithium ions in a short time, thereby improving the electronic conductivity of the material while avoiding the occurrence of electrochemical polarization on the surface of the material, increasing the number of active sites for the composite porous carbon layer to combine with lithium ions, and improving the rate performance and cycle performance of the secondary battery.

[0015] The present invention hydrolyzes ethyl orthosilicate to in-situ generate nano-silica within the pores of the boron-doped porous carbon layer. This ensures that the nano-silica is evenly dispersed within the pores of the boron-doped porous carbon layer, rather than being enriched and agglomerated on the surface of the boron-doped porous carbon layer. By loading the nano-silica within the pores of the boron-doped porous carbon layer, a synergistic effect is achieved between the nano-silica and the boron-doped porous carbon layer. On the one hand, the nano-silica, as an active material, has a theoretical specific capacity of up to 1965 mAh g -1, loading it in the pores of the boron-doped porous carbon layer can significantly improve the lithium storage capacity of the composite-coated lithium manganese oxide powder; in addition, the coating of the boron-doped porous carbon layer improves the conductivity of the composite-coated lithium manganese oxide powder, which is conducive to the rapid arrival of electrons at the surface of the nano-silica; on the other hand, with the help of the pore structure of the boron-doped porous carbon layer, the volume change and mechanical strain of the nano-silica can be buffered, providing a good strain space for the volume expansion of the nano-silica, so that the volume expansion of the nano-silica is effectively suppressed, ensuring that the actual lithium insertion capacity of the nano-silica is fully utilized, and greatly improving the lithium storage performance of the composite-coated lithium manganese oxide powder, thereby improving the cycle life of the secondary battery.

[0016] Due to the severe Jahn-Teller effect and manganese dissolution of the composite-coated lithium manganate powder during the cycle, coupled with the poor electronic conductivity and ion transfer rate of lithium manganate, the discharge specific capacity of the composite-coated lithium manganate powder rapidly decays with increasing current density. To this end, the present invention combines the composite-coated lithium manganate powder with oxidized Mxene nanosheets, and uses an electrostatic self-assembly process to induce the oxidized Mxene nanosheets to coat the surface of the composite-coated lithium manganate powder, ultimately preparing a non-polar active material with high rate performance and cycling performance.

[0017] The oxidized Mxene nanosheets provided by the present invention are obtained by etching in an acid solution environment. The original oxidized Mxene nanosheets are nanosheet layers with smooth surfaces. In the present invention, the oxidized Mxene nanosheets are mixed with composite coated lithium manganate powder in a hexadecyltrimethylammonium bromide (CTAB) solvent system. CTAB can destroy the balance between the oxidized Mxene nanosheets by neutralizing positive and negative charges, thereby inducing the oxidized Mxene nanosheets to gradually transform from a flat sheet structure to a spatial wrinkled structure by using an electrostatic self-assembly process, and making the oxidized Mxene nanosheets with wrinkled structures uniformly cover the surface of the composite coated lithium manganate powder to form a coating coupling structure. The advantages of this coupling structure are: (1) it can form a better interface contact between the composite coated lithium manganate powder and the oxidized Mxene nanosheets, so that the surface area of ​​the non-polar active material exposed to the electrolyte is significantly reduced. During the charge and discharge process of the non-polar active material, Li +It can diffuse along the wrinkled structure of the oxidized Mxene nanosheets and reach the surface of the composite coated lithium manganate powder, which can not only improve the conductivity of the non-polar active material, but also protect the composite coated lithium manganate powder from the attack of the electrolyte, reduce the dissolution of manganese ions, reduce the occurrence of harmful reactions between the composite coated lithium manganate powder and the electrolyte, enhance the stability of the non-polar active material, and delay the capacity decay of the secondary battery; (2) The oxidized Mxene nanosheet coating layer can also make the electrons and lithium ions on the entire surface of the composite coated lithium manganate powder uniformly distributed during the charge and discharge cycle, so that the electrochemical polarization effect caused by electron aggregation of the non-polar active material during the charge and discharge cycle is weakened, thereby improving the rate performance of the secondary battery; (3) Coating the oxidized Mxene nanosheets on the surface of the composite coated lithium manganate powder can significantly improve the reversibility of the secondary battery, which is mainly due to the excellent electronic conductivity and low Li + Diffusion barrier, Mxene has 10 -10 ~10 - 9 cm 2 / s Gao Li + Diffusion mobility and low Li ion density of 0.07 eV + The diffusion barrier makes the inorganic active material have higher chemical reaction activity and charge transfer speed under high rate conditions; at the same time, the close coupling structure between the oxidized Mxene nanosheets and the composite coated lithium manganate powder has more electronic contact points, which can improve the electronic conductivity of the material, making the non-polar active material coated with the oxidized Mxene nanosheets show excellent Li + Transmission performance.

[0018] As a preferred technical solution of the present invention, in step (I), the manganese source is any one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate, or a combination of at least two thereof.

[0019] In some optional examples, the molar ratio of oxalic acid to manganese source is (4-5):1, for example, 4.0:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1 or 5.0:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In some optional examples, the mixed solvent is composed of polyethylene glycol and deionized water in a volume ratio of 1:(3~4), for example, it can be 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9 or 1:4.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0021] In some optional examples, the mixing and stirring time of the oxalic acid, manganese source and mixed solvent is 1 to 3 hours, for example, it can be 1.0h, 1.2h, 1.4h, 1.6h, 1.8h, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional examples, the concentration of the manganese source in the precursor solution is 1~2 mol / L, for example, it can be 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L or 2.0 mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0023] In some optional examples, the temperature of the hydrothermal reaction of the precursor solution is 160~180℃, for example, it can be 160℃, 162℃, 164℃, 166℃, 168℃, 170℃, 172℃, 174℃, 176℃, 178℃ or 180℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0024] In some optional examples, the hydrothermal reaction time of the precursor solution is 3 to 5 hours, for example, it can be 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours or 5.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional embodiments, the drying temperature of the filter cake is 80-90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional examples, the drying time of the filter cake is 10 to 15 hours, for example, it can be 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, 14.5 hours or 15 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] As a preferred technical solution of the present invention, in step (I), the lithium source is any one of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate, and dilithium hydrogen phosphate, or a combination of at least two thereof.

[0028] In some optional examples, the titanium source is any one of metatitanic acid, titanium trichloride, titanium tetrachloride, titanium dioxide, or a combination of at least two thereof.

[0029] In some optional examples, the molar ratio of the manganese element in the first precursor, the lithium element in the lithium source and the titanium element in the titanium source is 1:x:(2-x), wherein 1.9≤x<2, for example, it can be 1.9, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98 or 1.99, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0030] In some optional examples, the heating rate of the first calcination process is 1~3℃ / min, for example, it can be 1.0℃ / min, 1.2℃ / min, 1.4℃ / min, 1.6℃ / min, 1.8℃ / min, 2.0℃ / min, 2.2℃ / min, 2.4℃ / min, 2.6℃ / min, 2.8℃ / min or 3.0℃ / min, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0031] In some optional instances, the first temperature is 300~400℃, for example, it can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 360℃, 370℃, 380℃, 390℃ or 400℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional examples, the insulation time at the first temperature is 2 to 4 hours, for example, it can be 2.0 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours or 4.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional examples, the heating rate of the second calcination process is 2~5°C / min, for example, it can be 2.0°C / min, 2.2°C / min, 2.4°C / min, 2.6°C / min, 2.8°C / min, 3.0°C / min, 3.2°C / min, 3.4°C / min, 3.6°C / min, 3.8°C / min, 4.0°C / min, 4.2°C / min, 4.4°C / min, 4.6°C / min, 4.8°C / min or 5.0°C / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] In some optional instances, the second temperature is 700~800℃, for example, it can be 700℃, 710℃, 720℃, 730℃, 740℃, 750℃, 760℃, 770℃, 780℃, 790℃ or 800℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] The present invention specifically limits the second temperature to 700-800°C. When the second temperature is lower than 700°C, the Li + The diffusion rate of titanium doped lithium manganate is slow, and it cannot be well embedded in the crystal lattice of manganese dioxide to form a lithium manganate solid solution, resulting in a low degree of crystallinity of the prepared titanium doped lithium manganate powder. As the calcination temperature continues to increase, the high temperature causes the diffusion rate of various ions in the raw materials to increase, which can ensure more sufficient contact between different ions, reduce the formation of internal defects in the titanium doped lithium manganate powder, thereby forming a more perfect solid solution structure, and improving the crystallinity of the prepared titanium doped lithium manganate powder. When the second temperature reaches 800°C, the crystallinity of the titanium doped lithium manganate powder reaches the highest, generating a highly crystalline and relatively uniformly sized spinel-type one-dimensional rod-like structure of titanium doped lithium manganate powder. When the second temperature continues to increase to above 800°C, the primary particles of the prepared titanium doped lithium manganate powder show obvious agglomeration, resulting in the continuous increase in the particle size of the secondary particles. When the second temperature is within the range of 700-800℃, the particle size of the primary particles of lithium manganate prepared is 100-200nm. Due to the low calcination temperature, the agglomeration of the primary particles is not obvious. As the calcination temperature gradually increases, the particle size of the primary particles gradually increases, and the agglomeration phenomenon becomes more and more obvious. When the second temperature reaches 800℃, the particle size of the primary particles reaches 500-900nm, and the diameter of the secondary particles reaches 3μm. The particle size of the primary particles is too large, which will lead to the formation of Li +The diffusion distance in the solid phase increases, affecting the electrochemical performance of the secondary battery. In addition, due to the poor high-temperature resistance of titanium-doped lithium manganate powder, high temperatures will cause the structure of lithium manganate to collapse. In addition, high temperatures cause the primary particles to agglomerate, resulting in the particle size of the prepared titanium-doped lithium manganate powder being too large, causing the diffusion path of lithium ions to become longer during the charge and discharge process, increasing the diffusion resistance. The lithium ions deep inside the structure of the titanium-doped lithium manganate powder cannot achieve rapid and effective migration. These lithium ions will become "dead lithium" and cannot be effectively and reversibly embedded and migrated out during the charge and discharge process, resulting in a lower specific capacity of the secondary battery finally prepared.

[0036] In some optional examples, the holding time at the second temperature is 8 to 10 hours, for example, it can be 8.0 hours, 8.2 hours, 8.4 hours, 8.6 hours, 8.8 hours, 9.0 hours, 9.2 hours, 9.4 hours, 9.6 hours, 9.8 hours or 10.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] As a preferred technical solution of the present invention, in step (II), the carbon source is any one of glucose, citric acid, starch, and sucrose, or a combination of at least two thereof.

[0038] In some optional examples, the boron source is any one of boric acid, metaboric acid, and boron oxide, or a combination of at least two thereof.

[0039] In some optional examples, the solvent is any one of deionized water, N,N-dimethylpyrrolidone, and dimethyl sulfoxide, or a combination of at least two thereof.

[0040] In some optional examples, the concentration of the carbon source in the coating precursor solution is 5~10g / L, for example, it can be 5.0g / L, 5.5g / L, 6.0g / L, 6.5g / L, 7.0g / L, 7.5g / L, 8.0g / L, 8.5g / L, 9.0g / L, 9.5g / L or 10.0g / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] In some optional examples, the molar ratio of the carbon element in the carbon source to the boron element in the boron source is 1:(0.02~0.03), for example, it can be 1:0.02, 1:0.021, 1:0.022, 1:0.023, 1:0.024, 1:0.025, 1:0.026, 1:0.027, 1:0.028, 1:0.029 or 1:0.03, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0042] In some optional examples, the mass ratio of the titanium-doped lithium manganate powder, the carbon source in the coating precursor solution, and the pore-forming agent is 1:(18~20):(10~12), for example, it can be 1:18:10, 1:18.2:10.2, 1:18.4:10.4, 1:18.6:10.6, 1:18.8:10.8, 1:19:11, 1:19.2:11.2, 1:19.4:11.4, 1:19.6:11.6, 1:19.8:11.8 or 1:20:12, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0043] The present invention specifically limits the mass ratio of titanium-doped lithium manganate powder, carbon source and pore-forming agent to 1: (18-20): (10-12). As the amount of carbon source added increases, the specific capacity of the secondary battery prepared increases accordingly. When the amount of carbon source added exceeds the upper limit of the range defined by the present invention, the specific capacity of the prepared coated lithium manganate powder shows a downward trend. This is because when the amount of carbon source added is too much, the number of pores in the generated boron-doped porous carbon layer decreases, the pore size decreases, and the Li + diffusion channel, reducing Li + The diffusion power of the secondary battery is affected.

[0044] The specific charge capacity of the coated lithium manganate powder gradually increases with the increase in the amount of pore-forming agent added. This is because as the amount of pore-forming agent added increases, the number of pores formed by carbonization increases, the specific surface area of ​​the boron-doped porous carbon layer increases, and the number of lithium storage sites increases accordingly, resulting in a gradual increase in the initial charge capacity of the secondary battery finally prepared. When the amount of pore-forming agent added is lower than the lower limit of the range defined by the present invention, the cycle performance of the secondary battery prepared is poor. This is because the low amount of pore-forming agent added results in a low number of pores formed after carbonization, resulting in a small pore size. The embedded lithium ions enter the small pore structure and cannot be smoothly released. Therefore, as the charge and discharge process proceeds, the cycle performance of the secondary battery becomes increasingly poor. When the amount of pore-forming agent added exceeds the upper limit of the range specified in the present invention, the number of pore structures formed by carbonization is too large and the pore diameter is too large. The boron-doped porous carbon layer coated on the surface of the titanium-doped lithium manganese oxide powder cannot play a good supporting role, causing the pore structure of the boron-doped porous carbon layer to collapse and lead to pore blockage, hindering the adsorption and desorption of lithium ions in the pores, resulting in a reduction in the number of active sites for lithium ions, and ultimately affecting the cycle capacity of the secondary battery.

[0045] In some optional examples, the pore-forming agent is any one of ammonium chloride, calcium carbonate, and paraffin, or a combination of at least two of them.

[0046] In some optional embodiments, the spray drying temperature is 180~200°C, for example, it can be 180°C, 182°C, 184°C, 186°C, 188°C, 190°C, 192°C, 194°C, 196°C, 198°C or 200°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some optional embodiments, the feed rate of the spray drying is 10~20kg / h, for example, it can be 10kg / h, 11kg / h, 12kg / h, 13kg / h, 14kg / h, 15kg / h, 16kg / h, 17kg / h, 18kg / h, 19kg / h or 20kg / h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In some optional examples, the heating rate of the high-temperature carbonization treatment is 8~10℃ / min, for example, it can be 8.0℃ / min, 8.2℃ / min, 8.4℃ / min, 8.6℃ / min, 8.8℃ / min, 9.0℃ / min, 9.2℃ / min, 9.4℃ / min, 9.6℃ / min, 9.8℃ / min or 10.0℃ / min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0049] In some optional examples, the heating temperature of the high-temperature carbonization treatment is 600~700℃, for example, it can be 600℃, 610℃, 620℃, 630℃, 640℃, 650℃, 660℃, 670℃, 680℃, 690℃ or 700℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0050] The present invention specifically limits the temperature of the high-temperature carbonization treatment to 600~700℃. When the temperature of the high-temperature carbonization treatment is lower than 600℃, the discharge specific capacity of the secondary battery prepared is low. This is because when the carbonization temperature is too low, the carbonization degree of the carbon source is low, thereby affecting the electrochemical performance of the secondary battery. When the temperature of the high-temperature carbonization treatment is higher than 700℃, the discharge specific capacity of the secondary battery prepared is low. This is because the carbonization temperature is too high, resulting in serious agglomeration of the carbon source on the surface of the titanium-doped lithium manganese oxide powder. At the same time, the carbon source covering the surface of the titanium-doped lithium manganese oxide powder is locally rapidly carbonized to produce impurities, which ultimately affects the electrochemical performance of the secondary battery. In addition, when the temperature of the high-temperature carbonization treatment exceeds 700℃, the pore structure formed by carbonization will collapse and gradually become blocked, preventing the adsorption and desorption of lithium ions in the pores, resulting in a reduction in the number of active sites for lithium ions, and ultimately affecting the cycle capacity of the secondary battery.

[0051] In some optional examples, the holding time of the high-temperature carbonization treatment is 3 to 5 hours, for example, it can be 3.0 hours, 3.2 hours, 3.4 hours, 3.6 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours or 5.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0052] The present invention specifically limits the holding time of the high-temperature carbonization treatment to 3~5h. When the holding time of the high-temperature carbonization treatment is less than 3h, the insufficient holding time results in low crystallinity of the coated lithium manganate powder, low carbonization degree, and inability to form a fully effective pore structure, thereby affecting the electrochemical performance of the coated lithium manganate powder. When the holding time of the high-temperature carbonization treatment exceeds 5h, the discharge specific capacity of the prepared coated lithium manganate powder decreases. This is because as the holding time increases, the coated lithium manganate powder agglomerates, resulting in an increase in the particle size of the lithium manganate powder, thereby prolonging the Li + The migration path of the coated lithium manganate powder decreases the discharge specific capacity.

[0053] As a preferred technical solution of the present invention, in step (II), the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:(3-4), for example, it can be 1:3.0, 1:3.1, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.9 or 1:4.0, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0054] In some optional examples, the volume ratio of the ethyl orthosilicate to the ethanol aqueous solution is 1:(4~5), for example, it can be 1:4.0, 1:4.1, 1:4.2, 1:4.3, 1:4.4, 1:4.5, 1:4.6, 1:4.7, 1:4.8, 1:4.9 or 1:5.0, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0055] In some optional examples, the mass ratio of the coated lithium manganate powder to the ethyl orthosilicate in the mixed solution is (0.2~0.3):1, for example, it can be 0.2:1, 0.21:1, 0.22:1, 0.23:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.29:1 or 0.3:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0056] The present invention specifically limits the mass ratio of the coated lithium manganate powder to ethyl orthosilicate to (0.2~0.3):1. When the amount of ethyl orthosilicate added exceeds the upper limit of the range defined by the present invention, the amount of nano-silicon dioxide generated by the reaction is too large. The excess nano-silicon dioxide will be exposed to the surface of the boron-doped porous carbon layer, causing the volume expansion of this part of the nano-silicon dioxide during the charge and discharge process to be unable to be effectively suppressed by the boron-doped porous carbon layer, resulting in a reduction in the lithium insertion capacity of the composite coated lithium manganate powder. In addition, the excess nano-silicon dioxide will block the pores of the boron-doped porous carbon layer, hindering the lithium + The migration tunnel of Li + The migration speed of the secondary battery decreases, which ultimately affects the electrochemical performance of the secondary battery.

[0057] In some optional examples, the mass fraction of the ammonia water is 10~20wt%, for example, it can be 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0058] In some optional examples, the volume ratio of ethyl orthosilicate to the ammonia water in the reaction solution is 1:(0.2~0.4), for example, it can be 1:0.2, 1:0.22, 1:0.24, 1:0.26, 1:0.28, 1:0.30, 1:0.32, 1:0.34, 1:0.36, 1:0.38 or 1:0.4, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0059] In some optional examples, the dripping speed of the ammonia solution is 5~8mL / min, for example, it can be 5.0mL / min, 5.2mL / min, 5.4mL / min, 5.6mL / min, 5.8mL / min, 6.0mL / min, 6.2mL / min, 6.4mL / min, 6.6mL / min, 6.8mL / min, 7.0mL / min, 7.2mL / min, 7.4mL / min, 7.6mL / min, 7.8mL / min or 8.0mL / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] In some optional embodiments, the water bath heating temperature is 50~60℃, for example, it can be 50℃, 51℃, 52℃, 53℃, 54℃, 55℃, 56℃, 57℃, 58℃, 59℃ or 60℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0061] In some optional embodiments, the water bath heating time is 1 to 2 hours, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0062] As a preferred technical solution of the present invention, in step (III), the fluoride salt is any one of sodium fluoride, potassium fluoride, lithium fluoride, and calcium fluoride, or a combination of at least two thereof.

[0063] In some optional examples, the acid solution is any one of hydrochloric acid solution, sulfuric acid solution or hydrofluoric acid solution, or a combination of at least two of them.

[0064] In some optional examples, the concentration of the acid solution is 5~10mol / L, for example, it can be 5.0mol / L, 5.5mol / L, 6.0mol / L, 6.5mol / L, 7.0mol / L, 7.5mol / L, 8.0mol / L, 8.5mol / L, 9.0mol / L, 9.5mol / L or 10.0mol / L, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0065] In some optional examples, the mixing ratio of the fluoride salt and the acid solution is (0.05~0.1) g:1 mL, for example, it can be 0.05 g:1 mL, 0.055 g:1 mL, 0.06 g:1 mL, 0.065 g:1 mL, 0.07 g:1 mL, 0.075 g:1 mL, 0.08 g:1 mL, 0.085 g:1 mL, 0.09 g:1 mL, 0.095 g:1 mL or 0.1 g:1 mL, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0066] In some optional embodiments, the mixing time of the fluoride salt and the acid solution is 1 to 10 minutes, for example, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes or 10 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0067] In some optional examples, the mass ratio of the fluoride salt to the titanium aluminum carbide in the intercalation solution is (1~2):1, for example, it can be 1.0:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1 or 2.0:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0068] In some optional examples, the heating temperature of the precursor solution is 30~40℃, for example, it can be 30℃, 31℃, 32℃, 33℃, 34℃, 35℃, 36℃, 37℃, 38℃, 39℃ or 40℃, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0069] In some optional examples, the stirring time of the precursor solution is 12 to 24 hours, for example, it can be 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours or 24 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0070] In some optional examples, the ultrasonic power of the ultrasonic peeling is 500~600W, for example, it can be 500W, 510W, 520W, 530W, 540W, 550W, 560W, 570W, 580W, 590W or 600W, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0071] In some optional examples, the ultrasonic stripping treatment time is 30~60min, for example, it can be 30min, 32min, 34min, 36min, 38min, 40min, 42min, 44min, 46min, 48min, 50min, 52min, 54min, 56min, 58min or 60min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0072] In some optional examples, the rotation speed of the high-speed centrifugation is 3000~4000rpm, for example, it can be 3000rpm, 3100rpm, 3200rpm, 3300rpm, 3400rpm, 3500rpm, 3600rpm, 3700rpm, 3800rpm, 3900rpm or 4000rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0073] In some optional examples, the high-speed centrifugation time is 1 to 2 hours, for example, it can be 1.0 h, 1.1 h, 1.2 h, 1.3 h, 1.4 h, 1.5 h, 1.6 h, 1.7 h, 1.8 h, 1.9 h or 2.0 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] In some optional embodiments, the freeze-drying temperature is -40~-30°C, for example, it can be -40°C, -39°C, -38°C, -37°C, -36°C, -35°C, -34°C, -33°C, -32°C, -31°C or -30°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0075] In some optional examples, the freeze-drying time is 10 to 12 hours, for example, it can be 10 hours, 10.2 hours, 10.4 hours, 10.6 hours, 10.8 hours, 11.0 hours, 11.2 hours, 11.4 hours, 11.6 hours, 11.8 hours or 12.0 hours, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0076] In some optional examples, the oxygen-containing atmosphere is a mixed atmosphere of argon and oxygen.

[0077] In some optional examples, the volume ratio of argon and oxygen in the oxygen-containing atmosphere is (10~20):1, for example, it can be 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0078] The temperature of the heat treatment is 200~300℃, for example, it can be 200℃, 210℃, 220℃, 230℃, 240℃, 250℃, 260℃, 270℃, 280℃, 290℃ or 300℃, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0079] In some optional embodiments, the heat treatment time is 10~15h, for example, it can be 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h or 15h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] As a preferred technical solution of the present invention, in step (III), the concentration of the hexadecyltrimethylammonium bromide solution is 1-2 g / mL, for example, it can be 1.0 g / mL, 1.1 g / mL, 1.2 g / mL, 1.3 g / mL, 1.4 g / mL, 1.5 g / mL, 1.6 g / mL, 1.7 g / mL, 1.8 g / mL, 1.9 g / mL or 2.0 g / mL, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0081] In some optional examples, the mass ratio of the oxidized Mxene nanosheets, the composite-coated lithium manganate powder, and the cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide solution is 1: (15-25): (8-10), for example, 1:15:8, 1:16:8.2, 1:17:8.4, 1:18:8.6, 1:19:8.8, 1:20:9, 1:21:9.2, 1:22:9.4, 1:23:9.6, 1:24:9.8 or 1:25:10, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0082] The present invention specifically limits the mass ratio of oxidized MXene nanosheets, composite-coated lithium manganate powder, and cetyltrimethylammonium bromide. When the amount of oxidized MXene nanosheets added is lower than the lower limit of the range defined in the present invention, due to the large particle size of the composite-coated lithium manganate powder and the small size of the oxidized MXene nanosheets, the oxidized MXene nanosheets cannot completely cover the surface of the composite-coated lithium manganate powder, and cannot fully protect the composite-coated lithium manganate powder.

[0083] With the increase of the addition amount of oxidized MXene nanosheets, the electrochemical impedance of the non-polar active material gradually decreases, which is attributed to the excellent electronic conductivity and low Li + The diffusion barrier, coupled with the wrinkled structure of the Mxene nanosheets themselves and the close coupling with the composite-coated lithium manganate powder, produces a better conductive network, promotes the charge transfer surface reaction, improves the SEI layer and charge transfer of the non-polar active material, and makes the prepared secondary battery have excellent cycle stability and rate performance, greatly improving the electrochemical performance of the secondary battery.

[0084] When the amount of oxidized Mxene nanosheets added exceeds the upper limit of the range defined in the present invention, the discharge specific capacity of the secondary battery finally prepared will show a downward trend. This is because as the amount of oxidized Mxene nanosheets added increases, the oxidized Mxene nanosheet coating layer covering the surface of the composite coated lithium manganate powder becomes too thick; at the same time, due to the wrinkled structure of the oxidized Mxene nanosheets, the Li+ The steric hindrance of Li + transmission, resulting in some Li + The inability to reversibly embed and extract the non-polar active material ultimately affects the discharge capacity of the non-polar active material. In addition, adding too many oxidized Mxene nanosheets will also lead to a relatively low addition amount of composite-coated lithium manganese oxide powder, which will also affect the initial discharge capacity of the secondary battery.

[0085] In some optional examples, the mixing time of the oxidized Mxene nanosheets, the composite-coated lithium manganate powder and the cetyltrimethylammonium bromide solution is 30 to 40 minutes, for example, 30 minutes, 31 minutes, 32 minutes, 33 minutes, 34 minutes, 35 minutes, 36 minutes, 37 minutes, 38 minutes, 39 minutes or 40 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0086] Illustratively, the present invention provides a method for preparing a non-polar active substance, the preparation method specifically comprising the following steps:

[0087] (1) Oxalic acid and a manganese source are added to a mixed solvent in a molar ratio of (4-5):1, wherein the mixed solvent is composed of polyethylene glycol and deionized water in a volume ratio of 1:(3-4), and the mixture is stirred for 1-3 hours until the oxalic acid and the manganese source are completely dissolved in the mixed solvent to obtain a precursor solution. The concentration of the manganese source in the precursor solution is 1-2 mol / L;

[0088] The precursor solution is transferred to a hydrothermal kettle for hydrothermal reaction at a temperature of 160-180°C for 3-5 hours. After the reaction is completed, the reaction product is filtered to obtain a filter cake, which is then dried, crushed and ground in sequence at a drying temperature of 80-90°C for 10-15 hours to obtain a first precursor.

[0089] A first precursor, a lithium source, and a titanium source are uniformly mixed and placed in a tube furnace, wherein the molar ratio of manganese element in the first precursor, lithium element in the lithium source, and titanium element in the titanium source is 1:x:(2-x), wherein 1.9≤x<2; heating to 300-400°C at a heating rate of 1-3°C / min and holding the temperature for 2-4 hours to perform a first calcination; then continuing to heat the temperature to 700-800°C at a heating rate of 2-5°C / min and holding the temperature for 8-10 hours to perform a second calcination, and cooling the mixture to room temperature after the second calcination to obtain titanium-doped lithium manganate powder;

[0090] (2) uniformly mixing a carbon source, a boron source and a solvent to obtain a coating precursor solution, wherein the molar ratio of the carbon element in the carbon source to the boron element in the boron source is 1:(0.02~0.03), and the concentration of the carbon source in the coating precursor solution is 5~10 g / L; mixing the titanium-doped lithium manganate powder obtained in step (1), the coating precursor solution and the pore-forming agent, wherein the mass ratio of the titanium-doped lithium manganate powder, the carbon source in the coating precursor solution and the pore-forming agent is 1:(18~20):(10~12), spray drying the mixture to obtain a second precursor, the spray drying temperature is 180~200°C, and the feed amount is 10~20 kg / h; placing the second precursor under an inert atmosphere, heating it to 600~700°C at a heating rate of 8~10°C / min and keeping it warm for 3~5 hours to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder;

[0091] The method comprises the following steps: uniformly mixing tetraethyl orthosilicate and an ethanol aqueous solution in a volume ratio of 1:(4-5) to obtain a mixed solution, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:(3-4); dispersing coated lithium manganate powder in the mixed solution to obtain a reaction solution, wherein the mass ratio of the coated lithium manganate powder to the tetraethyl orthosilicate in the mixed solution is (0.2-0.3):1; heating the reaction solution in a water bath at a temperature of 50-60° C. for 1-2 h; and dripping 10-20 wt % ammonia water into the reaction solution at a dripping rate of 5-8 mL / min while heating in the water bath, wherein the volume ratio of the tetraethyl orthosilicate to the ammonia water in the reaction solution is 1:(0.2-0.4), so as to in situ grow nano-silica on the boron-doped porous carbon layer, and then filtering and drying to obtain a composite coated lithium manganate powder;

[0092] (3) Dissolve the fluoride salt in a 5-10 mol / L acid solution and stir for 1-10 min to obtain an intercalation solution. The mixing ratio of the fluoride salt to the acid solution is (0.05-0.1) g:1 mL. Add titanium aluminum carbide to the intercalation solution. The mass ratio of the fluoride salt to the titanium aluminum carbide is (1-2):1. Mix well to obtain a precursor solution. The precursor solution is stirred and heated to obtain an Mxene suspension. The heating temperature is 30-40 ° C and the stirring time is 12-24 h. The Mxene suspension is subjected to ultrasonic stripping and high-speed centrifugation in sequence. The ultrasonic power of the ultrasonic stripping is 500-600 W, the processing time of the ultrasonic stripping is 30-60 min, the centrifugal speed is 3000-4000 rpm, and the high-speed centrifugation time is 1-2 h. After centrifugation, the supernatant is placed at -40--30 ° C for freeze drying for 10-12 h to obtain Mxene nanosheets.

[0093] The MXene nanosheets are heat-treated in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere comprises argon and oxygen in a volume ratio of (10-20):1, the heat treatment temperature is 200-300° C., the heat treatment time is 10-15 hours, and the oxidized MXene nanosheets are obtained after the heat treatment;

[0094] The oxidized Mxene nanosheets and the composite coated lithium manganate powder obtained in step (2) are dispersed in a hexadecyltrimethylammonium bromide solution with a concentration of 1-2 g / mL and mixed and stirred for 30-40 minutes to form a dispersion. The mass ratio of the oxidized Mxene nanosheets, the composite coated lithium manganate powder and the hexadecyltrimethylammonium bromide is 1:(15-25):(8-10). The dispersion is filtered, washed and dried to obtain the non-polar active substance.

[0095] In a second aspect, the present invention provides a non-polar active material prepared by the preparation method described in the first aspect, wherein the non-polar active material comprises oxidized Mxene nanosheets and composite-coated lithium manganate powder; wherein the composite-coated lithium manganate powder comprises titanium-doped lithium manganate powder and a boron-doped porous carbon layer coated on its surface, and the boron-doped porous carbon layer is loaded with nano-silica.

[0096] In a third aspect, the present invention provides a non-polar pole piece, which includes a current collector and an active material layer located on the surface of the current collector. The active material layer is formed by drying an active slurry coated on the surface of the current collector. The active slurry includes the non-polar active material, conductive agent, binder and solvent described in the second aspect.

[0097] In a fourth aspect, the present invention provides a secondary battery comprising a battery cell and a shell, wherein the battery cell comprises a first non-polar pole piece, a diaphragm and a second non-polar pole piece stacked in sequence, the battery cell is encapsulated in the shell, and an electrolyte is injected into the shell.

[0098] Compared with the prior art, the present invention has the following beneficial effects:

[0099] The non-polar active material prepared by the present invention can be used as both a positive electrode active material and a negative electrode active material. When the non-polar active material provided by the present invention is used as a battery material for a secondary battery, there is no need to deliberately distinguish the installation direction of the positive and negative electrodes of the secondary battery. This can prevent the secondary battery from failing to work or even short-circuiting due to the reverse installation of the positive and negative electrodes, thereby improving the convenience of use of the secondary battery.

[0100] The cycle performance of spinel-type lithium manganese oxide is poor, which is caused by the dissolution of trivalent manganese, Jan-Taylor distortion and decomposition of the electrolyte. Among them, the dissolution of trivalent manganese and Jan-Taylor distortion mainly occur at the end of discharge. At this time, trivalent manganese ions are enriched on the surface of lithium manganese oxide. Therefore, the present invention uses oxalic acid as a precipitant and adopts a co-precipitation process to prepare a spinel-type lithium manganese oxide with a one-dimensional rod-like structure. This structure can effectively shorten the solid-phase diffusion path, reduce the enrichment of lithium ions on the surface, and also reduce the enrichment of trivalent manganese. At the same time, in the process of preparing lithium manganese oxide, titanium ions are doped to partially replace the trivalent manganese ions on 16d. By reducing the number of trivalent manganese ions and increasing the average valence of manganese, the Jan-Taylor effect can be weakened and the dissolution of trivalent manganese can be reduced. At the same time, the Mn-O bond can be strengthened, making the structure of lithium manganese oxide more stable, thereby improving the cycle performance of the non-polar active material. In addition, the manganese on the surface of lithium manganate has unpaired single electrons, so there are a large number of catalytic active sites. These active sites reduce the compatibility of lithium manganate and the electrolyte and accelerate the dissolution of manganese. Therefore, the present invention coats the surface of the titanium-doped lithium manganate powder with a boron-doped porous carbon layer. The boron-doped porous carbon layer not only provides an ion migration tunnel and accelerates the migration speed of lithium ions, but also prevents direct contact between the titanium-doped lithium manganate powder and the electrolyte, effectively avoiding the occurrence of electrolyte decomposition.

[0101] The present invention conducts a coprecipitation reaction in a mixed solvent system consisting of polyethylene glycol and deionized water. Utilizing the good dispersibility of the mixed solvent and using oxalic acid as a precipitant, the reaction produces a uniform, monodispersed, one-dimensional rod-shaped precursor, manganese oxalate. Subsequently, after a first calcination and a second calcination, a spinel-type titanium-doped lithium manganate powder with a well-maintained one-dimensional rod-shaped structure is obtained. The titanium-doped lithium manganate powder with a one-dimensional rod-shaped structure can maintain a consistent charge and discharge state during the charge and discharge process. Furthermore, the one-dimensional rod-shaped structure can shorten the diffusion path of lithium ions, effectively buffering the structural strain caused by the insertion and removal of lithium ions, improving the material's cyclic stability, and exhibiting excellent cycling performance under high-rate discharge conditions.

[0102] Under high current charge and discharge conditions, spinel lithium manganese oxide is prone to electrode polarization on the surface of the material, causing a decrease in discharge capacity. The more severe the electrode polarization, the worse the cycle stability. On the other hand, under high current charge and discharge conditions, the surface of the material is easily corroded by the electrolyte, resulting in a reduction in active substances and a decrease in capacity. The present invention combines bulk doping with surface coating to synthesize composite coated lithium manganate powder in two steps. First, titanium-doped lithium manganate powder is synthesized by a solid-phase method. Bulk doping allows titanium ions to enter the lattice of lithium manganate, effectively suppressing the Jahn-Teller effect and achieving the effect of stabilizing the spinel-type lithium manganate framework structure. Subsequently, a composite coated lithium manganate powder with a boron-doped porous carbon layer is prepared by spray drying and high-temperature carbonization. Surface coating reduces the direct contact between the titanium-doped lithium manganate powder and the electrolyte to reduce the dissolution of manganese. At the same time, the boron-doped porous carbon layer coated on the surface of the titanium-doped lithium manganate powder has a rich pore structure, provides an ion migration tunnel, accelerates the migration speed of lithium ions, and can quickly complete the deintercalation and embedding of lithium ions in a short time, thereby improving the electronic conductivity of the material while avoiding the occurrence of electrochemical polarization on the surface of the material, increasing the number of active sites for the composite porous carbon layer to combine with lithium ions, and improving the rate performance and cycle performance of the secondary battery.

[0103] The present invention hydrolyzes ethyl orthosilicate to in-situ generate nano-silica within the pores of the boron-doped porous carbon layer. This ensures that the nano-silica is evenly dispersed within the pores of the boron-doped porous carbon layer, rather than being enriched and agglomerated on the surface of the boron-doped porous carbon layer. By loading the nano-silica within the pores of the boron-doped porous carbon layer, a synergistic effect is achieved between the nano-silica and the boron-doped porous carbon layer. On the one hand, the nano-silica, as an active material, has a theoretical specific capacity of up to 1965 mAh g -1 , loading it in the pores of the boron-doped porous carbon layer can significantly improve the lithium storage capacity of the composite-coated lithium manganese oxide powder; in addition, the coating of the boron-doped porous carbon layer improves the conductivity of the composite-coated lithium manganese oxide powder, which is conducive to the rapid arrival of electrons at the surface of the nano-silica; on the other hand, with the help of the pore structure of the boron-doped porous carbon layer, the volume change and mechanical strain of the nano-silica can be buffered, providing a good strain space for the volume expansion of the nano-silica, so that the volume expansion of the nano-silica is effectively suppressed, ensuring that the actual lithium insertion capacity of the nano-silica is fully utilized, and greatly improving the lithium storage performance of the composite-coated lithium manganese oxide powder, thereby improving the cycle life of the secondary battery.

[0104] Due to the severe Jahn-Teller effect and manganese dissolution of the composite-coated lithium manganate powder during the cycle, coupled with the poor electronic conductivity and ion transfer rate of lithium manganate, the discharge specific capacity of the composite-coated lithium manganate powder rapidly decays with increasing current density. To this end, the present invention combines the composite-coated lithium manganate powder with oxidized Mxene nanosheets, and uses an electrostatic self-assembly process to induce the oxidized Mxene nanosheets to coat the surface of the composite-coated lithium manganate powder, ultimately preparing a non-polar active material with high rate performance and cycling performance.

[0105] The oxidized Mxene nanosheets provided by the present invention are obtained by etching in an acid solution environment. The original oxidized Mxene nanosheets are nanosheet layers with smooth surfaces. In the present invention, the oxidized Mxene nanosheets are mixed with composite coated lithium manganate powder in a hexadecyltrimethylammonium bromide (CTAB) solvent system. CTAB can destroy the balance between the oxidized Mxene nanosheets by neutralizing positive and negative charges, thereby inducing the oxidized Mxene nanosheets to gradually transform from a flat sheet structure to a spatial wrinkled structure by using an electrostatic self-assembly process, and making the oxidized Mxene nanosheets with wrinkled structures uniformly cover the surface of the composite coated lithium manganate powder to form a coating coupling structure. The advantages of this coupling structure are: (1) it can form a better interface contact between the composite coated lithium manganate powder and the oxidized Mxene nanosheets, so that the surface area of ​​the non-polar active material exposed to the electrolyte is significantly reduced. During the charge and discharge process of the non-polar active material, Li + It can diffuse along the wrinkled structure of the oxidized Mxene nanosheets and reach the surface of the composite coated lithium manganate powder, which can not only improve the conductivity of the non-polar active material, but also protect the composite coated lithium manganate powder from the attack of the electrolyte, reduce the dissolution of manganese ions, reduce the occurrence of harmful reactions between the composite coated lithium manganate powder and the electrolyte, enhance the stability of the non-polar active material, and delay the capacity decay of the secondary battery; (2) The oxidized Mxene nanosheet coating layer can also make the electrons and lithium ions on the entire surface of the composite coated lithium manganate powder uniformly distributed during the charge and discharge cycle, so that the electrochemical polarization effect caused by electron aggregation of the non-polar active material during the charge and discharge cycle is weakened, thereby improving the rate performance of the secondary battery; (3) Coating the oxidized Mxene nanosheets on the surface of the composite coated lithium manganate powder can significantly improve the reversibility of the secondary battery, which is mainly due to the excellent electronic conductivity and low Li + Diffusion barrier, Mxene has 10 -10 ~10 - 9 cm 2 / s Gao Li + Diffusion mobility and low Li ion density of 0.07 eV+ The diffusion barrier makes the inorganic active material have higher chemical reaction activity and charge transfer speed under high rate conditions; at the same time, the close coupling structure between the oxidized Mxene nanosheets and the composite coated lithium manganate powder has more electronic contact points, which can improve the electronic conductivity of the material, making the non-polar active material coated with the oxidized Mxene nanosheets show excellent Li + Transmission performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0106] Figure 1 This is a scanning electron microscope image of the titanium-doped lithium manganate powder prepared in Example 1 of the present invention;

[0107] Figure 2 This is a transmission electron micrograph of titanium-doped lithium manganate powder prepared in Example 1 of the present invention;

[0108] Figure 3 This is a scanning electron microscope image of the composite coated lithium manganate powder prepared in Example 1 of the present invention;

[0109] Figure 4 This is a transmission electron microscope image of the composite coated lithium manganate powder prepared in Example 1 of the present invention;

[0110] Figure 5 The first charge-discharge curve of a lithium-ion battery assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 in the charge-discharge voltage range of 3-4.9V;

[0111] Figure 6 The rate performance test curves of lithium-ion batteries assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 at different rates of 0.2-5C are shown;

[0112] Figure 7 The AC impedance spectrum of a lithium-ion battery assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 after 100 cycles at a current density of 1C. DETAILED DESCRIPTION

[0113] The technical solutions of the present invention are described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments described herein are specific embodiments of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be understood as limiting the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments described herein.

[0114] The chemical reagents used in the examples are all commercially available products, and their brands and manufacturer information are as follows:

[0115] Oxalic acid: B20132-100 mg, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0116] Manganese sulfate: industrial grade, purity ≥99%, purchased from Hubei Xinrunde Chemical Co., Ltd.

[0117] Manganese nitrate: industrial grade, purity ≥99%, purchased from Hubei Zhenbo Chemical Co., Ltd.

[0118] Manganese chloride: S24131-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0119] Manganese acetate: S49414-100 g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0120] Polyethylene glycol: S30184-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0121] Lithium carbonate: S30479-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0122] Lithium hydroxide: industrial grade, purity ≥99%, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0123] Lithium acetate: S48238-100g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0124] Lithium oxalate: S30485-100 g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0125] Lithium phosphate: industrial grade, purity ≥99%, purchased from Tianmen Hengchang Chemical Co., Ltd.

[0126] Metatitanic acid: industrial grade, purity ≥99%, purchased from Hubei Wonder Chemical Co., Ltd.

[0127] Titanium trichloride: industrial grade, purity ≥99%, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0128] Titanium tetrachloride: industrial grade, purity ≥99%, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0129] Titanium dioxide: S26013-100 g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0130] Glucose: S11022-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0131] Citric acid: B23391-20 mg, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0132] Starch: S11006-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0133] Sucrose: S11055-500 g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0134] Boric acid: industrial grade, purity ≥99%, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0135] Metaboric acid: industrial grade, purity ≥99%, purchased from Hubei Kewode Chemical Co., Ltd.

[0136] Boron oxide: industrial grade, purity ≥99%, purchased from Hubei Yongkuo Technology Co., Ltd.

[0137] N,N-dimethylpyrrolidone: Y34504-100 mg, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0138] Dimethyl sulfoxide: S24295-500ml, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0139] Ammonium chloride: industrial grade, purity ≥99%, purchased from Langfang Naco New Materials Technology Co., Ltd.

[0140] Calcium carbonate: S24297-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0141] Paraffin: T24461-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0142] Tetraethyl orthosilicate: industrial grade, purity ≥99%, purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0143] Ammonia: industrial grade, purchased from Shenyang Yilepux Chemical Co., Ltd.

[0144] Sodium fluoride: industrial grade, purity ≥99%, purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0145] Potassium fluoride: industrial grade, purity ≥99%, purchased from Wuhan Jiyesheng Chemical Co., Ltd.

[0146] Lithium fluoride: industrial grade, purity ≥99%, purchased from Wuhan Jixin Yibang Biotechnology Co., Ltd.

[0147] Calcium fluoride: S50691-500g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0148] Hydrochloric acid: industrial grade, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0149] Sulfuric acid: industrial grade, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0150] Hydrofluoric acid: industrial grade, purchased from Fuchen (Tianjin) Chemical Reagent Co., Ltd.

[0151] Titanium carbonized aluminum: T27062-2 g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.;

[0152] Hexadecyltrimethylammonium bromide: S15001-100 g, purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0153] Example 1

[0154] This embodiment provides a method for preparing a non-polar active material, which specifically includes the following steps:

[0155] (1) Oxalic acid and manganese sulfate were added to a mixed solvent at a molar ratio of 4:1, wherein the mixed solvent consisted of polyethylene glycol and deionized water at a volume ratio of 1:3, and the mixture was stirred for 1 hour until the oxalic acid and manganese sulfate were completely dissolved in the mixed solvent to obtain a precursor solution. The concentration of manganese sulfate in the precursor solution was 1 mol / L;

[0156] The precursor solution was transferred to a hydrothermal kettle for hydrothermal reaction at a temperature of 160°C and a time of 5 hours. After the reaction, the reaction product was filtered to obtain a filter cake, which was then dried, crushed and ground in sequence at a drying temperature of 80°C and a drying time of 15 hours to obtain a first precursor.

[0157] The first precursor, lithium carbonate and metatitanic acid were mixed evenly and placed in a tube furnace, wherein the molar ratio of manganese element in the first precursor, lithium element in the lithium carbonate and titanium element in the metatitanic acid was 1:1.9:0.1; the mixture was heated to 300°C at a heating rate of 1°C / min and kept at that temperature for 4 hours for a first calcination; the mixture was then heated to 700°C at a heating rate of 2°C / min and kept at that temperature for 10 hours for a second calcination; and after the second calcination, the mixture was cooled to room temperature in the furnace to obtain titanium-doped lithium manganate powder;

[0158] (2) Glucose, boric acid and deionized water are mixed uniformly to obtain a coating precursor solution, wherein the molar ratio of the carbon element in the glucose to the boron element in the boric acid is 1:0.02, and the concentration of glucose in the coating precursor solution is 5 g / L; the titanium-doped lithium manganate powder obtained in step (1), the coating precursor solution and ammonium chloride are mixed, and the mass ratio of the titanium-doped lithium manganate powder, the glucose in the coating precursor solution and the ammonium chloride is 1:18:10, and the mixture is spray-dried to obtain a second precursor, the spray-drying temperature is 180°C, and the feed rate is 10 kg / h; the second precursor is placed in an inert atmosphere, heated to 600°C at a heating rate of 8°C / min and kept warm for 5 hours to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder;

[0159] The ethyl orthosilicate and the ethanol aqueous solution are uniformly mixed in a volume ratio of 1:4 to obtain a mixed solution, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:3; the coated lithium manganate powder is dispersed in the mixed solution to obtain a reaction solution, wherein the mass ratio of the coated lithium manganate powder to the ethyl orthosilicate in the mixed solution is 0.2:1; the reaction solution is heated in a water bath at a temperature of 50° C. for 2 h; while heating in the water bath, 10 wt % ammonia water is added dropwise to the reaction solution at a rate of 5 mL / min, wherein the volume ratio of the ethyl orthosilicate to the ammonia water in the reaction solution is 1:0.2, so as to in situ grow nano-silica on the boron-doped porous carbon layer; and then filtered and dried to obtain a composite coated lithium manganate powder;

[0160] (3) Sodium fluoride was dissolved in 5 mol / L hydrochloric acid solution and stirred for 1 min to obtain an intercalation solution. The mixing ratio of sodium fluoride to hydrochloric acid solution was 0.05 g:1 mL. Titanium aluminum carbide was added to the intercalation solution. The mass ratio of sodium fluoride to titanium aluminum carbide was 1:1. The mixture was evenly mixed to obtain a precursor solution. The precursor solution was stirred and heated to obtain an Mxene suspension. The heating temperature was 30 ° C and the stirring time was 24 h. The Mxene suspension was subjected to ultrasonic stripping and high-speed centrifugation in sequence. The ultrasonic power of ultrasonic stripping was 500 W, the processing time of ultrasonic stripping was 60 min, the centrifugal speed was 3000 rpm, and the high-speed centrifugation time was 2 h. After centrifugation, the supernatant was placed at -40 ° C for freeze drying for 10 h to obtain Mxene nanosheets.

[0161] The MXene nanosheets were heat-treated in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere included argon and oxygen in a volume ratio of 10:1, the heat treatment temperature was 200° C., the heat treatment time was 15 h, and oxidized MXene nanosheets were obtained after the heat treatment;

[0162] The oxidized Mxene nanosheets and the composite coated lithium manganate powder obtained in step (2) are dispersed in a hexadecyltrimethylammonium bromide solution with a concentration of 1 g / mL and mixed and stirred for 30 minutes to form a dispersion. The mass ratio of the oxidized Mxene nanosheets, the composite coated lithium manganate powder and the hexadecyltrimethylammonium bromide is 1:15:8. The dispersion is filtered, washed and dried to obtain the non-polar active substance.

[0163] Figure 1 and Figure 2 The scanning electron microscope images and transmission electron microscope images of the titanium-doped lithium manganate powder prepared in this embodiment are shown in FIG. 3 , and it can be seen from the images that the spinel titanium-doped lithium manganate powder with a short rod-like structure was prepared in this embodiment. Figure 3 and Figure 4 The scanning electron microscope images and transmission electron microscope images of the composite coated lithium manganese oxide powder prepared in this embodiment are shown in FIG. 1 , and it can be seen from the images that a boron-doped porous carbon layer is formed on the surface of the titanium-doped lithium manganese oxide powder prepared in this embodiment.

[0164] Example 2

[0165] This embodiment provides a method for preparing a non-polar active material, which specifically includes the following steps:

[0166] (1) Oxalic acid and manganese nitrate were added to a mixed solvent at a molar ratio of 4.2:1, wherein the mixed solvent consisted of polyethylene glycol and deionized water at a volume ratio of 1:3.2, and the mixture was stirred for 1.5 h until the oxalic acid and manganese nitrate were completely dissolved in the mixed solvent to obtain a precursor solution. The concentration of manganese nitrate in the precursor solution was 1.2 mol / L;

[0167] The precursor solution was transferred to a hydrothermal kettle for hydrothermal reaction at a temperature of 165°C and a time of 4.5 hours. After the reaction, the reaction product was filtered to obtain a filter cake, which was then dried, crushed and ground in sequence at a drying temperature of 82°C and a drying time of 14 hours to obtain a first precursor.

[0168] The first precursor, lithium hydroxide and titanium trichloride are uniformly mixed and placed in a tube furnace, wherein the molar ratio of manganese element in the first precursor, lithium element in lithium hydroxide and titanium element in titanium trichloride is 1:1.92:0.08; the mixture is heated to 320°C at a heating rate of 1.5°C / min and kept at this temperature for 3.5 hours to perform a first calcination; the mixture is then heated to 720°C at a heating rate of 3°C / min and kept at this temperature for 9.5 hours to perform a second calcination; and after the second calcination, the mixture is cooled to room temperature in the furnace to obtain titanium-doped lithium manganate powder.

[0169] (2) citric acid, boric acid and N,N-dimethylpyrrolidone are mixed uniformly to obtain a coating precursor solution, wherein the molar ratio of carbon element in citric acid to boron element in boric acid is 1:0.022, and the concentration of citric acid in the coating precursor solution is 6 g / L; the titanium-doped lithium manganate powder obtained in step (1), the coating precursor solution and ammonium chloride are mixed, and the mass ratio of the titanium-doped lithium manganate powder, the citric acid in the coating precursor solution and the ammonium chloride is 1:18.5:10.5, and the mixture is spray-dried to obtain a second precursor, the spray-drying temperature is 185°C, and the feed rate is 12 kg / h; the second precursor is placed in an inert atmosphere, heated to 620°C at a heating rate of 8.5°C / min and kept warm for 4.5 hours to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder;

[0170] The tetraethyl orthosilicate and the ethanol aqueous solution are uniformly mixed in a volume ratio of 1:4.2 to obtain a mixed solution, the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:3.2, the coated lithium manganate powder is dispersed in the mixed solution to obtain a reaction solution, the mass ratio of the coated lithium manganate powder to the tetraethyl orthosilicate in the mixed solution is 0.22:1, the reaction solution is heated in a water bath, the water bath heating temperature is 52° C., the water bath heating time is 1.8 h, and 12 wt % ammonia water is added dropwise to the reaction solution at a dripping rate of 6 mL / min while heating in the water bath, the volume ratio of tetraethyl orthosilicate to ammonia water in the reaction solution is 1:0.25, so as to in situ grow nano-silica on the boron-doped porous carbon layer, and then filtered and dried to obtain a composite coated lithium manganate powder;

[0171] (3) Potassium fluoride was dissolved in 6 mol / L hydrochloric acid solution and stirred for 3 minutes to obtain an intercalation solution. The mixing ratio of potassium fluoride to hydrochloric acid solution was 0.06 g:1 mL. Titanium aluminum carbide was added to the intercalation solution. The mass ratio of potassium fluoride to titanium aluminum carbide was 1.2:1. After uniform mixing, a precursor solution was obtained. The precursor solution was stirred and heated to obtain an Mxene suspension. The heating temperature was 32 ° C and the stirring time was 22 h. The Mxene suspension was subjected to ultrasonic stripping and high-speed centrifugation in sequence. The ultrasonic power of ultrasonic stripping was 520 W, the processing time of ultrasonic stripping was 50 min, the centrifugal speed was 3200 rpm, and the high-speed centrifugation time was 1.8 h. After centrifugation, the supernatant was placed at -38 ° C and freeze-dried for 10.5 h to obtain Mxene nanosheets.

[0172] The MXene nanosheets were heat-treated in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere included argon and oxygen in a volume ratio of 12:1, the heat treatment temperature was 220° C., the heat treatment time was 14 h, and oxidized MXene nanosheets were obtained after the heat treatment;

[0173] The oxidized Mxene nanosheets and the composite coated lithium manganate powder obtained in step (2) are dispersed in a hexadecyltrimethylammonium bromide solution with a concentration of 1.2 g / mL and mixed and stirred for 32 minutes to form a dispersion. The mass ratio of the oxidized Mxene nanosheets, the composite coated lithium manganate powder and the hexadecyltrimethylammonium bromide is 1:18:8.5. The dispersion is filtered, washed and dried to obtain the non-polar active substance.

[0174] Example 3

[0175] This embodiment provides a method for preparing a non-polar active material, which specifically includes the following steps:

[0176] (1) Oxalic acid and manganese chloride were added to a mixed solvent at a molar ratio of 4.5:1, wherein the mixed solvent consisted of polyethylene glycol and deionized water at a volume ratio of 1:3.5, and the mixture was stirred for 2 h until the oxalic acid and manganese chloride were completely dissolved in the mixed solvent to obtain a precursor solution. The concentration of manganese chloride in the precursor solution was 1.5 mol / L;

[0177] The precursor solution was transferred to a hydrothermal kettle for hydrothermal reaction at a temperature of 170°C for 4 hours. After the reaction, the reaction product was filtered to obtain a filter cake, which was then dried, crushed and ground in sequence at a drying temperature of 85°C for 12 hours to obtain a first precursor.

[0178] The first precursor, lithium acetate and titanium tetrachloride were uniformly mixed and placed in a tube furnace, wherein the molar ratio of manganese element in the first precursor, lithium element in lithium acetate and titanium element in titanium tetrachloride was 1:1.95:0.05; the mixture was heated to 350°C at a heating rate of 2°C / min and kept at this temperature for 3 hours for a first calcination; the mixture was then heated to 750°C at a heating rate of 3°C / min and kept at this temperature for 9 hours for a second calcination; after the second calcination, the mixture was cooled to room temperature in the furnace to obtain titanium-doped lithium manganate powder;

[0179] (2) starch, metaboric acid and N, N-dimethylpyrrolidone are mixed uniformly to obtain a coating precursor solution, wherein the molar ratio of the carbon element in the starch to the boron element in the metaboric acid is 1:0.025, and the concentration of the starch in the coating precursor solution is 7 g / L; the titanium-doped lithium manganate powder obtained in step (1), the coating precursor solution and calcium carbonate are mixed, and the mass ratio of the titanium-doped lithium manganate powder, the starch in the coating precursor solution and the calcium carbonate is 1:19:11, and the mixture is spray-dried to obtain a second precursor, the spray drying temperature is 190°C, and the feed rate is 15 kg / h; the second precursor is placed in an inert atmosphere, heated to 650°C at a heating rate of 9°C / min and kept warm for 4 hours to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder;

[0180] The tetraethyl orthosilicate and the ethanol aqueous solution are uniformly mixed in a volume ratio of 1:4.5 to obtain a mixed solution, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:3.5; the coated lithium manganate powder is dispersed in the mixed solution to obtain a reaction solution, wherein the mass ratio of the coated lithium manganate powder to the tetraethyl orthosilicate in the mixed solution is 0.25:1, the reaction solution is heated in a water bath at a temperature of 55° C. for 1.5 h, and while heating in the water bath, 15 wt % ammonia water is added dropwise to the reaction solution at a dripping rate of 6 mL / min, wherein the volume ratio of tetraethyl orthosilicate to ammonia water in the reaction solution is 1:0.3, so as to in situ grow nano-silica on the boron-doped porous carbon layer, and then filtered and dried to obtain a composite coated lithium manganate powder;

[0181] (3) Lithium fluoride was dissolved in 7 mol / L sulfuric acid solution and stirred for 5 minutes to obtain an intercalation solution, and the mixing ratio of lithium fluoride to sulfuric acid solution was 0.07 g:1 mL; titanium aluminum carbide was added to the intercalation solution, and the mass ratio of lithium fluoride to titanium aluminum carbide was 1.5:1. After uniform mixing, a precursor solution was obtained, and the precursor solution was stirred and heated to obtain an Mxene suspension. The heating temperature was 35 ° C and the stirring time was 20 hours. The Mxene suspension was subjected to ultrasonic stripping and high-speed centrifugation in sequence. The ultrasonic power of ultrasonic stripping was 550 W, the processing time of ultrasonic stripping was 45 minutes, the centrifugal speed was 3500 rpm, and the high-speed centrifugation time was 1.5 hours. After centrifugation, the supernatant was placed at -35 ° C and freeze-dried for 11 hours to obtain Mxene nanosheets.

[0182] The MXene nanosheets were heat-treated in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere included argon and oxygen in a volume ratio of 15:1, the heat treatment temperature was 250° C., the heat treatment time was 12 h, and oxidized MXene nanosheets were obtained after the heat treatment;

[0183] The oxidized Mxene nanosheets and the composite coated lithium manganate powder obtained in step (2) are dispersed in a hexadecyltrimethylammonium bromide solution with a concentration of 1.5 g / mL and mixed and stirred for 35 minutes to form a dispersion. The mass ratio of the oxidized Mxene nanosheets, the composite coated lithium manganate powder and the hexadecyltrimethylammonium bromide is 1:20:9. The dispersion is filtered, washed and dried to obtain the non-polar active substance.

[0184] Example 4

[0185] This embodiment provides a method for preparing a non-polar active material, which specifically includes the following steps:

[0186] (1) Oxalic acid and manganese acetate were added to a mixed solvent at a molar ratio of 4.8:1, wherein the mixed solvent consisted of polyethylene glycol and deionized water at a volume ratio of 1:3.8, and the mixture was stirred for 2.5 hours until the oxalic acid and manganese acetate were completely dissolved in the mixed solvent to obtain a precursor solution. The concentration of manganese acetate in the precursor solution was 1.8 mol / L;

[0187] The precursor solution was transferred to a hydrothermal kettle for hydrothermal reaction at a temperature of 175°C and a time of 3.5 hours. After the reaction, the reaction product was filtered to obtain a filter cake, which was then dried, crushed and ground in sequence at a drying temperature of 88°C and a drying time of 11 hours to obtain a first precursor.

[0188] The first precursor, lithium oxalate and metatitanic acid were uniformly mixed and placed in a tube furnace, wherein the molar ratio of manganese element in the first precursor, lithium element in lithium oxalate and titanium element in metatitanic acid was 1:1.97:0.03; the mixture was heated to 380°C at a heating rate of 2.5°C / min and kept at this temperature for 2.5 hours to perform a first calcination; the mixture was then heated to 780°C at a heating rate of 4°C / min and kept at this temperature for 8.5 hours to perform a second calcination; after the second calcination, the mixture was cooled to room temperature in the furnace to obtain titanium-doped lithium manganate powder;

[0189] (2) sucrose, boron oxide and dimethyl sulfoxide are mixed uniformly to obtain a coating precursor solution, wherein the molar ratio of carbon element in sucrose to boron element in boron oxide is 1:0.028, and the sucrose concentration in the coating precursor solution is 8 g / L; the titanium-doped lithium manganate powder obtained in step (1), the coating precursor solution and paraffin are mixed, and the mass ratio of the titanium-doped lithium manganate powder, the sucrose in the coating precursor solution and the paraffin is 1:19.5:11.5, and the mixture is spray-dried to obtain a second precursor, the spray-drying temperature is 195°C, and the feed rate is 18 kg / h; the second precursor is placed in an inert atmosphere, heated to 680°C at a heating rate of 9.5°C / min and kept warm for 3.5 hours to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder;

[0190] The tetraethyl orthosilicate and the ethanol aqueous solution are uniformly mixed in a volume ratio of 1:4.8 to obtain a mixed solution, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:3.8; the coated lithium manganate powder is dispersed in the mixed solution to obtain a reaction solution, wherein the mass ratio of the coated lithium manganate powder to the tetraethyl orthosilicate in the mixed solution is 0.28:1, the reaction solution is heated in a water bath at a temperature of 58° C. for 1.2 h, and while heating in the water bath, 18 wt % ammonia water is added dropwise to the reaction solution at a dripping rate of 7 mL / min, wherein the volume ratio of tetraethyl orthosilicate to ammonia water in the reaction solution is 1:0.35, so as to in situ grow nano-silica on the boron-doped porous carbon layer, and then filtered and dried to obtain a composite coated lithium manganate powder;

[0191] (3) Calcium fluoride was dissolved in 8 mol / L sulfuric acid solution and stirred for 7 minutes to obtain an intercalation solution. The mixing ratio of calcium fluoride to sulfuric acid solution was 0.08 g:1 mL. Titanium aluminum carbide was added to the intercalation solution. The mass ratio of calcium fluoride to titanium aluminum carbide was 1.8:1. After uniform mixing, a precursor solution was obtained. The precursor solution was stirred and heated to obtain an Mxene suspension. The heating temperature was 38 ° C and the stirring time was 15 hours. The Mxene suspension was subjected to ultrasonic stripping and high-speed centrifugation in sequence. The ultrasonic power of ultrasonic stripping was 580 W, the processing time of ultrasonic stripping was 40 minutes, the centrifugal speed was 3800 rpm, and the high-speed centrifugation time was 1.2 hours. After centrifugation, the supernatant was placed at -32 ° C for freeze drying for 11.5 hours to obtain Mxene nanosheets.

[0192] The MXene nanosheets were heat-treated in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere included argon and oxygen in a volume ratio of 18:1, the heat treatment temperature was 280° C., the heat treatment time was 11 h, and oxidized MXene nanosheets were obtained after the heat treatment;

[0193] The oxidized Mxene nanosheets and the composite coated lithium manganate powder obtained in step (2) are dispersed in a hexadecyltrimethylammonium bromide solution with a concentration of 1.8 g / mL and mixed and stirred for 38 minutes to form a dispersion. The mass ratio of the oxidized Mxene nanosheets, the composite coated lithium manganate powder and the hexadecyltrimethylammonium bromide is 1:22:9.5. The dispersion is filtered, washed and dried to obtain the non-polar active substance.

[0194] Example 5

[0195] This embodiment provides a method for preparing a non-polar active material, which specifically includes the following steps:

[0196] (1) Oxalic acid and manganese acetate were added to a mixed solvent at a molar ratio of 5:1, wherein the mixed solvent consisted of polyethylene glycol and deionized water at a volume ratio of 1:4, and the mixture was stirred for 3 h until the oxalic acid and manganese acetate were completely dissolved in the mixed solvent to obtain a precursor solution. The concentration of manganese acetate in the precursor solution was 2 mol / L;

[0197] The precursor solution was transferred to a hydrothermal kettle for hydrothermal reaction at a temperature of 180°C for 3 hours. After the reaction, the reaction product was filtered to obtain a filter cake, which was then dried, crushed and ground in sequence at a drying temperature of 90°C for 10 hours to obtain a first precursor.

[0198] The first precursor, lithium phosphate and titanium dioxide were uniformly mixed and placed in a tube furnace, wherein the molar ratio of manganese element in the first precursor, lithium element in the lithium phosphate and titanium element in the titanium dioxide was 1:1.99:0.01; the mixture was heated to 400°C at a heating rate of 3°C / min and kept at this temperature for 2 hours to perform a first calcination; the mixture was then heated to 800°C at a heating rate of 5°C / min and kept at this temperature for 8 hours to perform a second calcination; after the second calcination, the mixture was cooled to room temperature in the furnace to obtain titanium-doped lithium manganate powder;

[0199] (2) sucrose, boron oxide and deionized water are mixed uniformly to obtain a coating precursor solution, wherein the molar ratio of carbon element in sucrose to boron element in boron oxide is 1:0.03, and the sucrose concentration in the coating precursor solution is 10 g / L; the titanium-doped lithium manganate powder obtained in step (1), the coating precursor solution and paraffin are mixed, and the mass ratio of the titanium-doped lithium manganate powder, the sucrose in the coating precursor solution and the paraffin is 1:20:12, and the mixture is spray-dried to obtain a second precursor, the spray drying temperature is 200°C, and the feed rate is 20 kg / h; the second precursor is placed in an inert atmosphere, heated to 700°C at a heating rate of 10°C / min and kept warm for 3 hours to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder;

[0200] The method comprises the following steps: uniformly mixing tetraethyl orthosilicate and an ethanol aqueous solution in a volume ratio of 1:5 to obtain a mixed solution, wherein the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:4; dispersing the coated lithium manganate powder in the mixed solution to obtain a reaction solution, wherein the mass ratio of the coated lithium manganate powder to the tetraethyl orthosilicate in the mixed solution is 0.3:1; heating the reaction solution in a water bath at a temperature of 60° C. for 1 h; and adding 20 wt % ammonia water dropwise to the reaction solution at a dripping rate of 8 mL / min while heating in the water bath, wherein the volume ratio of tetraethyl orthosilicate to ammonia water in the reaction solution is 1:0.4, to in situ grow nano-silica on the boron-doped porous carbon layer, and then filtering and drying to obtain a composite coated lithium manganate powder;

[0201] (3) Calcium fluoride was dissolved in 10 mol / L hydrofluoric acid solution and stirred for 10 min to obtain an intercalation solution, and the mixing ratio of calcium fluoride to hydrofluoric acid solution was 0.1 g:1 mL; titanium aluminum carbide was added to the intercalation solution, and the mass ratio of calcium fluoride to titanium aluminum carbide was 2:1. After uniform mixing, a precursor solution was obtained, and the precursor solution was stirred and heated to obtain an Mxene suspension. The heating temperature was 40 ° C and the stirring time was 12 h. The Mxene suspension was subjected to ultrasonic stripping and high-speed centrifugation in sequence. The ultrasonic power of ultrasonic stripping was 600 W, the processing time of ultrasonic stripping was 30 min, the centrifugal speed was 4000 rpm, and the high-speed centrifugation time was 1 h. After centrifugation, the supernatant was placed at -30 ° C and freeze-dried for 12 h to obtain Mxene nanosheets.

[0202] The MXene nanosheets were heat-treated in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere included argon and oxygen in a volume ratio of 20:1, the heat treatment temperature was 300° C., the heat treatment time was 10 h, and the oxidized MXene nanosheets were obtained after the heat treatment;

[0203] The oxidized Mxene nanosheets and the composite coated lithium manganate powder obtained in step (2) are dispersed in a 2 g / mL cetyltrimethylammonium bromide solution and mixed and stirred for 40 minutes to form a dispersion. The mass ratio of the oxidized Mxene nanosheets, the composite coated lithium manganate powder and the cetyltrimethylammonium bromide is 1:25:10. The dispersion is filtered, washed and dried to obtain the non-polar active substance.

[0204] Comparative Example 1

[0205] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that in step (2), the mass ratio of titanium-doped lithium manganate powder, glucose, and ammonium chloride is adjusted to 1:15:10, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0206] Comparative Example 2

[0207] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that in step (2), the mass ratio of titanium-doped lithium manganate powder, glucose, and ammonium chloride is adjusted to 1:23:10, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0208] Comparative Example 3

[0209] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that in step (2), the mass ratio of titanium-doped lithium manganate powder, glucose, and ammonium chloride is adjusted to 1:18:8, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0210] Comparative Example 4

[0211] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that in step (2), the mass ratio of titanium-doped lithium manganate powder, glucose, and ammonium chloride is adjusted to 1:18:15, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0212] Comparative Example 5

[0213] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that in step (2), the mass ratio of the coated lithium manganate powder to ethyl orthosilicate is adjusted to 0.15:1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0214] Comparative Example 6

[0215] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that the mass ratio of coated lithium manganate powder to ethyl orthosilicate is adjusted to 0.35:1, and the other process parameters and operating conditions are exactly the same as those in Example 1.

[0216] Comparative Example 7

[0217] This comparative example provides a method for preparing a non-polar active material. The difference from Example 1 is that step (2) is omitted, the surface of the titanium-doped lithium manganate powder is not coated with a boron-doped porous carbon layer, and the boron-doped porous carbon layer is not loaded with nano-silicon dioxide. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0218] The non-polar active materials provided in Examples 1-5 and Comparative Examples 1-7 were assembled into lithium-ion batteries, and the electrochemical properties of the lithium-ion batteries were tested.

[0219] The assembly process of lithium-ion batteries is as follows:

[0220] (1) The non-polar active material, polyvinylidene fluoride, and acetylene black provided in Examples 1-5 and Comparative Examples 1-7 were mixed and dissolved in N-methylpyrrolidone to obtain a first active slurry; based on the total mass fraction of the first active slurry being 100 wt%, the mass fraction of the non-polar active material was 94 wt%, the mass fraction of polyvinylidene fluoride was 3 wt%, and the mass fraction of acetylene black was 3 wt%;

[0221] (2) coating the first active slurry obtained in step (1) on the surface of an aluminum foil with a coating thickness of 0.15 mm, and then drying the aluminum foil coated with the first active slurry in a vacuum oven at 120° C. to obtain a first non-polar electrode;

[0222] (3) The non-polar active material, polyvinylidene fluoride, and acetylene black provided in Examples 1-5 and Comparative Examples 1-7 were mixed and dissolved in N-methylpyrrolidone to obtain a second active slurry; based on the total mass fraction of the second active slurry being 100 wt%, the mass fraction of the non-polar active material was 94 wt%, the mass fraction of polyvinylidene fluoride was 3 wt%, and the mass fraction of acetylene black was 3 wt%;

[0223] (4) coating the second active slurry obtained in step (3) on the surface of the copper foil to a coating thickness of 0.08 mm, and then drying the copper foil coated with the second active slurry in a vacuum oven at 120° C. to obtain a second non-polar electrode;

[0224] (5) The first non-polar electrode obtained in step (2), the polypropylene porous diaphragm, and the second non-polar electrode obtained in step (4) are stacked in sequence and then wound to form a battery cell, the battery cell is placed in a shell and encapsulated through a top cover, and an electrolyte is injected into the shell through the injection port on the top cover in a glove box, wherein the electrolyte is 1 mol / L LiPF6 / EC+DEC (wherein the volume ratio of EC and DEC is 1:1:1), to obtain a lithium-ion battery.

[0225] The electrochemical performance of the assembled lithium-ion battery is tested. The specific process is as follows:

[0226] (1) Constant current charge / discharge test analysis

[0227] The assembled lithium-ion battery was tested using a charge and discharge tester (Neware), and the charge and discharge range was selected as 3.0-4.9V.

[0228] First charge and discharge test: For the lithium ion battery assembled with the non-polar active material prepared in Example 1 and Comparative Example 7, the constant current charge and discharge performance test of the assembled lithium ion battery was carried out at a current density of 0.25C, and the results were as follows: Figure 5 The first charge and discharge curve is shown.

[0229] Rate performance test: For the lithium ion batteries assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7, constant current charge and discharge performance tests were performed on the assembled lithium ion batteries at current densities of 0.2C, 0.5C, 1C, 2C, 5C and 0.2C. Each current density was cycled 5 times, and the results were as follows: Figure 6 The rate performance test curve is shown.

[0230] Cycling performance test: For the lithium-ion batteries assembled with the non-polar active materials prepared in Examples 1-5 and Comparative Examples 1-7, the current density of constant current charge and discharge was selected to be 1.0C. The discharge specific capacity of the lithium-ion battery was tested after 100 cycles. The cycle capacity retention rate of the lithium-ion battery was calculated based on the initial discharge specific capacity and the discharge specific capacity after 100 cycles. The test results are shown in Table 1.

[0231] (2) Electrochemical impedance spectroscopy analysis

[0232] The lithium ion batteries assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 were tested using an electrochemical workstation, and the results were as follows: Figure 7 The AC impedance spectrum is shown.

[0233] Figure 5 The first charge-discharge curve of the lithium-ion battery assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 at 0.2C in the charge-discharge voltage range of 3-4.9V, wherein the surface of the titanium-doped lithium manganate powder in the non-polar active material in Comparative Example 7 is not coated with a boron-doped porous carbon layer, and the boron-doped porous carbon layer is not loaded with nano-silicon dioxide; while the surface of the titanium-doped lithium manganate powder in the non-polar active material in Example 1 is coated with a boron-doped porous carbon layer, and the boron-doped porous carbon layer is loaded with nano-silicon dioxide. Figure 5 It can be seen that the first discharge specific capacities of Comparative Example 7 and Example 1 are 106.1 mAh / g and 117.2 mAh / g, respectively, and that of Example 1 is significantly higher than that of Comparative Example 7.

[0234] Figure 6 The rate performance test curves of lithium-ion batteries assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 at different rates of 0.2-5C are shown. As the current density increases (0.2~5C), the discharge specific capacity of the non-polar active material prepared in Example 1 is higher than that of Comparative Example 7 when the current density is 0.2C, 0.5C, 1C, 2C and 5C, respectively. This shows that the rate performance of the non-polar active material prepared in Example 1 is improved. This is because after the boron-doped porous carbon layer is coated on the surface of the titanium-doped lithium manganese oxide powder, a good conductive path is formed during the charge and discharge process, thereby improving the charge transfer ability of the non-polar active material. In addition, when the current density returns from 5C to 0.2C, the discharge specific capacity of the lithium-ion battery prepared in Example 1 almost returns to the initial value, indicating that the boron-doped porous carbon layer coating can improve the cycle stability of the non-polar active material structure.

[0235] Figure 7This is the AC impedance spectrum of a lithium-ion battery assembled with the non-polar active materials prepared in Example 1 and Comparative Example 7 after 100 cycles at a current density of 1C. The AC impedance curve consists of a high-frequency semicircle, a medium-frequency semicircle, and a low-frequency oblique line. The high-frequency semicircle represents the impedance of lithium ions passing through the SEI film between the electrolyte and the electrode surface, the medium-frequency semicircle represents the diffusion impedance of lithium ions and electrons when they are transferred in the electrolyte, and the low-frequency oblique line represents the diffusion impedance of lithium ions in the non-polar active material. Figure 7 It can be seen that the semicircular diameter of the impedance curve of the non-polar active material prepared in Example 1 is smaller, which indicates that the non-polar active material prepared in Example 1 has better charge transfer ability; at the same time, compared with Comparative Example 7, the slope of the low-frequency oblique line of the impedance curve of Example 1 is closer to 1, which indicates that the non-polar active material prepared in Example 1 has better cycle performance and rate performance. This is because Example 1 uses a boron-doped porous carbon layer to surface-coat the titanium-doped lithium manganese oxide powder, which can not only effectively inhibit the side reactions between the titanium-doped lithium manganese oxide powder and the electrolyte, but also effectively inhibit the decomposition of the electrolyte and the occurrence of other side reactions, thereby improving the cycle performance and rate performance of the lithium-ion battery.

[0236]

[0237] It can be seen from the test data provided in Table 1 that the initial discharge specific capacity, the discharge specific capacity after 100 cycles, and the cycle capacity retention rate of the lithium ion batteries prepared in Examples 1-5 are all higher than those in Comparative Examples 1-7, indicating that the lithium ion batteries prepared by the preparation method provided by the present invention have excellent cycle performance.

[0238] From the test data provided by Example 1, Comparative Example 1 and Comparative Example 2, it can be seen that the initial discharge specific capacity, discharge specific capacity after 100 cycles and cycle capacity retention rate of the lithium ion batteries prepared in Comparative Example 1 and Comparative Example 2 are all lower than those in Example 1. This is because the amount of glucose added in Comparative Example 1 is too low, which affects the formation of the pore structure in the boron-doped porous carbon layer, resulting in the Li + The diffusion rate of the boron-doped porous carbon layer is reduced, which ultimately affects the electrochemical performance of the lithium-ion battery. In Comparative Example 2, the amount of glucose added is too high, and the number of pores in the generated boron-doped porous carbon layer is reduced, which will block the Li + The diffusion channels of lithium ion batteries are greatly affected.

[0239] From the test data provided by Example 1, Comparative Example 3 and Comparative Example 4, it can be seen that the initial discharge specific capacity, the discharge specific capacity after 100 cycles, and the cycle capacity retention rate of the lithium ion batteries prepared in Comparative Example 3 and Comparative Example 4 are all lower than those in Example 1. This is because the amount of ammonium chloride added in Comparative Example 3 is too low, resulting in a smaller pore size of the pore structure formed after carbonization, and the embedded lithium ions cannot smoothly escape from the pore structure with small pore size, which ultimately affects the electrochemical performance of the lithium ion battery; the amount of ammonium chloride added in Comparative Example 4 is too high, the number of pore structures formed by carbonization is too large, the pore size is too large, and the boron-doped porous carbon layer coated on the surface of the titanium-doped lithium manganate powder cannot play a good supporting role, causing the pore structure of the boron-doped porous carbon layer to collapse and cause pore blockage, which ultimately affects the electrochemical performance of the lithium ion battery.

[0240] It can be seen from the test data provided by Example 1, Comparative Example 5 and Comparative Example 6 that the initial discharge specific capacity, the discharge specific capacity after 100 cycles and the cycle capacity retention rate of the lithium ion batteries prepared in Comparative Example 5 and Comparative Example 6 are all lower than those in Example 1. This is because the addition amount of the coated lithium manganate powder in Comparative Example 5 is too low, and accordingly, the addition amount of ethyl orthosilicate is too high, resulting in an excessive amount of nano-silicon dioxide generated, which will block the pores of the boron-doped porous carbon layer, hinder the migration tunnel of the ions, and cause the migration speed of the lithium ions to decrease, ultimately affecting the electrochemical performance of the lithium ion battery; the addition amount of the coated lithium manganate powder in Comparative Example 6 is too high, and accordingly, the addition amount of ethyl orthosilicate is too low, and a sufficient amount of nano-silicon dioxide cannot be generated, which ultimately affects the electrochemical performance of the lithium ion battery.

[0241] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for preparing a non-polar active material that can be charged and discharged and recycled, characterized in that: The preparation method comprises: (I) adding oxalic acid and a manganese source to a mixed solvent, mixing and stirring until the oxalic acid and the manganese source are completely dissolved in the mixed solvent to obtain a precursor solution, transferring the precursor solution to a hydrothermal kettle for a hydrothermal reaction, filtering the reaction product after the reaction to obtain a filter cake, and drying, crushing and grinding the filter cake in sequence to obtain a first precursor; mixing the first precursor, a lithium source and a titanium source uniformly, placing the mixture in a tube furnace, heating to a first temperature and maintaining the temperature, performing a first calcination, and then continuing to heat the mixture to a second temperature and maintaining the temperature, performing a second calcination, wherein the second temperature is 700-800° C., and cooling the mixture to room temperature after the second calcination to obtain titanium-doped lithium manganate powder; (II) uniformly mixing a carbon source, a boron source and a solvent to obtain a coating precursor solution, spray-drying the titanium-doped lithium manganate powder, the coating precursor solution and a pore-forming agent, and obtaining a second precursor, wherein the mass ratio of the titanium-doped lithium manganate powder, the carbon source in the coating precursor solution and the pore-forming agent is 1:(18-20):(10-12); placing the second precursor under an inert atmosphere for high-temperature carbonization treatment to form a boron-doped porous carbon layer on the surface of the titanium-doped lithium manganate powder to obtain a coated lithium manganate powder, wherein the high-temperature carbonization treatment The heating temperature of the treatment is 600-700° C., and the holding time of the high-temperature carbonization treatment is 3-5 hours; ethyl orthosilicate is uniformly mixed with an ethanol aqueous solution to obtain a mixed solution, the coated lithium manganate powder is dispersed in the mixed solution to obtain a reaction solution, the mass ratio of the coated lithium manganate powder to the ethyl orthosilicate in the mixed solution is (0.2-0.3):1, the reaction solution is heated in a water bath while dripping ammonia water to in-situ grow nano-silica on the boron-doped porous carbon layer, and then filtered and dried to obtain a composite coated lithium manganate powder; (III) dissolving a fluoride salt in an acid solution to obtain an intercalation solution, adding titanium aluminum carbide to the intercalation solution, and mixing uniformly to obtain a precursor solution. The precursor solution is stirred and heated to obtain a MXene suspension. The MXene suspension is subjected to ultrasonic exfoliation and high-speed centrifugation in sequence. The supernatant after centrifugation is freeze-dried to obtain MXene nanosheets. The MXene nanosheets are heat-treated in an oxygen-containing atmosphere to obtain oxidized MXene nanosheets. The oxidized MXene nanosheets and the composite-coated lithium manganate powder are dispersed in a cetyltrimethylammonium bromide solution to form a dispersion, wherein the mass ratio of the oxidized MXene nanosheets, the composite-coated lithium manganate powder, and the cetyltrimethylammonium bromide in the cetyltrimethylammonium bromide solution is 1:(15-25):(8-10). The dispersion is filtered, washed, and dried to obtain the non-polar active material.

2. The preparation method according to claim 1, characterized in that In step (I), the manganese source is any one of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate, or a combination of at least two thereof; The molar ratio of the oxalic acid to the manganese source is (4-5):1; The mixed solvent consists of polyethylene glycol and deionized water in a volume ratio of 1:(3-4); The mixing time of the oxalic acid, manganese source and mixed solvent is 1 to 3 hours; The concentration of the manganese source in the precursor solution is 1-2 mol / L; The temperature of the hydrothermal reaction of the precursor solution is 160-180°C; The hydrothermal reaction time of the precursor solution is 3 to 5 hours; The drying temperature of the filter cake is 80-90°C; The drying time of the filter cake is 10 to 15 hours.

3. The preparation method according to claim 1, characterized in that In step (I), the lithium source is any one of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate, lithium phosphate, lithium dihydrogen phosphate, and dilithium hydrogen phosphate, or a combination of at least two thereof; The titanium source is any one of metatitanic acid, titanium trichloride, titanium tetrachloride, and titanium dioxide, or a combination of at least two thereof; The molar ratio of the manganese element in the first precursor, the lithium element in the lithium source, and the titanium element in the titanium source is 1:x:(2-x), wherein 1.9≤x<2; The heating rate of the first calcination process is 1-3°C / min; The first temperature is 300-400° C.; The holding time at the first temperature is 2 to 4 hours; The heating rate of the second calcination process is 2-5°C / min; The holding time at the second temperature is 8 to 10 hours.

4. The preparation method according to claim 1, characterized in that In step (II), the carbon source is any one of glucose, citric acid, starch, and sucrose, or a combination of at least two thereof; The boron source is any one of boric acid, metaboric acid, and boron oxide, or a combination of at least two thereof; The solvent is any one of deionized water, N,N-dimethylpyrrolidone, and dimethyl sulfoxide, or a combination of at least two thereof; The concentration of the carbon source in the coating precursor solution is 5-10 g / L; The molar ratio of the carbon element in the carbon source to the boron element in the boron source is 1:(0.02-0.03); The pore-forming agent is any one of ammonium chloride, calcium carbonate, and paraffin, or a combination of at least two thereof; The spray drying temperature is 180-200°C; The feed rate of the spray drying is 10-20 kg / h; The heating rate of the high-temperature carbonization treatment is 8-10°C / min.

5. The preparation method according to claim 1, characterized in that In step (II), the volume ratio of ethanol to deionized water in the ethanol aqueous solution is 1:(3-4); The volume ratio of the ethyl orthosilicate to the ethanol aqueous solution is 1:(4-5); The mass fraction of the ammonia water is 10-20wt%; The volume ratio of ethyl orthosilicate to ammonia water in the reaction solution is 1:(0.2-0.4); The ammonia solution is added at a rate of 5 to 8 mL / min. The water bath heating temperature is 50-60°C; The water bath heating time is 1 to 2 hours.

6. The preparation method according to claim 1, characterized in that In step (III), the fluoride salt is any one of sodium fluoride, potassium fluoride, lithium fluoride, and calcium fluoride, or a combination of at least two thereof; The acid solution is any one of hydrochloric acid solution, sulfuric acid solution or hydrofluoric acid solution, or a combination of at least two thereof; The concentration of the acid solution is 5-10 mol / L; The mixing ratio of the fluoride salt and the acid solution is (0.05-0.1) g:1 mL; The mixing time of the fluoride salt and the acid solution is 1 to 10 minutes; The mass ratio of the fluoride salt to the titanium aluminum carbide in the intercalation solution is (1-2):1; The heating temperature of the precursor solution is 30-40°C; The stirring time of the precursor solution is 12 to 24 hours; The ultrasonic power of the ultrasonic peeling is 500~600W; The ultrasonic peeling treatment time is 30 to 60 minutes; The high-speed centrifugation speed is 3000-4000 rpm; The high-speed centrifugation time is 1 to 2 hours; The freeze-drying temperature is -40 to -30°C; The freeze drying time is 10 to 12 hours; The oxygen-containing atmosphere is a mixed atmosphere of argon and oxygen; The volume ratio of argon to oxygen in the oxygen-containing atmosphere is (10-20):1; The heat treatment temperature is 200-300°C; The heat treatment time is 10 to 15 hours.

7. The preparation method according to claim 1, characterized in that In step (III), the concentration of the hexadecyltrimethylammonium bromide solution is 1-2 g / mL; The mixing and stirring time of the oxidized Mxene nanosheets, the composite-coated lithium manganate powder and the cetyltrimethylammonium bromide solution is 30 to 40 minutes.

8. A non-polar active material prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The non-polar active material includes oxidized Mxene nanosheets and composite-coated lithium manganate powder; wherein the composite-coated lithium manganate powder is composed of titanium-doped lithium manganate powder and a boron-doped porous carbon layer coated on the surface thereof, and the boron-doped porous carbon layer is loaded with nano-silicon dioxide.

9. A non-polar pole piece, characterized in that: The non-polar electrode includes a current collector and an active material layer located on the surface of the current collector. The active material layer is formed by drying an active slurry coated on the surface of the current collector. The active slurry includes the non-polar active material described in claim 8, a conductive agent, a binder and a solvent.

10. A secondary battery comprising the non-polar electrode according to claim 9, characterized in that: The secondary battery comprises a battery core and a shell. The battery core comprises a first non-polar pole piece, a separator and a second non-polar pole piece stacked in sequence. The battery core is encapsulated in the shell, and an electrolyte is injected into the shell.

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