Layered rock salt symbiotic positive electrode material, preparation method thereof, positive electrode and battery

Abstract

The invention relates to the field of lithium ion batteries, and discloses a layered rock salt symbiotic positive electrode material and a preparation method thereof, a positive electrode and a battery, and the preparation method of the positive electrode material comprises the following steps: (1) preparing a lithium-rich manganese-based precursor which comprises a nickel element, a manganese element and a cobalt element, the molar ratio of the nickel element to the manganese element to the cobalt element is a: b: c, a is more than or equal to 0.1 and less than or equal to 0.2, b is more than or equal to 0.6 and less than or equal to 0.8, and c is more than or equal to 0.1 and less than or equal to 0.2; (2) the lithium-rich manganese-based precursor, a lithium source and a dopant are sequentially subjected to dry mixing, pre-sintering and high-temperature sintering, the positive electrode material is obtained, the dopant is an oxide containing a doped metal element A, the A has a d0 electron configuration in the oxide of the A, and based on the total amount of substance of the lithium-rich manganese-based precursor and the lithium source, the d0 electron configuration in the oxide of the A is smaller than the d0 electron configuration in the oxide of the A, and the d0 electron configuration in the oxide of the A is smaller than the d0 electron configuration in the dopant. And the molar fraction of the element A in the dopant is 0.3%-1.5%. The positive electrode material has relatively high discharge specific capacity and good capacity retention ratio.

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and particularly to a cathode material with symbiotic layered rock salt, a preparation method thereof, a cathode and a battery. Background Art

[0002] The lithium-rich layered oxide has a high working voltage and specific capacity, and is considered to be the most promising cathode material for the next generation of lithium-ion batteries. The lithium-rich manganese-based cathode material has a low cobalt content or even no cobalt, which has significant cost advantages and high safety, and is an ideal choice for the cathode material of future lithium-ion batteries. However, there are still obstacles in the commercial application of the lithium-rich manganese-based cathode material. When the working voltage is higher than 4.5V, the lattice oxygen in the Li 2 MnO 3 phase participates in the redox reaction to provide extra electrons. This process is accompanied by the precipitation of irreversible oxygen at the interface, resulting in the formation of oxygen vacancies. These oxygen vacancies promote the migration of metal ions to the lithium layer, causing structural degradation, and ultimately leading to problems such as capacity decay of the lithium-rich manganese-based cathode material.

[0003] Through surface modification methods such as coating, surface corrosion and electrolyte decomposition can be inhibited, thereby inhibiting the capacity decline of lithium oxide and improving the electrochemical performance of the cathode material. However, when modifying by coating, there is a problem of lattice mismatch between the active material and the coating material, which will cause coating splitting during long-term cycling, and is not conducive to the improvement of cycle stability.

[0004] Therefore, providing a simple preparation method for the lithium-rich manganese-based cathode material to achieve the effects of stable structure and high capacity retention rate is a technical problem to be solved urgently at present. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problem of capacity loss of the lithium-rich manganese-based cathode material during long-term cycling in the prior art, and to provide a cathode material with symbiotic layered rock salt, a preparation method thereof, a cathode and a battery. This cathode material has a high discharge specific capacity and good capacity retention rate.

[0006] To achieve the above purpose, the first aspect of the present invention provides a preparation method of a cathode material, wherein the preparation method includes:

[0007] (1) Prepare a lithium-rich manganese-based precursor, the lithium-rich manganese-based precursor includes nickel element, manganese element and cobalt element, and the molar ratio of the nickel element, manganese element and cobalt element is a:b:c, 0.1≤a≤0.2, 0.6≤b≤0.8, 0.1≤c≤0.2;

[0008] (2) The lithium-rich manganese-based precursor, lithium source, and dopant are sequentially subjected to dry mixing, pre-sintering, and high-temperature sintering to obtain a cathode material. Among them, the dopant is an oxide containing a doped metal element A, where A has a d0 electron configuration in the oxide of A. Based on the total amount of substance of the lithium-rich manganese-based precursor and the lithium source, the molar fraction of element A in the dopant is 0.3% - 1.5%.

[0009] The second aspect of the present invention provides a cathode material, which is prepared by the preparation method according to the first aspect of the present invention. Among them, the structure of the cathode material includes a layered structure and a rock-salt structure.

[0010] The third aspect of the present invention provides a cathode, which includes the cathode material prepared by the preparation method according to the first aspect of the present invention or the cathode material according to the second aspect of the present invention.

[0011] The fourth aspect of the present invention provides a battery, which includes the cathode according to the third aspect of the present invention.

[0012] Through the above technical solutions, the present invention prepares a cathode material with a co-existing layered and rock-salt structure. The rock-salt structure provides a supporting effect, maintains the stability of the crystal structure, improves the thermal stability of the material, increases the electrochemical active sites, and the layered / rock-salt co-existing structure effectively improves the cycling performance of the cathode material. At the same time, the cathode material of the present invention is doped with a metal element having a d0 electron configuration, which has the effect of stabilizing the layered structure and improving the lithium layer spacing.

[0013] The first-cycle discharge specific capacity of the cathode material prepared by the present invention is above 260 mAh / g, and the first-cycle Coulombic efficiency is above 75%; the cycling stability is good. The discharge specific capacity after 200 cycles at 0.1C is above 150 mAh / g, and the capacity retention rate is above 55%. The discharge specific capacity after 140 cycles at 1C is above 180 mAh / g, and the capacity retention rate is above 65%. Description of the Drawings

[0014] Figure 1 is the XRD pattern of the cathode materials prepared in Comparative Example 1 and Example 1;

[0015] Figure 2 is the SEM pattern of the cathode materials prepared in Comparative Example 1, Example 1, and Example 6;

[0016] Figure 3 is the TEM pattern of the cathode material prepared in Example 1;

[0017] Figure 4 is the EDS pattern of the cathode material prepared in Example 1;

[0018] Figure 5It is a comparative atlas of the first-week charge-discharge curves of the batteries composed of the cathode materials in Comparative Example 1, Example 1, and Example 6;

[0019] Figure 6 It is the voltage-capacity curve of the batteries composed of the cathode materials prepared in Example 2 and Example 3 after 200 cycles at a rate of 0.1C;

[0020] Figure 7 It is the voltage-capacity curve of the batteries composed of the cathode materials prepared in Comparative Example 1, Example 1, and Example 6 after 140 cycles at a rate of 1C. Detailed implementation mode

[0021] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0022] The terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise specified, the meaning of "a plurality" is two or more.

[0023] In the present invention, the d0 electron configuration refers to the state in which there is no electron occupancy in the outermost d orbit of the A ion.

[0024] The first aspect of the present invention provides a method for preparing a cathode material, wherein the preparation method includes:

[0025] (1) Prepare a lithium-rich manganese-based precursor, the lithium-rich manganese-based precursor includes nickel element, manganese element, and cobalt element, and the molar ratio of the nickel element, manganese element, and cobalt element is a:b:c, 0.1≤a≤0.2, 0.6≤b≤0.8, 0.1≤c≤0.2;

[0026] (2) Dry-mix, pre-burn, and high-temperature sinter the lithium-rich manganese-based precursor, lithium source, and dopant in sequence to obtain a cathode material, wherein the dopant is an oxide containing a doped metal element A, and wherein A has a d0 electron configuration in the oxide of A. Based on the total amount of substance of the lithium-rich manganese-based precursor and the lithium source, the molar fraction of element A in the dopant is 0.3%-1.5%.

[0027] Nickel element can effectively improve the capacity and energy density of the cathode material. Manganese element is beneficial to improving the safety and thermal stability of the cathode material. Cobalt element helps to maintain the layered structure of the material, improve the cycle stability of the material, and is also conducive to improving the electronic conductivity of the material, thereby improving the rate performance of the battery. When the molar ratio of nickel element, manganese element and cobalt element is a:b:c and 0.1≤a≤0.2, 0.6≤b≤0.8, 0.1≤c≤0.2, the cathode material has both high specific capacity and good cycle stability.

[0028] In some embodiments, preferably, A is selected from one or more of titanium, niobium, molybdenum, and tungsten.

[0029] In some embodiments, preferably, the dopant is selected from one or more of titanium dioxide, niobium pentoxide, molybdenum trioxide, and tungsten trioxide.

[0030] In some embodiments, preferably, the dopant is selected from niobium pentoxide and / or tungsten trioxide.

[0031] In some embodiments, preferably, the dopant is niobium pentoxide and tungsten trioxide.

[0032] A ions with a d0 electron configuration can distort their electron configuration to improve the capacity retention rate because there are no electrons in the outermost d orbital. At the same time, doping with metal elements can stabilize the crystal structure by occupying lattice positions to reduce charge-discharge phase changes and volume changes, and can change the local electronic structure to improve the capacity retention rate. In addition, doping can improve the lithium layer spacing, increase the diffusion rate of lithium ions, and relieve the stress caused by volume changes. When the dopant is an oxide, it can effectively improve the structural stability of the material, increase the ion diffusion rate, improve the electrochemical performance, and at the same time inhibit adverse phenomena such as oxygen release and phase change.

[0033] When the addition amount of the dopant is too small, it may not be possible to achieve an ideal layered rock salt coexisting structure, so that a cathode material with excellent electrochemical performance cannot be obtained. When the addition amount of the dopant is too large, it will have a negative impact on the crystal structure, and then have an adverse effect on the insertion and extraction of lithium ions. Based on the amount of the lithium-rich manganese-based precursor, when the molar fraction of element A in the dopant is 0.3%-1.5%, the electrochemical properties such as the cycle stability and charge-discharge rate of the cathode material are effectively improved. Based on the amount of the lithium-rich manganese-based precursor, the molar fraction of element A in the dopant can be any value between any two of 0.3%, 0.5%, 0.8%, 1.0%, 1.3%, and 1.5%.

[0034] In some embodiments, preferably, the dry mixing process includes: at a temperature of 45-65 °C, first mixing a lithium-rich manganese-based precursor and a lithium source to obtain mixture 1, second mixing a dopant and mixture 1 to obtain mixture 2, adding a dispersant to mixture 2, and then performing dispersion. The present invention has no particular limitation on the specific dispersion method, such as the grinding method can be adopted.

[0035] In some embodiments, preferably, the time for the first mixing is 5-20 min, and the time for the second mixing is 5-20 min.

[0036] In some embodiments, preferably, the dispersant includes alcohol.

[0037] Dry mixing not only has simple operation and low cost, but also can effectively prevent the solvent from having an adverse effect on the material properties, achieve efficient mixing while maintaining the original characteristics of the material, thereby improving the electrochemical performance of the material.

[0038] In some embodiments, preferably, the temperature for pre-sintering is 350-550 °C, the time is 4-6 h, and the heating rate is 2-5 °C / min.

[0039] In some embodiments, preferably, the temperature for high-temperature sintering is 800-1000 °C, the time is 10-15 h, and the heating rate is 2-5 °C / min.

[0040] The main purpose of pre-sintering is to remove the organic matter or moisture in the lithium-rich manganese-based precursor, promote chemical reactions, and induce crystal growth. The time of 4-6 h is sufficient to ensure that all substances to be removed are fully evaporated or decomposed, and the initial crystal structure begins to form. The slower heating rate helps to prevent the accumulation of internal stress and possible crack formation caused by rapid heating, ensuring the uniformity and stability of the material. The temperature for pre-sintering can be any value between any two of 350 °C, 400 °C, 430 °C, 450 °C, 500 °C, 550 °C, the time can be any value between any two of 4 h, 4.5 h, 5 h, 5.5 h, 6 h, and the heating rate can be any value between any two of 2 °C / min, 3 °C / min, 4 °C / min, 5 °C / min.

[0041] High-temperature sintering is carried out at a higher temperature. The thermal motion between atoms inside the material is enhanced, enabling the material to reach a higher crystallinity, which is beneficial to the improvement of electrochemical performance. A time of 10 - 15 h ensures the full progress of the reaction and obtains a uniform and perfect crystal structure. The temperature of high-temperature sintering can be any value between any two numbers among 800 °C, 850 °C, 900 °C, 950 °C, and 1000 °C, the time can be any value between any two numbers among 10 h, 11 h, 12 h, 13 h, 14 h, and 15 h, and the heating rate can be any value between any two numbers among 2 °C / min, 3 °C / min, 4 °C / min, and 5 °C / min.

[0042] In some embodiments, preferably, the molar ratio of the metal elements in the lithium-rich manganese-based precursor to the lithium element in the lithium source is 1:1.4 - 1.65. An appropriate amount of lithium excess can compensate for the inevitable lithium loss during the cycling process and improve the initial Coulomb efficiency and cycling stability of the cathode material. The metal elements in the lithium-rich manganese-based precursor include nickel element, manganese element, and cobalt element. The ratio of the total molar amount of the metal elements in the lithium-rich manganese-based precursor to the molar amount of the lithium element in the lithium source can be any value between any two numbers among 1:1.4, 1:1.45, 1:1.5, 1:1.55, 1:1.6, and 1:1.65.

[0043] The second aspect of the present invention provides a cathode material, which is prepared by the preparation method according to the first aspect of the present invention, wherein the structure of the cathode material includes a layered structure and a rock-salt structure.

[0044] During charge and discharge, lithium ions are inserted and extracted, causing volume changes in the cathode material. At the same time, metal ions (Ni, Mn, and Co) dissolve and migrate, resulting in the collapse or phase change of the layered structure of the cathode material, leading to a decrease in the capacity and cycling stability of the cathode material. The rock-salt structure can provide a supporting role, maintain the stability of the crystal structure, and improve the thermal stability of the material. The layered rock-salt coexisting structure provides more interstitial positions and vacancies, provides additional ion transport paths, and has a high specific surface area and may exhibit surface reconstruction phenomena at the nanoscale or with special morphologies, which can increase the electrochemically active sites. Therefore, the layered rock-salt coexisting structure can effectively improve the cycling performance of the cathode material.

[0045] In some embodiments, preferably, based on the total mass of the positive electrode material, the mass fraction of the rock salt structure is 20-45%. When the mass fraction of the rock salt structure is within this range, it helps to support the integrity of the layered structure and effectively inhibits oxygen release, thereby enhancing the stability of the material during repeated charge and discharge processes; it can form a good synergistic effect with the ion diffusion channels inside the material, accelerate the transmission speed of lithium ions, and improve the rate performance of the material; it can increase the number of active sites and optimize the voltage platform, thereby improving the energy density of the material. The mass fraction of the rock salt structure can be any value between any two of 20%, 25%, 30%, 35%, 40%, and 45%.

[0046] The third aspect of the present invention provides a positive electrode, wherein the positive electrode comprises the positive electrode material prepared by the preparation method of the first aspect of the present invention or the positive electrode material of the second aspect of the present invention.

[0047] The fourth aspect of the present invention provides a battery, wherein the battery comprises the positive electrode of the third aspect of the present invention.

[0048] According to a particularly preferred embodiment of the present invention, a lithium-rich manganese-based precursor is prepared, and the lithium-rich manganese-based precursor comprises nickel element, manganese element and cobalt element, and the molar ratio of the nickel element, manganese element and cobalt element is 0.15-0.2:0.6-0.7:0.1-0.15;

[0049] The lithium-rich manganese-based precursor, a lithium source and a dopant are successively subjected to dry mixing, pre-sintering and high-temperature sintering to obtain a positive electrode material, wherein the dopant is an oxide containing a doped metal element A, and wherein A has a d0 electron configuration in the oxide of A. Based on the total amount of substances of the lithium-rich manganese-based precursor and the lithium source, the molar fraction of element A in the dopant is 0.5%-1%, and the dopant is selected from niobium pentoxide and / or tungsten trioxide;

[0050] More preferably, the dopant is selected from niobium pentoxide and tungsten trioxide. Based on the total amount of substances of the lithium-rich manganese-based precursor and the lithium source, the molar fraction of element A in the dopant is 0.5-1%, and the molar ratio of niobium element in the niobium pentoxide to tungsten element in the tungsten trioxide is 1:1-2.

[0051] The present invention will be described in detail below through examples. In the following examples, the characterization methods and instruments for the positive electrode material are as follows:

[0052] ① X-ray diffraction (XRD) test: X-ray diffractometer, instrument model: Rigaku Ultima IV-185, Japan; Import the XRD test data into GSAS or MDI Jade, and obtain the mass fraction of the rock salt structure in the positive electrode material through software analysis;

[0053] ② Scanning electron microscope (SEM) test: Scanning electron microscope, model: QUANTA, manufactured by FEI Company, USA;

[0054] ③ Transmission electron microscope (TEM) test: Transmission electron microscope, model: G2 F20, manufactured by FEI Company, USA;

[0055] ④ EDS test: Energy dispersive X-ray spectrometer, model: QUANTA, manufactured by FEI Company, USA;

[0056] ⑤ Battery cycle performance test: Land battery test system, model: CT 2001A, Wuhan Blue Electronic Co., Ltd.

[0057] All raw materials used in the present invention are commercially available products.

[0058] Example 1

[0059] (1) Dissolve MnSO 4 ·H 2 O, NiSO 4 ·6H 2 O and CoSO 4 ·7H 2 O in deionized water to prepare 1000 mL of a mixed salt solution with a concentration of 2 mol / L, where the molar ratio of nickel, manganese, and cobalt elements is 0.19:0.69:0.12. Prepare 1000 mL of an ammonia water solution with a concentration of 4 mol / L and 1000 mL of a sodium carbonate solution with a concentration of 2 mol / L.

[0060] Pour 1000 mL of deionized water as the bottom liquid into the reaction kettle, then pump 1000 mL of the mixed salt solution into the reactor at a feeding rate of 1500 mL / h. At the same time, pump the sodium carbonate solution and the ammonia water solution into the reactor. The feeding rate of the sodium carbonate solution is 1500 mL / h, and the feeding rate of the ammonia water solution is adjusted to about 1500 mL / h to ensure that the pH value is maintained within the range of 11 ± 0.2. Carry out the coprecipitation reaction under an argon atmosphere, control the reaction temperature at 55 °C, and the stirring speed at 350 r / min.

[0061] After the feeding of the mixed salt solution is completed, continue the reaction for 6 h, carry out suction filtration, wash the precipitate until the pH of the filtrate is close to neutral and is transparent and colorless, and dry it under vacuum for 24 h to obtain a lithium-rich manganese-based precursor.

[0062] (2) Carry out dry mixing at 55 °C. Carry out the first mixing of the lithium-rich manganese-based precursor and lithium carbonate at a molar ratio of 1:0.7 for 5 min to obtain mixture 1. Carry out the second mixing of mixture 1 and tungsten trioxide at a molar ratio of 1:0.005 for 5 min to obtain mixture 2.

[0063] Add alcohol to the mixture 2, grind it until the alcohol evaporates, and repeat this operation 3 times to obtain mixture 3.

[0064] (3) Place mixture 3 in a muffle furnace, heat it up to 500 °C at a heating rate of 5 °C / min, pre-sinter for 5 h, then heat it up to 900 °C at a heating rate of 5 °C / min, and perform high-temperature sintering for 12 h to obtain the positive electrode material. Based on the total mass of the positive electrode material, the mass fraction of the rock salt structure is 29.5%.

[0065] Examples 1-9 have similar XRD patterns. Taking Example 1 as an example. Figure 1 It is the XRD comparison pattern of the positive electrode materials prepared in Example 1 and Comparative Example 1 (Pristine in the figure is Comparative Example 1, and W-005 is Example 1). It can be seen that compared with Comparative Example 1, the diffraction peak of the positive electrode material of Example 1 becomes weaker at about 44°, indicating that the Li + / Ni 2+ mixing disorder is weakened, the crystallinity is improved, and the order degree is increased.

[0066] Examples 1-9 have similar SEM patterns. Taking Examples 1 and 6 as examples. Figure 2 From left to right are the SEM patterns of the positive electrode materials prepared in Comparative Example 1, Example 1, and Example 6. All three materials are secondary microspheres composed of primary particles.

[0067] Examples 1-9 have similar TEM patterns. Taking Example 1 as an example. Figure 3 It is the TEM pattern of the positive electrode material prepared in Example 1. The yellow circle indicates the layered structure, and the red circle indicates the denser layered / rock salt symbiotic structure with a smaller layer spacing, indicating that the layered rock salt symbiotic structure has been successfully realized in the material.

[0068] Examples 1-9 have similar EDS patterns. Taking Example 1 as an example. Figure 4 It is the EDS pattern of the positive electrode material prepared in Example 1. The first row from left to right is the scanning electron microscope image and the elemental distribution maps of O and Mn elements respectively. The second row from left to right is the elemental distribution maps of Co, Ni, and W elements respectively, indicating that the positive electrode material of Example 1 has been successfully doped with W element and the distribution of each element is uniform.

[0069] Example 2

[0070] It is carried out according to the method of Example 1, with the only difference being that titanium dioxide is used instead of tungsten trioxide, and the molar amount of titanium element in titanium dioxide is equal to that of tungsten element in tungsten trioxide. Based on the total mass of the prepared positive electrode material, the mass fraction of the rock salt structure is 27.1%.

[0071] Example 3

[0072] It is carried out according to the method of Example 1, except that: niobium pentoxide is used instead of tungsten trioxide, and based on the total amount of substance of the lithium-rich manganese-based precursor and the lithium source, the molar fraction of niobium element in niobium pentoxide is 1%. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure is 34.5%.

[0073] Example 4

[0074] It is carried out according to the method of Example 3, the difference is only that: niobium pentoxide and tungsten trioxide are used instead of niobium pentoxide, and the mixture 1 is secondarily mixed with niobium pentoxide and tungsten trioxide, and based on the total amount of substance of the lithium-rich manganese-based precursor and the lithium source, the sum of the molar fraction of niobium element in niobium pentoxide and the molar fraction of tungsten element in tungsten trioxide is 1%, and the molar ratio of niobium element in niobium pentoxide to tungsten element in tungsten trioxide is 1:1. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure is 28.6%.

[0075] Example 5

[0076] It is carried out according to the method of Example 4, the difference is only that: the mixture 1 is secondarily mixed with niobium pentoxide and tungsten trioxide, and the molar ratio of niobium element in niobium pentoxide to tungsten element in tungsten trioxide is 1:2. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure is 29.1%.

[0077] Example 6

[0078] It is carried out according to the method of Example 1, the difference is only that: the molar ratio of the mixture 1 to tungsten trioxide is 1:0.01. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure is 35.8%.

[0079] Example 7

[0080] It is carried out according to the method of Example 1, the difference is only that: the molar ratio of the mixture 1 to tungsten trioxide is 1:0.015. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure is 41.3%.

[0081] Example 8

[0082] It is carried out according to the method of Example 1, except that: the molar ratio of the lithium-rich manganese-based precursor to lithium carbonate is 1:0.75, that is, the molar ratio of the metal element in the lithium-rich manganese-based precursor to the lithium element in lithium carbonate is 1:1.5, and it is heated to 400 °C at a heating rate of 3 °C / min and pre-sintered for 6 h, and then heated to 800 °C at a heating rate of 3 °C / min and sintered at high temperature for 15 h. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure is 32.3%.

[0083] Example 9

[0084] The method of Example 1 was followed, except that: the molar ratio of the lithium-rich manganese-based precursor to lithium carbonate was 1:0.82, that is, the molar ratio of the metal elements in the lithium-rich manganese-based precursor to the lithium element in lithium carbonate was 1:1.64. It was heated to 550 °C at a heating rate of 2 °C / min, pre-calcined for 4 h, and then heated to 1000 °C at a heating rate of 2 °C / min and sintered at high temperature for 10 h. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure was 29.5%.

[0085] Comparative Example 1

[0086] The method of Example 1 was followed, with the difference only being that: tungsten trioxide was not added and the second mixing was not carried out. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure was 3.4%.

[0087] Comparative Example 2

[0088] The method of Example 1 was followed, with the difference only being that: the molar ratio of Mixture 1 to tungsten trioxide was 1:0.02. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure was 45.2%.

[0089] Comparative Example 3

[0090] The method of Example 1 was followed, with the difference only being that: the molar ratio of nickel, manganese, and cobalt elements in the mixed salt solution was 0.4:0.55:0.05. Based on the total mass of the prepared cathode material, the mass fraction of the rock salt structure was 33.1%.

[0091] Test Example

[0092] The cathode materials prepared in Examples 1-9 and Comparative Examples 1-3 were taken and mixed with Super P and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, and ground into a slurry with N-methylpyrrolidone (NMP). It was coated on an aluminum foil with a 125 μm doctor blade, dried, and cut into pieces to make a cathode sheet. A CR2032 coin-type half-cell was assembled in an argon glove box (water < 0.01 ppm, oxygen < 0.01 ppm), where the cathode was the above-mentioned cathode sheet, the counter electrode was a lithium sheet, the separator was Celgard 2500, and the electrolyte was 1 mol / L LiPF 6 solution (the solvent was EC and DMC with a volume ratio of 1:1).

[0093] Figure 5It is a comparative graph of the first-week charge-discharge curves of the batteries assembled with the cathode materials in Comparative Example 1, Example 1, and Example 6 at 30 °C, 2.0 - 4.8 V, and 0.1C rate (in the figure, Pristine is Comparative Example 1, W-010 is Example 6, and W-005 is Example 1). As can be seen from the figure, the discharge specific capacity of Comparative Example 1 is 261.1 mAh / g. Compared with Comparative Example 1, the discharge specific capacity of Example 1 is 280.1 mAh / g, and the discharge specific capacity of Example 6 is 269.3 mAh / g. It can be seen that the discharge specific capacities of the cathode materials prepared by the method provided by the present invention are all improved, and when the dopant is added in an appropriate amount, the improvement amplitude of the discharge specific capacity is greater.

[0094] Figure 6 It is the voltage-capacity curve of the batteries composed of the cathode materials prepared in Example 2 and Example 3 after 200 cycles at 30 °C, 2.0 - 4.8 V, and 0.1C rate (in the figure, Ti-005 is Example 2, and Nb-010 is Example 3). As can be seen from the figure, the first-week discharge specific capacities of the materials prepared by the present invention can all reach more than 250 mAh / g. Among them, the discharge specific capacity of the cathode material in Example 2 is 273.5 mAh / g, and the first-week Coulomb efficiency is 88.26%. The electrochemical performance is significantly improved. At the same time, the cathode material in Example 3 shows excellent cycle stability.

[0095] Figure 7 It is the voltage-capacity curve of the batteries composed of the cathode materials prepared in Comparative Example 1, Example 1, and Example 6 after 140 cycles at 30 °C, 2.0 - 4.8 V, and 1C rate (in the figure, Pristine is Comparative Example 1, W-005 is Example 1, and W-010 is Example 6). As can be seen from the figure, the capacity retention rate of Comparative Example 1 is 35.73%, the capacity retention rate of Example 1 is 68.13%, and the retention rate of Example 6 is 70.91%. Compared with Comparative Example 1, the cycle stabilities of the materials in the examples are all significantly improved.

[0096] After assembling the cathode materials prepared in Examples 1 - 9 and Comparative Examples 1 - 3 into batteries, their electrochemical performances were tested. The test conditions were: temperature 30 °C, voltage range 2.0 - 4.8 V. The first-week charge-discharge test was carried out at 0.1C rate, and the cycle performance test was carried out at 0.1C rate for 200 cycles and at 1C for 140 cycles. 1C = 250 mA / g. The results are shown in Table 1.

[0097] Table 1 Proportion of rock salt structure and electrochemical performance of cathode materials

[0098]

[0099] As can be seen from the results in Table 1, the positive electrode material prepared by the present invention has good specific capacity and cycle stability. In particular, when both W element and Nb element are doped simultaneously (Examples 4 and 5), the positive electrode material exhibits higher first-cycle discharge specific capacity and capacity retention rate than when only W element is doped (Example 6) or only Nb element is doped (Example 3). In Examples 1, 6, 7 and Comparative Examples 1, 2, the addition amount of the dopant was changed. As the addition amount of the dopant increased, the first-cycle discharge specific capacity, first-cycle Coulombic efficiency and capacity retention rate of the positive electrode material showed a trend of first increasing and then decreasing. The electrochemical performance of the positive electrode material in Example 1 was significantly better than that in Comparative Example 3, indicating that when the ratio of nickel, manganese and cobalt elements in the positive electrode material is within a suitable range, it is beneficial to improve the electrochemical performance of the positive electrode material.

[0100] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited thereto. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, including any other suitable combination of each technical feature. These simple modifications and combinations should also be regarded as the content disclosed by the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: The preparation method comprises: (1) preparing a lithium-rich manganese-based precursor, wherein the lithium-rich manganese-based precursor comprises nickel, manganese and cobalt, wherein the molar ratio of the nickel, manganese and cobalt is a:b:c, 0.1≤a≤0.2, 0.6≤b≤0.8, 0.1≤c≤0.2; (2) A lithium-rich manganese-based precursor, a lithium source and a dopant are dry-mixed, pre-fired and sintered at high temperature in sequence to obtain a positive electrode material, wherein the dopant is an oxide containing a doped metal element A, wherein A has a d0 electronic configuration in the oxide of A, and based on the total amount of the lithium-rich manganese-based precursor and the lithium source, the molar fraction of the A element in the dopant is 0.3%-1.5%.

2. The preparation method according to claim 1, wherein The dry mixing process comprises: first mixing a lithium-rich manganese-based precursor and a lithium source at a temperature of 45-65° C. to obtain a mixture 1, second mixing a dopant and the mixture 1 to obtain a mixture 2, adding a dispersant to the mixture 2, and then dispersing; Preferably, the first mixing time is 5-20 min, and the second mixing time is 5-20 min; Preferably, the dispersant comprises alcohol.

3. The preparation method according to claim 1 or 2, wherein A is selected from one or more of titanium, niobium, molybdenum and tungsten; Preferably, the dopant is selected from one or more of titanium dioxide, niobium pentoxide, molybdenum trioxide, and tungsten trioxide; Preferably, the dopant is selected from niobium pentoxide and / or tungsten trioxide; More preferably, the dopant is niobium pentoxide and tungsten trioxide.

4. The preparation method according to any one of claims 1 to 3, wherein The high temperature sintering temperature is 800-1000° C., the time is 10-15 hours, and the heating rate is 2-5° C. / min.

5. The preparation method according to any one of claims 1 to 4, wherein: The pre-calcination temperature is 350-550°C, the time is 4-6h, and the heating rate is 2-5°C / min.

6. The preparation method according to any one of claims 1 to 5, wherein: The molar ratio of the metal element in the lithium-rich manganese-based precursor to the lithium element in the lithium source is 1:1.4-1.

65.

7. A positive electrode material, characterized in that: Prepared according to the preparation method according to any one of claims 1 to 6, wherein the structure of the positive electrode material includes a layered structure and a rock salt structure.

8. The positive electrode material according to claim 7, wherein Based on the total mass of the positive electrode material, the mass fraction of the rock salt structure is 20-45%.

9. A positive electrode, characterized in that: The positive electrode comprises a positive electrode material prepared by the preparation method described in any one of claims 1 to 6 or a positive electrode material described in any one of claims 7 to 8.

10. A battery, characterized in that: The battery comprises the positive electrode according to claim 9.

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