Cathode material, preparation method thereof, cathode and battery

Abstract

The application relates to the field of lithium ion batteries, and discloses a positive electrode material, a preparation method of the positive electrode material, a positive electrode and a battery, wherein the preparation method of the positive electrode material comprises the following steps: (1) preparing a lithium-rich manganese base body material, the chemical formula of the lithium-rich manganese base body material being Li 1+x (Ni a Mn b Co c ) 1‑x O2,0

Description

Technical Field

[0001] The present invention relates to the field of lithium-ion batteries, and in particular to a cathode material, a preparation method thereof, a cathode and a battery. Background Art

[0002] The electrochemical performance of lithium-ion batteries is closely related to the properties of cathode materials, and currently commonly used cathode materials on the market can hardly meet the existing requirements. Lithium-rich manganese-based cathode material is a cathode material with great potential, which has high specific capacity and is expected to be widely used in the fields of electric vehicles and energy storage in the future, but there are still some problems at present.

[0003] First, irreversible oxygen release occurs when lithium-rich manganese-based cathode materials are charged at high voltage, which not only increases the safety risk of the battery, but also causes irreversible loss of capacity and voltage. Second, after multiple charge-discharge cycles, the layered structure of the material undergoes irreversible changes, leading to gradual decrease in capacity and voltage and poor cycle life. In addition, when lithium-rich manganese-based cathode materials are charged and discharged at high rate, the diffusion rate of lithium ions is low and the interface resistance increases, resulting in poor rate performance. Finally, during the cycling process of the material, due to oxygen release, structural degradation and other reasons, the voltage plateau gradually decreases, which affects the electrochemical performance such as energy density of the battery. Summary of the Invention

[0004] The object of the present invention is to provide a cathode material, a preparation method thereof, a cathode and a battery to overcome the problems of low capacity and poor cycle stability of cathode materials existing in the prior art. The cathode material has high specific capacity and good cycle stability.

[0005] In order to achieve the above object, a first aspect of the present invention provides a preparation method of a cathode material, wherein the preparation method comprises:

[0006] (1) preparing a lithium-rich manganese-based bulk material, the chemical formula of the lithium-rich manganese-based bulk material is Li 1+x (Ni a Mn b Co c ) 1-x O2, 0<x<1, wherein when c is 0, the ratio of a:b is 1:3-4, and when c is not 0, the ratio of a:b:c is 1:3-4:1-2;

[0007] (2) mixing the lithium-rich manganese-based bulk material with a tungsten-containing dopant, followed by a first calcination to obtain a cathode material, wherein the temperature of the first calcination is not lower than 300°C.

[0008] A second aspect of the present invention provides a cathode material, wherein the cathode material is prepared according to the preparation method described in the first aspect of the present invention.

[0009] A third aspect of the present invention provides a positive electrode, wherein the positive electrode comprises a positive electrode material prepared by the preparation method described in the first aspect of the present invention or a positive electrode material described in the second aspect of the present invention.

[0010] A fourth aspect of the present invention provides a battery, wherein the battery includes the positive electrode described in the third aspect of the present invention.

[0011] This invention introduces W element by mixing and calcining a lithium-rich manganese matrix material with a tungsten-containing dopant. The higher bond energy of the W-WO bonds allows for a tighter bond between the transition metal and oxygen layers, preventing transition metal ions from migrating into the lithium layer. This helps maintain the layered structure of the cathode material and improves the cycle stability of the battery. Furthermore, the introduction of W element optimizes the lithium-ion diffusion path, reducing the transport resistance of lithium ions during charging and discharging, thereby improving the electrochemical activity of the material.

[0012] The cathode material prepared by this invention has high specific capacity, with a first-cycle discharge specific capacity of over 240 mAh / g at 0.1C and a first-cycle coulombic efficiency of over 60%, and a first-cycle discharge specific capacity of over 180 mAh / g at 1C. It also exhibits good cycle stability, with a specific capacity of over 155 mAh / g after 100 cycles at 1C, a capacity retention rate of over 80%, and an average weekly voltage drop of less than 4.6 mV. Attached Figure Description

[0013] Figure 1 This is a scanning electron microscope (SEM) image of the cathode material in Example 1;

[0014] Figure 2 This is a scanning electron microscope (SEM) image of the cathode material in Example 1;

[0015] Figure 3 The image shows the Mn 2p spectra obtained by X-ray photoelectron spectroscopy (XPS) sputtering of the cathode material in Example 1, with sputtering depths of 0 nm, 20 nm, and 40 nm.

[0016] Figure 4 This is the X-ray diffraction (XRD) pattern of the cathode material in Example 2;

[0017] Figure 5 This is a scanning electron microscope (SEM) image of the cathode material in Example 2;

[0018] Figure 6 This is a scanning electron microscope (SEM) image of the cathode material in Example 3;

[0019] Figure 7 These are the electrochemical impedance spectroscopy (EIS) spectra of the cathode materials in Example 4 and Comparative Example 1;

[0020] Figure 8 is a graph of average medium discharge voltage after 100 cycles of batteries assembled with the cathode materials of Example 1 and Comparative Example 1 at 30°C and 1C;

[0021] Figure 9 is a discharge capacity graph after 100 cycles of batteries assembled with the cathode materials of Example 2 and Comparative Example 1 at 30°C and 1C;

[0022] Figure 10 is a graph of first-cycle charge and discharge of batteries assembled with the cathode materials of Example 3 and Comparative Example 1 at 30°C and 0.1C. Detailed Description of the Embodiments

[0023] Any endpoint and any value of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values shall be understood to include values close to these ranges or values. For numerical ranges, endpoints of each range, endpoints of each range in combination with individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, and these new numerical ranges shall be considered as specifically disclosed herein.

[0024] The terms "first" and "second" are only used for description purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the recited technical features. Therefore, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. Unless otherwise stated, the term "plurality" in the description of the present application means two or more.

[0025] In a first aspect, the present invention provides a method for preparing a cathode material, wherein the preparation method comprises:

[0026] (1) preparing a lithium-rich manganese-based host material, wherein the chemical formula of the lithium-rich manganese-based host material is Li 1+x (Ni a Mn b Co c ) 1-x O2, 0<x<1, wherein when c is 0, the ratio of a:b is 1:3-4, and when c is not 0, the ratio of a:b:c is 1:(3-4):(1-2);

[0027] (2) mixing the lithium-rich manganese-based host material with a tungsten-containing dopant, and then performing a first calcination to obtain the cathode material, wherein the temperature of the first calcination is not lower than 300°C.

[0028] The present invention prepares the cathode material by mixing the lithium-rich manganese-based host material with the tungsten-containing dopant, performing calcination and introducing W element. The bond energy of the W-O bond is 598-632 kJ·mol -1 , and the bond energy of the Mn-O bond is about 402 kJ·mol-1 The bond energy of the Ni-O bond is approximately 391.6 kJ·mol⁻¹. -1 Doping with W, introducing higher bond energy WO bonds, can make the transition metal-oxygen layer more tightly bonded, preventing transition metal ions from migrating into the lithium layer. This helps maintain the layered structure of the cathode material and improves the cycle stability of the battery. Furthermore, the introduction of W can optimize the lithium-ion diffusion path of the material, reducing the transport resistance of lithium ions during charging and discharging, thereby improving the electrochemical activity of the material.

[0029] In some embodiments, preferably, the amount of the tungsten-containing dopant is 0.5-1.5 wt%, based on the amount of the lithium-rich manganese matrix material.

[0030] In some embodiments, preferably, the amount of the tungsten-containing dopant is 0.5-1 wt%, based on the amount of the lithium-rich manganese matrix material.

[0031] The amount of tungsten-containing dopant added affects the doping amount and depth of W element in the cathode material. Selecting an appropriate amount of tungsten-containing dopant is beneficial to further improve the capacity and cycle stability of the cathode material. Based on the amount of the lithium-rich manganese matrix material, the amount of tungsten-containing dopant can be any value between any two of the following: 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, and 1.5wt%.

[0032] In some embodiments, preferably, the first calcination temperature is 300-800°C and the time is 3-8 hours.

[0033] In some embodiments, preferably, the temperature of the first calcination is 500-800°C.

[0034] The temperature or time of the first calcination affects the grain size of the cathode material. When the temperature or time of the first calcination is within the above range, the cathode material has a suitable grain size, which is beneficial to the lithium-ion insertion / extraction reaction and improves the cycle stability of the cathode material. The temperature of the first calcination can be any value between any two numbers from 300℃, 400℃, 500℃, 600℃, 700℃, and 800℃, and the time of the first calcination can be any value between any two numbers from 3h, 4h, 5h, 6h, 7h, and 8h.

[0035] In some embodiments, preferably, the heating rate of the first calcination is 1-5 °C / min. A slower heating rate is beneficial for uniform grain growth because the material has more time for atomic rearrangement, resulting in larger and more complete grains. This helps maintain the electrochemically active sites of the material, reduces the occurrence of side reactions, and thus improves the cycle stability of the battery. The heating rate of the first calcination can be any value between any two of 1 °C / min, 2 °C / min, 3 °C / min, 4 °C / min, and 5 °C / min.

[0036] In some embodiments, preferably, the tungsten-containing dopant is selected from one or more of ammonium metatungstate, ammonium tungstate, tungsten oxide, and tungstic acid.

[0037] In some embodiments, preferably, the mixing is carried out in the presence of a solvent.

[0038] In some embodiments, preferably, the mixing process includes: dissolving the tungsten-containing dopant in the solvent to form a suspension, then adding the lithium-rich manganese matrix material to the suspension, and then evaporating the solvent.

[0039] Mixing the lithium-rich manganese matrix material and the tungsten-containing dopant in a solvent allows for a more uniform mixing. Since the amount of tungsten-containing dopant is much smaller than that of the lithium-rich manganese matrix material, during mixing, the tungsten-containing dopant is first uniformly dispersed in the solvent to form a suspension, and then the lithium-rich manganese matrix material is added to the suspension. This avoids excessively high or low local concentrations of the tungsten-containing dopant, which is beneficial for forming a uniform coating layer. The solvent can be one or more of isopropanol, ethanol, and acetone.

[0040] Evaporating the solvent means heating the solvent to 55-65℃ and weighing it every 30 minutes. If the difference between two consecutive weighings does not exceed 0.05g, it means that constant weight has been reached and the solvent has been evaporated.

[0041] In some embodiments, preferably, the process of preparing the lithium-rich manganese matrix material includes:

[0042] (1) Prepare a metal salt solution, wherein the metal salt solution comprises a salt of a transition metal element, wherein the transition metal element comprises nickel and manganese and optionally cobalt; mix the metal salt solution, a precipitant and a chelating agent, and perform a co-precipitation reaction to obtain a precursor containing the transition metal element.

[0043] The molar ratio of nickel, manganese and optional cobalt in the metal salt solution is a:b:c. When c is 0, the ratio of a:b is 1:3-4. When c is not 0, the ratio of a:b:c is 1:3-4:1-2.

[0044] (2) The lithium source and the precursor are mixed and subjected to a second calcination to obtain the lithium-rich manganese matrix material.

[0045] The molar ratio of the transition metal element in the precursor to the lithium element in the lithium source is 1:1-1.5.

[0046] The electrochemical performance of the cathode material can be optimized by adjusting the molar ratio of nickel, manganese, and cobalt in the metal salt solution. Nickel ions provide a higher redox potential, increasing the energy density of the material. The presence of manganese helps maintain the structural integrity of the cathode material during multiple charge-discharge cycles, thereby extending the battery's lifespan. Cobalt stabilizes the layered structure of the cathode material, contributing to improved cycle stability and thermal stability, and enhancing the battery's power performance. When the molar ratio of nickel, manganese, and cobalt in the metal salt solution is within the range described in this invention, the cathode material exhibits good capacity and cycle stability. The concentration of the metal salt solution is 1-3 mol / L, and the anions in the metal salt solution are selected from sulfate and / or nitrate.

[0047] A molar ratio of transition metal element in the precursor to lithium element in the lithium source within the range of 1:1-1.5 helps maintain the structural stability of the cathode material and improves its cycle life; it also facilitates rapid lithium-ion diffusion, thereby improving the battery's rate performance. The molar ratio of transition metal element in the precursor to lithium element in the lithium source can be any value between any two numbers from 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, and 1:1.5. The lithium source is selected from lithium carbonate and / or lithium hydroxide.

[0048] In some embodiments, preferably, the second calcination process includes: a first calcination step and a second calcination step. The first calcination step is to remove water from the precursor and lithium source, decompose anions in the precipitant, and promote the uniform mixing of lithium ions and metal ions. The second calcination step is carried out at a higher temperature to form a more stable crystal structure with better crystallinity.

[0049] In some embodiments, preferably, the temperature of the first calcination step is 400-600℃, the time is 5-7 hours, and the heating rate is 4-6℃ / min. The temperature of the first calcination step can be any value between any two numbers from 400℃, 450℃, 500℃, 550℃, and 600℃; the time can be any value between any two numbers from 5 hours, 5.5 hours, 6 hours, 6.5 hours, and 7 hours; and the heating rate can be any value between any two numbers from 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, and 6℃ / min.

[0050] In some embodiments, preferably, the second calcination step is carried out at a temperature of 850-950℃ for 10-14 hours, with a heating rate of 4-6℃ / min. The calcination temperature can be any value between any two of the following: 850℃, 870℃, 900℃, 920℃, and 950℃; the time can be any value between any two of the following: 10 hours, 11 hours, 12 hours, 13 hours, and 14 hours; and the heating rate can be any value between any two of the following: 4℃ / min, 4.5℃ / min, 5℃ / min, 5.5℃ / min, and 6℃ / min.

[0051] In some embodiments, preferably, the coprecipitation reaction is carried out at a pH of 8-9, a temperature of 55-65°C, and a time of 11-13 hours.

[0052] Within a specific pH range, the precipitant can effectively promote the precipitation of transition metal ions in solution. The pH of the coprecipitation reaction can be any value between any two of 8, 8.2, 8.5, 8.7, and 9. The concentration of the precipitant is 1-3 mol / L, and the precipitant is selected from sodium carbonate and / or sodium bicarbonate.

[0053] The higher the temperature of the coprecipitation reaction, the greater the reaction rate, but the greater the solubility of the substance, which is unfavorable for the reaction to move towards precipitation. A coprecipitation reaction time in the range of 11-13 hours is beneficial for obtaining crystals with moderate particle size, stable crystal phase, and good morphology. The temperature of the coprecipitation reaction can be any value between any two of 55℃, 57℃, 60℃, 63℃, and 65℃, and the time can be any value between any two of 11h, 11.5h, 12h, 12.5h, and 13h.

[0054] In some embodiments, preferably, the molar concentration of the chelating agent is 9-11 mol / L, and the chelating agent is preferably ammonia.

[0055] A second aspect of the present invention provides a cathode material, wherein the cathode material is prepared by the preparation method described in the first aspect of the present invention.

[0056] A third aspect of the present invention provides a positive electrode, wherein the positive electrode comprises a positive electrode material prepared by the preparation method described in the first aspect of the present invention or a positive electrode material described in the second aspect of the present invention.

[0057] A fourth aspect of the present invention provides a battery, wherein the battery includes the positive electrode described in the third aspect of the present invention.

[0058] The present invention will be described in detail below through examples. In the following examples, the scanning electron microscope (SEM) image of the cathode material was obtained by scanning electron microscopy (FEIQuanta600); the X-ray electron spectroscopy (XPS) image was obtained by X-ray photoelectron spectroscopy (AXIS SUPRA+); the X-ray diffraction (XRD) image was obtained by X-ray diffractometer (Rigaku Dmax-2400); and the electrochemical impedance spectroscopy (EIS) image was obtained by electrochemical workstation (CHI660D). The electrochemical performance of the cathode material was tested on the assembled battery using a LANDCT 2001A tester purchased from Wuhan Landian Electronics Co., Ltd.

[0059] All raw materials used in this invention are commercially available products.

[0060] Example 1

[0061] (1) Preparation of precursor

[0062] NiSO4·6H2O and MnSO4·H2O were dissolved in distilled water at a molar ratio of 1:3 to prepare a 2 mol / L metal salt solution, a 2 mol / L sodium carbonate solution, and a 9 mol / L ammonia solution.

[0063] A 0.3 L metal salt solution was pumped into the reactor at a feed rate of 3 mL / min. Simultaneously, sodium carbonate solution and ammonia solution were pumped into the reactor at feed rates of 3 mL / min and 3 mL / min respectively. The co-precipitation reaction was carried out under a nitrogen atmosphere, with the pH controlled at 8.5, the temperature at 60 °C, and the stirring speed at 600 rpm.

[0064] After the metal salt solution is fed in, the reaction continues for 12 hours. The mixture is then vacuum filtered, and the precipitate is washed until the pH of the filtrate is close to neutral and it is transparent and colorless. After drying, a precursor is obtained, which contains 2 mol of nickel and manganese.

[0065] (2) Preparation of lithium-rich manganese matrix materials

[0066] Weigh out 3g of precursor and 1.4233g of lithium carbonate, wherein the molar ratio of transition metal element in the precursor to lithium element in lithium carbonate is 2:3. First, grind the lithium carbonate in a mortar for 5 minutes until it becomes a uniform powder. Then, add the precursor and grind until it is evenly mixed. Add anhydrous ethanol and continue grinding for 20 minutes until the ethanol evaporates completely to obtain the sample with complete lithium mixing.

[0067] The lithium-mixed sample was spread evenly on a ceramic boat and placed in a muffle furnace for a second calcination in air. First, a first calcination was performed, with the temperature increased to 500℃ at a rate of 5℃ / min and calcined for 6 hours. Then, a second calcination was performed, with the temperature increased to 900℃ at a rate of 5℃ / min and calcined for 12 hours, yielding the lithium-rich manganese matrix material Li. 1.2 Mn 0.6 Ni 0.2 O2.

[0068] (3) Preparation of cathode materials

[0069] 0.0025g of ammonium metatungstate ((NH4)6H2W) 12 O 40 Add 6H₂O to a 100mL beaker, add 20mL of isopropanol, stir until a homogeneous suspension is formed, add 0.5g of lithium-rich manganese matrix material, and continue mixing for 10min. Based on the amount of the lithium-rich manganese matrix material, the amount of ammonium metatungstate is 0.5wt%.

[0070] The solvent was continuously stirred and heated in a 60°C water bath until it evaporated completely, and then dried in a vacuum oven at 80°C for 12 hours to further remove the solvent and moisture. Then, a first calcination was performed, in which the temperature was increased to 500°C at a rate of 5°C / min and calcined for 5 hours to obtain the cathode material.

[0071] In the preparation process of cathode materials, primary particles with specific crystal structures are first formed, and then multiple primary particles aggregate into larger and more stable secondary particles. The SEM image of the secondary particles of the cathode material in Example 1 is shown below. Figure 1 As shown, the cathode material has a spherical structure with a particle size of 10 μm. The SEM image of the primary particles of the cathode material in Example 1 is shown below. Figure 2 As shown, the primary particles are clearly visible and evenly distributed.

[0072] The cathode material prepared in Example 1 was etched to a depth of 5 nm, and then tested at sputtering depths of 0 nm, 20 nm, and 40 nm. Its Mn 2p XPS diagram is shown below. Figure 3 As shown, where Mn 2p 1 / 2 Peaks and Mn 2p 3 / 2 The peaks are two characteristic peaks of the 2p electrons in Mn. With increasing sputtering depth, the Mn 2p... 1 / 2 Peaks and Mn 2p 3 / 2 The peak shifts towards lower energies, indicating that the Mn 2p binding energy in the cathode material decreases from the surface to the bulk phase. This suggests that Mn has a higher average valence state at the surface. It can be seen that from the bulk phase to the surface of the cathode material, Mn, which is less easily dissolved... 4+ Increased levels of easily soluble Mn 3+Reducing the number of cathode materials helps improve their cycle stability.

[0073] Example 2

[0074] The method was carried out according to Example 1, except that the amount of ammonium metatungstate was 0.005 g, i.e., based on the amount of lithium-rich manganese matrix material, the amount of ammonium metatungstate was 1 wt%, the first calcination temperature was 600 °C, and the time was 6 h.

[0075] The cathode materials of Examples 1-22 have similar XRD patterns; Example 2 is used as an example. The XRD pattern of the cathode material of Example 2 is shown below. Figure 4 As shown, there are obvious peak divisions at the (006) / (102) peak near 38°(2θ) and the (108) / (110) peak near 65°(2θ), indicating that the prepared cathode material has a good layered structure and no obvious impurity peaks, which is beneficial to Li + The insertion and extraction of [the material]. The superlattice peak near 22° (2θ) is a characteristic peak of the Li2MnO3 phase in the cathode material, reflecting the unique honeycomb superstructure unit.

[0076] SEM image of the cathode material in Example 2 is shown below. Figure 5 As shown, the primary particles are clearly visible and evenly distributed.

[0077] Example 3

[0078] The method was carried out according to Example 2, except that the temperature of the first calcination was 700°C and the time was 8 hours.

[0079] SEM image of the cathode material in Example 3 is shown below. Figure 6 As shown, the primary particles are clearly visible and evenly distributed.

[0080] Example 4

[0081] The method was carried out according to Example 1, except that the amount of ammonium metatungstate was 0.0075g, i.e., based on the amount of lithium-rich manganese matrix material, the amount of ammonium metatungstate was 1.5wt%, the first calcination temperature was 800°C, and the time was 7h.

[0082] Example 5

[0083] The method of Example 1 was followed, except that the amount of ammonium metatungstate was 0.005 g, which is 1 wt% based on the amount of lithium-rich manganese matrix material.

[0084] Example 6

[0085] The method of Example 1 was followed, except that the amount of ammonium metatungstate was 0.0075 g, which is 1.5 wt% based on the amount of lithium-rich manganese matrix material.

[0086] Example 7

[0087] The method of Example 1 was followed, except that the temperature of the first calcination was 300°C.

[0088] Example 8

[0089] The method of Example 1 was followed, except that the temperature of the first calcination was 800°C.

[0090] Example 9

[0091] The method of Example 1 was followed, except that the first calcination time was 3 hours.

[0092] Example 10

[0093] The procedure was carried out according to the method of Example 1, except that the first calcination time was 8 hours.

[0094] Example 11

[0095] The method of Example 1 was followed, except that the heating rate of the first calcination was 1°C / min.

[0096] Example 12

[0097] The method of Example 1 was followed, except that the heating rate of the first calcination was 3°C / min.

[0098] Example 13

[0099] The procedure was carried out according to Example 1, except that ammonium metatungstate was replaced with an equal mass of tungsten oxide.

[0100] Example 14

[0101] The procedure was carried out according to Example 1, except that ammonium metatungstate was replaced with an equal mass of tungstic acid.

[0102] Example 15

[0103] The procedure was carried out according to Example 1, except that the molar ratio of NiSO4·6H2O and MnSO4·H2O in the metal salt solution was 1:4.

[0104] Example 16

[0105] The method of Example 1 was followed, except that NiSO4·6H2O, MnSO4·H2O and CoSO4·6H2O were weighed in a molar ratio of 1:3:1 and dissolved in distilled water to prepare a metal salt solution.

[0106] Example 17

[0107] The method of Example 1 was followed, except that the amount of ammonium metatungstate was 0.0005 g, which is 0.1 wt% based on the amount of lithium-rich manganese matrix material.

[0108] Example 18

[0109] The method of Example 1 was followed, except that the amount of ammonium metatungstate was 0.01 g, which is 2 wt% based on the amount of lithium-rich manganese matrix material.

[0110] Example 19

[0111] The method of Example 1 was followed, except that the temperature of the first calcination was 1000°C.

[0112] Example 20

[0113] The procedure was carried out according to the method of Example 1, except that the first calcination time was 1 hour.

[0114] Example 21

[0115] The procedure was carried out according to the method of Example 1, except that the first calcination time was 10 hours.

[0116] Example 22

[0117] The method of Example 1 was followed, except that the heating rate of the first calcination was 8°C / min.

[0118] Comparative Example 1

[0119] The lithium-rich manganese matrix material of Example 4 is used as Comparative Example 1.

[0120] The EIS diagrams of the materials prepared in Example 4 and Comparative Example 1 are shown below. Figure 7 As shown in the figure, the impedance of the cathode material prepared in Example 4 is much lower than that of the lithium-rich manganese matrix material in Comparative Example 1. This is because W doping enhances the electronic conductivity of the cathode material, reduces the resistance to electron transport in the material, and makes the crystal structure of the material more stable, which is conducive to the diffusion of lithium ions and reduces the migration resistance of lithium ions in the material.

[0121] Comparative Example 2

[0122] (1) Preparation of precursor

[0123] NiSO4·6H2O, CoSO4·7H2O and MnSO4·H2O were dissolved in distilled water in a molar ratio of 8:1:1 to prepare a 2 mol / L metal salt solution, a 2 mol / L sodium hydroxide solution and a 2 mol / L ammonia solution.

[0124] The metal salt solution and ammonia solution were pumped into the reactor at a feed rate of 0.4 mL / min, while the feed rate of the sodium hydroxide solution was adjusted to maintain the pH at 11. The temperature was set at 55℃ and the stirring speed at 600 r / min. The feeding time was 4 h, and after the feeding was completed, argon gas was continuously introduced for stirring for another 4 h. The mixture was then vacuum filtered, and the precipitate was washed until the pH of the filtrate was close to neutral and it was transparent and colorless. After drying, the precursor was obtained, which contained 2 mol of nickel, cobalt, and manganese.

[0125] (2) Preparation of cathode materials

[0126] Lithium hydroxide powder, precursor, and ammonium metatungstate solution were uniformly mixed by grinding to obtain a mixture, wherein the molar ratio of lithium hydroxide to precursor was 1.05:1, and the molar ratio of ammonium metatungstate to precursor was 1:2400. The mixture was placed in a muffle furnace and pre-calcined at 500℃ for 5 hours under an oxygen atmosphere at a heating rate of 2℃ / min, and then calcined at 750℃ for 15 hours at a heating rate of 2℃ / min to obtain the cathode material.

[0127] Comparative Example 3

[0128] The method of Example 1 was followed, except that the temperature of the first calcination was 100°C.

[0129] Test case

[0130] The positive electrode materials prepared in Examples 1-22 and Comparative Examples 1-3 were mixed with Super P and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, respectively. N-methylpyrrolidone (NMP) was added and ground into a slurry. The slurry was coated onto aluminum foil using a 125 μm doctor blade, dried, and cut into sheets to form positive electrode plates. CR2032 coin cell half-cells were assembled in an argon glove box (water < 0.01 ppm, oxygen < 0.01 ppm). The positive electrode was the aforementioned positive electrode plate, the counter electrode was a lithium sheet, the separator was Celgard 2500, and the electrolyte was a 1 mol / L LiPF6 solution (solvent: EC and DMC in a 1:1 volume ratio).

[0131] The assembled battery was subjected to charge-discharge tests at 30°C. The test procedure was as follows: charge and discharge at a rate of 0.1C within a voltage range of 2.0V-4.8V for 2 cycles, and then charge and discharge at a rate of 1C within a voltage range of 2.0V-4.6V for 100 cycles, where 1C = 250mA / g.

[0132] The batteries assembled using the cathode materials of Examples 1-22 have similar average discharge mid-pressure profiles, with Example 1 as an example. The average discharge mid-pressure profiles of the batteries assembled using the cathode materials of Example 1 and Comparative Example 1 after 100 cycles at 30°C and 1C are shown below. Figure 8As shown, Example 1 showed an average weekly voltage reduction of 3.126 mV, while Comparative Example 1 showed an average weekly voltage reduction of 4.044 mV. Example 1's voltage reduction was significantly lower than Comparative Example 1, indicating that the voltage decay problem was effectively improved.

[0133] The batteries assembled using the cathode materials of Examples 1-22 have similar discharge capacity diagrams, with Example 2 as an example. The discharge capacity diagrams of the batteries assembled using the cathode materials of Example 2 and Comparative Example 1 after 100 cycles at 30°C and 1C are shown below. Figure 9 As shown, the capacity retention rate after 100 cycles in Example 2 was 92.27%, while the capacity retention rate after 100 cycles in Comparative Example 1 was 83.57%.

[0134] The batteries assembled using the cathode materials of Examples 1-22 have similar first-cycle charge-discharge patterns, with Example 3 as an example. The first-cycle charge-discharge patterns of the batteries assembled using the cathode materials of Example 3 and Comparative Example 1 at 30°C and 0.1C are shown below. Figure 10 As shown, the first-week coulomb efficiency of Example 3 was 80.03%, while that of Comparative Example 1 was 74.21%.

[0135] Table 1 Electrochemical performance of cathode materials

[0136]

[0137]

[0138] As shown in Table 1, the cathode material prepared using this invention exhibits excellent specific capacity and cycle performance. Compared to Example 1, Examples 5, 6, 17, and 18 varied the amount of tungsten dopant. Based on the amount of lithium-rich manganese matrix material, when the amount of tungsten dopant is in the range of 0.5-1.5 wt%, the cathode material exhibits excellent specific capacity, capacity retention, and per-cycle voltage drop. Compared to Example 1, Examples 7, 8, 19, and Comparative Example 3 varied the first calcination temperature. When the temperature was too low (Comparative Example 3), the specific capacity and cycle performance of the cathode material decreased. Compared to Example 1, Examples 9, 10, 20, and 21 varied the first calcination time. With increasing time, the 0.1C first-cycle discharge specific capacity and first-cycle coulombic efficiency of the cathode material showed a trend of first increasing and then decreasing, while the average per-cycle voltage drop showed a trend of first decreasing and then increasing. Compared with Example 1, Examples 11, 12, and 22 changed the heating rate of the first calcination. When the heating rate was higher (Example 22), the specific capacity, first-cycle coulombic efficiency, and cycle stability of the cathode material all decreased.

[0139] Compared with Comparative Example 1, the capacity retention rate of the cathode material prepared by this invention after being assembled into a battery is improved. This may be because the cathode material has a WO3 and Li2WO4 coating layer on its surface. The Li2WO4 layer is located between the WO3 layer and the core. The presence of the WO3 layer can be confirmed by infrared spectroscopy, Raman spectroscopy, and thermogravimetric analysis. The core is composed of Li, transition metal elements, W, and oxygen. The elemental composition of the core can be confirmed by XRD and TEM analysis. The presence of the WO3 and Li2WO4 layers on the surface of the cathode material, especially the WO3 layer, reduces the interfacial side reactions between the cathode material and the electrolyte on the one hand, and reduces the volume change of the cathode material during charging and discharging on the other hand, thereby enhancing the structural stability of the cathode material and improving its cycle stability.

[0140] Compared to Comparative Example 2, where a nickel-cobalt-manganese hydroxide precursor was mixed with lithium hydroxide and ammonium metatungstate and then calcined in one step to obtain a ternary cathode material with a surface coating of lithium tungstate and W doping, this invention mixes a precursor (carbonate) containing nickel, manganese, and optionally cobalt with a lithium source (lithium carbonate) and then performs a second calcination to obtain a lithium-rich manganese matrix material. This lithium-rich manganese matrix material is then mixed with a tungsten-containing dopant and subjected to a first calcination to obtain the cathode material. The cathode material of this invention exhibits higher cycle stability, and Examples 1-16 also demonstrate higher discharge specific capacity and first-cycle coulombic efficiency.

[0141] 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 inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that, The preparation method includes: (1) Preparing a lithium-rich manganese-based bulk material, the chemical formula of the lithium-rich manganese-based bulk material is Li 1+x (Ni a Mn b Co c ) 1-x O₂, 0 < x < 1, wherein when c is 0, the ratio of a to b is 1:3-4, and when c is not 0, the ratio of a:b:c is 1:3-4:1-2; (2) The lithium-rich manganese matrix material and the tungsten-containing dopant are mixed and then subjected to a first calcination to obtain a cathode material, wherein the temperature of the first calcination is not lower than 300°C.

2. The preparation method according to claim 1, wherein, Based on the amount of the lithium-rich manganese matrix material, the amount of the tungsten-containing dopant is 0.5-1.5 wt%. And / or, the temperature of the first calcination is 300-800℃, and the time is 3-8h.

3. The preparation method according to claim 1 or 2, wherein, Based on the amount of the lithium-rich manganese matrix material, the amount of the tungsten-containing dopant is 0.5-1 wt%. And / or, the temperature of the first calcination is 500-800℃; And / or, the heating rate of the first calcination is 1-5℃ / min; And / or, the tungsten-containing dopant is selected from one or more of ammonium metatungstate, ammonium tungstate, tungsten oxide, and tungstic acid.

4. The preparation method according to any one of claims 1-3, wherein, The mixing is carried out in the presence of a solvent; Preferably, the mixing process includes: dissolving the tungsten-containing dopant in the solvent to form a suspension, then adding the lithium-rich manganese matrix material to the suspension, and then evaporating the solvent.

5. The preparation method according to any one of claims 1-4, wherein, The process for preparing the lithium-rich manganese matrix material includes: (1) Prepare a metal salt solution, wherein the metal salt solution comprises a salt of a transition metal element, wherein the transition metal element comprises nickel and manganese and optionally cobalt; mix the metal salt solution, a precipitant and a chelating agent, and perform a co-precipitation reaction to obtain a precursor containing the transition metal element. The molar ratio of nickel, manganese and optional cobalt in the metal salt solution is a:b:c. When c is 0, the ratio of a:b is 1:3-4. When c is not 0, the ratio of a:b:c is 1:3-4:1-2. (2) The lithium source and the precursor are mixed and subjected to a second calcination to obtain the lithium-rich manganese basic material, wherein the molar ratio of the transition metal element in the precursor to the lithium element in the lithium source is 1:1-1.

5.

6. The preparation method according to claim 5, wherein, The second calcination process includes: a first calcination step and a second calcination step; Preferably, the temperature of the first calcination step is 400-600℃, the time is 5-7h, and the heating rate is 4-6℃ / min; Preferably, the second calcination step is carried out at a temperature of 850-950℃ for 10-14 hours, with a heating rate of 4-6℃ / min.

7. The preparation method according to any one of claims 1-6, wherein, The coprecipitation reaction is carried out at a pH of 8-9, a temperature of 55-65℃, and a time of 11-13 hours.

8. A positive electrode material, characterized in that, Prepared by the method according to any one of claims 1-7.

9. A positive electrode, characterized in that, The cathode material includes the cathode material prepared by the preparation method according to any one of claims 1-7 or the cathode material according to claim 8.

10. A battery, characterized in that, The battery includes the positive electrode as described in claim 9.

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