Functional material and preparation method thereof, positive electrode material, positive plate and lithium ion battery

Abstract

The invention discloses a functional material and a preparation method thereof, a positive electrode material, a positive plate and a lithium ion battery, the chemical formula of the functional material is LiaNixMnyM1-x-yWb, 0.1 < a < 1.2, 0.6 < = x < 1, 0 < = y < = 0.4, 0 < = 1-x-y < = 0.4, 1.0 < b < 3.2, and M is at least one of Co, Al, Mg, Ti, Zr and rare earth elements; w is at least one of CO3 < 2->, O2 <->, OH <->, COO <->, F <->, PO4 < 3-> and C2O4 < 2->; when the functional material is used for preparing the positive electrode material, a lithium element and a nickel element can be subjected to a solid-phase reaction nearby, the lithium ion diffusion path is short, the diffusion resistance is small, nickel-lithium mixed arrangement is favorably inhibited, the utilization rate of the lithium element is high, the positive electrode material has relatively low pH, and the phenomena of relatively high residual lithium on the surface of the positive electrode material and nickel-lithium mixed arrangement in the prior art are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium - ion batteries, and particularly relates to a functional material and a preparation method thereof, a cathode material, a cathode sheet and a lithium - ion battery. Background Art

[0002] Lithium - ion battery layered materials (where the proportion of nickel element in the total moles of transition metals ≥ 60%) have high capacity at 4.2 - 4.55V. However, there are the following problems in the material preparation process: (1) The ionic radii of nickel ions and lithium ions are relatively close, and nickel / lithium mixing occurs in the layered structure, and lithium ions are not in the interlayer position, resulting in a lower capacity of the prepared cathode material; (2) Conventional cathode materials use a solid - phase sintering process after mixing a precursor with a lithium source. Lithium ions diffuse from the surface of the precursor into the interior of the precursor and undergo a solid - phase reaction with nickel elements, etc. In the later stage of the reaction, as the lithium element in the interior of the precursor increases and the basic structure of the material takes shape, the resistance to the diffusion of lithium elements on the outer surface into the interior increases, resulting in difficulty for surface lithium ions to diffuse into the interior lattice of the material to form a complete crystal phase structure. In order to ensure that sufficient lithium elements enter the interior of the precursor, it is necessary to moderately increase the lithium source during the mixing of the lithium source, increase the sintering temperature or extend the sintering time during sintering. This will result in a high surface lithium residue and high pH of the material, which is not conducive to the dispersibility and stability of the cathode material slurry. In addition, adopting this solution will push up the manufacturing cost of the material, and increasing the sintering temperature will also exacerbate nickel - lithium mixing.

[0003] Currently, low - temperature sintering in a rich - oxygen atmosphere (oxygen partial pressure > 0.35 atm) is usually adopted to inhibit nickel - lithium mixing; a water - washing or / and coating process is used to reduce the pH of the material. In view of the analysis of the preparation process of lithium - ion battery layered materials, adopting the current solution cannot improve the process of lithium - ion diffusion from the surface of the precursor into the interior. Therefore, lithium ions need to overcome the diffusion resistance at a higher temperature; the existing process characteristics result in a relatively high surface residual lithium content in the cathode material. Summary of the Invention

[0004] The object of the present invention is to provide a functional material and a preparation method thereof. A functional material is prepared from a transition metal compound and a lithium-containing compound. The transition metal compound may include a nickel compound and elements such as manganese and cobalt, and the molar proportion of nickel element is ≥60%. There is good dispersion between lithium element and nickel element in the functional material. During the preparation process of the functional material, the molar ratio of lithium element and transition metals such as nickel element can be adjusted, and other required doping elements can be further introduced. When using this functional material to prepare a nickel-based cathode material, the lithium element and nickel element can undergo a solid-phase reaction nearby, with a short diffusion path and small diffusion resistance for lithium ions, which is beneficial to inhibiting nickel-lithium mixing, high utilization rate of lithium element, and the cathode material has a low pH, solving the problems of high surface residual lithium amount and nickel-lithium mixing in the existing cathode material. The preparation method can be a homogeneous mixing method or a coprecipitation method.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A functional material, the chemical formula of the functional material is Li a Ni x Mn y M 1-x-y W b , where 0.1 < a < 1.2, 0.6 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.4, 1.0 < b < 3.2, M is at least one of Co, Al, Mg, Ti, Zr, rare earth elements; W is at least one of CO3 2- , O 2- , OH-, COO-, F-, PO4 3- , C2O4 2- in.

[0007] Preferably, the functional material is treated in an air atmosphere at a temperature of 350 - 500 °C for 3 - 8 h and cooled to room temperature. The XRD spectrum of the copper target Kα1 at a 2θ diffraction angle has the following characteristic peaks: 18 - 20°, 42 - 44°, 44 - 46°, and the ratio I1 / I2 of the diffraction peak intensity I1 at 18 - 20° to the diffraction peak intensity I2 at 44 - 46° is > 0.

[0008] The present invention also provides a preparation method of the above functional material.

[0009] One of the preparation methods of the above functional material:

[0010] Step S1, take metal salts according to the molar ratio of each element in the chemical formula Li a Ni x Mn y M 1-x-y W b of the functional material, and prepare a uniform slurry using a dispersant;

[0011] Step S2: Dry the obtained uniform slurry while stirring, and then further dry it at 100 - 200°C in an air atmosphere to obtain the functional material.

[0012] The metal salt can be acetate, citrate, carbonate, dihydrogen phosphate, phosphate, oxalate, hydroxide, etc. Preferably, the metal salt can be acetate, oxalate or carbonate.

[0013] The dispersant can be deionized water, acetic acid, ethanol, isopropanol or a mixture thereof. Preferably, the dispersant is deionized water or a mixture of deionized water and acetic acid.

[0014] The second method for preparing the above functional material:

[0015] Step S1: Prepare a metal salt solution A, a precipitating agent solution B, and an auxiliary agent solution according to the molar ratios of the respective elements in the chemical formula of the functional material Li a Ni x Mn y M 1-x-y W b ;

[0016] Step S2: Under a protective atmosphere, add the auxiliary agent solution to deionized water and stir to mix as the reaction bottom liquid, and simultaneously drip the metal salt solution A and the precipitating agent solution B to obtain a precipitation product;

[0017] Step S3: Age, filter, wash, and dry the precipitation product to obtain the functional material.

[0018] The metal salt can be a soluble salt, specifically one or more of sulfate, acetate, citrate, chloride, nitrate, etc.

[0019] Preferably, the concentration of the metal salt solution A is 0.5 - 4 mol / L, the concentration of the precipitating agent solution B is 0.5 - 3 mol / L, the feeding rate of the metal salt solution A and the precipitating agent solution C is 0.1 - 2 ml / min, and the pH of the reaction system is 8 - 13.

[0020] The present invention also provides a positive electrode material, which is prepared by sintering and crushing and screening the above functional material in a sintering device in an oxygen-containing atmosphere (oxygen partial pressure > 0.35 atm).

[0021] Preferably, the chemical general formula of the positive electrode material is Li 1.0～1.2 Ni x Mn y M 1-x-y O2V z, where 0.6 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.4, 0 ≤ z ≤ 0.2, M is at least one of Co, Al, Mg, Ti, Zr, and rare earth elements, and V can be F - , PO4 3- and at least one of the following

[0022] Preferably, there is no diffraction peak between 20° and 25° in the XRD pattern of the positive electrode material at the Kα1 of the copper target at 2θ diffraction angle, and the intensity A1 of the diffraction peak between 40° and 50° and the intensity A2 of the diffraction peak between 15° and 20° satisfy the relationship: 0.2 < A1 / A2 < 1

[0023] Preferably, the pH of the positive electrode material is 10.5 - 12.5, and the free lithium content < 0.3%

[0024] The present invention also provides a positive electrode sheet, which includes a current collector and a positive electrode slurry coated on the current collector. The positive electrode slurry includes the above positive electrode material, and the mass fraction of nickel element after drying the positive electrode slurry coated on the positive electrode sheet is 32 - 58%

[0025] The present invention also provides a lithium-ion battery. The discharge capacity of the lithium-ion battery is 160 mAh / g - 220 mAh / g under the conditions of a maximum cut-off voltage of 4.2 - 4.55 V, a minimum cut-off voltage of 2.75 V, and a discharge rate of 0.1C

[0026] Compared with the prior art, the present invention has at least the following beneficial effects

[0027] (1) By introducing a lithium source into the functional material, the present invention improves the dispersion of lithium element and metal elements such as nickel element

[0028] (2) Different from the preparation process of conventional lithium-ion battery positive electrode materials, the conventional lithium-ion battery positive electrode materials directly mix the precursor with the lithium source and then carry out solid-phase sintering. However, the functional material of the present invention can supplement lithium in a small amount or directly carry out solid-phase sintering reaction to prepare the lithium-ion battery positive electrode material, simplifying the batching / mixing process

[0029] (3) Different from the sintering process of conventional lithium-ion battery positive electrode materials, when the conventional lithium-ion battery positive electrode materials are sintered, lithium ions diffuse and migrate from the surface of the precursor to the inside of the precursor, and the solid-phase reaction starts. However, in the present invention, the functional material is used to obtain the lithium-ion battery positive electrode material through solid-phase sintering reaction. The lithium element reacts with metals such as nickel element nearby to form a layered structure. The diffusion distance of lithium ions is short, the diffusion resistance is small, the required sintering temperature is low, the utilization rate of lithium ions is high, and the degree of nickel-lithium mixing is small. Therefore, the lithium-ion battery positive electrode material prepared thus has a low pH, low free lithium, and high specific capacity per gram of the material Description of the Drawings

[0030] Figure 1 SEM of the functional material prepared in an embodiment of the present invention;

[0031] Figure 2 XRD pattern of the functional material prepared in an embodiment of the present invention after being treated in an air atmosphere at 400 °C for 4 h and cooled to room temperature;

[0032] Figure 3 SEM of the cathode material prepared in an embodiment of the present invention;

[0033] Figure 4 XRD pattern of the cathode material prepared in an embodiment of the present invention;

[0034] Figure 5 Charge-discharge curve of the cathode material prepared in an embodiment of the present invention;

[0035] Figure 6 Charge-discharge curve of the cathode material prepared in a comparative example of the present invention; Detailed implementation manners

[0036] To make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0037] In the first aspect according to the present invention, the present invention provides a functional material, and the chemical formula of the functional material is Li a Ni x Mn y M 1-x-y W b , where 0.1 < a < 1.2, 0.6 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.4, 1.0 < b < 3.2, M is at least one of Co, Al, Mg, Ti, Zr, rare earth elements; W is at least one of CO3 2- , O 2- , OH-, COO-, F - , PO4 3- , C2O4 2- .

[0038] By introducing a lithium source into the functional material, the present invention improves the dispersion of metals such as lithium and nickel elements. Different from the preparation process of conventional lithium-ion battery cathode materials, the conventional lithium-ion battery cathode materials directly mix the precursor with the lithium source and then carry out solid-phase sintering, while the functional material of the present invention can supplement lithium in small amounts or directly carry out solid-phase sintering reaction to prepare lithium-ion battery cathode materials, simplifying the batching / mixing process; different from the sintering process of conventional lithium-ion battery cathode materials, during the sintering of conventional lithium-ion battery cathode materials, lithium ions diffuse and migrate from the surface of the precursor to the inside of the precursor, and the solid-phase reaction begins. However, the present invention uses the solid-phase sintering reaction of the functional material to obtain the lithium-ion battery cathode material. The lithium element reacts with metals such as nickel element nearby to form a layered structure. The diffusion distance of lithium ions is short, the diffusion resistance is small, the required sintering temperature is low, the utilization rate of lithium ions is high, and the degree of nickel-lithium mixing is small. The cathode material prepared thus has a low pH and a high specific capacity per gram of the material.

[0039] In one embodiment according to the present invention, the functional material is treated in an air atmosphere at a temperature of 350-500 °C for 3-8 h and cooled to room temperature. The XRD spectrum of the copper target Kα1 at a 2θ diffraction angle has the following characteristic peaks: 18-20°, 42-44°, 44-46°. The ratio I1 / I2 of the diffraction peak intensity I1 at 18-20° to the diffraction peak intensity I2 at 44-46° is >0. The treatment temperature can specifically be 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, 410 °C, 420 °C, 430 °C, 440 °C, 450 °C, 460 °C, 470 °C, 480 °C, 490 °C, 500 °C, and preferably 400 °C. The treatment time can specifically be 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h, 6.5 h, 7 h, 7.5 h, 8 h, and preferably 4 h.

[0040] In the second aspect according to the present invention, the present invention also provides a preparation method of the above-mentioned functional material.

[0041] One of the preparation methods of the above-mentioned functional material:

[0042] Step S1: Take metal salts according to the molar ratios of the elements in the chemical formula of the functional material Li a Ni x Mn y M 1-x-y W b and prepare a uniform slurry using a dispersant;

[0043] Step S2: Dry the obtained uniform slurry while stirring, and then further dry it in an air atmosphere at 100-200 °C to obtain the functional material.

[0044] In one embodiment according to the present invention, the metal salt may be acetate, citrate, carbonate, dihydrogen phosphate, phosphate, oxalate, hydroxide, etc. Specifically, the lithium salt may be lithium acetate, lithium citrate, lithium oxalate, lithium carbonate, lithium hydroxide, lithium phosphate, lithium fluoride, lithium methylcellulose, etc. The nickel salt may be nickel acetate, nickel citrate, nickel carbonate, nickel oxide, nickel oxalate, etc.

[0045] In one embodiment according to the present invention, the dispersant used may be deionized water, acetic acid, ethanol, isopropanol or a mixture thereof.

[0046] The second method for preparing the above functional material:

[0047] Comprises the following steps:

[0048] Step S1: Prepare a metal salt solution A, a precipitant solution B, and an auxiliary solution according to the molar ratios of the respective elements in the functional material chemical formula Li a Ni x Mn y M 1-x-y W b ;

[0049] Step S2: Under a protective atmosphere, add the auxiliary solution to deionized water and stir to mix as a reaction bottom liquid, and simultaneously dropwise add the metal salt solution A and the precipitant solution B to obtain a precipitate product;

[0050] Step S3: Age, filter, wash, and dry the precipitate product to obtain the functional material.

[0051] In one embodiment according to the present invention, the metal salt may be a soluble salt, specifically one or more of sulfate, acetate, citrate, chloride, nitrate, etc. Preferably, the lithium salt may be lithium sulfate, lithium chloride, lithium nitrate, lithium acetate, lithium carbonate, lithium citrate, lithium oxalate. Metal salts such as nickel, cobalt, manganese, aluminum, magnesium, zirconium, etc. may be nickel sulfate hexahydrate, cobalt sulfate heptahydrate, manganese sulfate monohydrate, nickel chloride, manganese chloride, cobalt chloride, magnesium chloride, aluminum chloride, cobalt nitrate, nickel nitrate, manganese nitrate, aluminum nitrate, cobalt acetate, nickel acetate, manganese acetate, aluminum acetate, magnesium acetate, etc.

[0052] In one embodiment according to the present invention, the concentration of the metal salt solution A is 0.5 - 4 mol / L, preferably 2 mol / L, specifically it may be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L; the concentration of the precipitant solution B is 0.5 - 3 mol / L, preferably 2 mol / L, specifically it may be 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L; the feeding rate of the metal salt solution A and the precipitant solution B is 0.1 - 2 ml / min, preferably 0.2 ml / min, specifically it may be 0.1 ml / min, 0.2 ml / min, 0.3 ml / min, 0.5 ml / min, 1.0 ml / min, 1.3 ml / min, 1.6 ml / min, 1.8 ml / min, 2.0 ml / min; the pH of the reaction system is 8 - 13, preferably 10 - 11, specifically it may be 8, 9, 10, 11, 12, 13.

[0053] In the third aspect according to the present invention, the present invention further provides a positive electrode material, which includes a current collector and a positive electrode paste coated on the current collector. The positive electrode paste includes the above positive electrode material, and the mass fraction of nickel element after drying the positive electrode paste coated on the positive electrode sheet is 32 - 58%.

[0054] In one embodiment according to the present invention, the chemical general formula of the positive electrode material is Li 1.0～1.2 Ni x Mn y M 1-x- y O2V z , where 0.6 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.4, 0 ≤ z ≤ 0.2, M is at least one of Co, Al, Mg, Ti, Zr, rare earth elements, and W may be F - , PO4 3- or at least one of them.

[0055] In one embodiment according to the present invention, there is no diffraction peak between 20 - 25° in the XRD pattern of the copper target Kα1 at the 2θ diffraction angle of the positive electrode material, and the intensity A1 of the diffraction peak between 40 - 50° and the intensity A2 of the diffraction peak between 15 - 20° satisfy the relationship: 0.2 < A1 / A2 < 1.

[0056] The positive electrode material of the present invention has no diffraction peak between 20° and 25° in the XRD pattern of Cu target Kα1 at 2θ diffraction angle, indicating that the positive electrode material of the present invention has no lithium-rich phase, further indicating that there is no nickel-lithium mixing phenomenon in the positive electrode material, and a positive electrode material with a complete crystal phase structure and a layered structure is obtained.

[0057] In an embodiment according to the present invention, the pH of the positive electrode material is 10.5 - 12.5, and the free lithium content is <0.3%. Thus, it can be seen that the residual lithium content on the surface of the positive electrode material of the present invention is less, making the material structure better and more stable in the air.

[0058] In the fourth aspect according to the present invention, the present invention also provides a positive electrode sheet, which includes a current collector and a positive electrode material coated on the current collector. The positive electrode material is the above-mentioned positive electrode material, and the mass fraction of nickel element in the positive electrode sheet to the dried slurry material coated on the current collector is 32 - 58%. Specifically, it can be 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%.

[0059] In the fifth aspect according to the present invention, the present invention also provides a lithium-ion battery.

[0060] The preparation method of the lithium-ion battery of the present invention is well-known to those skilled in the art. Generally speaking, the preparation method of this battery includes placing the battery core into the battery case, adding electrolyte, and then sealing to obtain the battery. Among them, the sealing method, the composition and dosage of the electrolyte are well-known to those skilled in the art.

[0061] The discharge capacity of the lithium-ion battery under the conditions of the highest cut-off voltage of 4.2 - 4.55V, the lowest cut-off voltage of 2.75V, and the discharge rate of 0.1C is 160 mAh / g - 220 mAh / g. Specifically, it can be 160 mAh / g, 170 mAh / g, 180 mAh / g, 190 mAh / g, 200 mAh / g, 210 mAh / g, 220 mAh / g.

[0062] The present invention will be further described below through specific examples.

[0063] Example 1

[0064] This example provides a preparation method of a functional material, and the specific steps are as follows:

[0065] Weigh lithium acetate, nickel acetate, manganese acetate and cobalt acetate according to the molar ratio of lithium:nickel:manganese:cobalt of 1:0.85:0.1:0.05, add appropriate amount of deionized water to obtain a solution, add 1% lithium methyl cellulose calculated by the total weight of the solution, stir and dry, and further dry in air at 200 °C to obtain a functional material.

[0066] This example also provides a method for preparing a cathode material, and the specific steps are as follows:

[0067] Take the above functional material, place it in an atmosphere furnace, and introduce an oxygen-containing gas. Among them, the oxygen partial pressure ≥ 0.95 atm, the heating rate is 3 - 5 °C / min, and sinter at 720 °C for 8 h. After the sample is cooled to room temperature, crush it and pass through a 350-mesh sieve to obtain the black cathode material LiNi 0.85 Mn 0.1 Co 0.05 O2.

[0068] Example 2

[0069] The difference between this example and Example 1 is that the preparation method of the functional material in this example is different, including the following steps:

[0070] Step S1: Weigh lithium acetate, nickel sulfate hexahydrate, manganese sulfate monohydrate and cobalt sulfate heptahydrate according to the molar ratio of lithium:nickel:manganese:cobalt elements of 1:0.85:0.1:0.05, and configure a total of 1 L of a solution with a total molar concentration of nickel, cobalt and manganese of 2 mol / L, denoted as solution A; weigh 129 g of lithium hydroxide monohydrate, add deionized water to obtain a solution, dilute and make up the volume to 1 L to prepare a 2 mol / L lithium hydroxide solution, denoted as solution B; weigh 0.2 g of polyacrylamide as an auxiliary agent;

[0071] Step S2: Mix and stir the auxiliary agent with appropriate amount of deionized water in a reaction kettle; the inside of the reaction kettle is a carbon dioxide atmosphere, and the carbon dioxide gas flow rate is 0.5 - 5 L / min; then simultaneously drop solution A and solution B into the reaction kettle, and a co-precipitation reaction occurs to obtain a precipitation product. Among them, the temperature of the reaction kettle is 70 °C, the rotation speed of the stirrer is 1000 rpm, the feeding speed of solution A and solution C is 0.1 - 2 ml / min, and an appropriate amount of concentrated ammonia water is added during the reaction to control the pH of the reaction system to be 8 - 12;

[0072] Step S3: Age the precipitation product at 70 °C for 12 h, filter by suction, separate the filter cake and the filtrate, wash the filter cake 4 times with 70 °C deionized water, and dry it in an oven at 120 °C to constant weight to obtain a functional material.

[0073] The scanning electron microscope (SEM) of the obtained functional material is shown in Figure 1 After being treated in an air atmosphere at 400 °C for 4 h and cooled to room temperature, the XRD pattern is shown in Figure 2 .

[0074] This embodiment also provides a method for preparing a cathode material, and the specific steps are as follows:

[0075] Take the above functional material, place it in an atmosphere furnace, and introduce an oxygen-containing gas, wherein the oxygen partial pressure ≥ 0.95 atm, the heating rate is 3 - 5 °C / min, and sinter at 720 °C for 8 h. After the sample is cooled to room temperature, it is pulverized and passed through a 350-mesh sieve to obtain the black cathode material LiNi 0.85 Mn 0.1 Co 0.05 O2.

[0076] The scanning electron microscope (SEM) and XRD patterns of the obtained cathode material are shown in Figure 3 and Figure 4 . The charge-discharge curves of the battery assembled with the cathode material under the conditions of 3.0 V - 4.35 V and 0.1C are as shown in Figure 5 .

[0077] Example 3

[0078] The difference between this embodiment and Example 2 is that the sintering temperature of the cathode material is 750 °C, and the rest is the same as that of Example 2, which will not be repeated here.

[0079] Comparative Example 1

[0080] Preparation of the precursor:

[0081] Weigh nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate monohydrate according to the molar ratio of nickel, cobalt, and manganese elements of 85:5:10, and configure them into a metal solution with a total metal molar concentration of 2 mol / L; weigh 80 g of sodium hydroxide, add deionized water to obtain a solution, and dilute and fix the volume to 1 L to prepare a 2 mol / L sodium hydroxide solution; add the metal solution and the sodium hydroxide solution to the reaction kettle together, introduce nitrogen protective gas into the reaction kettle, and perform a co-precipitation reaction to obtain a precipitate product. Among them, the temperature of the reaction kettle is 70 °C, the rotation speed of the stirrer is 1000 rpm, the feeding speed of the metal solution and the sodium hydroxide solution is 0.1 - 2 ml / min, and the pH of the reaction system is controlled to be 9 - 12. The obtained precipitate product is aged at 70 °C for 12 h, filtered by suction, the filter cake and the filtrate are separated, and the filter cake is washed 4 times with deionized water at 70 °C and dried in an oven at 120 °C to constant weight to obtain Ni 0.85 Co 0.01 Mn 0.15 (OH)2 precursor.

[0082] Preparation of the cathode material:

[0083] Take 300 g of the aforementioned precursor and 137.6 g of lithium hydroxide monohydrate, and mix them using a small high-speed mixer. Place the mixed powder in an atmosphere furnace, and introduce a gas containing oxygen, where the oxygen partial pressure ≥ 0.95 atm, the heating rate is 3 - 5 °C / min, and sinter at 720 °C for 8 h. After the sample cools to room temperature, crush it and pass it through a 350-mesh sieve to obtain the black cathode material LiNi 0.85 Mn 0.1 Co 0.05 O2..

[0084] Comparative Example 2

[0085] The difference from Comparative Example 1 is that the sintering temperature of the cathode material is 780 °C, and the rest are the same, which will not be elaborated here; the charge-discharge curves of the obtained cathode material under the conditions of 3.0 V - 4.35 V and 0.1C are as Figure 6 shown.

[0086] The instruments and equipment involved in the present invention are shown in the following table

[0087]

[0088] Among them, the main instrument test methods of the present invention are as follows:

[0089] (1) For the component analysis, borrow the method in the national standard of lithium cobaltate (GB / T 20252 - 2014), and the content of all metal elements (including cobalt element) is determined by inductively coupled plasma emission spectrometry.

[0090] (2) XRD test: Cu target, scanning rate 4° / min, 2θ range is 10 - 80°.

[0091] (3) pH test: After preheating the instrument for 15 min, calibrate it using a standard buffer solution; weigh 4 g of the sample in a clean container, add 36 g of deionized water, place it on a magnetic stirrer and stir for 10 min; filter it using a water-based filter head (0.22 μm). The filtrate is the test solution; clean the pH meter electrode with deionized water again, and dry it with dust-free paper, then immerse the electrode in the test filtrate; wait for the reading to be stable and record the reading and the current temperature; after the test, clean the electrode head until the reading is neutral, screw on the protective cover and rubber stopper, and turn off the machine.

[0092] (4) Free lithium test: Refer to "GB / T 41704 - 2022 Test Methods for Cathode Materials of Lithium-Ion Batteries - Determination of Magnetic Foreign Matter Content and Residual Alkali Content".

[0093] Among them, the main raw materials / auxiliary materials involved in the present invention are shown in the following table:

[0094] Name Purity Supplier Manganese Sulfate Monohydrate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Nickel Acetate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Cobalt Acetate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Lithium Acetate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Nickel Sulfate Hexahydrate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Cobalt Sulfate Heptahydrate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Sodium Hydroxide Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Lithium Carbonate Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd. Lithium Hydroxide Analytical Reagent Grade Sinopharm Chemical Reagent Co., Ltd.

[0095] The cathode materials prepared in Examples 1-2 and Comparative Example 1 were used in lithium-ion batteries, and performance tests were carried out. The test results are shown in Table 1 as follows:

[0096] Table 1

[0097]

[0098] It can be seen from the test results in Table 1 that the functional material prepared by the present invention can significantly reduce the sintering temperature when preparing the cathode material. The pH of the obtained cathode material is <12, the free lithium content on the material surface is <0.3%, and the battery capacity can also be maintained at 210 mAh / g or more.

[0099] Furthermore, it can be seen from the test results of Example 1 and Comparative Example 1 that when the functional material prepared by the present invention and the precursor prepared in Comparative Example 1 are sintered at the same temperature, there are significant differences in the pH, free lithium content and specific capacity of the obtained cathode materials. The reason is that during the sintering of the cathode material in Comparative Example 1, lithium ions diffuse and migrate from the surface of the precursor to the inside of the precursor, and the solid-phase reaction begins. However, the functional material of the present invention contains lithium and nickel elements. Through the solid-phase sintering reaction to obtain the cathode material, lithium elements react with metals such as nickel elements nearby to form a layered structure. The diffusion distance of lithium ions is short, the diffusion resistance is small, the required sintering temperature is low, the utilization rate of lithium ions is high, and the degree of nickel-lithium mixing is small. Therefore, the obtained cathode material has a low pH, low free lithium, and a high specific capacity.

[0100] Furthermore, it can be seen from the test results of Example 1 and Comparative Examples 1-2 that when Comparative Example 1 and Example 1 have the same sintering temperature, there are significant differences in their pH, free lithium content and capacity performance compared with Example 1. This is because the sintering temperature of 720°C used in Example 1 is too low for Comparative Example 1. In Comparative Example 2, the sintering temperature was increased to 780°C. Between Comparative Examples 1-2, appropriately increasing the sintering temperature can improve the ability of lithium ions to diffuse and migrate from the surface of the precursor to the inside, reduce the pH and free lithium content of the material, and improve the capacity performance of the cathode material; comparing Example 1 and Comparative Example 2, the pH of Comparative Example 2 increases relatively, the free lithium content increases relatively, and the specific capacity also decays relatively. The reason is that in order to allow sufficient lithium ions to enter the precursor material, increasing the sintering temperature will exacerbate nickel-lithium mixing, and the nickel-lithium mixing phenomenon leads to a high surface lithium residue and high pH of the material, which in turn results in a low capacity of the lithium-ion battery.

[0101] In summary, for the functional material and its preparation method provided by the present invention, a precursor material is prepared from a transition metal compound and a lithium-containing compound. Among them, the transition metal compound may include nickel compounds, elements containing manganese, cobalt, etc., and the molar proportion of nickel element is ≥60%. There is good dispersion between lithium element and nickel element in this precursor; during the preparation process of the precursor, the molar ratio of lithium element and transition metals such as nickel element can be adjusted, and other required doping elements can be further introduced; when preparing the nickel-based cathode material with this precursor, the lithium element and the nickel element can undergo a solid-phase reaction in the vicinity, the diffusion path of lithium ions is short, the diffusion resistance is small, which is beneficial to inhibiting the mixing of nickel and lithium, the utilization rate of lithium element is high, the cathode material has a lower pH, and the problems of high surface residual lithium amount and nickel-lithium mixing phenomenon in the existing cathode materials are solved.

[0102] According to the revelation and teaching of the above specification, those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention all belong to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A functional material, characterized in that, The chemical formula of the functional material is Li a Ni x Mn y M 1-x-y W b , where 0.1 < a < 1.2, 0.6 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.4, 1.0 < b < 3.2, and M is at least one of Co, Al, Mg, Ti, Zr, and rare earth elements; W is at least one of CO3 2- , O 2- , OH - , COO - , F - , PO4 3- , C2O4 2- and at least one of the following.

2. The functional material according to claim 1, wherein The functional material is treated in an air atmosphere at a temperature of 350 - 500 °C for 3 - 8 h and then cooled to room temperature. The XRD pattern of the copper target Kα1 at a 2θ diffraction angle has the following characteristic peaks: 18 - 20°, 42 - 44°, 44 - 46°. The ratio I1 / I2 of the diffraction peak intensity I1 at 18 - 20° to the diffraction peak intensity I2 at 44 - 46° is greater than 0.

3. A method for preparing the functional material according to any one of claims 1-2, characterized in that, It includes the following steps: Step S1: Take metal salts according to the molar ratios of the respective elements in the functional material chemical formula Li a Ni x Mn y M 1-x-y W b and prepare a uniform slurry using a dispersant; Step S2: The obtained uniform slurry is dried under stirring and then further dried in an air atmosphere at 100 - 200 °C to obtain the functional material.

4. A preparation method of the functional material according to any one of claims 1-2, characterized in that, It includes the following steps: Step S1: Prepare metal salt solution A, precipitant solution B, and additive solution according to the molar ratios of the respective elements in the functional material chemical formula Li a Ni x Mn y M 1-x-y W b and prepare the additive solution; Step S2: Under a protective atmosphere, an auxiliary agent solution is added to deionized water and stirred and mixed as a reaction bottom liquid, and a metal salt solution A and a precipitant solution B are simultaneously dropped to obtain a precipitate product. Step S3: The precipitate product is aged, filtered, washed, and dried to obtain the functional material.

5. The preparation method of the functional material according to claim 4, characterized in that, The concentration of the metal salt solution A is 0.5 - 4 mol / L, the concentration of the precipitant solution B is 0.5 - 3 mol / L, the feeding rate of the metal salt solution A and the precipitant solution B is 0.1 - 2 mL / min, and the pH of the reaction system is 8 - 13.

6. A cathode material, characterized in that, It is prepared by sintering, crushing, and screening the functional material described in any one of claims 1 - 2, wherein the oxygen partial pressure in the sintering equipment is > 0.35 atm.

7. The cathode material according to claim 6, characterized in that, The chemical general formula of the positive electrode material is Li 1.0～1.2 Ni x Mn y M 1-x-y O2V z , where 0.6 ≤ x < 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.4, 0 ≤ z ≤ 0.2, M is at least one of Co, Al, Mg, Ti, Zr, and rare earth elements, and V is at least one of F - , PO4 3- .

8. The cathode material according to claim 6, characterized in that, In the XRD pattern of the copper target Kα1 at a 2θ diffraction angle of the positive electrode material, there is no diffraction peak between 20 - 25°, and the intensity A1 of the diffraction peak between 40 - 50° and the intensity A2 of the diffraction peak between 15 - 20° satisfy the relationship: 0.2 < A1 / A2 < 1.

9. The cathode material according to claim 6, characterized in that, The pH of the positive electrode material is 10.5 - 12.5, and the free lithium content is < 0.3%.

10. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode slurry coated on the current collector. The positive electrode slurry includes the positive electrode material described in any one of claims 6 - 9. After the positive electrode slurry coated on the positive electrode sheet is dried, the mass fraction of nickel element is 32 - 58%.

11. A lithium-ion battery, characterized in that, The discharge capacity of the lithium - ion battery under the conditions of a working voltage of 4.2 - 4.55 V and a discharge rate of 0.1C is 160 mAh / g - 220 mAh / g.

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