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

Abstract

The invention discloses a positive electrode material and a preparation method thereof, a positive plate and a lithium ion battery, the positive electrode material is Li (1.0-1.2) CoxNiyM (1-x-y) O2, x is more than or equal to 0.6 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 0.4, 1-x-y is more than or equal to 0 and less than or equal to 0.2, and M is at least one of Mn, Al, Mg, Ti, Zr and rare earth elements; compared with a pure lithium cobalt oxide positive electrode material, the positive electrode material provided by the invention has relatively high capacity and excellent cycle performance under the highest cut-off voltage of 4.2-4.55 V, and the raw material cost is lower.

Description

Technical Field

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

[0002] Lithium cobaltate materials have obvious advantages in the field of 3C consumer electronics products due to their high tap density, high platform voltage, etc. However, in the voltage range of the highest cut-off voltage of 4.2 - 4.55V, the capacity performance of lithium cobaltate limits its application and promotion. To make up for this deficiency of lithium cobaltate, the industry often uses a mixture of lithium cobaltate and ternary materials to make up for the capacity performance of lithium cobaltate in this voltage range. In the voltage range of the highest cut-off voltage of 4.2 - 4.55V, the voltage platforms of lithium cobaltate and ternary materials are different, indicating that the electrochemical reaction activities and the surface electric potentials of the materials of lithium cobaltate and ternary materials are different. Therefore, in the system where lithium cobaltate and ternary materials are used in combination, there are internal electrochemical polarizations caused by inconsistent electrochemical reaction activities between lithium cobaltate and ternary materials, and side reactions caused by potential imbalance between lithium cobaltate and ternary materials, that is, the cycle and storage performances of the lithium cobaltate and ternary mixed material system are worse than those of single materials.

[0003] Therefore, there is an urgent need for a new technical solution to solve the above problems. Summary of the Invention

[0004] One of the purposes of the present invention is to provide a cobalt-based lithium-ion battery cathode material. Compared with pure lithium cobaltate, other metal elements such as nickel, manganese, titanium, and rare earth elements are introduced. The introduced metal elements do not destroy the crystal phase structure of lithium cobaltate, but the chemical environment around cobalt elements changes, improving the structural stability of the material, and having higher capacity performance and better cycle performance at the same working cut-off voltage (the highest cut-off voltage of 4.2 - 4.55V).

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A cobalt-based lithium-ion battery cathode material: Li 1.0～1.2 Co x Ni y M 1-x-y O2, where 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.2, and M is at least one of Mn, Al, Mg, Ti, Zr, and rare earth elements.

[0007] In the XRD pattern of the positive electrode material with Cu target Kα1 at a 2θ diffraction angle, there is no diffraction peak between 20° and 25°, and there are diffraction peaks between 15° and 20°, 35° and 40°, and 43° and 47°. The ratio of the diffraction peak intensity I1 at 15° - 20° to the diffraction peak intensity I2 at 43° - 47° is I1 / I2, and 1 < I1 / I2 < 100.

[0008] Preferably, the pH of the positive electrode material is 10 - 12.

[0009] Preferably, the D50 of the positive electrode material is 3 - 20 μm.

[0010] The second object of the present invention is to provide a preparation method of a cobalt-based lithium battery positive electrode material.

[0011] According to the molar ratio of each element in the positive electrode material chemical formula Li 1.0～1.2 Co x Ni y M 1-x-y O2, the lithium source, cobalt source, and doping element are weighed respectively. After being mixed evenly by solid-phase or liquid-phase methods, the dried powder is sintered, crushed, and sieved in a sintering device with an oxygen-containing atmosphere to obtain the positive electrode material; or

[0012] The positive electrode material precursor is prepared from the cobalt source and the doping element by the co-precipitation method. After the obtained precursor is mixed evenly with the lithium source, it is sintered at a high temperature, crushed, and sieved in a sintering device with an oxygen-containing atmosphere to obtain the positive electrode material; or

[0013] The functional material is prepared from the lithium source, cobalt source, and doping element by the co-precipitation method. The obtained functional material is sintered, crushed, and sieved after supplementing the lithium source or directly in a sintering device with an oxygen-containing atmosphere to obtain the positive electrode material.

[0014] Among them, the oxygen partial pressure in the oxygen-containing atmosphere is ≥ 0.21 atm, and the sintering temperature is 850 - 1000 °C.

[0015] The third object of the present invention is that the positive electrode material contains a functional material, and the chemical formula of the functional material is Li a Co x Ni 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 ≤ 0.2, 0.5 < b < 3.0, M is at least one of Mn, Al, Mg, Ti, Zr, and rare earth elements, and W is CO3 2- 、OH - 、F-, PO4 3- 、CH3COO-, C2O4 2- At least one of them.

[0016] Preferably, the functional material is treated in an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) at a temperature of 300 - 500 °C for 3 - 8 h and then cooled to room temperature. Its XRD has the following characteristics: diffraction peaks are present at 2theta of 16 - 20°, 34 - 38°, and 42 - 48°. The ratio A1 / A2 of the diffraction peak intensity A1 at 16 - 20° to the diffraction peak intensity A2 at 42 - 48° satisfies the relation: 0.5 < A1 / A2 < 100.

[0017] Preferably, the D50 median particle size of the functional material is 1.5 - 20 μm.

[0018] A fourth object of the present invention is to provide a positive electrode sheet, comprising a current collector and a positive electrode paste coated on the current collector. The positive electrode paste is the above-mentioned positive electrode material. After drying the positive electrode paste coated on the positive electrode sheet, the mass fraction of cobalt element is 30 - 58%.

[0019] A fifth object of the present invention is to prepare a lithium-ion battery, comprising the above-mentioned positive electrode sheet.

[0020] Preferably, the highest cut-off voltage of the lithium-ion battery is 4.55 - 4.2 V, and the lowest cut-off voltage is 2.75 V.

[0021] Preferably, the 0.1C discharge capacity of the lithium-ion battery is 150 - 220 mAh / g, the discharge median voltage ≥ 3.7 V. The proportion of the discharge capacity from the highest cut-off voltage of 4.55 - 4.2 V to 4.0 V in the total discharge capacity is 25 - 45%; the proportion of the discharge capacity from the highest cut-off voltage of 4.55 - 4.2 V to 3.8 V in the total discharge capacity is 70 - 98%.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects:

[0023] (1) Compared with pure lithium cobaltate, other elements are introduced into the lithium cobaltate material in the present invention to form a solid solution phase material (cobalt-based lithium-ion battery positive electrode material). When the highest cut-off voltage is 4.55 - 4.2 V, the cobalt-based lithium-ion battery positive electrode material has a higher capacity than the lithium cobaltate material.

[0024] (2) Compared with pure lithium cobaltate, when the highest cut-off voltage is 4.55 - 4.2 V, the cobalt-based lithium-ion battery positive electrode material in the present invention has higher structural stability during the process of lithium deintercalation and intercalation, and the material has more excellent cycle performance.

[0025] (3) The present invention provides a cobalt-based lithium-ion battery cathode material prepared from a functional material. Since there is lithium element inside the functional material, during the sintering process, the fluxing effect of the lithium element inside the functional material is conducive to the introduced element and the cobalt element forming a solid solution phase, improving the structural stability of the cathode material and enhancing the cycling performance of the cathode material.

[0026] (4) The element introduced in the present invention is cheaper than the cobalt element, which can reduce the raw material cost of the cobalt-based lithium-ion battery cathode material to a certain extent. Description of the Drawings

[0027] Figure 1 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;

[0028] Figure 2 XRD pattern of the cobalt-based lithium-ion battery cathode material prepared in an embodiment of the present invention;

[0029] Figure 3 XRD pattern of the lithium cobaltate cathode material prepared in a comparative example of the present invention;

[0030] Figure 4 Charge-discharge curve of an embodiment and a comparative example of the present invention;

[0031] Figure 5 Cycling curve of an embodiment of the present invention;

[0032] Figure 6 Cycling curve of a comparative example of the present invention; Detailed Description of the Invention

[0033] To make the technical solutions and advantages of the present invention clearer, the following will clearly and completely describe the technical solutions of the present invention in combination with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0034] In the first aspect according to the present invention, the present invention provides a cobalt-based lithium-ion battery cathode material, and the chemical formula of the cathode material is Li 1.0～1.2 Co x Ni y M 1-x-y O2, where 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.2, and M is at least one of Mn, Al, Mg, Ti, Zr, and rare earth elements.

[0035] In the cobalt-based lithium-ion battery cathode material, other metal elements such as nickel, manganese, aluminum, zirconium, titanium, and rare earth elements are introduced. The introduced metal elements do not destroy the crystal phase structure of lithium cobaltate and form a solid solution phase. Compared with pure lithium cobaltate, the foreign metal elements introduced in the solid solution phase are present around the cobalt element, which changes the chemical environment around the cobalt element, is beneficial to alleviating the accumulation and release of structural stress during the lithium deintercalation / insertion process, improves the structural stability of the cathode material, and ultimately improves the cycle performance. In addition, when the introduced elements contain nickel elements, due to the electrochemical activity of nickel elements, the cobalt-based lithium-ion battery cathode material has a higher capacity performance than pure lithium cobaltate in the same voltage range (the highest cut-off voltage is 4.55 - 4.2V).

[0036] In an embodiment according to the present invention, the cobalt-based lithium-ion battery cathode material has the following characteristics in the XRD spectrum of copper target Kα1 at a 2θ diffraction angle: there is no diffraction peak between 20 - 25°, there are diffraction peaks between 15 - 20°, 35 - 40°, and 43 - 47°, and the diffraction peak intensity I1 at 15 - 20° and the peak intensity I2 of the diffraction peak at 43 - 47° satisfy the relationship: 1 < I1 / I2 < 100. The absence of a diffraction peak between 20 - 25° in the cobalt-based lithium-ion battery cathode material of the present invention indicates that there is no lithium-rich phase in the material, the structure of the material is pure, and thus its cycle performance is improved.

[0037] In an embodiment according to the present invention, the pH of the cathode material is 10 - 12, specifically it can be 10.2, 10.5, 10.8, 11.2, 11.5, 11.8, 12. Thus, it can be seen that the cobalt-based lithium-ion battery cathode material of the present invention has less residual lithium on the surface, high lithium utilization rate, and improves the stability of the cathode material in air.

[0038] In the second aspect according to the present invention, the present invention provides a preparation method of a cobalt-based lithium-ion battery cathode material.

[0039] Method 1: Weigh the lithium source, cobalt source, and doping elements according to the molar ratios of each element in the cathode material chemical formula Li 1.0～1.2 Co x Ni y M 1-x-y O2. After mixing them evenly by solid phase or liquid phase, sinter, crush, and screen the dried powder in a sintering device with an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) to obtain the cathode material; wherein, the sintering temperature is 850 - 1000 °C, specifically it can be 850 °C, 900 °C, 950 °C, 1000 °C.

[0040] In one embodiment according to the present invention, the cobalt source may be one or more of cobalt acetate, cobalt hydroxide, cobalt oxalate, cobalt tetroxide, cobalt citrate, etc.; the lithium source may be one or more of lithium acetate, lithium hydroxide, lithium oxalate, lithium citrate, lithium carbonate, etc. The nickel source may be one or more of nickel acetate, nickel oxide, nickel oxalate, nickel carbonate, nickel citrate, etc. Other introduced elements such as metal elements like manganese, aluminum, zirconium, titanium and rare earths may be one or more of corresponding acetates, oxalates, hydroxides, carbonates, oxides, citrates, etc.

[0041] Method 2: The cobalt source and the doping elements are used to obtain a cathode material precursor by a co-precipitation method. After the obtained precursor is uniformly mixed with the lithium source, it is sintered at a high temperature, crushed and sieved in a sintering device with an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) to obtain the cathode material; wherein, the sintering temperature is 850 - 1000 °C, specifically, it can be 850 °C, 900 °C, 950 °C, 1000 °C.

[0042] In one embodiment according to the present invention, the cobalt source and the doping elements such as nickel, manganese, aluminum and other metal sources used are all metal soluble salts, that is, they can be one or more of sulfates, acetates, chlorides, nitrates, etc. Preferably, the metal salt is a sulfate, such as cobalt sulfate, nickel sulfate, manganese sulfate, aluminum sulfate, etc.

[0043] Method 3: The lithium source, the cobalt source and the doping elements are used to obtain a functional material by a co-precipitation method. The obtained functional material is sintered, crushed and sieved after supplementing the lithium source or directly in a sintering device with an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) to obtain the cathode material, wherein the sintering temperature is 850 - 1000 °C, specifically, it can be 850 °C, 900 °C, 950 °C, 1000 °C.

[0044] In one embodiment according to the present invention, the lithium source used is a soluble salt, that is, it can be one or more of sulfates, acetates, chlorides, nitrates, citrates, dihydrogen phosphates, etc. The lithium salt can be one or more of lithium acetate, lithium citrate, lithium oxalate, lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate.

[0045] In one embodiment according to the present invention, the cobalt source and the doping elements such as nickel, manganese, aluminum, magnesium and other metal sources used are all metal soluble salts, that is, they can be one or more of sulfates, acetates, chlorides, nitrates, etc. The metal salt can 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, zirconium acetate, magnesium acetate, etc. Preferably, the metal salts are sulfates such as cobalt sulfate, nickel sulfate, manganese sulfate, aluminum sulfate, etc.

[0046] In a third aspect according to the present invention, the present invention provides a functional material for preparing the above cobalt-based lithium battery cathode material.

[0047] The chemical formula of the functional material is Li a Co x Ni 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 ≤ 0.2, 0.5 < b < 3.0, M is at least one of Mn, Al, Mg, Ti, Zr, rare earth elements, and W is CO3 2- , OH-, F-, PO4 3- , CH3COO-, C2O4 2- at least one of them.

[0048] In an embodiment according to the present invention, the functional material is treated in an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) at a temperature of 300 - 500 °C for 3 - 8 h and cooled to room temperature. In the XRD spectrum of the copper target Kα1 at a 2θ diffraction angle, diffraction peaks are shown at 16 - 20°, 34 - 38°, and 42 - 48°. The ratio A1 / A2 of the intensity A1 of the diffraction peak at 16 - 20° to the intensity A2 of the diffraction peak at 42 - 48° satisfies the relationship: 0.5 < A1 / A2 < 100.

[0049] In an embodiment according to the present invention, the D50 median particle size of the functional material is 1.5 - 20 μm, specifically it can be 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 20 μm. When the D50 median particle size of the functional material is controlled within the above range, the prepared cathode material can have a similar particle size, and the cathode material can have practical application significance such as being easy to screen and adjust the slurry and obtaining a higher tap density.

[0050] In a fourth aspect according to the present invention, the present invention further provides a lithium-ion battery including the above cathode material.

[0051] 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 cell into the battery case, adding the 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.

[0052] In an embodiment according to the present invention, the maximum cut-off voltage of the lithium-ion battery is 4.55 - 4.2V, specifically it can be 4.2V, 4.25V, 4.3V, 4.35V, 4.36V, 4.37V, 4.38V, 4.39V, 4.40V, 4.41V, 4.42V, 4.43V, 4.44V, 4.45V, 4.46V, 4.47V, 4.48V, 4.49V, 4.50V, 4.51V, 4.52V, 4.53V, 4.54V, 4.55V, and the minimum cut-off voltage is 2.75V. Thus, it can be seen that the cobalt-based lithium battery cathode material prepared by the present invention has high structural stability and can work at a relatively high cut-off voltage.

[0053] In an embodiment according to the present invention, the lithium-ion battery has a maximum cut-off voltage of 4.55 - 4.2V and a discharge capacity of 150 - 220 mAh / g at 0.1C, specifically it can be 150 mAh / g, 160 mAh / g, 170 mAh / g, 180 mAh / g, 190 mAh / g, 200 mAh / g, 210 mAh / g, 220 mAh / g. It can be seen that the cobalt-based lithium battery cathode material of the present invention has a relatively high discharge capacity with the change of the maximum cut-off voltage.

[0054] In an embodiment according to the present invention, the discharge capacity of the lithium-ion battery from the maximum cut-off voltage to 4.0V accounts for 25 - 45% of the total discharge capacity, specifically it can be 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 43%, 44%, 45%, and the discharge capacity from the maximum cut-off voltage to 3.8V accounts for 70 - 98% of the total discharge capacity, specifically it can be 70%, 75%, 78%, 82%, 85%, 89%, 92%, 95%, 96%, 98%.

[0055] The following further illustrates the present invention through specific embodiments.

[0056] Example 1

[0057] Weigh lithium acetate, cobalt acetate and nickel acetate according to the molar ratio of lithium: cobalt, nickel elements of 1.02:0.8:0.2, dissolve them in deionized water, stir and dry. Place the obtained dry powder in an atmosphere furnace, introduce air, with a heating rate of 3 - 5 °C / min, sinter at 940 °C for 8h. After the sample is cooled to room temperature, crush it and pass through a 350-mesh sieve to obtain the black cathode material LiCo 0.8 Ni 0.2 O2.

[0058] Example 2

[0059] This example provides a cathode material precursor, and its preparation method is as follows:

[0060] Weigh cobalt sulfate heptahydrate and nickel sulfate hexahydrate according to the molar ratio of cobalt to nickel elements of 8:2, and prepare a total of 1 L of a metal solution with a total metal molar concentration of 1 mol / L; weigh 80 g of sodium hydroxide, add deionized water to obtain a solution, and dilute and make up 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 as a protective gas into the reaction kettle, and carry out a co-precipitation reaction 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 the metal solution and the sodium hydroxide solution is 0.1 - 0.3 ml / min, and the pH of the reaction system is controlled to be 9 - 12. The obtained precipitation product is aged at 70 °C for 12 h, filtered by suction, the filter cake and the filtrate are separated, 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 a precursor material;

[0061] This example also provides a cathode material, and its preparation method is as follows:

[0062] Take 300 g of the above precursor material and 124.2 g of lithium carbonate, and mix them using a small high-speed mixer. Put the mixed powder into a crucible, place it in an atmosphere furnace, introduce an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm), with a heating rate of 3 - 5 °C / min, sinter at 940 °C for 8 h. After the sample is cooled to room temperature, it is crushed and passed through a 350-mesh sieve to obtain a black cathode material LiCo 0.8 Ni 0.2 O2.

[0063] Example 3

[0064] This example provides a functional material, and its preparation method includes the following steps:

[0065] Step S1: Weigh lithium chloride, cobalt sulfate heptahydrate and nickel sulfate hexahydrate according to the molar ratio of lithium: cobalt, nickel elements of 1.02:0.8:0.2, and prepare a total of 1 L of a solution with a total metal molar concentration of 2 mol / L, denoted as solution A; weigh 129 g of lithium hydroxide monohydrate, add deionized water to obtain a solution, and dilute and make up the volume to 1 L to prepare a 2 mol / L lithium hydroxide solution, denoted as solution B; weigh 0.25 g of polyacrylamide as an auxiliary agent.

[0066] Step S2: Mix and stir the auxiliary agent with an appropriate amount of deionized water in the 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 drip solution A and solution B into the reaction kettle, and carry out a co-precipitation reaction to obtain a precipitation product. Among them, the temperature of the reaction kettle is 70 - 80 °C, the rotation speed of the stirrer is 800 - 1200 rpm, the feeding speed of solution A and solution B is 0.2 - 0.5 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 9 - 12.

[0067] Step S3: Aging the precipitation product at 70 °C for 12 - 16 h, performing suction filtration to separate the filter cake and the filtrate, washing the filter cake 2 - 4 times with deionized water at 70 °C, and drying it in an oven at 120 °C until constant weight to obtain the functional material; subjecting the obtained functional material to treatment in an air-containing atmosphere at 400 °C for 4 h, cooling it to room temperature, and then performing XRD testing. The obtained spectrum is shown in Figure 1 .

[0068] This example also provides a cathode material, and its preparation method is as follows:

[0069] Take 500 g of the above functional material, place it in a muffle furnace, introduce an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm), with a heating rate of 3 - 5 °C / min, and sinter at 940 °C for 8 h. After the sample is cooled to room temperature, crush it and pass it through a 350-mesh sieve to obtain the black cathode material LiCo 0.8 Ni 0.2 O2.

[0070] Perform XRD testing on the obtained cathode material. The obtained spectrum is shown in Figure 2 . It can be seen from Figure 2 that the structure of the solid solution type cobalt-based lithium-ion battery cathode material obtained after introducing the foreign metal nickel still maintains a layered structure. The capacity performance of the fabricated lithium-ion battery at 4.35 V is shown in Figure 4 , and the cycling performance at 4.4 V is shown in Figure 5 . In Figure 4 , the 0.1C discharge capacity of the lithium-ion battery is 172 mAh / g, and the median voltage > 3.7 V. The capacity from the cut-off voltage of 4.35 V to 4.0 V is 61 mAh / g, accounting for 35.5% of the total discharge capacity; the capacity from the cut-off voltage of 4.35 V to 3.8 V is 160 mAh / g, accounting for 93% of the total discharge capacity.

[0071] Example 4

[0072] The difference from Example 1 is that lithium acetate, cobalt acetate, nickel acetate, and metatitanic acid are weighed according to the molar ratio of lithium: cobalt, nickel: titanium elements of 1.02:0.8:0.1:0.1. The remaining processes are the same as those in Example 1 and will not be elaborated here.

[0073] Example 5

[0074] The difference from Example 2 is that cobalt sulfate heptahydrate, nickel sulfate hexahydrate, and aluminum sulfate octadecahydrate are weighed according to the molar ratio of cobalt: nickel: aluminum elements of 8:1:1. The remaining processes are the same as those in Example 2 and will not be elaborated here.

[0075] Example 6

[0076] The difference from Example 3 is that lithium chloride, cobalt sulfate heptahydrate, nickel sulfate hexahydrate and manganese sulfate monohydrate are weighed according to the molar ratio of lithium:cobalt:nickel:manganese elements of 1.02:0.8:0.2:0.1, and the remaining processes are the same as those in Example 3, which will not be elaborated here.

[0077] Comparative Example 1

[0078] Lithium carbonate and cobalt tetroxide were weighed according to the lithium:cobalt molar ratio of 1.02:1. After being mixed by a high-speed disperser, they were placed in a muffle furnace, an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) was introduced, the heating rate was 3-5 °C / min, and sintering was carried out at 940 °C for 8 h. After the sample was cooled to room temperature, it was pulverized and passed through a 350-mesh sieve to obtain the black cathode material LiCoO2.

[0079] The obtained cathode material was subjected to XRD test, and the obtained spectrum is shown in Figure 3 . The capacity performance of the fabricated lithium-ion battery at 4.35 V is shown in Figure 4 , and the cycling performance at 4.4 V is shown in Figure 5 .

[0080] The instruments and equipment involved in the present invention are shown in the following table

[0081]

[0082] Among them, the main instrument test methods of the present invention are as follows:

[0083] (1) For the analysis of moisture and components, the methods in the national standard of lithium cobaltate (GB / T 20252-2014) are borrowed, and the contents of all metal elements (including cobalt element) are determined by inductively coupled plasma emission spectrometry.

[0084] (2) XRD test: Cu target, scanning rate 4° / min, 2θ range is 10-80°.

[0085] Among them, the main raw materials / auxiliary materials involved in the present invention are shown in the following table:

[0086]

[0087]

[0088] Examples 1-6 are cobalt-based lithium-ion battery cathode materials formed by introducing foreign metal elements into lithium cobaltate, and Comparative Example 1 is a pure lithium cobaltate cathode material. The cathode materials prepared in Examples 1-3 and Comparative Example 1 were applied to lithium-ion batteries and subjected to performance tests, and the test results are shown in the following table:

[0089]

[0090] As can be seen from the above table, at the cut-off voltages of 4.35V, 4.4V, 4.45V, 4.55V, etc., the capacity performance of the cobalt-based lithium-ion battery cathode material prepared by the present invention is higher than that of pure lithium cobaltate. It shows that after introducing foreign metal elements into pure lithium cobaltate, under the same test conditions, the prepared solid solution type cobalt-based lithium-ion battery cathode material has a higher capacity performance. Under the condition of a cut-off voltage of 4.4V, the capacity retention rate of the cobalt-based lithium-ion battery cathode material prepared by the present invention is greater than 90% after 2500 cycles at 1C / 1C, while the capacity of pure lithium cobaltate decays to 90% after 1000 cycles at 1C / 1C, indicating that the solid solution type cobalt-based lithium-ion battery cathode material has a more stable structure in the lithium deintercalation / insertion behavior than the lithium cobaltate cathode material.

[0091] According to the disclosure and teachings 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 based on the present invention all fall within 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 cathode material with the chemical formula Li 1.0～1.2 Co x Ni y M 1-x-y O2, where 0.6 ≤ x ≤ 1, 0 ≤ y ≤ 0.4, 0 ≤ 1 - x - y ≤ 0.2, and M is at least one of Mn, Al, Mg, Ti, Zr, and rare earth elements.

2. The cathode material according to claim 1, characterized in that, The positive electrode material has the following characteristics in the XRD pattern of Cu target Kα1 at a 2θ diffraction angle: There is no diffraction peak between 20° and 25°, and there are diffraction peaks between 15° and 20°, 35° and 40°, and 43° and 47°. Moreover, the peak intensity I1 at 15° - 20° and the peak intensity I2 at 43° - 47° satisfy the relationship: 1 < I1 / I2 < 100.

3. The cathode material according to claim 1, characterized in that, The positive electrode material contains a functional material; the chemical formula of the functional material is Li a Co x Ni 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 ≤ 0.2, 0.5 < b < 3, M is at least one of Mn, Al, Mg, Ti, Zr, and rare earth elements, and W is CO3 2- , OH−, F - , PO4 3- , CH3COO - , C2O4 2- and at least one of the following.

4. The cathode material according to claim 3, characterized in that, The functional material is treated in an oxygen-containing atmosphere (oxygen partial pressure ≥ 0.21 atm) at a temperature of 300 - 500 °C for 3 - 8 h and then cooled to room temperature. Its XRD pattern has the following characteristics: there are diffraction peaks at 2theta of 16° - 20°, 34° - 38°, and 42° - 48°. The intensity ratio A1 / A2 of the diffraction peak at 16° - 20° to the diffraction peak at 42° - 48° satisfies the relationship: 0.5 < A1 / A2 < 100. Among them, the oxygen partial pressure in the oxygen-containing atmosphere ≥ 0.21 atm, and the D50 median particle size of the functional material is 1.5 - 20 μm.

5. A method for preparing the cathode material according to any one of claims 1-4, characterized in that, According to the molar ratio of each element in the cathode material chemical formula Li 1.0～1.2 Co x Ni y M 1-x-y O2, the lithium source, cobalt source and doping elements are weighed respectively, and after being uniformly mixed by solid phase or liquid phase, the dried powder is sintered, crushed and screened in a sintering equipment in an oxygen-containing atmosphere to obtain the cathode material; or The positive electrode material precursor is prepared by co-precipitation of a cobalt source and a doping element. After the obtained precursor is mixed evenly with a lithium source, it is sintered at a high temperature, crushed, and sieved in a sintering device in an oxygen-containing atmosphere to obtain the positive electrode material; or The functional material is prepared by co-precipitation of a lithium source, a cobalt source, and a doping element. The obtained functional material is sintered, crushed, and sieved after supplementing the lithium source or directly in a sintering device in an oxygen-containing atmosphere to obtain the positive electrode material; Among them, the oxygen partial pressure in the oxygen-containing atmosphere ≥ 0.21 atm, and the sintering temperature is 850 - 1000 °C.

6. 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 1 - 4. The mass fraction of cobalt element after the positive electrode slurry coated on the positive electrode sheet is dried is 30 - 58%.

7. A lithium-ion battery, characterized in that, It includes the positive electrode sheet described in claim 6.

8. The lithium ion battery according to claim 7, wherein The highest cut-off voltage of the lithium-ion battery is 4.2 - 4.55 V, and the lowest cut-off voltage is 2.75 V.

9. The lithium ion battery according to claim 7, wherein The lithium-ion battery has a discharge capacity of 150 - 220 mAh / g at 0.1C, a median voltage ≥ 3.7 V. The discharge capacity from the highest cut-off voltage of 4.55 - 4.2 V to 4.0 V accounts for 25 - 45% of the total discharge capacity, and the discharge capacity from the highest cut-off voltage of 4.55 - 4.2 V to 3.8 V accounts for 70 - 98% of the total discharge capacity.

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