A cathode material, a preparation method thereof, and a lithium-ion battery

Abstract

An embodiment of the present application provides a cathode material, a preparation method thereof, and a lithium-ion battery, which are used to improve the stability of the cathode material without affecting the specific capacity of the cathode material. The molecular formula of the cathode material is: Li<subgt;n< / subgt;Ni<subgt;x< / subgt;Co<subgt;e< / subgt;Mn<subgt;y< / subgt>Al<subgt;m< / subgt>M<subgt;1-x-y-e-m< / subgt>O<subgt;2< / subgt>, and the content of Ni<supgt;2+ on the surface of the cathode material is less than (y / x + 0.3); wherein, the content of Ni<supgt;2+ on the surface of the cathode material is measured by an X-ray photoelectron spectrometer, M is a doping element and a coating element, and the doping element and the coating element are each independently selected from at least one of: H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; 1 < n < 1.1, 0.6 ≤ x < 1, 0 < e ≤ 0.4, 0 ≤ y ≤ 0.4, 0 ≤ m ≤ 0.4, 0 < 1 - x - y - e - m ≤ 0.05; and y and m are not both 0 at the same time.

Description

Technical Field

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

[0002] Although lithium - ion batteries have been widely used due to their high energy density, in the face of application scenarios such as electric vehicles, the energy density and service life of lithium - ion batteries, that is, the cycle stability performance, still needs to be improved urgently. One of the methods to improve the energy density and cycle stability of lithium - ion batteries is to regulate the composition and content of their cathode materials.

[0003] Among various types of lithium - ion battery cathode materials, nickel - cobalt - manganese cathode materials and nickel - cobalt - aluminum cathode materials have become the main development targets at present due to their high energy density advantages. To further improve nickel - cobalt - manganese cathode materials and nickel - cobalt - aluminum cathode materials, the current methods mostly involve adding dopants during the solid - phase synthesis process to enable the corresponding doping elements to enter the layered structure of the ternary cathode material, thereby improving the stability of the ternary cathode material and further extending the life of the corresponding lithium - ion battery. Or during the solid - phase synthesis process, the ternary cathode material is coated with a coating agent to improve the stability of the ternary cathode material by alleviating the side reaction between the ternary cathode material and the electrolyte.

[0004] Although the cathode materials prepared by the above two methods can improve the cycle stability of the ternary cathode material to a certain extent, they do not solve the problem of low cycle stability caused by the crystal structure defects on the surface of the ternary cathode material. Therefore, there is a lack of a cathode material with good cycle stability in the prior art. Summary of the Invention

[0005] Aiming at the lack of a cathode material with good stability in the prior art, the present application provides a cathode material to improve the stability of the cathode material without affecting the specific capacity of the cathode material.

[0006] In the first aspect, the present application provides a cathode material, comprising:

[0007] The molecular formula of the cathode material is: Li n Ni x Co e Mn y Al m M 1-x-y-e-m O2, and the Ni content on the surface of the cathode material is less than (y / x + 0.3); wherein, the Ni on the surface of the cathode material 2+ content is less than (y / x + 0.3); where the Ni on the surface of the cathode material 2+The content is measured by X-ray photoelectron spectrometer. M is a doping element and a coating element, and the doping element and the coating element are each independently selected from at least one of H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; 1 < n < 1.1, 0.6 ≤ x < 1, 0 < e ≤ 0.4, 0 ≤ y ≤ 0.4, 0 ≤ m ≤ 0.4, 0 < 1 - x - y - e - m ≤ 0.05; and y and m are not both 0.

[0008] The cathode material provided by the embodiment of the present application is a high-nickel material because it has the characteristic of high energy density. On this basis, due to the surface Ni 2+ content is less than (y / x + 0.3), ensuring that the Ni on the surface of the cathode material 2+ content is at a relatively low level. That is, in the cathode material of the embodiment of the present application, due to the Ni corresponding to the defective phase (NiO-like structure) of the spinel phase and the rock salt phase on its surface 2+ content is less than (y / x + 0.3), so this cathode material has the advantage of low crystal defect content. Therefore, the cathode material provided by the embodiment of the present application can effectively alleviate the problem of low stability of the cathode material in the prior art due to high crystal defect content, and further can alleviate the problem that the crystal defect content of the cathode material increases due to the diffusion of crystal defects to the inside during the charge-discharge process, which further causes the deterioration of the stability of the cathode material during the charge-discharge cycle process.

[0009] In a possible implementation manner, in the XRD pattern of the cathode material, the ratio of the peak intensity of the (003) crystal plane to the peak intensity of the (104) crystal plane is not less than 0.8.

[0010] In a possible implementation manner, when 0.6 ≤ x < 0.7, the specific capacity Z of the cathode material is: 140 mAh / g ≤ Z < 200 mAh / g; when 0.7 ≤ x < 0.8, 160 mAh / g ≤ Z < 220 mAh / g; when 0.8 ≤ x < 0.9, 180 mAh / g ≤ Z < 240 mAh / g; when 0.9 ≤ x < 1, 200 mAh / g ≤ Z < 260 mAh / g.

[0011] In a possible implementation manner, the capacity retention rate of the cathode material is not less than 80%; wherein, the capacity retention rate is the capacity ratio obtained by testing the capacity of the full cell corresponding to the cathode material after 300 cycles of charge-discharge at 2.8 - 4.25 V and 0.1 C and the capacity after the first charge-discharge.

[0012] In a possible implementation manner, the cathode material is a polycrystalline material, and / or, a single crystal material.

[0013] A possible implementation manner, wherein the positive electrode material is a polycrystalline material, and the median particle size D of the positive electrode material 50 ≤25 μm.

[0014] A possible implementation manner, wherein the positive electrode material is a polycrystalline material, and the △U 300 / △U2 of the positive electrode material is 0.8 - 2.0; wherein,

[0015] △U2 is the voltage difference obtained by testing the first voltage after charging - discharging the full cell corresponding to the positive electrode material once under the conditions of 2.8 - 4.25 V and 0.1 C, then charging to 4.25 V and powering off for 300 s, and the second voltage after discharging for 30 s at 1 C after powering off for 300 s; △U 300 is the voltage difference obtained by testing the third voltage after charging - discharging the full cell 300 cycles under the conditions of 2.8 - 4.25 V and 0.1 C, then charging to 4.25 V and powering off for 300 s, and the fourth voltage after discharging for 30 s at 1 C.

[0016] A possible implementation manner, wherein the positive electrode material is a single - crystal material, and the median particle size D of the positive electrode material 50 ≤10 μm.

[0017] A possible implementation manner, wherein the positive electrode material is a single - crystal material, and the cycle performance of the positive electrode material is calculated by △U 300 / △U2, and the △U 300 / △U2 is 0.8 - 2.4; wherein,

[0018] △U2 is the voltage difference obtained by testing the first voltage after charging - discharging the full cell corresponding to the positive electrode material once under the conditions of 2.8 - 4.25 V and 0.1 C, then charging to 4.25 V and powering off for 300 s, and the second voltage after discharging for 30 s at 1 C after powering off for 300 s; △U 300 is the voltage difference obtained by testing the third voltage after charging - discharging the full cell 300 cycles under the conditions of 2.8 - 4.25 V and 0.1 C, then charging to 4.25 V and powering off for 300 s, and the fourth voltage after discharging for 30 s at 1 C.

[0019] In a second aspect, an embodiment of the present application provides a preparation method of the positive electrode material as described in the first aspect and any one of the possible implementation manners, including:

[0020] Performing a first sintering treatment on a mixture of a precursor, a dopant, and a lithium source in an atmosphere with an oxygen content of not less than 20%.

[0021] In an atmosphere with an oxygen content of not less than 20%, a second sintering treatment is performed on a mixture of the first sintering treatment product and a coating agent to obtain a cathode material; wherein, the second sintering temperature of the second sintering treatment is lower than the first sintering temperature of the first sintering treatment; and the intermediate sintering product is washed with water and dried before the end of the second sintering treatment.

[0022] In a possible implementation manner, the first sintering treatment is carried out in a box furnace, a roller hearth kiln, a rotary kiln, or an orbital kiln.

[0023] In a possible implementation manner, the dopant is an inorganic compound corresponding to the doped element in the cathode material, and the coating agent is an inorganic compound corresponding to the coating element in the cathode material.

[0024] In a possible implementation manner, the time for washing with water does not exceed 30 minutes.

[0025] In a possible implementation manner, the precursor is selected from: hydroxide with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d (OH)2, oxide with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d O, salt precursor with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d TM; wherein, Q is a doped element, and Q is selected from at least one of H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; TM represents a salt anion, and each of a, b, c, and d is respectively selected from: 0.6 ≤ a < 1, 0 < b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.4, 0 ≤ 1 - a - b - c - d ≤ 0.05; and c and d are not both 0 at the same time.

[0026] In a possible implementation manner, when a ≥ 0.75, the first sintering treatment is carried out in an atmosphere with an oxygen content of not less than 80%, and the second sintering treatment is carried out in an atmosphere with an oxygen content of not less than 75%.

[0027] A possible implementation manner, wherein the precursor is a single-crystal precursor. When 0.6 ≤ a < 0.7, the first sintering temperature is 850 - 1000 °C; when 0.7 ≤ a < 0.8, the first sintering temperature is 800 - 950 °C; when 0.8 ≤ a < 0.9, the first sintering temperature is 750 - 900 °C; when 0.9 ≤ a < 1, the first sintering temperature is 700 - 850 °C.

[0028] A possible implementation manner, wherein the precursor is a polycrystalline precursor. When 0.6 ≤ a < 0.7, the first sintering temperature is 770 - 940 °C; when 0.7 ≤ a < 0.8, the first sintering temperature is 730 - 900 °C; when 0.8 ≤ a < 0.9, the first sintering temperature is 700 - 870 °C; when 0.9 ≤ a < 1, the first sintering temperature is 680 - 850 °C.

[0029] In a third aspect, an embodiment of the present application provides a lithium-ion battery, including:

[0030] The positive electrode material as described in the first aspect and any possible implementation manner, or the positive electrode material obtained by the method as described in the second aspect and any possible implementation manner. Description of the Drawings

[0031] Figure 1 It is a scanning electron microscope image of Synthesis Example 1 provided by an embodiment of the present application;

[0032] Figure 2 It is a scanning electron microscope image of Synthesis Example 4 provided by an embodiment of the present application. Detailed Embodiments

[0033] According to "Direct observation of defect-aided structural evolution in Ni-rich layered cathode" (DOI: 10.1002, ange.202008144), in the Ni-rich ternary cathode material, there are three crystal phase structures: layered, spinel, and rock salt phases. Among them, the spinel and rock salt phases are crystal defects formed by different connection methods of the layered phase. When the Ni-rich ternary cathode material undergoes an electrochemical reaction, that is, when it is applied to a lithium-ion battery, due to factors such as the extension of the antiphase boundary (APB) corresponding to different connection methods of the layered phase, phase transformation near the twin boundary (TB), and the formation of disordered rock salt, the crystal defects in the Ni-rich ternary cathode material continuously diffuse during charge-discharge. Especially, the crystal defects on the material surface gradually diffuse from the material interior, which leads to a continuous increase in the crystal defects in the Ni-rich ternary cathode material, resulting in the deterioration of the cycle stability of the Ni-rich ternary cathode material.

[0034] It can be seen that the stability of the lithium-ion battery is closely related to the attenuation of the cycle stability of the Ni-rich ternary cathode material. The cycle stability of the Ni-rich ternary cathode material is mainly determined by the content of crystal defects in it. Specifically, a high content of crystal defects in the Ni-rich ternary cathode material not only means that its crystal structure cannot provide a stable and unobstructed channel for the extraction and insertion of lithium ions during charge-discharge for a long time, but also exacerbates the diffusion of crystal defects in the Ni-rich ternary cathode material during charge-discharge, thereby more significantly causing a decline in the cycle stability of the Ni-rich ternary cathode material.

[0035] Based on this, an embodiment of the present application proposes a cathode material Li n Ni x Co e Mn y Al m M 1-x-y-e-m O2. By controlling the Ni 2+ content on the surface of this cathode material to be less than (y / x + 0.3), the Ni 2+ content on the surface of the cathode material is controlled, and then the purpose of controlling crystal defects is achieved. Therefore, for the cathode material provided in the embodiment of the present application, due to the low content of its surface intrinsic defects (i.e., crystal defects), the diffusion phenomenon of crystal defects during charge-discharge can be effectively alleviated, thus improving the cycle stability of the Ni-rich ternary cathode material.

[0036] The molecular formula of the cathode material provided in the embodiment of the present application is: Li n Ni x Co eMn y Al m M 1-x-y-e-m O2, and the Ni content on the surface of the positive electrode material 2+ is less than (y / x + 0.3); wherein, the Ni content on the surface of the positive electrode material 2+ is measured by an X-ray photoelectron spectrometer. M is a doping element and a coating element, and the doping element and the coating element are each independently selected from at least one of H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; 1 < n < 1.1, 0.6 ≤ x < 1, 0 < e ≤ 0.4, 0 ≤ y ≤ 0.4, 0 ≤ m ≤ 0.4, 0 < 1 - x - y - e - m ≤ 0.05; and y and m are not both 0. Preferably, the Ni content on the surface of the positive electrode material 2+ is less than (y / x + 0.25).

[0037] It should be noted that the Ni content on the surface of the positive electrode material described in the embodiments of the present application 2+ refers to the ratio of the Ni content in the measurable depth by an X-ray photoelectron spectrometer to the ions of various valence states of all Ni elements (Ni 2+ , Ni, and Ni 3+ , Ni 2+ ) in the aforementioned measurable depth.

[0038] In the X-ray photoelectron spectrometer used to test the positive electrode material in the embodiments of the present application, the X-ray source can be an X-ray tube with Al as the anode, or an X-ray tube with Mg or an Al / Mg double-line source as the anode.

[0039] Furthermore, since the fewer the crystal defects in the ternary cathode material, correspondingly, the better the crystallinity of the ternary cathode material, that is, the fewer the crystal defects between the lamellar phases. In the XRD (X-ray diffraction) pattern of the ternary cathode material, the ternary cathode material exhibits a hexagonal α-NaFeO2 lamellar structure without impurity peaks. At the same time, when the Li-Ni mixing phenomenon in the ternary cathode material decreases, the intensity value of the (003) crystal plane peak is relatively large in the XRD pattern of the ternary cathode material, and correspondingly, the ratio of the intensity of the (003) crystal plane peak to the intensity of the (004) crystal plane peak (i.e., the value of I(003) / I(004)) is also relatively large. It can be seen that there is a causal relationship between the Li-Ni mixing phenomenon in the ternary cathode material and the degree of crystallization in the ternary cathode material. Therefore, in an embodiment of the present application, the ratio of the intensity of the (003) crystal plane peak to the intensity of the (104) crystal plane peak in the XRD pattern of the ternary cathode material is not less than 0.8. That is, I(003) / I(104) ≥ 0.8. That is, by ensuring the ratio of the intensity of the (003) crystal plane peak to the intensity of the (104) crystal plane peak in the ternary cathode material, the crystallization degree of the ternary cathode material is relatively good to inhibit the Li-Ni mixing phenomenon in the ternary cathode material. Preferably, I(003) / I(104) ≥ 1.2.

[0040] Furthermore, in the cathode material of the embodiment of the present application, as the stoichiometric ratio of Ni increases, the specific capacity of the cathode material is effectively improved, and correspondingly, the energy density of the lithium-ion battery corresponding to the cathode material is also increased. Therefore, in an embodiment of the present application, when 0.6 ≤ x < 0.7, the specific capacity Z of the cathode material in the voltage range of 3 - 4.25V and 0.2C is: 140 mAh / g ≤ Z < 200 mAh / g; when 0.7 ≤ x < 0.8, 160 mAh / g ≤ Z < 220 mAh / g; when 0.8 ≤ x < 0.9, 180 mAh / g ≤ Z < 240 mAh / g; when 0.9 ≤ x < 1, 200 mAh / g ≤ Z < 260 mAh / g.

[0041] Furthermore, in an embodiment of the present application, the cycle stability of the cathode material is measured by the capacity retention rate, and the capacity retention rate of the cathode material is not less than 80%; preferably, the capacity retention rate of the cathode material is not less than 85%.

[0042] Among them, the capacity retention rate is the capacity ratio obtained by testing the capacity of the full cell corresponding to the cathode material after 300 cycles of charging-discharging under the conditions of 2.8 - 4.25V and 0.1C and the capacity after the first charging-discharging.

[0043] Furthermore, the above-mentioned cathode material is a polycrystalline material, and / or, a polycrystalline material.

[0044] In one embodiment of the present application, the cycle stability of the positive electrode material is represented by ΔU 300 / ΔU2. Wherein, ΔU2 is the first voltage of the full cell corresponding to the positive electrode material after charging and discharging once at 2.8 - 4.25V and 0.1C, then charging to 4.25V at 1C and cutting off the power for 300s, and the second voltage obtained by testing the voltage after discharging for 30s at 1C after cutting off the power for 300s; ΔU 300 is the voltage difference obtained by testing the third voltage of the full cell after charging and discharging 300 cycles at 2.8 - 4.25V and 1C, then charging to 4.25V and cutting off the power for 300s, and the fourth voltage obtained by discharging for 30s at 1C. The above ΔU2 and ΔU 300 represent the polarization degree of the corresponding full cell. Since the change in polarization represents the deterioration degree of the material during the cycling process, the greater the change in polarization, the lower the cycle stability of the positive electrode material.

[0045] Therefore, when the positive electrode material is polycrystalline, ΔU 300 / ΔU2 is 0.8 - 2.0. When the positive electrode material is single crystal, ΔU 300 / ΔU2 is 0.8 - 2.4.

[0046] To avoid the phenomenon that during the charging and discharging process caused by the large particle size of the positive electrode material, the primary particles in the positive electrode material are broken due to stress, resulting in the emergence of new grain boundaries and thus the aforementioned crystal defects. When the positive electrode material is a polycrystalline material, the median particle size D of the positive electrode material 50 ≤25μm. Preferably, D 50 ≤20μm. When the positive electrode material is a single crystal material, the median particle size D of the positive electrode material 50 ≤10μm. Preferably, D 50 ≤8μm.

[0047] Based on the same inventive concept, an embodiment of the present application proposes a preparation method of a positive electrode material for preparing a positive electrode material with fewer crystal defects, thereby suppressing the problem of poor cycle stability caused by the diffusion of crystal defects in the positive electrode material during the charging and discharging process. The method includes the following steps:

[0048] Step 101, perform a first sintering treatment on the mixture of the precursor, the dopant and the lithium source in an atmosphere with an oxygen content of not less than 20%.

[0049] The first sintering treatment can be carried out in a box furnace, a roller hearth kiln, a rotary kiln, or an orbital kiln, so that the mixture of the precursor, the dopant and the lithium source undergoes a chemical reaction in a uniform thermal field, thereby reducing the generation of crystal defects in the first sintering treatment product. Preferably, it is a roller hearth kiln, a rotary kiln, or an orbital kiln.

[0050] The above precursor is selected from: with the molecular formula Nia Co b Mn c Al d Q 1-a-b-c-d (OH)2 hydroxide, with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d O oxide, with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d Salt precursor of TM; wherein, Q is a doping element, and Q is selected from at least one of: H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; TM represents a salt anion, and each of a, b, c, and d is respectively selected from: 0.6 ≤ a < 1, 0 < b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.4, 0 ≤ 1 - a - b - c - d ≤ 0.05; and c and d are not both 0.

[0051] The above doping agent is an inorganic compound corresponding to the doping element in the positive electrode material in step 102. It should be noted that even if the value of 1 - a - c - d in the precursor is not 0, that is, the precursor contains a doping element, when the doping element is insufficient, the same or different doping elements can still be introduced through the doping agent. The above inorganic compound can be an oxide corresponding to the doping element, or a fluoride or carbonate, hydroxide, nitride, boride, nitrate, or any combination. For example, sodium carbonate, sodium oxide, sodium hydroxide, sodium nitrate, etc.

[0052] Furthermore, when a ≥ 0.75, the first sintering treatment is carried out in an atmosphere with an oxygen content of not less than 80%.

[0053] Furthermore, when the precursor is a single-crystal precursor, the corresponding positive electrode material in step 102 is a single-crystal material. When the precursor is a polycrystalline precursor, the corresponding positive electrode material in step 102 is a polycrystalline material.

[0054] Furthermore, the precursor is a single-crystal precursor. When 0.6 ≤ a < 0.7, the first sintering temperature is 850 - 1000 °C. When 0.7 ≤ a < 0.8, the first sintering temperature is 800 - 950 °C. When 0.8 ≤ a < 0.9, the first sintering temperature is 750 - 900 °C. When 0.9 ≤ a < 1, the first sintering temperature is 700 - 850 °C.

[0055] When the precursor is a polycrystalline precursor, when 0.6≤a<0.7, the first sintering temperature is 770-940℃; when 0.7≤a<0.8, the first sintering temperature is 730-900℃; when 0.8≤a<0.9, the first sintering temperature is 700-870℃; when 0.9≤a<1, the first sintering temperature is 680-850℃.

[0056] Step 102: In an atmosphere with an oxygen content of not less than 20%, the mixture of the first sintering product and the coating agent is subjected to a second sintering treatment to obtain a positive electrode material.

[0057] The second sintering temperature of the second sintering process is lower than the first sintering temperature of the first sintering process. The second sintering temperature may be 250-700°C.

[0058] The coating agent is an inorganic compound of the coating element in the positive electrode material. The inorganic compound can be an oxide corresponding to the coating element, or a fluoride, carbonate, hydroxide, nitride, boride, nitrate, or any combination thereof. Examples include sodium carbonate, sodium oxide, sodium hydroxide, and sodium nitrate.

[0059] The cathode material prepared is Li n Ni x Co e Mn y Al m M 1-x-y-e-m O2, Ni on the surface of the positive electrode material 2+ The content is less than (y / x+0.3); wherein the Ni on the surface of the positive electrode material 2+ The content is measured by X-ray photoelectron spectrometer, M is a doping element and a coating element, and the doping element and the coating element are each independently selected from: at least one of H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; 1<n<1.1, 0.6≤x<1, 0<e≤0.4, 0≤y≤0.4, 0≤m≤0.4, 0<1-xyem≤0.05; and y and m are not 0 at the same time.

[0060] Further, when a≧0.75, the second sintering process is performed in an atmosphere having an oxygen content of not less than 75%.

[0061] The embodiment of the present application does not limit the number of the first sintering treatment and the second sintering treatment. When the first sintering treatment and / or the second sintering treatment are multiple sintering treatments, except for the last sintering treatment, the products of all previous sintering treatments are intermediate sintering treatment products, including the first sintering treatment product as an intermediate sintering treatment product.

[0062] It should be noted that before the end of the second sintering treatment, the intermediate sintered product is washed with water and dried to avoid damage to the coating layer on the surface of the sintered product caused by washing the sintered product with water after the end of the second sintering treatment.

[0063] That is to say, this water washing step can be carried out after the first sintering treatment, so that the residual alkali (lithium carbonate, lithium hydroxide) on the surface of the intermediate sintered product dissolves in water and is washed away, avoiding that in the process of preparing the battery with materials with high residual alkali, due to the reaction between the residual lithium and the binder, the slurry becomes jelly-like and the preparation of the electrode sheet cannot be carried out, or in the battery cycle process, reacting with the electrolyte, resulting in too much gas generation in the battery and bringing a series of negative reactions, thus affecting the battery life.

[0064] Furthermore, when there are multiple second sintering treatments, that is, multiple coatings, the intermediate sintered product can be washed with water and dried before the last coating sintering to achieve the aforementioned purpose. For example, if the second sintering treatment process corresponds to n coatings, then after (n - 1) coatings, the cooled intermediate sintered product can be washed with water and dried, and then the last, that is, the nth coating is carried out.

[0065] In the embodiment of the present application, the water washing time does not exceed 30 min to avoid substances other than residual alkali on the surface of the positive electrode material dissolving in water due to too long water washing time, resulting in the precipitation of lithium ions on the surface and inside of the positive electrode material due to the lithium ion concentration difference, and further leading to the problem of generating Ni(OH)2 on the surface of the surface material. During the above water washing process, the water-to-material ratio can be 0.5:1 - 1:1. Under the high-temperature action in the subsequent drying step, the above Ni(OH)2 will generate crystal defects - rock salt phase Ni0.

[0066] Therefore, in an embodiment of the present application, the first sintering treatment product is used as the intermediate sintered product to be washed with water, that is, the stirring rate of the water washing is 100 - 240 r / min. When 0.6 ≤ a < 0.7, the water washing time does not exceed 25 min. When 0.7 ≤ a < 0.8, the water washing time does not exceed 20 min. When 0.8 ≤ a < 0.9, the water washing time does not exceed 15 min. When 0.9 ≤ a < 1, the water washing time ≤ 10 min.

[0067] In an embodiment of the present application, the number of sintering times for preparing the positive electrode material is 3, that is, the second sintering treatment includes two coating sintering treatments. Then the stirring rate during water washing after the first coating in the second sintering treatment is still 100 - 240 r / min. When 0.6 ≤ a < 0.7, the water washing time does not exceed 30 min. When 0.7 ≤ a < 0.8, the water washing time does not exceed 25 min. When 0.8 ≤ a < 0.9, the water washing time does not exceed 20 min. When 0.9 ≤ a < 1, the water washing time ≤ 15 min.

[0068] Further, the above drying can be carried out in a vacuum environment at a temperature of 100-200 °C, and the corresponding drying time can be 2-16 hours.

[0069] The following will be described in detail through Synthesis Examples 1-12, Comparative Synthesis Examples 1-9, Device Examples 101-112, 201-212, and Device Comparative Examples 101-109, 201-209.

[0070] First, it should be noted that in the following examples, the oxygen content was measured by an HT-LA561 high-content oxygen analyzer, the crystal plane intensity ratio was tested by an XRD-7000L type X-ray diffractometer, and the XRD diffraction pattern was compared with the standard card PDF#74-0919 to obtain the Ni 2+ content was measured by an X-ray tube with an Al anode tube, and the corresponding X-ray photoelectron spectrometer was Kratos-AXIS SUPRA of Shimadzu, Japan.

[0071] Synthesis Example 1

[0072] S1. A polycrystalline precursor with a molar ratio of Ni, Co, and Mn of 8:1:1 was mixed with lithium hydroxide and ZrO in a high-speed mixer for 120 min. Among them, the molar ratio of the polycrystalline precursor to lithium hydroxide was 1:1.04, and the added mass of ZrO was 1% of the mass of the ternary precursor.

[0073] S2. In an orbital kiln, under the condition that the oxygen content was 98%, the mixed material was subjected to a first sintering treatment.

[0074] Among them, in the first sintering treatment, the first sintering temperature was 800 °C, and the first sintering time was 12 h.

[0075] S3. The product of the first sintering treatment was put into a stirring kettle, washed with water for 12 min at a stirring rate of 150 r / min, and dried for 12 hours at 120 °C and -101 KPa.

[0076] S4. The dried material and Al2O3 were mixed evenly in a high-speed mixer, oxygen was introduced, and the mixture was subjected to a second sintering treatment in an orbital kiln with an oxygen content of 80% to obtain a cathode material with a ratio of Li, Ni, Co, and Mn of 1.01:0.8:0.1:0.1. Please refer to the morphology diagram of this cathode material Figure 1 .

[0077] Among them, the added mass of Al2O3 was 1% of the dried material. In the second sintering treatment, the second sintering temperature was 400 °C, and the second sintering time was 5 hours.

[0078] The preparation steps in Synthesis Examples 2-12 and Synthesis Comparative Examples 1-9 are similar to those in Synthesis Example 1. The crystal form of the precursor, the first sintering treatment temperature, and / or the water washing time are controlled respectively. The obtained cathode materials are tested by an X-ray photoelectron spectrometer with an Al anodic tube, as well as the intensity ratio of the (003) crystal plane and the (104) crystal plane of the cathode material. See Table 1 for the specific changes in the preparation steps and the test results. For those not listed in the preparation steps and process parameters in Table 1, they are the same as those in Synthesis Example 1. Among them, for the morphology diagram of the cathode material obtained in Synthesis Example 4, please refer to Figure 2 。

[0079] Table 1

[0080]

[0081]

[0082] As can be seen from Table 1, for the same material, the greater the difference between the Ni 2+ content and (y / x + 0.3) in the corresponding material, the greater the ratio of I(104) / I(003). Obviously, the lower the Ni 2+ in the cathode material, the better its crystallinity.

[0083] Device Examples 101-112 and Device Comparative Examples 101-109

[0084] Device Examples 101-112 and Device Comparative Examples 101-109 are respectively button cells prepared by coating the cathode materials in Synthesis Examples 1-12 and Synthesis Comparative Examples 1-9 on the cathode current collector.

[0085] The preparation of the button cell is described as follows:

[0086] S1. Active material (ternary cathode material): Conductive additive (Super P): Binder (PVDF) = 90:6:4 (mass ratio). Weigh each substance according to a total amount of 100 g. First, place the active material (90 g) and the conductive additive acetylene black (6 g) in a weighing bottle, then add 4 g of the binder (PVDF), dry mix and stir for 30 min to make the powder mixture uniform. Then, add 200 - 300 g of N-methylpyrrolidone (NMP) dropwise and stir magnetically for 4 h to form a slurry. Finally, the slurry should just flow.

[0087] S2. Use a manual coating machine to uniformly coat the stirred slurry on a 30-cm-wide current collector (aluminum foil), and control the areal density at 17 mg / cm 2 , put the coated copper foil or aluminum foil into a vacuum oven, dry it at 110 °C for 12 h, and after cooling, roll the electrode sheet to make the electrode sheet reach 3.4 mg / cm 3Compaction density.

[0088] S3. Use a punching machine to punch the electrode sheet into a positive electrode sheet with Φ = 14 mm. At the same time, punch 10 pieces of blank aluminum foil for the electrode sheet. Take the average mass of the 10 pieces of aluminum foil as the mass of Φ = 14 mm. Put the punched electrode sheet into a vacuum oven at 60 °C under vacuum for 4 h.

[0089] S4. Select complete and undamaged positive electrode sheets. Use insulating tweezers to test the electrode sheets, separators, lithium metal negative electrodes, gaskets, and spring sheets of the positive electrode case (CR2032 button cell). Drop 4 - 6 drops of electrolyte (the electrolyte is a conventional electrolyte, mainly composed of EC, DMC, DEC, containing additives such as VC and PS, and the lithium salt is 1 mol / L LiPF6). Finally, cover the negative electrode case to assemble the button cell. Use insulating tweezers to place the button cell with the negative electrode side facing up on the die of the button cell sealer, adjust the pressure to 800 Pa, and press for 5 s to complete the assembly and prepare the button cell.

[0090] Under the conditions of 3 - 4.25 V and 0.1 C, test the capacities of device examples 101 - 112 and device comparative examples 101 - 109. This capacity is used to represent the gram capacity of the positive electrode material. For specific test data, please refer to Table 2.

[0091] Table 2

[0092]

[0093]

[0094] Note: The crystal form of the positive electrode material in the table corresponds to that of its precursor material.

[0095] As can be seen from Table 2, the capacities of device examples 101 - 112 are higher than those of device comparative examples 101 - 109.

[0096] Device examples 201 - 212, and device comparative examples 201 - 209

[0097] Device examples 201 - 212 and device comparative examples 201 - 209 are respectively full cells prepared using the positive electrode materials in synthesis examples 1 - 12 and synthesis comparative examples 1 - 9.

[0098] The following is an explanation of the preparation of the full cell:

[0099] S1. Mix the positive electrode slurry according to the ratio of active material: SP&KS - 6&PVDF = 94.5%: 2%: 1%: 2.5%. Among them, there is 300 g of the positive electrode, about 600 - 900 g of NMP, stir for 4 h, and the final slurry should just flow appropriately.

[0100] S2. Coating is carried out in an automatic coater, and the positive electrode sheet is produced in the rolling process, with the areal density of the electrode sheet controlled at 16 mg / cm2.

[0101] S3. Artificial graphite is used for the negative electrode, and homogenization is carried out according to the ratio of graphite:SP:CMC:SBR = 95.5%:1%:1.5%:2%, and the coating areal density is controlled at 10 mg / cm 2 .

[0102] S4. A 20-μm dry-process PP / PE / PP separator is used, and the electrolyte is a conventional electrolyte, the main components of which are EC, DMC, and DEC, containing additives such as VC and PS, and the lithium salt is 1 mol / L LiPF6.

[0103] S5. Assemble a battery of model 503048, with the battery capacity of about 800 mAh, and use it for testing, the voltage range is 3.0 - 4.20 V; the 1C charge-discharge cycle is carried out for 300 weeks at 45 °C to compare its capacity retention rate.

[0104] For device examples 201 - 222 and device comparative examples 201 - 209, test △U300 / △U2 and the capacity retention rate. For specific test data, please refer to Table 3.

[0105] Table 3

[0106]

[0107]

[0108] As can be seen from Table 3, due to Ni 2+ satisfying (y / x + 0.3), the cycle stability of device examples 201 - 212 is higher than that of device comparative examples 201 - 209.

[0109] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A cathode material, characterized in that, Including: The molecular formula of the positive electrode material is: Li n Ni x Co e Mn y Al m M 1-x-y-e-m O2, Ni on the surface of the positive electrode material 2+ The content is less than E, E=y / x+0.3; wherein the Ni on the surface of the positive electrode material 2+ The content refers to the Ni content that can be measured by X-ray photoelectron spectrometer. 2+ The ratio of the content to the ion content of all Ni elements in various valence states in the measurable depth, M is a doping element and a coating element, and the doping element and the coating element are each independently selected from at least one of H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; 1<n<1.1, 0.6≤x<1, 0<e≤0.4, 0≤y≤0.4, 0≤m≤0.4, 0<1-xyem≤0.05; and y and m are not both 0; In the XRD pattern of the positive electrode material, the ratio of the peak intensity of the (003) crystal plane to the peak intensity of the (104) crystal plane is not less than 0.

8.

2. The cathode material according to claim 1, wherein When 0.6 ≤ x < 0.7, the specific capacity Z of the positive electrode material is: 140 mAh / g ≤ Z < 200 mAh / g; when 0.7 ≤ x < 0.8, 160 mAh / g ≤ Z < 220 mAh / g; when 0.8 ≤ x < 0.9, 180 mAh / g ≤ Z < 240 mAh / g; when 0.9 ≤ x < 1, 200 mAh / g ≤ Z < 260 mAh / g.

3. The positive electrode material according to claim 1, characterized in that, The capacity retention rate of the positive electrode material is not less than 80%; wherein, the capacity retention rate is the capacity ratio obtained by testing the capacity of the full cell corresponding to the positive electrode material after 300 cycles of charge-discharge at 2.8 - 4.25 V and 0.1 C and the capacity after the first charge-discharge.

4. The cathode material according to any one of claims 1-3, characterized in that, The positive electrode material is a polycrystalline material, and / or, a single crystal material.

5. The cathode material according to claim 4, characterized in that, The positive electrode material is a polycrystalline material, and the median particle size D of the positive electrode material 50 is ≤ 25 μm.

6. The cathode material according to claim 4, characterized in that, The positive electrode material is a polycrystalline material, and △U 300 / △U2 of the positive electrode material is 0.8 - 2.0; wherein, △U2 is the voltage difference obtained by testing the first voltage after the full cell corresponding to the positive electrode material is charged and discharged once at 2.8 - 4.25V and 0.1C, and then charged to 4.25V and powered off for 300s, and the second voltage when discharging for 30s at 1C after 300s of power off; △U 300 is the voltage difference obtained by testing the third voltage after the full cell is charged and discharged 300 cycles at 2.8 - 4.25V and 0.1C, then charged to 4.25V and powered off for 300s, and the fourth voltage when discharging for 30s at 1C.

7. The cathode material according to claim 4, wherein The positive electrode material is a single crystal material, and the median particle size D of the positive electrode material 50 is ≤ 10 μm.

8. The cathode material according to claim 4, characterized in that, The positive electrode material is a single crystal material, and the cycle performance of the positive electrode material is calculated by △U 300 / △U2. The △U 300 / △U2 is 0.8 - 2.4; wherein, △U2 is the voltage difference obtained by testing the first voltage after charging and discharging the full cell corresponding to the positive electrode material once at 2.8 - 4.25V and 0.1C and then powering off for 300s after charging to 4.25V, and the second voltage after discharging for 30s at 1C after powering off for 300s; △U 300 is the voltage difference obtained by testing the third voltage after charging and discharging the full cell 300 cycles at 2.8 - 4.25V and 0.1C and then powering off for 300s after charging to 4.25V, and the fourth voltage after discharging for 30s at 1C.

9. A method for preparing a cathode material according to any one of claims 1-8, characterized in that, Including: Performing a first sintering treatment on a mixture of a precursor, a dopant, and a lithium source in an atmosphere with an oxygen content of not less than 20%. Performing a second sintering treatment on a mixture of the first sintering treatment product and a coating agent in an atmosphere with an oxygen content of not less than 20% to obtain a positive electrode material; wherein, the second sintering temperature of the second sintering treatment is lower than the first sintering temperature of the first sintering treatment; and washing and drying the intermediate sintering product before the end of the second sintering treatment.

10. The method according to claim 9, wherein The first sintering treatment is carried out in a box furnace, a roller hearth kiln, a rotary kiln, or a track kiln.

11. The method according to claim 9, wherein The dopant is an inorganic compound corresponding to the doping element in the positive electrode material, and the coating agent is an inorganic compound corresponding to the coating element in the positive electrode material.

12. The method according to claim 9, characterized in that The time for the water washing does not exceed 30 minutes.

13. The method according to any one of claims 9 to 12, characterized in that, The precursor is selected from: hydroxides with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d (OH)2, oxides with the molecular formula Ni a Co b Mn c Al d Q 1-a-b-c-d O, and salt precursors of Ni a Co b Mn c Al d Q 1-a-b-c-d TM; where Q is a doping element, and Q is selected from at least one of H, Zr, Sr, Mo, Ba, W, B, Ti, N, K, Na, Mg, Li, C, F, Si, Ca, Cu, La, and P; TM represents a salt anion, and each of a, b, c, d is respectively selected from: 0.6 ≤ a < 1, 0 < b ≤ 0.4, 0 ≤ c ≤ 0.4, 0 ≤ d ≤ 0.4, 0 ≤ 1 - a - b - c - d ≤ 0.05; and c and d are not both 0.

14. The method according to claim 13, wherein, When a ≥ 15. The method according to claim 13, wherein ​ 16. The method according to claim 13, characterized in that, ​ 17. A lithium-ion battery, characterized in that, ​ ​

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