Ternary positive electrode material with coating layer and preparation method thereof

Abstract

The application discloses a ternary positive electrode material with a coating layer and a preparation method thereof, so as to improve the stability of the ternary positive electrode material. The molecular formula of the ternary positive electrode material substrate is: Li p Ni x Co y Mn z Al k N 1‑x‑y‑z‑k O2, and the coating layer comprises LiBO2 and Li2B4O7; wherein N is one or more of Cr, V, Nb, P, Ta, Zr, Ti, Mo and W; p, x, y, z and k each independently satisfy: p≥1, 0.6≤x<1, 0≤y<0.4, 0<z<0.4, 0<k<0.4, 0<1‑x‑y‑z‑k<0.1; and z and k are not 0 at the same time.

Description

Technical Field

[0001] This application relates to the field of lithium battery materials technology, and in particular to a ternary cathode material with a coating layer and its preparation method. Background Technology

[0002] With the development of new energy technologies, ternary (nickel, cobalt, manganese) cathode materials are used in lithium batteries due to their high energy density. However, ternary cathode materials suffer from poor stability. This is mainly because the layered structure of the ternary cathode material undergoes a phase transition during the charging and discharging process of the lithium battery, and because the ternary cathode material undergoes side reactions with the electrolyte in the lithium battery.

[0003] Currently, to improve the stability of ternary cathode materials and promote their widespread use, existing technologies involve adding various types of dopants to the ternary cathode material. These dopants are distributed between the layers of the material, thus supporting its layered structure. However, this method cannot control the uniform distribution of dopants within the layered structure and fails to effectively address the problem of side reactions between the ternary cathode material and the electrolyte in lithium batteries, leading to a decrease in stability. Furthermore, existing technologies also control the crystal growth process of primary particles within the ternary cathode material, causing them to grow into elongated shapes. This aims to increase the porosity within the ternary cathode material (secondary particles) and improve its stability. However, this method suffers from difficulties in controlling the growth direction of primary particles and uneven porosity, making it prone to sudden drops in stability and performance degradation during battery charging and discharging. Therefore, existing technologies lack an effective method for improving the stability of ternary cathode materials, as well as a stable ternary cathode material itself. Summary of the Invention

[0004] This application provides a ternary cathode material with a coating layer and a method for preparing the same, in order to improve the stability of the ternary cathode material.

[0005] In a first aspect, this application provides a ternary cathode material with a coating layer, comprising:

[0006] The molecular formula of the ternary cathode material matrix is: Li p Ni x Co y Mn z Al k N 1-x-y-z-kO2, the coating layer of the ternary cathode material includes LiBO2, Li2B4O7; wherein, N is one or more of Cr, V, Nb, P, Ta, Zr, Ti, Mo, and W; p, x, y, z, k each independently satisfy: p≥1, 0.6≤x<1, 0≤y<0.4, 0<z<0.4, 0<k<0.4, 0<1-xyzk<0.1; and z and k are not simultaneously 0.

[0007] The aforementioned ternary cathode material contains doped elements in its matrix, which can effectively improve the stability of the matrix. Furthermore, the LiBO2 and Li2B4O7 in the coating layer can effectively reduce the impedance of lithium ions at the grain boundaries, thereby synergistically improving the efficiency of lithium ion insertion and extraction, and thus effectively improving the stability of the ternary cathode material.

[0008] In one possible implementation, the coating layer further includes NiO and A; and when N is one or more of Cr, Zr, and Ti, A is Li2NO3; when N is one or more of V, Nb, P, and Ta, A is LiNO3; when N is Mo and / or W, A is Li2NO4.

[0009] In the above-mentioned embodiments, the NiO in the coating layer is a rock salt phase, which has stable performance and can effectively isolate the inner layer of the ternary cathode material from the electrolyte, avoiding side reactions between the inner layer of the ternary cathode material and the electrolyte, and effectively improving the stability of lithium ions. Simultaneously, the A (i.e., Li₂NO₃, LiNO₃, and / or Li₂NO₄) in the coating layer is a spinel phase, which can effectively expand the lithium ion channels, and LiBO₂ and Li₂B₄O₇ can effectively reduce the impedance of lithium ions at grain boundaries, thereby synergistically improving the efficiency of lithium ion insertion and extraction. Furthermore, since the LiBO₂ and Li₂B₄O₇ in the coating layer adhere to the surface of the ternary cathode material in a glassy state, they can further improve the stability of the ternary cathode material by increasing the grain boundary strength and mitigating the erosion of the ternary cathode material by electrolysis.

[0010] In one possible implementation, the NiO content is no more than 0.2 wt%, and the A content is no more than 0.5 wt%.

[0011] Secondly, this application provides a method for preparing a ternary cathode material with a coating layer as described in the first aspect, comprising:

[0012] A first sintering process is performed on a mixture of ternary precursor, lithium source and dopant source to obtain intermediate ternary cathode material;

[0013] The mixture of the intermediate ternary cathode material and the boron-containing material is subjected to a second high-temperature sintering treatment to obtain the ternary cathode material; wherein the second sintering temperature is lower than the first sintering temperature.

[0014] In one possible implementation, the doping source is selected from one or more of the following: CrO2, V2O5, NbO2, P2O5, TaO2, ZrO2, TiO2, MoO3, and WO3.

[0015] In one possible implementation, when the doping source includes WO3, the content of NiO in the coating layer of the intermediate ternary cathode material is no more than 0.2 wt%, and the content of Li2WO4 is no more than 0.5 wt%.

[0016] In one possible implementation, the boron-containing substance is any one of LiBO2, Li2B4O7, Li3BO3, and H3BO3.

[0017] In one possible implementation, the first sintering temperature of the first sintering treatment is 650-900℃, and the first sintering time is 2-14 hours; the second sintering temperature of the second sintering treatment is 250-600℃, and the second sintering time is 6-12 hours.

[0018] One possible implementation includes, before obtaining the intermediate ternary cathode material:

[0019] The mixture is subjected to a first sintering treatment;

[0020] The product of the first sintering treatment is washed with water to obtain a hydrated ternary cathode material.

[0021] The aqueous ternary cathode material is centrifuged and dried to obtain the intermediate ternary cathode material.

[0022] One possible implementation is that the ternary precursor is selected from: molecules with the general formula Ni a Co b Mn c Al 1-a-b-c The hydroxide precursor of (OH)₂, with the general molecular formula Ni a Co b Mn c Al 1-a-b-c O oxide precursors; each of a, b, and c independently satisfies: 0.6 ≤ a < 1, 0 ≤ b < 0.4, 0 ≤ c < 1, 0 ≤ 1-abc, and c and 1-abc are not simultaneously 0.

[0023] In one possible implementation, the lithium source is lithium hydroxide or lithium carbonate.

[0024] Thirdly, this application provides a lithium battery, comprising:

[0025] The ternary cathode material with a coating layer as described in the first aspect and any possible embodiment, or the ternary cathode material with a coating layer prepared by the method described in the second aspect and any possible embodiment. Attached Figure Description

[0026] Figure 1 SEM image of the positive electrode material of Example 1 provided in this application;

[0027] Figure 2 SEM image of the positive electrode material of Example 2 provided in this application;

[0028] Figure 3 SEM image of the positive electrode material of Example 3 provided in this application;

[0029] Figure 4 TEM image of the cathode material of Example 3 provided in this application;

[0030] Figure 5 This is a SEM image of the cathode material synthesized in Comparative Example 1 provided in the embodiments of this application;

[0031] Figure 6 This is a SEM image of the synthesized cathode material of Comparative Example 2 provided in the embodiments of this application. Detailed Implementation

[0032] To address the problem of poor stability in existing ternary cathode materials, this application proposes a ternary cathode material with a coating layer: the molecular formula of the ternary cathode material matrix is: Li p Ni x Co y Mn z Al k N 1-x-y-z-k O2, the ternary cathode material coating layer includes LiBO2, Li2B4O7; wherein, N is one or more of Cr, V, Nb, P, Ta, Zr, Ti, Mo, and W; p, x, y, z, k each independently satisfy: p≥1, 0.6≤x<1, 0≤y<0.4, 0<z<0.4, 0<k<0.4, 0<1-xyzk<0.1; and z and k are not simultaneously 0.

[0033] To better understand the above technical solutions, the technical solutions of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of this application and the specific features in the embodiments are detailed descriptions of the technical solutions of this application, rather than limitations on the technical solutions of this application. In the absence of conflict, the embodiments of this application and the technical features in the embodiments can be combined with each other.

[0034] Firstly, this application proposes a ternary cathode material with a coating layer, which exhibits good cycle stability. The molecular formula of the matrix of the ternary cathode material is: Li p Ni x Co y Mn z Al k N 1-x-y-z-k O2, the coating layer includes LiBO2, Li2B4O7.

[0035] Wherein, N is one or more of Cr, V, Nb, P, Ta, Zr, Ti, Mo, and W; p, x, y, z, and k each independently satisfy: p ≥ 1, 0.6 ≤ x < 1, 0 ≤ y < 0.4, 0 < z < 0.4, 0 < k < 0.4, 0 < 1 - xyzk < 0.1; and z and k are not simultaneously 0.

[0036] Furthermore, since the dopant element is enriched on the surface of the ternary cathode material and reacts with the lithium source and oxygen to form product A, and since the dopant element is a high-valence metal ion, its electron-withdrawing ability is superior to that of nickel ions, thus promoting the formation of NiO on the surface of the ternary cathode material. Therefore, the coating layer also includes NiO and A; and when the N is one or more of Cr, Zr, and Ti, the A is Li2NO3; when the N is one or more of V, Nb, P, and Ta, the A is LiNO3; when the N is Mo and / or W, the A is Li2NO4. Moreover, the content of NiO in the coating layer is not greater than 0.2 wt%, and the content of A is not greater than 0.5 wt%. Specifically, the NiO content can be 0.01 wt%, 0.03 wt%, or 0.05 wt%. The A content can be 0.01 wt%, 0.1 wt%, 0.2 wt%, or 0.3 wt%.

[0037] The inclusion of elements in this ternary cathode material makes its layered structure more stable. Furthermore, the presence of NiO in the coating layer effectively isolates the electrolyte from the active components of the ternary cathode material, preventing side reactions and ensuring that the cathode material does not collapse due to side reactions during lithium battery use. Simultaneously, the lithium borate (LiBO2, Li2B4O7) in the coating layer can enhance the stability of the ternary cathode material by expanding lithium-ion channels, and A (i.e., Li2NO3, LiNO3, and / or Li2NO4) can enhance the stability of the ternary cathode material by reducing the impedance of lithium-ion transport at grain boundaries; therefore, lithium borate and A in the coating layer synergistically improve the stability of the ternary cathode material.

[0038] Secondly, this application proposes a method for preparing a cathode material as described in the first aspect, the method comprising:

[0039] Step 101: Perform a first sintering treatment on the mixture of ternary precursor, lithium source and dopant source to obtain intermediate ternary cathode material.

[0040] The doping source is selected from at least one of the following substances: CrO2, V2O5, NbO2, P2O5, TaO2, ZrO2, TiO2, MoO3, WO3.

[0041] Specifically, the boron-containing substance can be any one of LiBO2, Li2B4O7, Li3BO3, and H3BO3. The lithium source is lithium hydroxide or lithium carbonate.

[0042] The ternary precursor is selected from: the general molecular formula Ni a Co b Mn c Al 1-a-b-c The hydroxide precursor of (OH)₂, with the general molecular formula Ni a Co b Mn c Al 1-a-b-c O oxide precursors; each of a, b, and c independently satisfies: 0.6 ≤ a < 1, 0 ≤ b < 0.4, 0 ≤ c < 1, 0 ≤ 1-abc, and c and 1-abc are not simultaneously 0.

[0043] The molar ratio between the ternary precursor and the lithium source can be determined according to the lithium content in the ternary cathode material. The mass ratio between the ternary precursor and the additive can also be determined according to the content of the dopant element in the target product, i.e., the ternary cathode material. In the embodiments of this application, the amount of dopant source added is 1‰-2% of the mass of the ternary precursor.

[0044] Furthermore, the first sintering temperature of the first sintering treatment is 650-900℃, and the first sintering time is 2-14 hours. The heating rate can be 2℃ / min or 3℃ / min, to obtain an intermediate ternary cathode material with NiO and A as the coating layer. Preferably, the first sintering temperature is 700-850℃, and the first sintering time is 4-10 hours.

[0045] Furthermore, when the doping source includes WO3, WO3 reacts with the lithium source and oxygen during the first sintering process to generate lithium tungstate. Therefore, the coating layer A of the obtained intermediate ternary cathode material includes Li2WO4. Moreover, the NiO content in the coating layer of this intermediate ternary cathode material is no greater than 0.2 wt%, and the Li2WO4 content is no greater than 0.5 wt%. Specifically, the NiO content can be 0.01 wt%, 0.03 wt%, or 0.05 wt%. The Li2WO4 content can be 0.01 wt%, 0.1 wt%, 0.2 wt%, or 0.3 wt%.

[0046] Because the intensity of photoelectrons emitted from the surface of the sample (i.e., the peak area of ​​the characteristic peak) after X-ray irradiation has a linear relationship with the concentration (n) of the corresponding substance (atom) in the sample, NiO, Li2WO4, or other substances in the coating layer can be quantitatively determined by XPS (X-ray Photoelectron Spectroscopy) of the intermediate ternary cathode material. Specifically, the determination method can be to remove the background in the spectrum, measure the peak area of ​​the corresponding substance / element, and finally determine the content of NiO, Li2WO4, or other substances based on the sensitivity factor.

[0047] Furthermore, the formation of the intermediate ternary cathode material coating layer after the first sintering treatment will be explained below.

[0048] On the one hand, although the temperature conditions of the first sintering treatment are 650-900℃, the metal dopant element corresponding to the dopant source will gradually be incorporated into the interior of the intermediate ternary cathode material during the first sintering process. However, doping is a thermodynamic diffusion phenomenon, which means that the diffusion difficulty increases the further the dopant element diffuses into the material; moreover, the element distribution and structure in the intermediate ternary cathode material are not uniform throughout, which also leads to the metal dopant element being incorporated into the interior of the intermediate ternary cathode material in small quantities. Therefore, the A (e.g., Li2WO4, Li3PO4) formed by the dopant source during the first sintering process is ultimately enriched on the surface of the intermediate ternary cathode material. On the other hand, the dopant element corresponding to the dopant source in the embodiments of this application is a high-valence metal ion, and the electron-acquiring ability of high-valence metal ions is stronger than that of nickel ions in the intermediate ternary cathode material. Therefore, high-valence metal ions can promote the formation of NiO from Ni ions on the surface of the intermediate ternary cathode material. Thus, the intermediate ternary cathode material obtained after the first sintering treatment is an intermediate ternary cathode material with a coating layer, and the coating layer is NiO and A.

[0049] Furthermore, before performing step 102, to avoid introducing impurities that could affect the performance of the intermediate ternary cathode material, the product of the first sintering treatment can be washed with water to obtain a water-containing ternary cathode material. Then, the ternary cathode material is thoroughly dried through centrifugation and drying steps to obtain an intermediate ternary cathode material with a coating layer including NiO and A.

[0050] Step 102: Perform a second sintering treatment on the mixture of the intermediate ternary cathode material and the boron-containing material to obtain the ternary cathode material.

[0051] The second sintering temperature is lower than the first sintering temperature.

[0052] The second sintering treatment involves a second sintering temperature of 250-600℃ and a second sintering time of 6-12 hours, with a heating rate of either 2℃ / min or 3℃ / min. Preferably, the second sintering temperature is 300-500℃ and the second sintering time is 8-11 hours.

[0053] Furthermore, the product from the second sintering treatment is sieved and demagnetized (e.g., to remove iron) to obtain a ternary cathode material. The molecular formula of the ternary cathode material matrix is: Li p Ni x Co y Mn z Al k N 1-x-y-z-k O2, the molecular formula of the coating layer is: NiO,LiBO2,Li2B4O7,A.

[0054] Wherein, N is one or more of Cr, V, Nb, P, Ta, Zr, Ti, Mo, and W; and when N is one or more of Cr, Zr, and Ti, A is Li2NO3; when N is one or more of V, Nb, P, and Ta, A is LiNO3; when N is Mo and / or W, A is Li2NO4; p, x, y, z, and k each independently satisfy: p≥1, 0.6≤x<1, 0≤y<0.4, 0<z<0.4, 0<k<0.4, 0<1-xyzk<0.1; and z and k are not both 0.

[0055] Based on the preparation method described in steps 101-102 above, the ternary cathode material contains Li p Ni x Co y Mn z Al k N 1-x-y-z-k O2 forms the matrix, and NiO, LiBO2, Li2B4O7, and A form the coating layer. In reality, each phase in the coating layer is an independent layer; that is, from the outside in, the coating layer consists of: a surface layer composed of LiBO2 and Li2B4O7, a sublayer composed of A, and a secondary sublayer composed of NiO. On one hand, the presence of dopants in the matrix of the ternary cathode material effectively supports the layered structure of the matrix. On the other hand, NiO in the coating layer, being a rock salt phase, possesses the advantage of stable performance, thus continuously isolating the matrix from the electrolyte solution, avoiding the impact of side reactions on the cycle stability of the ternary cathode material during lithium battery use. Furthermore, the NiO layer is relatively thin, having almost no impact on the extraction and insertion of lithium ions. Furthermore, the spinel phase in the coating layer can expand lithium-ion channels, while the glassy state of LiBO2 and Li2B4O7 can reduce the impedance at the grain boundaries during lithium-ion extraction and insertion, thereby synergistically improving the efficiency of lithium-ion extraction and insertion, and further enhancing the cycle stability and rate performance of the ternary cathode material.

[0056] The following description uses synthetic examples 1-3 and synthetic comparative examples 1-2 to further illustrate the process:

[0057] Synthesis Example 1

[0058] Step S1: Add 1 kg of precursor Ni to a ball mill jar (4 L) at a molar ratio of 1:1.05. 0.85 Co 0.06 Mn 0.09 (OH)2, 475g LiOH. At the same time, add 2.5g WO3 and stir at 300rpm for 120min to ensure that all components in the mixture are mixed evenly.

[0059] Step S2: The mixture is introduced into the casing, and an oxygen atmosphere (oxygen concentration ≥80%) is introduced for the first sintering treatment. The first sintering temperature is 750℃, the heating rate is 2℃ / min, and the first sintering time is 12 hours.

[0060] Step S3: After cooling the product of the first sintering treatment, crush, wash with water and dry to obtain a ternary cathode material with NiO and Li2WO4 coating.

[0061] Step S4: After uniformly mixing the ternary cathode material with 0.5 wt% H3BO3, place it in a sagger and then into a box furnace. Introduce an oxygen atmosphere (oxygen concentration ≥ 80%) for a second sintering treatment to obtain a ternary cathode material with a coating of NiO, Li2WO4, and LiBO2,Li2B4O7. The morphology of this ternary cathode material is as follows... Figure 1 As shown.

[0062] The second sintering temperature for the second sintering treatment is 320℃, and the second sintering time is 10 hours.

[0063] Synthesis Example 2

[0064] Step S1: Add 1 kg of precursor Ni to a ball mill jar (4 L) at a molar ratio of 1:1.05. 0.85 Co 0.06 Mn 0.09 (OH)2, 475g LiOH monohydrate; at the same time, add 4.2g TiO2, stir at 300rpm for 120min to make the components in the mixture uniform.

[0065] Step S2: The mixture is introduced into the casing, and an oxygen atmosphere (oxygen concentration ≥80%) is introduced for the first sintering treatment. The first sintering temperature is 750℃, the heating rate is 2℃ / min, and the first sintering time is 12 hours.

[0066] Step S3: After cooling the product from the first sintering treatment, crush, wash with water, and dry it to obtain a coating layer of NiO and Li4Ti5O. 12 Ternary cathode materials.

[0067] Step S4: After uniformly mixing the ternary cathode material with 0.5wt% H3BO3, place it in a sagger and then into a box furnace. Introduce an oxygen atmosphere (oxygen concentration ≥80%) for a second sintering treatment to obtain a coating layer of NiO and Li4Ti5O. 12 And LiBO2,Li2B4O7 ternary cathode material. The morphology of this ternary cathode material is as follows: Figure 2 As shown.

[0068] The second sintering temperature for the second sintering treatment is 320℃, and the second sintering time is 10 hours.

[0069] Synthesis Example 3

[0070] Step S1: Add 1 kg of precursor Ni to a ball mill jar (4 L) at a molar ratio of 1:1.05. 0.85 Co 0.06 Mn 0.09 (OH)2, 475g LiOH monohydrate; at the same time, add 5.4g ZrO2, stir at 300rpm for 120min to make the components in the mixture uniform.

[0071] Step S2: The mixture is introduced into the casing, and an oxygen atmosphere (oxygen concentration ≥80%) is introduced for the first sintering treatment. The first sintering temperature is 750℃, the heating rate is 2℃ / min, and the first sintering time is 12 hours.

[0072] Step S3: After cooling the product of the first sintering treatment, crush, wash with water and dry to obtain a ternary cathode material with NiO and Li2ZrO3 coating layers.

[0073] Step S4: After uniformly mixing the ternary cathode material with 0.5 wt% H3BO3, place it in a sagger and then into a box furnace. Introduce an oxygen atmosphere (oxygen concentration ≥ 80%) for a second sintering treatment to obtain a ternary cathode material with a coating of NiO, Li2ZrO3, and Li3BO3. The morphology of this ternary cathode material is as follows: Figure 3 As shown. TEM image of the ternary cathode material, as shown. Figure 4 As shown. By Figures 3-4 It can be seen that the ternary cathode material is composed of spinel phase, rock salt phase, and layered phase. Obviously, the spinel phase is Li2ZrO3 and LiBO2,Li2B4O7 in the coating layer, the rock salt phase is NiO in the coating layer, and the layered phase is the matrix of the ternary cathode material.

[0074] The second sintering temperature for the second sintering treatment is 320℃, and the second sintering time is 10 hours.

[0075] Synthetic Comparative Example 1

[0076] Step S1: Add 1 kg of precursor Ni to a ball mill jar (4 L) at a molar ratio of 1:1.05. 0.85 Co 0.06 Mn 0.09 (OH)2, 475g LiOH monohydrate, were stirred at 300rpm for 120min to ensure that all components in the mixture were homogeneous.

[0077] Step S2: The mixture is introduced into the casing, and an oxygen atmosphere (oxygen concentration ≥80%) is introduced for the first sintering treatment. The first sintering temperature is 750℃, the heating rate is 2℃ / min, and the first sintering time is 12 hours.

[0078] Step S3: After cooling the product from the first sintering treatment, crush, wash with water, and dry it to obtain the ternary cathode material.

[0079] Step S4: After uniformly mixing the ternary cathode material with 0.5 wt% H3BO3, place it in a sagger and then into a box furnace. Introduce an oxygen atmosphere (oxygen concentration ≥ 80%) for a second sintering treatment to obtain the ternary cathode material. The morphology of this ternary cathode material is as follows: Figure 5 As shown.

[0080] The second sintering temperature for the second sintering treatment is 320℃, and the second sintering time is 10 hours.

[0081] Synthetic Comparative Example 2

[0082] Step S1: Add 1 kg of precursor Ni to a ball mill jar (4 L) at a molar ratio of 1:1.05. 0.85 Co 0.06 Mn 0.09 (OH)2, 475g LiOH monohydrate, were stirred at 300rpm for 120min to ensure that all components in the mixture were homogeneous.

[0083] Step S2: The mixture is introduced into the casing, and an oxygen atmosphere (oxygen concentration ≥80%) is introduced for the first sintering treatment. The first sintering temperature is 750℃, the heating rate is 2℃ / min, and the first sintering time is 12 hours.

[0084] Step S3: After cooling the product from the first sintering treatment, crush, wash with water, and dry it to obtain the ternary cathode material.

[0085] Step S4: The ternary cathode material is mixed evenly with 0.5 wt% H3BO3 and WO3, placed in a sagger, and then placed in a box furnace. An oxygen atmosphere (oxygen concentration ≥ 80%) is introduced for a second sintering treatment to obtain the ternary cathode material. The morphology of the ternary cathode material is as follows: Figure 6 As shown.

[0086] The second sintering temperature for the second sintering treatment is 320℃, and the second sintering time is 10 hours.

[0087] Device Examples 1-3, Device Comparative Examples 1-2

[0088] Device Examples 1-3 and Device Comparative Examples 1-2 correspond to the ternary cathode materials prepared in Synthesis Examples 1-3 and Synthesis Comparative Examples 1-2, respectively. That is, the cathode materials in Device Examples 1-3 and Device Comparative Examples 1-2 are the ternary cathode materials prepared in Synthesis Examples 1-3 and Synthesis Comparative Examples 1-2.

[0089] The following describes the fabrication of devices in Examples 1-3 and Comparative Examples 1-2:

[0090] First, the ternary cathode material, acetylene black, and polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 94:3:3. Then, N-methylpyrrolidone (NMP) is added and stirred for 2 hours to obtain a viscous slurry.

[0091] Then, the viscous slurry is coated onto aluminum foil, baked at 80°C under vacuum, pressed into sheets, and cut into round sheets with a diameter of 16mm.

[0092] Finally, the disc was used as the positive electrode, a 16mm diameter pure lithium sheet was used as the negative electrode, a 1mol / L LiPF6+DEC / EC (volume ratio 1:1) mixed solution was used as the electrolyte, and a polyCelgard propylene microporous membrane was used as the separator. The discs were assembled into a button cell in an argon-filled glove box.

[0093] Rate performance, capacity retention, and gas production at 70°C for 7 days were tested on devices in Examples 1-3 and Comparative Examples 1-2, respectively. Please refer to Table 1 for specific test data.

[0094] First, let's explain the performance testing of the magnification ratio:

[0095] The test was conducted using the Landian CT2001A with a constant voltage cutoff current of 0.05C at 25℃.

[0096] Step S1: Charge at 0.1C to the cutoff voltage, let stand for 2 minutes, discharge at 0.1C to the termination voltage, and let stand for 2 minutes.

[0097] Step S2: Charge at 0.2C to the cutoff voltage, then discharge at 0.2C to the termination voltage.

[0098] Step S3: Charge at 0.5C to the cutoff voltage, then discharge at 0.5C to the termination voltage.

[0099] Step S4: Charge at 0.5C to the cutoff voltage, then discharge at 1C to the termination voltage.

[0100] Step S5: Charge at 0.5C to the cutoff voltage, and discharge at 1.3C to the termination voltage.

[0101] Step S6: Charge at 0.5C to the cutoff voltage, and discharge at 1.5C to the termination voltage.

[0102] Step S7: Charge at 0.5C to the cutoff voltage, then discharge at 2C to the termination voltage.

[0103] Step S8: Charge at 0.5C to the cutoff voltage, then discharge at 3C to the termination voltage.

[0104] Step S9: Charge at 0.5C to the cutoff voltage, then discharge at 5C to the termination voltage to obtain the corresponding rate performance data. This rate performance data is obtained by dividing the 5C discharge capacity by the 0.1C discharge capacity.

[0105] Next, the capacity retention test is explained: using the Xinwei test cabinet (CT3008-5V3A-A1), at 45℃, the cyclic voltage is 4.25~3V, the constant voltage cutoff current is 20mA, and the cycle is 300 times.

[0106] Finally, the 7-day 70°C gas production performance test is explained: First, the battery was fully charged and its volume was measured. Then, the fully charged battery was stored at 70°C for 7 days, and its volume was measured again. The difference between the two measurements was calculated. The volume was measured using an electronic solid density meter TW-120E.

[0107] Table 1

[0108] Device Example 1 0.7854 92.68％ 6.4％ Device Example 2 0.7882 92.84％ 6.1％ Device Example 3 0.7889 92.90％ 7.0％ Device Comparison Example 1 0.7342 89.63％ 17.5％ Device Comparison Example 2 0.7886 91.51％ 12.3％

[0109] As shown in Table 1, the rate performance and capacity retention of devices in Examples 1-3 are superior to those in Comparative Examples 1-2. Therefore, the cycle stability of devices in Examples 1-3 is superior to that of Comparative Examples 1-2.

[0110] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A ternary cathode material with a coating layer, characterized in that, include: The molecular formula of the ternary cathode material matrix is: Li p Ni x Co y Mn z Al k N 1-x-y-z-k O2, the coating layer includes LiBO2, Li2B4O7; wherein, N is one or more of Cr, V, Nb, P, Ta, Zr, Ti, Mo, and W; p, x, y, z, k each independently satisfy: p≥1, 0.6≤x<1, 0≤y<0.4, 0<z<0.4, 0≤k<0.4, 0<1-xyzk<0.1; and z and k are not simultaneously 0; The coating layer further includes NiO and A; and when A is Li2NO3, N is one or more of Cr, Zr, and Ti; when A is LiNO3, N is one or more of V, Nb, P, and Ta; when A is Li2NO4, N is Mo and / or W.

2. The ternary cathode material as described in claim 1, characterized in that, The content of NiO is no more than 0.2 wt%, and the content of A is no more than 0.5 wt%.

3. A method for preparing a ternary cathode material with a coating layer as described in claim 1 or 2, characterized in that, include: A first sintering process is performed on a mixture of ternary precursor, lithium source and dopant source to obtain intermediate ternary cathode material; The mixture of the intermediate ternary cathode material and the boron-containing substance is subjected to a second sintering treatment to obtain the ternary cathode material; wherein the second sintering temperature is lower than the first sintering temperature; and the boron-containing substance is H3BO3.

4. The method as described in claim 3, characterized in that, The doping source is selected from one or more of the following: CrO2, V2O5, NbO2, P2O5, TaO2, ZrO2, TiO2, MoO3, and WO3.

5. The method as described in claim 3 or 4, characterized in that, The first sintering temperature of the first sintering treatment is 650-900℃, and the first sintering time is 2-14 hours; the second sintering temperature of the second sintering treatment is 250-600℃, and the second sintering time is 6-12 hours.

6. The method according to any one of claims 3-5, characterized in that, Before obtaining the intermediate ternary cathode material, the process also includes: The product of the first sintering treatment is washed with water to obtain a hydrated ternary cathode material. The aqueous ternary cathode material is centrifuged and dried to obtain the intermediate ternary cathode material.

7. The method according to any one of claims 3-6, characterized in that, The ternary precursor is selected from: the general molecular formula Ni a Co b Mn c Al 1-a-b-c The hydroxide precursor of (OH)₂, with the general molecular formula Ni a Co b Mn c Al 1-a-b-c O oxide precursor; each a, b, c independently satisfies: 0.6≤a<1, 0≤b<0.4, 0≤c<1, 0≤1-abc, and c and 1-abc are not simultaneously 0.

8. A lithium battery, characterized in that, include: The ternary cathode material with a coating layer as described in claim 1 or 2, or the ternary cathode material with a coating layer prepared by the method described in any one of claims 3-7.

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