A modified lithium-rich positive electrode material and a preparation method thereof

Abstract

The application provides a modified lithium-rich positive electrode material and a preparation method thereof. The modified lithium-rich positive electrode material comprises a lithium-rich positive electrode body and a double-layer coating structure of an outer layer of the lithium-rich positive electrode body, wherein the outermost layer of the double-layer coating structure is a fast ion conductor layer, and the next outer layer is an active spinel layer; the active spinel layer has lithium vacancies, and the lithium vacancies account for 1mol% to 10mol% of the total amount of lithium ions of the modified lithium-rich positive electrode material. The fast ion conductor layer located at the outermost layer of the modified lithium-rich positive electrode material can inhibit the interface side reaction, reduce the interface impedance, improve the interface stability, promote the diffusion of lithium ions and improve the rate performance; the active spinel layer located at the next outer layer of the modified lithium-rich positive electrode material has a certain content of lithium vacancies, so that the coulomb efficiency and the discharge capacity can be improved, the migration of oxygen and transition metal ions can be inhibited, the structure can be stabilized, and the cycle performance can be improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries and relates to a modified lithium-rich cathode material and its preparation method. Background Technology

[0002] Currently, electric vehicles have increasingly higher requirements for driving range, low cost, and safety. The trend of lithium-ion battery cathode materials developing towards high specific capacity, high voltage, and low cost is becoming increasingly clear. Compared with commonly used ternary materials and lithium iron phosphate and other commercial cathode materials, lithium-rich cathode materials have significant advantages in terms of specific capacity, cost, and thermal stability.

[0003] Lithium-rich cathode materials are typically prepared by first using a co-precipitation method to prepare transition metal carbonate or hydroxide precursors, which are then mixed with a lithium source solid phase and sintered at high temperature. Because carbonates release a large amount of gas during high-temperature sintering, while hydroxides produce less gas, lithium-rich cathode materials prepared using hydroxide precursors have lower porosity and smaller specific surface area compared to those prepared using carbonate precursors. Consequently, they are inferior to the latter in terms of discharge capacity, first-cycle coulombic efficiency, and rate performance. However, they exhibit significant advantages in compaction density, cycle stability, storage capacity, and gas production.

[0004] Therefore, improving the initial coulombic efficiency, discharge capacity, and rate performance of lithium-rich cathode materials based on hydroxide systems is of great significance for enhancing the energy density of lithium-rich cathode materials and their commercial application. Summary of the Invention

[0005] This invention provides a modified lithium-rich cathode material. By sequentially coating the surface of the lithium-rich cathode material with an active spinel-like layer and a fast ion conductor layer, the modified lithium-rich cathode material effectively improves the defects of low initial coulombic efficiency and poor rate performance, and significantly reduces the capacity and voltage decay during long-cycle processes, thereby improving capacity retention.

[0006] The present invention also provides a method for preparing a modified lithium-rich cathode material. This method employs a specific liquid-phase treatment technique, which can simultaneously achieve precise control of the amount of lithium removed from the substrate surface and in-situ coating of the fast ion conductor layer, thereby preparing the aforementioned modified lithium-rich cathode material. Furthermore, this method has good process stability and coating uniformity, which is beneficial for large-scale production applications.

[0007] The first aspect of the present invention provides a modified lithium-rich cathode material, comprising a lithium-rich cathode body and a double-layer coating structure of an outer layer, wherein the outermost layer of the double-layer coating structure is a fast ion conductor layer and the next outermost layer is an active spinel-like layer.

[0008] The lithium-rich cathode body is composed of Li. 1+a Mn x Co yNi z M k O 2-b D b The compound, wherein 0 < a ≤ 1, 0.5 ≤ x < 1, 0 < y + z + k ≤ 0.5, 0 ≤ k ≤ 0.1, 0 ≤ b ≤ 0.25, M is selected from one or more of Ti, Mo, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, Zn, Na, K, and D is selected from one or more of F, S, P, N, B;

[0009] The active spinel layer has lithium vacancies, and the lithium vacancies account for 1 mol% to 10 mol% of the total lithium ions in the modified lithium-rich cathode material.

[0010] The modified lithium-rich cathode material as described above, wherein the fast ion conductor layer is a fast ion conductor compound formed by an oxide containing one or more elements selected from Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, Bi, P, B, Si, N, and S and lithium, or a mixture of the oxide and the fast ion conductor compound.

[0011] In the modified lithium-rich cathode material described above, the thickness of the active spinel-like layer is no greater than 4 nm;

[0012] And / or, the average thickness of the fast ion conductor layer is 2 to 15 nm.

[0013] A second aspect of this invention provides a method for preparing a modified lithium-rich cathode material, comprising the following steps:

[0014] 1) After mixing the lithium-rich cathode material of the hydroxide system with deionized water, a first suspension is obtained. A buffer complexing agent containing ammonium ions is added to the first suspension to obtain a second suspension with a pH of 7 to 10.

[0015] The molecular formula of the lithium-rich cathode material in the hydroxide system is Li. 1+a Mn x Co y Ni z M k O 2-b D b Wherein, 0 < a ≤ 1, 0.5 ≤ x < 1, 0 < y + z + k ≤ 0.5, 0 ≤ k ≤ 0.1, 0 ≤ b ≤ 0.25, M is selected from one or more of Ti, Mo, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, Zn, Na, and K, and D is selected from one or more of F, S, P, N, and B;

[0016] 2) The second suspension is mixed with an acidic coating source solution to obtain a third suspension with a pH value of 2.8 to 5.8;

[0017] 3) The third suspension is subjected to solid-liquid separation treatment. The solid components obtained after solid-liquid separation treatment are dried and then calcined at 150-350°C to obtain modified lithium-rich cathode material.

[0018] The preparation method described above, wherein the hydroxide system lithium-rich cathode material is prepared by calcining a mixture of a nickel-cobalt-manganese ternary material hydroxide precursor, a lithium source, an M source, and a D source in an oxygen-containing atmosphere.

[0019] In the preparation method described above, the acidic coating source solution is selected from acidic salt solutions of metallic elements and / or oxyacid solutions of non-metallic elements.

[0020] The metallic element is selected from one or more of Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, and Bi;

[0021] The non-metallic element is selected from one or more of P, B, Si, N, and S.

[0022] In the preparation method described above, in step 1), the buffer complexing agent is selected from one or more of ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium acetate, ammonium phosphate, and ammonium borate.

[0023] In the preparation method described above, in step 2), the concentration of the acidic coating source solution is 0.1–10 mol / L.

[0024] In the preparation method described above, in step 1), the mass ratio of the lithium-rich cathode material in the hydroxide system to the deionized water is (0.5-5):1.

[0025] In the preparation method described above, in step 3), the drying temperature is 90–130°C.

[0026] The present invention has at least the following beneficial effects:

[0027] 1) The modified lithium-rich cathode material of the present invention involves in-situ coating an active spinel-like layer and a fast ion conductor layer onto the surface of a hydroxide-based lithium-rich cathode material. The fast ion conductor layer, located on the outermost layer of the modified lithium-rich cathode material, can suppress interfacial side reactions, reduce interfacial impedance, improve interfacial stability, and promote lithium ion diffusion, thereby improving rate performance. The active spinel-like layer, located on the second outermost layer of the modified lithium-rich cathode material, has a certain amount of lithium vacancies, thus improving coulombic efficiency and discharge capacity, while suppressing oxygen release and the migration of transition metal ions, achieving the effects of stabilizing the structure and improving cycle performance.

[0028] 2) The preparation method of the modified lithium-rich cathode material of the present invention uses an ammonium-containing buffer complexing agent combined with an acidic coating source solution under specific pH conditions to simultaneously achieve precise control of the amount of lithium delithiation on the surface of the lithium-rich cathode material and uniform in-situ coating. This results in the in-situ formation of an active spinel-like layer and a fast ion conductor layer on the surface of the lithium-rich cathode material in the hydroxide system. The preparation method has good process stability and coating uniformity, which is beneficial for large-scale production and application.

[0029] 3) The preparation method of the modified lithium-rich cathode material of the present invention also has the advantages of low raw material cost, simple process and no introduction of other impurity elements. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 Here is a SEM image of the modified lithium-rich cathode material prepared in Example 1;

[0032] Figure 2 Here is a SEM image of the lithium-rich cathode material prepared in Comparative Example 1;

[0033] Figure 3 Here is a SEM image of the modified lithium-rich cathode material prepared in Comparative Example 2;

[0034] Figure 4 The graph shows a comparison of the half-cell cycle capacity retention rates of the modified lithium-rich cathode materials prepared in Example 1, Comparative Examples 2-4, and the lithium-rich cathode material prepared in Comparative Example 1.

[0035] Figure 5 The graph shows a comparison of the average half-cell cycle discharge voltage of the modified lithium-rich cathode materials prepared in Example 1, Comparative Examples 2-4, and the lithium-rich cathode material prepared in Comparative Example 1.

[0036] Figure 6 TEM image of the modified lithium-rich cathode material prepared in Example 1;

[0037] Figure 7 This is a TEM image of the lithium-rich cathode material prepared in Comparative Example 1. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0039] The first aspect of the present invention provides a modified lithium-rich cathode material, comprising a lithium-rich cathode body and a double-layer coating structure of an outer layer, wherein the outermost layer of the double-layer coating structure is a fast ion conductor layer and the next outermost layer is an active spinel-like layer.

[0040] The lithium-rich cathode is composed of Li 1+a Mn x Co y Ni z M k O 2-b D b The hydroxide system is a lithium-rich cathode material, wherein 0 < a ≤ 1, 0.5 ≤ x < 1, 0 < y + z + k ≤ 0.5, 0 ≤ k ≤ 0.1, 0 ≤ b ≤ 0.25, M is selected from one or more of Ti, Mo, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, Zn, Na, and K, and D is selected from one or more of F, S, P, N, and B;

[0041] The active spinel layer has lithium vacancies, which account for 1 mol% to 10 mol% of the total lithium ions in the modified lithium-rich cathode material.

[0042] The modified lithium-rich cathode material of the present invention involves sequentially coating the surface of a hydroxide-based lithium-rich cathode material with an active spinel-like layer and a fast-ion conductor layer. The fast-ion conductor layer, located on the outermost layer of the modified lithium-rich cathode material, can suppress interfacial side reactions, reduce interfacial impedance, improve interfacial stability, and promote lithium-ion diffusion, thereby improving rate performance. The active spinel-like layer, located on the second outermost layer of the modified lithium-rich cathode material, has a certain amount of lithium vacancies, thus improving coulombic efficiency and discharge capacity, while suppressing oxygen release and transition metal ion migration, achieving a stable structure and improved cycle performance.

[0043] Furthermore, when lithium vacancies account for 2 mol% to 6 mol% of the total lithium ions in the modified lithium-rich cathode material, the coulombic efficiency, discharge capacity, and cycle performance of the cathode active material are even more superior.

[0044] Furthermore, the fast ion conductor layer is a fast ion conductor compound formed by an oxide of one or more elements selected from Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, Bi, P, B, Si, N, and S with lithium, or a mixture of its oxide and fast ion conductor compound. For example, it can be a mixture of Li3PO4, Li4SiO4, LiAlO2, LiAlSiO4, Li3Al(PO4)2, LiAlO2, and Al2O3.

[0045] When the thickness of the active spinel layer is controlled to be no greater than 4 nm, and / or the average thickness of the fast ion conductor layer is 2–15 nm, the active spinel layer and the fast ion conductor layer can play a better coating role.

[0046] A second aspect of this invention provides a method for preparing a modified lithium-rich cathode material, comprising the following steps:

[0047] 1) After mixing the lithium-rich cathode material of the hydroxide system with deionized water, a first suspension is obtained. A buffer complexing agent containing ammonium ions is added to the first suspension to obtain a second suspension with a pH of 7 to 10.

[0048] The molecular formula of lithium-rich cathode material in hydroxide system is Li 1+a Mn x Co y Ni z M k O 2-b D b Wherein, 0 < a ≤ 1, 0.5 ≤ x < 1, 0 < y + z + k ≤ 0.5, 0 ≤ k ≤ 0.1, 0 ≤ b ≤ 0.25, M is selected from one or more of Ti, Mo, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, Zn, Na, and K, and D is selected from one or more of F, S, P, N, and B;

[0049] 2) The second suspension was mixed with an acidic coating source solution to obtain a third suspension with a pH value of 2.8–5.8;

[0050] 3) The third suspension is subjected to solid-liquid separation treatment. The solid components obtained after solid-liquid separation treatment are dried together and then calcined at 150-350℃ to obtain modified lithium-rich cathode material.

[0051] In step 1), by introducing a buffer complexing agent containing ammonium ions into the first suspension, the initial pH value can be controlled and reduced, thereby avoiding the uneven delithiation degree on the surface of the lithium-rich cathode material caused by an overly vigorous reaction when the acidic coating source solution is added later. On the other hand, the ammonium ions in the buffer complexing agent can complex with the cations in the acidic coating source, thereby slowing down the rate of the in-situ coating reaction and forming a more complete, uniform and dense coating layer on the surface of the lithium-rich cathode material.

[0052] In step 2), by controlling the pH value of the third suspension within the range of 2.8 to 5.8, the amount of acidic coating source solution used can be controlled, and the lithium-hydrogen exchange rate between the acidic coating source solution and the surface of the lithium-rich cathode material can be controlled. This not only achieves precise control over the degree of delithiation on the material surface and the amount of in-situ precipitation of the coating source, eliminating the problem of poor consistency between different batches of lithium-rich cathodes due to differences in residual lithium, but also forms a spinel-like transition layer with lithium vacancies on the material surface, inhibiting structural degradation, improving the first-cycle coulombic efficiency, and increasing the diffusion rate of lithium ions, thus improving the rate performance of the material.

[0053] In step 3), the solid components after solid-liquid separation of the third suspension are dried and then calcined at a low temperature of 150-350°C. The low calcination temperature allows the fast ion conductor coating layer formed by in-situ precipitation to exist in an amorphous form, which has good toughness, so that the positive electrode material will not detach from the body layer due to expansion and contraction during the charging and discharging process.

[0054] In summary, this invention utilizes an ammonium-containing buffer complexing agent combined with an acidic coating source solution to perform appropriate surface treatment and in-situ coating on lithium-rich cathode materials in a hydroxide system under specific pH conditions. Following low-temperature calcination, a complete and uniform active spinel-like layer with lithium vacancies and a fast-ion conductor layer are sequentially formed on the lithium-rich cathode material. This improves the lithium-ion diffusion rate and interfacial stability, thereby significantly enhancing the discharge capacity, initial coulombic efficiency, rate performance, and cycle stability of the lithium-rich cathode material in the hydroxide system, while significantly suppressing voltage decay. Furthermore, the preparation method of this invention also has advantages such as low raw material cost, simple process, and no introduction of other impurity elements.

[0055] In one specific embodiment, the hydroxide system lithium-rich cathode material having the above composition can be prepared by calcining a mixture of a nickel-cobalt-manganese ternary material hydroxide precursor, a lithium source, an M source, and a D source in an oxygen-containing atmosphere.

[0056] In this field, the preparation process of the above-mentioned lithium-rich cathode material is usually completed by co-precipitation method combined with high-temperature solid-state sintering method. Specifically, the precursor, lithium source, M source and D source are weighed according to the stoichiometric ratio, mixed evenly and placed in a high-temperature heating device for high-temperature calcination. After cooling, the lithium-rich cathode material is obtained by sieving.

[0057] The lithium source is selected from one or more of lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, and lithium oxalate.

[0058] The M source is selected from the oxide corresponding to its metal element. For example, the M source is selected from one or more of TiO2, MoO3, WO3, Nb2O5, Ta2O5, V2O5, Sb2O5, SnO2, SiO2, ZrO2, CrO2, Al2O3, La2O3, Y2O3, SrO, MgO, ZnO, Na2CO3, and K2CO3.

[0059] The D source includes one or more of the following: F source, S source, P source, N source, and B source. The F source is selected from one or more of NaF, LiF, KF, and NH4F. The S source is one or more of Li2S and Na2S. The N source is one or more of BN, AlN, and Si3N4. The P source is one or more of NH4H2PO4, (NH4)2HPO4, Li3PO4, and Na3PO4.

[0060] This invention does not specifically limit the high-temperature heating equipment, as long as it can provide a high-temperature heating environment, such as tube furnace, muffle furnace, chamber furnace, roller kiln, pusher kiln or rotary kiln.

[0061] High-temperature calcination is preferably carried out under segmented calcination conditions. First, the temperature is increased to 400–600℃ at a heating rate of 1–5℃ / min and held for 0–6 hours. Then, the temperature is increased to 750–950℃ at a heating rate of 1–5℃ / min and held for 10–20 hours, thus completing the calcination process. To save costs, calcination can be carried out in an air atmosphere.

[0062] The acidic coating source solution of the present invention is selected from acidic salt solutions of metallic elements and / or oxyacid solutions of non-metallic elements; wherein, the metallic elements are selected from one or more of Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, and Bi; and the non-metallic elements are selected from one or more of P, B, Si, N, and S.

[0063] Among these, acidic salt solutions of metallic elements are preferably nitrate solutions, such as aluminum nitrate, zirconium nitrate, magnesium nitrate, and zinc nitrate. Oxyacid solutions of non-metallic elements can be H3BO3, H3PO4, H4SiO4, etc.

[0064] The aforementioned coating source solution can react with lithium on the surface of lithium-rich cathode materials in a hydroxide system to form a fast-ion conductor coating layer. For example, when the acidic coating source solution is selected from H4SiO4, the formed fast-ion conductor coating layer is composed of lithium silicate; when the acidic coating source solution is selected from H3PO4, the formed fast-ion conductor coating layer is composed of lithium phosphate; when the acidic coating source solution is selected from zirconium nitrate, the formed fast-ion conductor coating layer is composed of a mixture of zirconium oxide and lithium zirconate; and when the acidic coating source is selected from aluminum nitrate, the formed fast-ion conductor coating layer is composed of a mixture of aluminum oxide and lithium aluminate. Specifically, the composition of the fast-ion conductor coating layer can be tested using XPS. The fast-ion conductor layer not only stabilizes the material interface but also accelerates lithium-ion transport, compensating for the poor rate performance of lithium-rich cathode materials.

[0065] To make the reaction between the acidic coated source solution and the surface of the lithium-rich cathode material more moderate, the concentration of the acidic coated source solution can be controlled at 0.1–10 mol / L.

[0066] This invention does not specifically limit the type of buffer complexing agent, as long as it has ammonium ions and can also be used as a buffer solution, including but not limited to one or more of ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium acetate, ammonium phosphate, and ammonium borate.

[0067] In step 1), to facilitate the uniform dispersion of the lithium-rich cathode material in the hydroxide system in water and to adjust the pH of the first suspension, the mass ratio of the lithium-rich cathode material to water in the hydroxide system can be controlled to be (0.5–5):1. Furthermore, to avoid excessive dissolution of the lithium-rich cathode material by water, the temperature of the added water can be controlled to be 0–30°C.

[0068] During the mixing process in steps 1) and 2), to ensure a more uniform mixture, the raw materials forming the first and second suspensions can be stirred for 1–30 minutes. This is to allow the Li-rich cathode material surface to be coated with a layer of Li. + / H + The exchange reaction and coating reaction are more complete and uniform. The raw materials that form the third suspension are stirred for 3 to 30 minutes.

[0069] In step 3), solid-liquid separation can be performed using centrifugation, vacuum filtration, or pressure filtration. Drying can be completed at 90–130℃ for 8–24 hours. Calcination can be performed for 2–12 hours depending on the requirements, with the heating rate controlled within 1–10 minutes, under an oxygen-containing atmosphere.

[0070] The modified lithium-rich cathode material of this invention, through control of various reaction conditions in the above preparation process, can exhibit superior interfacial stability, and show better initial coulombic efficiency, rate performance, cycle capacity retention, and voltage stability. Its relevant physicochemical parameters are within the following range: specific surface area of ​​0.2–4 m². 2 / g, Na content 50–3000ppm, surface residual alkali (total mass concentration of hydroxide and carbonate ions) 200–3000ppm, pH (suspension of 10g positive electrode material mixed with 100mL deionized water) 10.5–12.5, particle size D50 2–10μm, 3.5T powder compaction density 2.5–3.5g / m³ 3 The average thickness of the fast ion conductor coating layer is 2–15 nm, the thickness of the lithium vacancy spinel transition coating layer is no more than 4 nm, and the total amount of non-lithium and non-oxygen elements in the fast ion conductor coating layer accounts for 300–10000 ppm of the mass of the modified lithium-rich cathode material.

[0071] The modified lithium-rich cathode material and its preparation method provided by the present invention will be further described in detail below through specific embodiments.

[0072] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0073] Example 1

[0074] The preparation method of the modified lithium-rich cathode material in this embodiment includes the following steps:

[0075] 1) Using lithium source Li2CO3 and hydroxide precursor Ni 0.34 Co 0.06 Mn 0.6 (OH)2, dopant Nb2O5, and NH4F are mixed evenly in a certain proportion, placed in a muffle furnace, heated to 500℃ at 2℃ / min and held for 5 hours, then heated to 850℃ and held for 12 hours. After sintering, the mixture is sieved to obtain the lithium-rich cathode material Li. 1.3 Ni 0.34 Co 0.06 Mn 0.6 Nb 0.01 O 1.99 F 0.01 ;

[0076] 2) The lithium-rich cathode material obtained in step 1) is mixed with deionized water at 0°C at a mass ratio of 1:1 and stirred for 5 minutes to form the first suspension.

[0077] 3) Add a 0.5 mol / L ammonium acetate solution to the first suspension and stir for 5 minutes to form a second suspension with a pH of 9;

[0078] 4) Add a 1 mol / L aluminum nitrate solution to the second suspension and stir for 15 min to form a third suspension with a pH of 3.5;

[0079] 5) The third suspension was filtered, and the resulting filter cake was dried at 110°C and then calcined at 250°C for 8 hours in air at a heating rate of 2°C / min. After calcination, the modified lithium-rich cathode material was obtained by sieving.

[0080] Example 2

[0081] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that the ammonium acetate solution in step 3) is replaced with the ammonium oxalate solution, while the other conditions remain the same.

[0082] Example 3

[0083] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that in step 3), a second suspension with a pH of 8 is formed, while the other conditions remain the same.

[0084] Example 4

[0085] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that the aluminum nitrate solution in step 4) is replaced with zirconium nitrate solution, while the other conditions remain the same.

[0086] Example 5

[0087] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that in step 4), a third suspension with a pH of 4.5 is formed, while the other conditions remain the same.

[0088] Example 6

[0089] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that the calcination temperature in step 5) is replaced with 350℃, while the other conditions remain the same.

[0090] Example 7

[0091] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that the calcination temperature in step 5) is replaced with 150°C, while the other conditions remain the same.

[0092] Example 8

[0093] The preparation method of the modified lithium-rich cathode material in this embodiment is basically the same as that in Example 1. The difference is that the aluminum nitrate solution with a concentration of 1 mol / L in step 4) is replaced with an H3PO4 solution with a concentration of 0.3 mol / L, while the other conditions remain the same.

[0094] Comparative Example 1

[0095] This comparative example did not modify the lithium-rich cathode material; the lithium-rich cathode material was prepared simply by following the same steps as step 1) of Example 1.

[0096] Comparative Example 2

[0097] The preparation method of this comparative modified lithium-rich cathode material includes the following steps:

[0098] Steps 1) and 2) are the same as in Example 1;

[0099] 3) Add 1 mol of aluminum nitrate solution to the first suspension and stir for 15 min to form a second suspension with a pH of 3.5;

[0100] 4) The second suspension was filtered, and the resulting filter cake was dried at 110°C and then calcined at 250°C for 8 hours in air at a heating rate of 2°C / min. After calcination, the modified lithium-rich cathode material was obtained by sieving.

[0101] Comparative Example 3

[0102] The preparation method of the modified lithium-rich cathode material in this comparative example is basically the same as that in Example 1. The difference is that in step 4), a third suspension with a pH of 6 is formed, while the other conditions remain the same.

[0103] Comparative Example 4

[0104] The preparation method of this comparative modified lithium-rich cathode material is basically the same as that of Example 1, except that the calcination temperature in step 5) is replaced with 550℃, while the other conditions remain the same.

[0105] Comparative Example 5

[0106] The preparation method of the modified lithium-rich cathode material in this comparative example is basically the same as that in Example 1. The difference is that in step 4), a third suspension with a pH of 2.5 is formed, while the other conditions remain the same.

[0107] Comparative Example 6

[0108] The preparation method of this comparative modified lithium-rich cathode material is basically the same as that of Example 1, except that the ammonium acetate solution in step 3) is replaced with sodium dihydrogen phosphate solution, while the other conditions remain the same.

[0109] Test case

[0110] A. Characterization of cathode materials

[0111] 1) The specific surface area of ​​the cathode materials prepared in the above examples and comparative examples was determined by nitrogen adsorption BET method, and the Li vacancies [(Li / TM] were determined by ICP (Inductively Coupled Plasma Mass Spectrometry). 改性前 -Li / TM 改性后 ) / Li / TM 改性前 The following parameters were measured: Na content, surface residual alkali amount by potentiometric titration, pH by pH meter after dissolving 10g of cathode material in 100mL of deionized water at room temperature, particle size D50 by Malvern laser particle size analyzer, compaction density of powder at 3.5T pressure by powder compaction tester, average thickness of coating layer by TEM (Transmission Electron Microscope), and mass ratio of non-lithium and non-oxygen elements in fast ion conductor layer to cathode material by ICP (Inductively Coupled Plasma Mass Spectrometry). The test results are shown in Table 1.

[0112] Table 1

[0113]

[0114]

[0115] Note: The average thickness of the fast ion conductor layer in Comparative Example 2 is 0-18 nm, indicating that the fast ion conductor layer is not uniformly coated and that some locations are not coated with the fast ion conductor layer.

[0116] 2) The cathode materials obtained in Example 1, Comparative Example 1, and Comparative Example 2 were tested using scanning electron microscopy and transmission electron microscopy. Figure 1 This is a SEM image of the modified lithium-rich cathode material prepared in Example 1. Figure 2 The image shows a SEM image of the lithium-rich cathode material prepared in Comparative Example 1. Figure 3 The image shows the SEM image of the modified lithium-rich cathode material prepared in Comparative Example 2. Figure 6 This is a TEM image of the modified lithium-rich cathode material prepared in Example 1. Figure 7 This is a TEM image of the lithium-rich cathode material prepared in Comparative Example 1.

[0117] pass Figure 1 and Figure 2 The comparison shows that the lithium-rich cathode material prepared by this invention forms a distinct coating layer on its surface; through Figure 1 and Figure 3 The comparison shows that the present invention, by introducing a buffer complexing agent containing ammonium ions, forms a more uniform, complete, and dense coating layer on the surface of the lithium-rich cathode material; through Figure 6 and Figure 7 The comparison allows for a clearer observation that the lithium-rich cathode prepared in this invention has a distinct double-layer coating structure.

[0118] B. Cathode Material Performance Testing

[0119] The cathode materials prepared in the above examples and comparative examples were assembled into liquid half-cells. The assembly method was as follows: the prepared lithium-rich cathode material or modified lithium-rich cathode material, conductive agent Super-P, and binder PVDF were added to NMP solvent in a ratio of 90:5:5 and mixed evenly to obtain a slurry. The obtained slurry was then coated, dried, stamped, and rolled to obtain a cathode electrode. The stainless steel shell of the button cell, the cathode electrode, the PP separator, and the lithium sheet were stacked in sequence, a certain amount of electrolyte was added, and the cells were sealed and allowed to stand to obtain a liquid half-cell.

[0120] The following performance tests were performed on the assembled liquid half-cell battery:

[0121] 1. 0.2C discharge capacity

[0122] Test method: After the assembled battery has been left to stand for 5 hours, it is charged at a constant current of 0.2C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is equal to 0.05C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to 2.5V. The resulting discharge capacity is the 0.2C discharge capacity.

[0123] 2. First Coulomb efficiency

[0124] Test method: After the assembled battery has been left to stand for 5 hours, it is charged at a constant current of 0.2C to 4.55V, then charged at a constant voltage of 4.55V until the cutoff current is equal to 0.05C. After standing for 5 minutes, it is discharged at a constant current of 0.2C to 2.5V. The resulting discharge capacity / charge capacity is the initial coulombic efficiency.

[0125] 3. 1C / 0.2C rate performance

[0126] Test method: Charge and discharge the obtained half cell at 0.2C rate for 1 cycle, and then charge and discharge it at 1C rate for 1 cycle. The result of 1C discharge capacity / 0.2C discharge capacity is its 1C / 0.2C rate performance.

[0127] 4. Capacity retention rate at 100T in 1C cycle

[0128] Test method: The obtained half-cell is charged and discharged at a rate of 1C for 100 cycles. The discharge capacity of the 100th cycle / the discharge capacity of the 1st cycle is its capacity retention rate after 100T cycles at 1C.

[0129] 5. 1C cycle 100T voltage decay

[0130] Test method: The obtained half-cell was charged and discharged at a rate of 1C for 100 cycles. The average discharge voltage of the 100th cycle minus the average discharge voltage of the 1st cycle is the voltage decay of the half-cell after 100T of 1C cycle (average discharge voltage = discharge energy / discharge capacity).

[0131] The test results for the above parameters are shown in Table 2.

[0132] Table 2

[0133]

[0134]

[0135] As can be seen from Table 2:

[0136] The test results of Examples 1-8 are significantly improved compared with Comparative Example 1. That is, the surface modification process proposed in this paper significantly improves the first coulombic efficiency, discharge capacity, rate capability and cycle performance of lithium-rich cathode materials. The test results of Comparative Examples 2-6 prove that the key factors of this surface modification are the use of buffer complexing agent, dual pH control and appropriate calcination temperature. The reasons are: (1) the early introduction of buffer complexing agent slows down the rate of in-situ precipitation reaction, ensures the integrity and uniformity of the coating layer, and improves the interfacial stability of cathode material; (2) pH control ensures that the acidic solution reacts with the Li on the material surface. + / H + The degree of exchange is precisely controlled, forming a stable spinel-like transition layer on the material surface, suppressing structural degradation, and accelerating Li + (3) The lower calcination temperature allows the fast ion conductor coating layer to exist in an amorphous form, which has good toughness and ensures that it will not crack or detach from the substrate due to the expansion and contraction of the positive electrode material during the charging and discharging process.

[0137] To provide a more intuitive comparison, the half-cell cycle capacity retention and voltage decay of the modified lithium-rich cathode materials prepared in Example 1, Comparative Examples 2-4, and the lithium-rich cathode material prepared in Comparative Example 1 are presented as curves. Figure 4 This is a comparison chart showing the half-cell cycle capacity retention of the modified lithium-rich cathode materials prepared in Example 1, Comparative Examples 2-4, and the lithium-rich cathode material prepared in Comparative Example 1. Figure 5 This is a comparison chart of the average half-cell cycle discharge voltage of the modified lithium-rich cathode materials prepared in Example 1, Comparative Examples 2-4, and the lithium-rich cathode material prepared in Comparative Example 1. (Based on...) Figure 4 and Figure 5A comparison between Example 1 and Comparative Example 1 shows that the modified lithium-rich cathode material significantly improves the 1C discharge capacity of the half-cell and increases the average discharge voltage. Capacity and voltage decay during cycling are also significantly suppressed. This is attributed to the increased oxygen vacancies on the surface of the modified material, which promotes the activation of Li₂MnO₃ and Li₂MnO₃. + The improved diffusion rate and the complete and uniform coating layer resulted in better interfacial stability, suppressing side reactions and the increase in interfacial impedance under high voltage. In contrast, the modified lithium-rich cathodes prepared in Comparative Examples 2–4, while showing some improvement in discharge capacity compared to Comparative Example 1, did not exhibit significant improvement in cycle stability. Comparative Example 4 even showed a deterioration in capacity retention. The capacity improvement was attributed to the Li coating on the surface under acidic conditions. + / H + The reaction promoted the activation of Li₂MnO₃, leading to an increase in the first-cycle coulombic efficiency, but Li + / H + If the reaction level is too low, the improvement effect will be limited; if it is too high, it will damage the material structure, deteriorate the material performance, and affect the integrity and uniformity of the surface coating.

[0138] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A modified lithium-rich cathode material, characterized in that, The modified lithium-rich cathode material includes a lithium-rich cathode body and a double-layer coating structure, wherein the outermost layer of the double-layer coating structure is a fast ion conductor layer and the next outermost layer is an active spinel layer. The lithium-rich cathode body is composed of Li. 1+a Mn x Co y Ni z M k O 2-b D b The hydroxide system is a lithium-rich cathode material, wherein 0 < a ≤ 1, 0.5 ≤ x < 1, 0 < y + z + k ≤ 0.5, 0 ≤ k ≤ 0.1, 0 ≤ b ≤ 0.25, M is selected from one or more of Ti, Mo, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, Zn, Na, and K, and D is selected from one or more of F, S, P, N, and B; The active spinel-like layer is a spinel-like transition layer with lithium vacancies, wherein the lithium vacancies account for 1 mol% to 10 mol% of the total lithium ions in the modified lithium-rich cathode material; and the thickness of the active spinel-like layer is no greater than 4 nm. The fast ion conductor layer exists in an amorphous form; the average thickness of the fast ion conductor layer is 2~15nm. 2.The modified lithium-rich cathode material of claim 1, characterized in that, The fast ion conductor layer is a fast ion conductor compound formed by an oxide containing one or more elements selected from Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, Bi, P, B, Si, N, and S and lithium, or a mixture of the oxide and the fast ion conductor compound.

3. A method of producing the modified lithium-rich cathode material of claim 1 or 2, characterized in that, Includes the following steps: 1) After mixing the lithium-rich cathode material of the hydroxide system with deionized water, a first suspension is obtained. A buffer complexing agent containing ammonium ions is added to the first suspension to obtain a second suspension with a pH of 7-10. The molecular formula of the lithium-rich cathode material in the hydroxide system is Li. 1+a Mn x Co y Ni z M k O 2-b D b Wherein, 0 < a ≤ 1, 0.5 ≤ x < 1, 0 < y + z + k ≤ 0.5, 0 ≤ k ≤ 0.1, 0 ≤ b ≤ 0.25, M is selected from one or more of Ti, Mo, W, Nb, Ta, V, Sb, Sn, Si, Zr, Cr, Al, La, Y, Sr, Mg, Zn, Na, and K, and D is selected from one or more of F, S, P, N, and B; 2) The second suspension is mixed with an acidic coating source solution to obtain a third suspension with a pH value of 2.8 to 5.8; 3) The third suspension is subjected to solid-liquid separation treatment. The solid components obtained after solid-liquid separation treatment are dried and then calcined at 150~350℃ to obtain modified lithium-rich cathode material.

4. The production method according to claim 3, characterized by, The lithium-rich cathode material of the hydroxide system is prepared by calcining a mixture of a nickel-cobalt-manganese ternary material hydroxide precursor, a lithium source, an M source, and a D source in an oxygen-containing atmosphere.

5. The preparation method according to claim 3, characterized in that, The acidic coating source solution is selected from acidic salt solutions of metallic elements and / or oxyacid solutions of non-metallic elements. The metallic element is selected from one or more of Al, Zr, W, Zn, Mg, Ti, La, Nb, Sb, V, Y, Ce, and Bi; The non-metallic element is selected from one or more of P, B, Si, N, and S.

6. The method of any one of claims 3-5, wherein, In step 1), the buffer complexing agent is selected from one or more of ammonium carbonate, ammonium bicarbonate, ammonium oxalate, ammonium acetate, ammonium phosphate, and ammonium borate.

7. The method of any one of claims 3-5, wherein, In step 2), the concentration of the acidic coating source solution is 0.1~10 mol / L.

8. The method of any one of claims 3-5, wherein, In step 1), the mass ratio of the lithium-rich cathode material in the hydroxide system to the deionized water is (0.5~5):

1.

9. The preparation method according to any one of claims 3-5, characterized in that, In step 3), the drying temperature is 90~130℃.

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