Lithium composite metal oxide and preparation method therefor, and lithium-ion battery

Abstract

The present application relates to the field of lithium battery positive electrode materials, and provides a lithium composite metal oxide and a preparation method therefor, and a lithium-ion battery. The lithium composite metal oxide comprises an inner core and a strontium-doped lithium cobalt oxide coating layer covering the surface of the inner core; the inner core is secondary particles formed by stacking single-crystal primary particles; strontium-doped lithium cobalt oxide in the strontium-doped lithium cobalt oxide coating layer is uniformly distributed on the surface of the inner core in an island shape. The strontium-doped lithium cobalt oxide coating layer reduces the formation of nickel oxide on the surface of a positive electrode material in the charging and discharging process of a battery, avoids the generation of micro-cracks, improves the structural stability, not only can protect the surface structure during subsequent water washing and avoid the generation of excessive rock salt phases, but also can avoid the dissolution of cobalt at high temperature. In addition, the present application also improves the initial efficiency and the cycle performance, and reduces the initial DCR and circulating DCR increase.

Description

Lithium composite metal oxides and their preparation methods, lithium-ion batteries

[0001] This application claims priority to Chinese Patent Application No. 202410486920.2, filed on April 22, 2024, entitled "Lithium Composite Metal Oxide and Preparation Method Thereof, Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium battery cathode material technology, and in particular to a lithium composite metal oxide and its preparation method, and a lithium-ion battery. Background Technology

[0003] Lithium nickel cobalt manganese oxide (NCM) ternary cathode materials combine the advantages of nickel, cobalt, and manganese, possessing numerous benefits such as high specific capacity, long lifespan, safety, and environmental friendliness, making them a mainstream direction for the development of power lithium-ion batteries. Nickel primarily plays a role in improving the material's specific capacity, cobalt primarily improves the rate capability and supports the layered structure, while manganese primarily stabilizes the overall crystal structure and ensures high cycle life. High-nickel ternary cathode materials, such as Li(Ni) ternary cathode materials, are also important. x Co y Mn 1-x-y O2 (x≥0.6) is widely used in power lithium-ion battery systems due to its high specific capacity, good safety, and simple preparation process. Meanwhile, polycrystalline high-nickel ternary cathode materials, with their ultra-high discharge specific capacity, suitable rate performance, high operating voltage, low cobalt content, and low production cost, have become the main development direction for cathode materials in power lithium-ion battery systems.

[0004] However, during charging, lithium-ion batteries using high-nickel ternary materials as the cathode will generate a significant amount of Ni in the delithiation state of the cathode surface. 4+ Ni 4+ It readily reacts with the electrolyte to be reduced to Ni. 2+ This process combines with oxygen to form cubic rock salt phase NiO. Besides the deposition of new material on the cathode material surface, the reaction also promotes the gradual transformation of the bulk material from a hexagonal layered structure to a spinel structure, ultimately becoming a rock salt phase. This irreversible phase transition deteriorates the battery's cycle stability. Simultaneously, the generated NiO is an insulating material, affecting the Li... + Ion conductivity in the material reduces Li +The diffusion coefficient increases the surface resistance of the cathode material, reducing the battery capacity. In particular, polycrystalline high-nickel ternary cathode materials, due to the grain boundaries between the grains in their polycrystalline structure, are more prone to forming microcracks on the surface of lithium composite metal oxides. Moreover, the damage to the material surface during lithium ion insertion and extraction is more pronounced, leading to a more significant decrease in cycle stability. Summary of the Invention

[0005] Therefore, it is necessary to provide a lithium composite metal oxide to address the above problems. This cathode material has strontium-doped lithium cobalt oxide coated on the surface of the lithium composite metal oxide, and the strontium-doped lithium cobalt oxide is distributed in an island-like pattern on the surface of the lithium composite metal oxide, thereby optimizing the initial efficiency, cycle stability and capacity of lithium composite metal oxides in the prior art.

[0006] Another objective of this application is to provide a method for preparing lithium composite metal oxides.

[0007] Another object of this application is to provide a lithium-ion battery.

[0008] In a first aspect, this application provides a lithium composite metal oxide, including a core and a strontium-doped lithium cobalt oxide coating layer covering the surface of the core; the core is a secondary particle formed by the stacking of single-crystal primary particles;

[0009] The lithium strontium cobalt oxide in the strontium-doped lithium cobalt oxide coating layer is uniformly distributed in an island-like pattern on the surface of the core.

[0010] Furthermore, in some embodiments of this application, the size of the island-like coated particles formed by the strontium-doped lithium cobalt oxide is 10–300 nm.

[0011] Furthermore, in some embodiments of this application, the weight percentage of the strontium-doped lithium cobalt oxide in the lithium composite metal oxide is 0.2% to 3%; and the weight percentage of strontium in the strontium-doped lithium cobalt oxide coating layer in the lithium composite metal oxide is 0.01% to 0.5%.

[0012] Furthermore, in some embodiments of this application, the lithium composite metal oxide further includes an oxide coating layer located on the outer surface of the lithium composite metal oxide.

[0013] Furthermore, in some embodiments of this application, the non-oxygen elements in the oxide coating layer account for no more than 3% of the weight of the lithium composite metal oxide.

[0014] Furthermore, in some embodiments of this application, the chemical formula of the core in the lithium composite metal oxide is: Li m Ni a Co b Mnc M d O2; wherein, 0.98 ≤ m ≤ 1.20, 0.80 ≤ a < 1.00, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 < d ≤ 0.03; M is a core doping element selected from at least one of Mg, Mo, K, Mn, Co, Ta, Sr, Y, Ti, Zr, W, Sb, Al, Bi, Sn.

[0015] Further, in some embodiments of the present application, the D50 of the lithium composite metal oxide is 7 - 13 μm, and SPAN[(D90 - D10) / D50] is 1.0 - 1.6.

[0016] Further, in some embodiments of the present application, the specific surface area of the lithium composite metal oxide is 0.3 - 0.9 m 2 / g.

[0017] Further, in some embodiments of the present application, at 25°C and under a pressure of 12 MPa, the volume resistivity of the lithium composite metal oxide is 100 ohm-cm - 5000 ohm-cm.

[0018] In a second aspect, the present application also provides a method for preparing the lithium composite metal oxide described in the first aspect, including the following steps:

[0019] Mix a high-nickel ternary hydroxide precursor, a lithium salt, and an additive to obtain a primary mixture, and through primary sintering, pulverization, and sieving, obtain a primary sintered material;

[0020] Mix the primary sintered material, a cobalt source, and a strontium source to obtain a secondary mixture, and through secondary sintering, obtain a secondary sintered material, which is the lithium composite metal oxide; wherein, during the secondary sintering process, the sintering temperature is not higher than 720°C.

[0021] Further, in some embodiments of the present application, the chemical formula of the high-nickel ternary hydroxide precursor is Ni x Co y Mn 1-x-y (OH)2, wherein, 0.8 ≤ x < 1, 0 < y ≤ 0.2, the high-nickel ternary hydroxide precursor is a polycrystalline precursor obtained by a continuous method, D50 is 7 - 13 μm, and SPAN[(D90 - D10) / D50] is 1 - 1.7.

[0022] Further, in some embodiments of the present application, the cobalt source is a nano-cobalt source, the D50 of the cobalt source is 0.1 - 2.0 μm, and the specific surface area is 70 - 110 m 2 / g.

[0023] Furthermore, in some embodiments of this application, the cobalt source is selected from at least one of cobalt tetroxide, cobalt oxide, cobalt hydroxide, and cobalt hydroxyoxide.

[0024] Furthermore, in some embodiments of this application, the strontium source is selected from at least one of strontium oxide, strontium hydroxide, and strontium carbonate.

[0025] Furthermore, in some embodiments of this application, the lithium salt is selected from at least one of lithium carbonate and lithium hydroxide.

[0026] Furthermore, in some embodiments of this application, the additive is selected from at least one of oxides containing element M, hydroxides containing element M, or phosphates containing element M, wherein element M is selected from at least one of Mg, Mo, K, Mn, Co, Ta, Sr, Y, Ti, Zr, W, Sb, Al, Bi, and Sn.

[0027] Furthermore, in some embodiments of this application, the mass ratio of the high-nickel ternary hydroxide precursor, lithium salt, and additive is 100:(46.6-48.5):(0.14-2.7).

[0028] Furthermore, in some embodiments of this application, the mass ratio of the primary sintering material, cobalt source, and strontium source is 100:(0.3-2.3):(0.06-0.35).

[0029] Furthermore, in some embodiments of this application, the process conditions for the first sintering are as follows: heating rate of 1-5°C / min to 700-900°C, holding at that temperature for 8-16 hours, and an oxygen-containing atmosphere.

[0030] Furthermore, in some embodiments of this application, the secondary sintering process conditions are as follows: heating rate of 1-5°C / min to 600-720°C, holding at that temperature for 8-16 hours, and an oxygen-containing atmosphere.

[0031] Furthermore, in some embodiments of this application, after the secondary sintering, a water washing process and a tertiary sintering process are also included;

[0032] The water washing process includes: washing and drying the cooled secondary sintering material to remove residual lithium on the surface of the secondary sintering material, thereby obtaining dried material;

[0033] The three-stage sintering process includes: mixing the dried material with the coating agent, and sintering in an oxygen-containing atmosphere to obtain a lithium composite metal oxide coated with an oxide coating layer.

[0034] Furthermore, in some embodiments of this application, the coating agent is selected from at least one of magnesium oxide, magnesium hydroxide, titanium oxide, aluminum oxide, aluminum hydroxide, manganese oxide, tungsten oxide, tungstic acid, tantalum oxide, tin oxide, strontium oxide, strontium carbonate, yttrium oxide, zirconium oxide, aluminum fluoride, boron oxide, boric acid, cerium fluoride, zirconium fluoride, and yttrium fluoride.

[0035] Furthermore, in some embodiments of this application, the process conditions for the three-stage sintering are: heating rate of 1-5°C / min to 200-400°C, and holding at that temperature for 6-16 hours.

[0036] Furthermore, in some embodiments of this application, the mass ratio of the drying material to the coating agent is 100:(0.1~1).

[0037] Thirdly, this application also provides a lithium-ion battery comprising the lithium composite metal oxide described in the first aspect.

[0038] This application provides a lithium composite metal oxide, its preparation method, and a lithium-ion battery. The lithium composite metal oxide is coated with strontium-doped lithium cobalt oxide in an island-like distribution. This reduces the formation of nickel oxide on the surface of the lithium composite metal oxide, prevents the formation of microcracks during cycling, and improves the stability of the cathode material. Simultaneously, the island-like distribution of strontium-doped lithium cobalt oxide increases the specific surface area of ​​the lithium composite metal oxide and provides ion diffusion channels, increasing the diffusion rate of lithium ions. The lithium cobalt oxide used for coating employs strontium, an element with a relatively large atomic radius, as the dopant. This prevents the dopant element from entering the core, avoiding capacity reduction in the cathode and achieving true outer layer coating. Furthermore, the in-situ doping of strontium improves the stability of the lithium cobalt oxide, giving it good flexibility and mechanical stress resistance, and making it more stable in the electrolyte. This not only mitigates the damage to the material surface caused by lithium ion insertion or extraction at high voltage, improving the material's storage performance, but also prevents changes in electrolyte performance and a decrease in battery capacity and cycle performance due to cobalt dissolution and coating layer damage at high temperatures.

[0039] Furthermore, the strontium-doped lithium cobalt oxide coating on the surface of lithium composite metal oxides can reduce the use of conductive agents during battery fabrication, increase the amount of active material, and thus improve capacity. The lithium composite metal oxides provided in this application can improve the electrical properties of the cathode material, such as initial efficiency and cycle performance, at a relatively low strontium-doped lithium cobalt oxide coating rate, avoiding the capacity reduction caused by the need for large amounts of doping or coating.

[0040] This application also provides a method for preparing lithium composite metal oxides, which is simple, controllable, low-cost, and conducive to widespread application. Attached Figure Description

[0041] Figure 1 is a SEM image of a primary sintering material provided in Embodiment 1 of this application;

[0042] Figure 2 is a SEM image of a secondary sintering material provided in Embodiment 1 of this application;

[0043] Figure 3 is a SEM image of a secondary sintering material provided in Embodiment 2 of this application;

[0044] Figure 4 is a SEM image of a secondary sintering material provided in Embodiment 3 of this application;

[0045] Figure 5 is a SEM image of a secondary sintering material provided in Embodiment 4 of this application;

[0046] Figure 6 is a SEM image of a secondary sintering material provided in Comparative Example 1 of this application;

[0047] Figure 7 is a SEM image of a secondary sintering material provided in Comparative Example 2 of this application;

[0048] Figure 8 is a SEM image of a secondary sintering material provided in Comparative Example 3 of this application;

[0049] Figure 9 is a SEM image of a secondary sintering material provided in Comparative Example 4 of this application;

[0050] Figure 10 is a SEM image of a secondary sintering material provided in Comparative Example 5 of this application;

[0051] Figure 11 is a SEM image of a secondary sintering material provided in Comparative Example 6 of this application;

[0052] Figure 12 is a SEM image of a secondary sintering material provided in Comparative Example 7 of this application. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0054] Cobalt plays a crucial role in ternary cathode materials, enhancing rate capability and supporting the layered structure, which is beneficial for lithium-ion migration, transport, and diffusion. However, cobalt exhibits poor stability in ternary cathode materials, readily dissolving into the electrolyte. Furthermore, driven by the demand for high-capacity batteries, high-nickel, low-cobalt ternary cathode materials have become a primary research focus. However, after sintering, the surface of high-nickel, low-cobalt ternary cathode materials retains not only alkaline lithium (such as lithium hydroxide) but also a significant amount of nickel oxide, resulting in a high nickel content on the surface. This instability leads to structural instability, making the material prone to cracking during cycling and reducing cycle life. Moreover, the presence of residual lithium hydroxide and lithium carbonate on the surface of ternary cathode materials after sintering can further contribute to capacity decay, leading to lithium-nickel mixing and causing the layered cathode material to transform into a rock salt phase. This, in turn, increases the capacity decay rate (DCR) and results in rapid capacity reduction. In particular, for polycrystalline ternary cathode materials, since there are grain boundaries between the grains, cracks are very likely to occur along the grain boundaries. Residual lithium hydroxide and lithium carbonate are also likely to exist at the grain boundaries, accelerating the formation of cracks.

[0055] In the prior art, in order to solve this problem, a water washing process is often used to treat ternary cathode materials with high nickel and low cobalt to remove residual alkaline lithium, thereby improving the material cycle performance caused by lithium hydroxide and lithium carbonate. However, the inventors found in the research and development process that there is little research on the material structure instability and microcrack problems caused by highly active nickel oxide.

[0056] In response, this application proposes a lithium composite metal oxide with a discontinuous island-like layer of strontium-doped lithium cobalt oxide coated on its surface. This not only neutralizes some alkaline lithium but also reduces the nickel content on the surface of the lithium composite metal oxide, thereby reducing the risk of microcracks forming during cycling due to high nickel content on the material surface, improving material stability, and thus optimizing cycling performance. At the same time, since the strontium-doped lithium cobalt oxide acts as a fast ion conductor coating, it also provides ion diffusion channels, thereby increasing the diffusion rate of lithium ions and improving the material's first efficiency and capacity.

[0057] Therefore, this application provides a lithium composite metal oxide comprising: a core and a strontium-doped lithium cobalt oxide coating layer covering the surface of the core; the core is a secondary particle formed by the stacking of single-crystal primary particles; the strontium-doped lithium cobalt oxide in the strontium-doped lithium cobalt oxide coating layer is uniformly distributed in an island-like manner on the surface of the core.

[0058] In this application, strontium is used as a dopant in the lithium cobalt oxide used for coating, and in-situ doping is performed on the lithium cobalt oxide, which improves the stability of the lithium cobalt oxide and avoids the high-temperature dissolution of cobalt. At the same time, due to the large ionic radius of strontium, it is difficult for it to enter the core during sintering, thus achieving substantial surface doping and surface coating of strontium-doped lithium cobalt oxide, avoiding the capacity reduction of the material caused by the dopant element in the surface coating entering the core. Since strontium-doped lithium cobalt oxide has better stability, flexibility, and mechanical stress, it can further mitigate the damage to the material surface caused by lithium ion insertion and extraction under high pressure, thereby improving the storage performance of the material.

[0059] In this application, strontium-doped lithium cobalt oxide achieves this by creating island-like discontinuous coatings on the core surface. On one hand, this increases the specific surface area of ​​the lithium composite metal oxide, enhancing the material's surface activity. On the other hand, it achieves synergy between electronic and ionic conductors in the coating layer. The gaps between the island-like coating regions provide ion diffusion channels, while the island-like strontium-doped lithium cobalt oxide itself provides electron diffusion channels, thus increasing the electron diffusion rate and consequently improving the material's capacity. Furthermore, strontium-doped lithium cobalt oxide can reduce the use of conductive agents during battery fabrication, increasing the amount of active material and further enhancing capacity.

[0060] In fact, those skilled in the art generally believe that a high nickel content on the surface of polycrystalline ternary cathode materials is beneficial to improving the material's capacity. Therefore, a decrease in the nickel content on the material's surface will inevitably reduce the material's capacity. Thus, while setting a coating layer on the surface of polycrystalline ternary cathode materials can improve the cycle performance of polycrystalline ternary cathode materials, it is detrimental to the material's capacity. However, the lithium composite metal oxide provided in this application can not only improve the material's stability, reduce the formation of microcracks on the material's surface, and optimize the material's cycle performance, but also improve the material's capacity, improve the material's first efficiency, reduce the initial DCR, and optimize the material's cycle DCR.

[0061] During the research and development process, the inventors also discovered that the strontium-doped lithium cobalt oxide coating on the surface of the lithium composite metal oxide provided in this application is actually mainly concentrated at the grain boundaries of the core. Since the lithium composite metal oxide provided in this application is a polycrystalline material, the electrolyte is relatively easy to penetrate from the grain boundaries during cycling, thus cracks are very likely to first appear at the grain boundaries; moreover, during the water washing process, moisture can also easily penetrate from the grain boundaries, damaging the material's surface structure. Therefore, the concentration of strontium-doped lithium cobalt oxide mainly at the grain boundaries can better improve the problem of microcracks easily occurring in polycrystalline materials, thereby greatly improving the material's stability; it can also reduce the damage to the material's surface structure caused by the water washing process.

[0062] In some embodiments, the particle size of the strontium-doped lithium cobaltate forming the island-like coating is 10 - 300 nm, preferably 10 - 250 nm. Since the strontium-doped lithium cobaltate is coated on the surface of the inner core in an island-like manner, it actually forms one projection after another on the surface of the inner core, thereby achieving the coating. It can be understood that the particle size of the island-like coating is the thickness of the projection formed by the island-like coating.

[0063] Furthermore, the weight percentage of the strontium-doped lithium cobaltate in the lithium composite metal oxide is 0.2% - 3%, preferably 1% - 2%; the weight percentage of strontium in the strontium-doped lithium cobaltate coating in the lithium composite metal oxide is 0.01% - 0.5%, preferably 0.1% - 0.3%.

[0064] In some embodiments, the lithium composite metal oxide further includes an oxide coating layer, and the oxide coating layer is located on the outer surface of the lithium composite metal oxide.

[0065] After coating with strontium-doped lithium cobaltate, an oxide coating layer is further coated on the surface of the ternary cathode material, which can not only further improve the stability of the material and increase the capacity of the material, but also improve the stability of the surface coating of strontium-doped lithium cobaltate, and further reduce the dissolution of cobalt in the electrolyte.

[0066] In some embodiments, the weight percentage of non-oxygen elements in the oxide coating layer in the lithium composite metal oxide is not higher than 3%, preferably 0.7% - 1.5%.

[0067] In some embodiments, the chemical formula of the inner core in the lithium composite metal oxide is: Li m Ni a Co b Mn c M d O2; where 0.98 ≤ m ≤ 1.20, 0.80 ≤ a < 1.00, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 < d ≤ 0.03; M is an inner layer doping element, and the inner layer doping element is selected from at least one of Mg, Mo, K, Mn, Co, Ta, Sr, Y, Ti, Zr, W, Sb, Al, Bi, Sn.

[0068] In some embodiments, the lithium composite metal oxide can be expressed as: Li m Ni a Co b Mn c M d O2·N e ·C fWhere N represents lithium strontium cobalt oxide, and the value of e is the coating percentage of lithium strontium cobalt oxide: 0.2% to 3%; C represents the oxide coating layer, wherein the non-oxygen elements in the oxide coating layer can be selected from one or more of Mg, Ti, Al, Mn, W, Ta, Sn, Sr, Y, Zr, Sb, B, and F.

[0069] In some embodiments, the D50 of the lithium composite metal oxide is 7–13 μm, preferably 8–12, and the SPAN[(D90-D10) / D50] is 1.0–1.6, preferably 1.2–1.5. Here, D50 is the particle size corresponding to a cumulative particle size distribution number of 50%, and the corresponding D10 and D90 are the particle sizes corresponding to a cumulative particle size distribution number of 10% and 90%, respectively.

[0070] In some embodiments, the specific surface area of ​​the lithium composite metal oxide is 0.3–0.9 m². 2 / g, its specific surface area is larger and its activity is stronger than that of uncoated lithium strontium cobalt oxide.

[0071] In some embodiments, under pressure of 25°C and 12 MPa, the volume resistivity of the lithium composite metal oxide is 100 ohm-cm to 5000 ohm-cm.

[0072] In some embodiments, the strontium-doped lithium cobalt oxide is obtained by reacting a cobalt source, a strontium source, and a lithium compound, such as lithium hydroxide or lithium carbonate, remaining on the core surface. This not only reduces the amount of alkaline lithium remaining on the material surface but also forms island-like strontium-doped lithium cobalt oxide on the material surface, thereby improving the material's capacity and first-time efficiency, and optimizing cycle performance and cycle DCR.

[0073] The specific capacity of the cathode material provided in this application can be 195-220 mAh / g, specifically 195-210 mAh / g, and the capacity retention rate after 300 cycles at 45℃ is not less than 90%, and the initial efficiency is not less than 83%.

[0074] Secondly, this application also provides a method for preparing the lithium composite metal oxide described in the first aspect, comprising the following steps:

[0075] A primary mixture is obtained by mixing a high-nickel ternary hydroxide precursor, lithium salt, and additives. This mixture is then sintered, pulverized, and sieved to obtain a primary sintered material.

[0076] A secondary mixture is obtained by mixing a primary sintering material, a cobalt source, and a strontium source. This mixture is then sintered a second time to obtain a secondary sintering material, which is the lithium composite metal oxide. During the secondary sintering process, the sintering temperature does not exceed 720°C.

[0077] In some embodiments, the high-nickel ternary hydroxide precursor is represented as Ni x Co y Mn 1-x-y (OH)2, where 0.8 ≤ x < 1, 0 < y ≤ 0.2. The high-nickel ternary hydroxide precursor is a polycrystalline precursor prepared by a continuous method, with D50 being 7 - 13 μm and SPAN [(D90 - D10) / D50] being 1 - 1.7.

[0078] In some embodiments, the cobalt source is a nano-cobalt source, with the D50 of the cobalt source being 0.1 - 2.0 μm, preferably 0.2 - 1.5 μm, and more preferably 0.3 - 1.4 μm; the specific surface area is 70 - 110 m 2 / g, preferably 80 - 100 m 2 / g. In this application, a nano-level cobalt source is used as the cobalt source, which has a relatively large specific surface area and is more conducive to reacting with the lithium compounds remaining on the surface of the inner core and coating on the surface of the inner core to form strontium-doped lithium cobaltate distributed in an island shape.

[0079] In some embodiments, the cobalt source is selected from at least one of cobalt tetroxide, cobalt oxide, cobalt hydroxide, and cobalt oxyhydroxide.

[0080] In some embodiments, the strontium source is selected from at least one of strontium oxide, strontium carbonate, and strontium hydroxide.

[0081] In some embodiments, the lithium salt is selected from at least one of lithium carbonate and lithium hydroxide.

[0082] In the first sintering, the mass ratio of the high-nickel ternary hydroxide precursor, the lithium salt, and the additive is 100:(46.6 - 48.5):(0.14 - 2.7). In the second sintering, the mass ratio of the first-sintered material, the cobalt source, and the strontium source is 100:(0.3 - 2.3):(0.06 - 0.35).

[0083] In some embodiments, the additive is adjusted according to the elements doped in its inner core, and it can be selected from at least one of an oxide containing M element, a hydroxide containing M element, or a phosphate containing M element. The M element is selected from at least one of Mg, Mo, K, Mn, Co, Ta, Sr, Y, Ti, Zr, W, Sb, Al, Bi, and Sn. The M element is preferably Zr and Y. For example, the oxide containing M element can include one or more of zirconium oxide and yttrium oxide.

[0084] In some embodiments, the coating agent used in the oxide coating layer sintering preparation process is selected from at least one of acid containing element A, oxide containing element A, hydroxide containing element A, or phosphate containing element A. Element A is preferably at least one of W, Al, Ti, and B, such as tungstic acid, alumina, titanium dioxide, and boric acid.

[0085] In some embodiments, the process conditions for the first sintering are: heating rate of 1-5°C / min to 700-900°C, holding at that temperature for 8-16 hours, and an oxygen-containing atmosphere.

[0086] The secondary sintering process conditions are as follows: heating rate of 1-5℃ / min to 600-720℃, holding for 8-16 hours, and oxygen-containing atmosphere.

[0087] In this application, the temperature of the secondary sintering should not exceed 720°C to avoid the lithium composite metal oxide from melting during the secondary sintering process and damaging the surface morphology of the lithium composite metal oxide; preferably, the sintering temperature in the secondary sintering is 600-720°C, more preferably 620-700°C.

[0088] In some embodiments, after the secondary sintering, a water washing process and a tertiary sintering process are further included.

[0089] The water washing process includes: washing and drying the cooled secondary sintered material to remove residual lithium on the surface of the secondary sintered material, thereby obtaining dried material.

[0090] The three-stage sintering process includes: mixing the dried material with the coating agent, and sintering in an oxygen-containing atmosphere to obtain a lithium composite metal oxide coated with an oxide coating layer.

[0091] In some embodiments, the process conditions for the three-stage sintering are: heating rate of 1–5 °C / min to 200–400 °C, and holding at that temperature for 6–16 h. In the three-stage sintering, the mass ratio of the dried material to the coating agent is 100:(0.1–1).

[0092] Thirdly, this application also provides a lithium-ion battery comprising the lithium composite metal oxide described in the first aspect. This lithium-ion battery can be fabricated using the aforementioned positive electrode material to prepare a positive electrode sheet, and then the battery can be fabricated using the positive electrode sheet comprising the aforementioned positive electrode material to obtain a battery with excellent capacity, initial efficiency, and cycle performance.

[0093] The preparation process of the positive electrode sheet can be an existing positive electrode sheet preparation process, such as: mixing positive electrode material, conductive agent, solvent and binder to obtain positive electrode slurry, setting the positive electrode slurry on at least one functional surface of the positive electrode current collector, and drying to obtain a positive electrode sheet containing a positive electrode active layer.

[0094] The following will illustrate the lithium composite metal oxide and its preparation method, as well as the battery, according to specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative and should not be construed as limiting the scope of this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to conventional techniques or conditions in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0095] In the following embodiments, the D50 of the lithium composite metal oxide is in the range of 7–13 μm, and the SPAN [(D90-D10) / D50] is in the range of 1.0–1.6; the specific surface area of ​​the lithium composite metal oxide is in the range of 0.3–0.9 m². 2 Within the range of / g; under pressure of 25℃ and 12MPa, the volume resistivity of lithium composite metal oxides is in the range of 100 ohm-cm to 5000 ohm-cm; the D50 of the high-nickel ternary hydroxide precursor is in the range of 7 to 13 μm, and the SPAN[(D90-D10) / D50] is in the range of 1 to 1.7; the D50 of the cobalt source is in the range of 0.1 to 2.0 μm, and the specific surface area is in the range of 70 to 110 m². 2 Within the range of / g.

[0096] Example 1

[0097] This embodiment provides a method for preparing lithium composite metal oxide, including the following steps:

[0098] Step 1:

[0099] Ni was taken in a mass ratio of 100:48.05:0.27 0.85 Co 0.07 Mn 0.08 (OH2) (D50 is 10μm), lithium hydroxide, and zirconium dioxide (ZrO2) were placed in a high-speed mixer and mixed at 600 rpm. Then, the mixture was placed in a sintering furnace for primary sintering. The sintering process conditions were as follows: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 800℃ at 2℃ / min, and the temperature was held for 10h. The mixture was then crushed and passed through a 325-mesh sieve to obtain the primary sintered material. Referring to Figure 1, it can be seen that the surface of the primary sintered material is composed of primary particle agglomeration.

[0100] Step Two:

[0101] The primary sintering material, strontium oxide, and cobalt tetroxide were taken in a molar mass ratio of 100:0.118:0.817 and placed in a high-speed mixer. They were mixed at 600 rpm and then placed in a sintering furnace for secondary sintering. The sintering process conditions were as follows: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 700℃ at 2℃ / min, and the temperature was held for 6 hours. The secondary sintering material was obtained by passing it through a 325-mesh sieve. Referring to Figure 2, it can be seen that the particle size of the island-like coating on the surface is about 10-200 nm.

[0102] Step 3:

[0103] The secondary sintering material was mixed with deionized water at a mass ratio of 1:1, filtered, and vacuum dried at 150°C for 4 hours to obtain the water-washed material (i.e., the dried material).

[0104] Step Four:

[0105] The washed material was mixed with boric acid at a mass ratio of 100:0.57 (i.e., the dried material was mixed with boric acid at a mass ratio of 100:0.57), and then sintered three times. The sintering process conditions were: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 300℃ at a rate of 2℃ / min, and the temperature was held for 10h; the mixture was then passed through a 325-mesh sieve to obtain lithium composite metal oxide.

[0106] The cathode material has a D50 of 10 micrometers; SPAN(D90-D10) / D50 = 1.30; and a specific surface area of ​​0.55.

[0107] Example 2

[0108] This embodiment provides a method for preparing lithium composite metal oxide, including the following steps:

[0109] Step 1:

[0110] Ni was taken in a mass ratio of 100:48.05:0.27. 0.85 Co 0.07 Mn 0.08 (OH)2, lithium hydroxide, and ZrO2 are placed in a high-speed mixer and mixed at 600 rpm. The mixture is then placed in a sintering furnace for primary sintering. The sintering process conditions are as follows: the sintering atmosphere is oxygen atmosphere, the temperature is increased to 810℃ at 3℃ / min, and the temperature is held for 10h; the mixture is then crushed and passed through a 325-mesh sieve to obtain the primary sintered material.

[0111] Step Two:

[0112] The primary sintering material, strontium oxide, and cobalt hydroxide were taken in a mass ratio of 100:0.118:0.47 and placed in a high-speed mixer. They were mixed at a speed of 600 ppm and then placed in a sintering furnace for secondary sintering. The sintering process conditions were as follows: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 690℃ at a rate of 3℃ / min, and the temperature was held for 6 hours. The secondary sintering material was obtained by passing it through a 325-mesh sieve. Referring to Figure 3, it can be seen that the particle size of the island-like coating on the surface is about 10-200 nm.

[0113] Step 3:

[0114] The secondary sintering material was mixed with deionized water at a mass ratio of 1:1, filtered, and vacuum dried at 150°C for 4 hours to obtain the water-washed material (i.e., the dried material).

[0115] Step Four:

[0116] The washed material was mixed with boric acid at a mass ratio of 100:0.57 (i.e., the dried material was mixed with boric acid at a mass ratio of 100:0.57), and then sintered three times. The sintering process conditions were: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 290℃ at a rate of 2℃ / min, and the temperature was held for 10h; the mixture was then passed through a 325-mesh sieve to obtain lithium composite metal oxide.

[0117] Example 3

[0118] This embodiment provides a method for preparing lithium composite metal oxide, including the following steps:

[0119] Step 1:

[0120] Ni was taken in a mass ratio of 100:47.82:0.317 0.90 Co 0.05 Mn 0.05 (OH)2, lithium hydroxide, and yttrium oxide (Y2O3) are placed in a high-speed mixer and mixed at 600 rpm. The mixture is then placed in a sintering furnace for primary sintering. The sintering process conditions are as follows: the sintering atmosphere is oxygen atmosphere, the temperature is increased to 820℃ at 3℃ / min and held for 8 hours; the mixture is then crushed and passed through a 325-mesh sieve to obtain the primary sintered material.

[0121] Step Two:

[0122] The primary sintering material, strontium oxide, and cobalt hydroxide were taken in a mass ratio of 100:0.177:0.788 and placed in a high-speed mixer. They were mixed at 600 rpm and then placed in a sintering furnace for secondary sintering. The sintering process conditions were as follows: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 710℃ at 3℃ / min, and the temperature was held for 8 hours. The secondary sintering material was obtained by passing it through a 325-mesh sieve. Referring to Figure 4, it can be seen that the particle size of the island-like coating on the surface is about 10-200 nm.

[0123] Step 3:

[0124] The secondary sintering material was mixed with deionized water at a mass ratio of 1:1, filtered, and vacuum dried at 140℃ for 5 hours to obtain the washed material (i.e., the dried material).

[0125] Step Four:

[0126] The washed material was mixed with boric acid at a mass ratio of 100:0.57 (i.e., the dried material was mixed with boric acid at a mass ratio of 100:0.57), and then sintered three times. The sintering process conditions were: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 285℃ at 3℃ / min, and the temperature was held for 8h; the mixture was passed through a 325-mesh sieve to obtain lithium composite metal oxide.

[0127] Example 4

[0128] This embodiment provides a method for preparing lithium composite metal oxide, including the following steps:

[0129] Step 1:

[0130] Ni was taken in a mass ratio of 100:46.8:0.28 0.90 Co 0.05 Mn 0.05 (OH)2, lithium hydroxide, and alumina are placed in a high-speed mixer and mixed at 600 rpm. Then, they are placed in a sintering furnace for primary sintering. The sintering process conditions are as follows: the sintering atmosphere is oxygen atmosphere, the temperature is increased to 890°C at 3°C / min and held for 12 hours; the material is crushed and passed through a 325-mesh sieve to obtain the primary sintered material.

[0131] Step Two:

[0132] The primary sintering material, strontium carbonate, and cobalt hydroxyl oxide were taken in a mass ratio of 100:0.252:0.780 and placed in a high-speed mixer. They were mixed at a speed of 550 rpm and then placed in a sintering furnace for secondary sintering. The sintering process conditions were as follows: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 680℃ at a rate of 3℃ / min, and the temperature was held for 9 hours. The secondary sintering material was obtained by passing it through a 325-mesh sieve. Referring to Figure 5, it can be seen that the particle size of the island-like coating on the surface is about 10-200 nm.

[0133] Step 3:

[0134] The secondary sintering material was mixed with deionized water at a mass ratio of 1:1, filtered, and vacuum dried at 150°C for 5 hours to obtain the water-washed material (dried material).

[0135] Step Four:

[0136] The washed material was mixed with boric acid at a mass ratio of 100:0.57 (i.e., the dried material was mixed with boric acid at a mass ratio of 100:0.57), and then sintered three times. The sintering process conditions were: the sintering atmosphere was oxygen atmosphere, the temperature was increased to 290℃ at 3℃ / min, and the temperature was held for 10h; the mixture was passed through a 325-mesh sieve to obtain lithium composite metal oxide.

[0137] Comparative Example 1

[0138] Compared to Example 1, in step two of this comparative example, strontium oxide is not added, and the remaining preparation steps are the same as in Example 1 to obtain the cathode material. The surface morphology of the secondary sintered material is shown in Figure 6.

[0139] Comparative Example 2

[0140] Compared to Example 1, in step two of this comparative example, strontium oxide and cobalt tetroxide are not added, and only the primary sintering material is sintered a second time. The remaining preparation steps are the same as in Example 1, and the cathode material is obtained, as shown in Figure 7.

[0141] The cathode material has a D50 of 10.2 micrometers, a SPAN[(D90-D10) / D50] = 1.29, and a specific surface area of ​​0.55.

[0142] Comparative Example 3

[0143] Compared to Example 1, in step two of this comparative example, aluminum hydroxide and cobalt tetroxide are added, and the remaining preparation steps are the same as in Example 1 to obtain the cathode material. The surface morphology of the secondary sintered material is shown in Figure 8.

[0144] Comparative Example 4

[0145] Compared to Example 1, in step two of this comparative example, yttrium oxide and cobalt tetroxide are added, and the remaining preparation steps are the same as in Example 1 to obtain the cathode material. The surface morphology of the secondary sintered material is shown in Figure 9.

[0146] Comparative Example 5

[0147] Compared to Example 1, in step two of this comparative example, strontium oxide and titanium dioxide are added, and the remaining preparation steps are the same as in Example 1 to obtain the cathode material. The surface morphology of the secondary sintered material is shown in Figure 10.

[0148] Comparative Example 6

[0149] Compared to Example 1, in step two of this comparative example, the secondary sintering temperature is 750°C, and the remaining preparation steps are the same as in Example 1, to obtain the cathode material. The surface morphology of the secondary sintered material is shown in Figure 11.

[0150] Comparative Example 7

[0151] Compared to Example 1, in step two of this comparative example, the secondary sintering temperature is 590°C, and the remaining preparation steps are the same as in Example 1, to obtain the cathode material. The surface morphology of the secondary sintered material is shown in Figure 12.

[0152] The surface morphology of the examples and comparative examples was characterized using a transmission electron microscope (purchased from Hitachi Regulus 8100 / SU 8010). The figures show that the surface of the secondary sintered material contains several island-like particles, which are strontium-doped lithium cobalt oxide particles coating the core surface; it can also be seen that the strontium-doped lithium cobalt oxide particles are mainly distributed at the grain boundaries of the secondary particles.

[0153] The elemental content of the cathode materials obtained in the examples and comparative examples was determined by X-ray photoelectron spectroscopy (XPS) using a Shimadzu AXIS Supra instrument (purchased from Japan). The elemental analysis results of the cathode materials obtained in the examples and comparative examples are shown in Table 1 below.

[0154] Table 1

[0155] As can be seen from Table 1, coating the surface with Sr-doped lithium cobalt oxide can reduce the surface nickel content and increase the cobalt content, which is positively correlated with the cobalt content of the coating and has a certain positive proportional relationship with the sintering temperature. The higher the temperature, the lower the surface Co residue tends to be.

[0156] The high-nickel cathode material prepared in the embodiments and comparative examples of this application is assembled into a coin cell using the following method: High-nickel cathode material, acetylene black, and polyvinylidene fluoride (PVDF) are weighed at a mass ratio of 94:3:3, mixed evenly, and NMP is added and stirred for 2 hours to form a viscous slurry. This slurry is then evenly coated onto aluminum foil, vacuum baked at 80°C, pressed into sheets, and cut into cathode sheets with a diameter of 14 mm. A 16 mm diameter pure lithium sheet is used as the anode sheet, a 1 mol / L LiPF6 + DEC / EC (volume ratio 1:1) mixed solution is used as the electrolyte, and a polyCelgard propylene microporous membrane is used as the separator. The coin cell is assembled in an argon-filled glove box.

[0157] The 0.2C capacity of the coin cells prepared from the high-nickel cathode materials obtained in the above embodiments and comparative examples was tested. The test conditions were as follows: the assembled coin cells were tested in a Blue Electric device at a temperature of 25±1℃ and a test voltage of 2.5~4.25V. The cells were charged and discharged at 0.2C / 0.2C, and the charging cutoff current was 0.05C (1C nominal capacity 200mAh / g).

[0158] The gas production was tested at 60℃ for 28 days. The test method was as follows: first, the battery was fully charged and the battery volume was measured. Then, the fully charged battery was stored at 60℃ for 28 days and the battery volume was measured again. The difference between the two was the gas production. The volume measurement device was an electronic solid density meter TW-120E.

[0159] The capacity retention rate was tested after 300 cycles at 45°C. The test method was as follows: using a Xinwei CT3008-5V3A-A1 electrode, at 45°C, with a cycling voltage of 4.25–3V and a constant voltage cutoff current of 20mA, for 300 cycles, the DC internal resistance growth rate was calculated. The electrochemical performance of the coin cells based on the cathode materials of Examples 1–4 and Comparative Examples 1–7 is shown in Table 2.

[0160] Table 2

[0161] Table 2 shows that, within a suitable coating sintering temperature range, coating with Sr-doped lithium cobalt oxide can simultaneously improve capacity, gas production, cycle retention, and increase cycle DCR. Using other elements such as Al and Y does not improve gas production as effectively as using Sr-doped lithium cobalt oxide.

[0162] To further investigate the stability of the lithium composite metal oxide provided in this application, the inventors also tested the elemental content of the negative electrode after the total charge of the button cell was circulated at 70°C for 28 days to produce gas. The testing instrument was an ICP elemental analyzer, and the test results are shown in Table 3.

[0163] Table 3

[0164] Table 3 shows that coating with Sr-doped lithium cobalt oxide within a suitable coating sintering temperature range can reduce the dissolution of Ni and Co during storage. Replacing it with other elements has no significant effect on inhibiting the dissolution of Ni and Co.

[0165] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A lithium composite metal oxide, characterized in that, It includes a core and a strontium-doped lithium cobalt oxide coating layer covering the surface of the core; the core is a secondary particle formed by the stacking of single-crystal primary particles; The strontium-doped lithium cobalt oxide coating layer is uniformly distributed in an island-like pattern on the surface of the core.

2. The lithium composite metal oxide according to claim 1, characterized in that, The island-like coating particles formed by the strontium-doped lithium cobalt oxide have a particle size of 10–300 nm.

3. The lithium composite metal oxide according to claim 1, characterized in that, The weight percentage of strontium-doped lithium cobalt oxide in the lithium composite metal oxide is 0.2% to 3%; the weight percentage of strontium in the strontium-doped lithium cobalt oxide coating layer in the lithium composite metal oxide is 0.01% to 0.5%.

4. The lithium composite metal oxide according to claim 1, characterized in that, The lithium composite metal oxide further includes an oxide coating layer, which is located on the outer surface of the lithium composite metal oxide.

5. The lithium composite metal oxide according to claim 4, characterized in that, The non-oxygen elements in the oxide coating layer account for no more than 3% of the weight of the lithium composite metal oxide.

6. The lithium composite metal oxide according to claim 1, characterized in that, The chemical formula of the core in the lithium composite metal oxide is: Li m Ni a Co b Mn c M d O2; wherein, 0.98 ≤ m ≤ 1.20, 0.80 ≤ a < 1.00, 0 < b ≤ 0.2, 0 < c ≤ 0.2, 0 < d ≤ 0.03; M is a core doping element, and the core doping element is selected from at least one of Mg, Mo, K, Mn, Co, Ta, Sr, Y, Ti, Zr, W, Sb, Al, Bi, Sn.

7. The lithium composite metal oxide according to any one of claims 1 to 6, characterized in that, The lithium composite metal oxide has a D50 of 7–13 μm and a SPAN[(D90-D10) / D50] of 1.0–1.6; And / or, the specific surface area of ​​the lithium composite metal oxide is 0.3–0.9 m². 2 / g; And / or, under pressure of 25°C and 12MPa, the volume resistivity of the lithium composite metal oxide is 100 ohm-cm to 5000 ohm-cm.

8. The method for preparing the lithium composite metal oxide according to any one of claims 1 to 7, characterized in that, Includes the following steps: A primary mixture is obtained by mixing a high-nickel ternary hydroxide precursor, lithium salt, and additives. This mixture is then sintered, pulverized, and sieved to obtain a primary sintered material. A secondary mixture is obtained by mixing a primary sintering material, a cobalt source, and a strontium source. This mixture is then sintered a second time to obtain a secondary sintering material, which is the lithium composite metal oxide. During the secondary sintering process, the sintering temperature does not exceed 720°C.

9. The method for preparing lithium composite metal oxide according to claim 8, characterized in that, The chemical formula of the high-nickel ternary hydroxide precursor is Ni x Co y Mn 1-x-y (OH)2, where 0.8 ≤ x < 1, 0 < y ≤ 0.

2. The high-nickel ternary hydroxide precursor is a polycrystalline precursor prepared by a continuous method, with D50 being 7 - 13 μm and SPAN [(D90 - D10) / D50] being 1 - 1.7; And / or, the cobalt source is a nano-cobalt source, the cobalt source having a D50 of 0.1–2.0 μm and a specific surface area of ​​70–110 m². 2 / g; And / or, the cobalt source is selected from at least one of cobalt tetroxide, cobalt oxide, cobalt hydroxide, and cobalt hydroxyoxide; And / or, the strontium source is selected from at least one of strontium oxide, strontium carbonate, and strontium hydroxide; And / or, the lithium salt is at least one of lithium carbonate and lithium hydroxide; And / or, the additive is selected from at least one of oxides containing element M, hydroxides containing element M, or phosphates containing element M, wherein element M is selected from at least one of Mg, Mo, K, Mn, Co, Ta, Sr, Y, Ti, Zr, W, Sb, Al, Bi, and Sn; And / or, the mass ratio of the high-nickel ternary hydroxide precursor, lithium salt, and additive is 100:(46.6~48.5):(0.14~2.7); And / or, the mass ratio of the primary sintering material, cobalt source, and strontium source is 100:(0.3-2.3):(0.06-0.35).

10. The method for preparing lithium composite metal oxide according to claim 8, characterized in that, The process conditions for the first sintering are: heating rate of 1-5℃ / min to 700-900℃, holding for 8-16 hours, and an oxygen-containing atmosphere. And / or, the secondary sintering process conditions are: heating rate of 1-5℃ / min to 600-720℃, holding for 8-16 hours, and an oxygen-containing atmosphere.

11. The method for preparing lithium composite metal oxide according to claim 8, characterized in that, After the secondary sintering, the process also includes a water washing process and a tertiary sintering process; The water washing process includes: washing and drying the cooled secondary sintering material to remove residual lithium on the surface of the secondary sintering material, thereby obtaining dried material; The three-stage sintering process includes: mixing the dried material with the coating agent, and sintering in an oxygen-containing atmosphere to obtain a lithium composite metal oxide coated with an oxide coating layer.

12. The method for preparing lithium composite metal oxide according to claim 11, characterized in that, The coating agent is selected from at least one of magnesium oxide, magnesium hydroxide, titanium oxide, aluminum oxide, aluminum hydroxide, manganese oxide, tungsten oxide, tungstic acid, tantalum oxide, tin oxide, strontium oxide, strontium carbonate, yttrium oxide, zirconium oxide, aluminum fluoride, boron oxide, boric acid, cerium fluoride, zirconium fluoride, and yttrium fluoride. And / or, the process conditions for the three sinterings are: heating rate of 1-5℃ / min to 200-400℃, and holding at that temperature for 6-16 hours; And / or, the mass ratio of the dried material to the coating agent is 100:(0.1~1).

13. A lithium-ion battery, characterized in that, It comprises the lithium composite metal oxide as described in any one of claims 1 to 7.

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