A lithium cobalt oxide cathode material and a preparation method thereof

Abstract

The application discloses a lithium cobalt oxide positive electrode material and a preparation method thereof, wherein the lithium cobalt oxide positive electrode material comprises a lithium cobalt oxide base material obtained by adopting metal elements for bulk doping and a composite coating layer coated on the surface of the lithium cobalt oxide base material; the composite coating layer comprises a fast ion conductor and a lithium salt material; the fast ion conductor is in island-shaped coating, and the lithium salt material serves as supplementary coating. The lithium cobalt oxide base material is obtained by adopting metal elements for bulk doping, and the fast ion conductor and the lithium salt material are used to jointly form a "fast ion conductor island-shaped coating-lithium salt supplementary coating layer" to wrap the surface of the lithium cobalt oxide base material, so that the lithium cobalt oxide positive electrode material has a combined stable coating layer, thereby enabling the lithium cobalt oxide positive electrode material to exhibit excellent high-voltage cycle performance at room temperature and high temperature.

Description

Technical Field

[0001] This invention relates to the field of battery materials, and in particular to a lithium cobalt oxide cathode material and its preparation method. Background Technology

[0002] With the further application and development of lithium-ion batteries in energy storage, power, and consumer electronics, the market urgently needs lithium-ion batteries with higher energy density, greater safety, and lower cost. Cathode materials, as one of the key components of lithium-ion batteries, significantly influence their energy density, safety, and cost. Common commercial cathode materials include lithium cobalt oxide, lithium iron phosphate, ternary materials, and lithium manganese oxide. Lithium cobalt oxide, due to its high tap density (2.0–2.4 g / cm³), is particularly valuable. 3 Commercial-grade lithium cobalt oxide), high theoretical capacity (220mAh / g, 4.6V vs Li) + The superior properties of lithium cobalt oxide (Li₂O₃) make it the preferred cathode material for consumer electronics. Increasing the charging cutoff voltage (greater than 4.5V) is an effective measure to further improve the energy density of lithium cobalt oxide materials. However, lithium cobalt oxide materials exhibit rapid deterioration in thermal stability and cycle stability at high voltages. This is because the high-voltage performance of lithium cobalt oxide materials is limited by the unstable bulk structure (irreversible phase transitions, volume changes, etc.) and severe surface and interface side reactions (oxygen release, electrolyte oxidation, etc.).

[0003] Currently, bulk doping and surface coating are the two main modification methods for improving the high-voltage performance (above 4.5V) of lithium cobalt oxide materials. However, the modification methods and effects have not yet reached the standards for commercial application. Common bulk doping methods for high-voltage lithium cobalt oxide often require the introduction of rare earth elements (such as lanthanum, cerium, gadolinium, etc.) and elements harmful to humans (such as fluorine, chlorine, phosphorus, etc.) into the lithium cobalt oxide matrix. The doping elements used are costly or pose potential hazards to the environment and human health. Furthermore, conventional doping methods alone cannot improve the high-voltage performance of lithium cobalt oxide materials. On the other hand, surface coating modification methods for high-voltage lithium cobalt oxide are typically carried out in a wet chemical environment, while commercial-grade lithium cobalt oxide production environments require dry coating processes. This is because wet chemical environments cause significant environmental pollution and require substantial modifications to related production equipment, further increasing production costs. Currently, companies generally use oxides as coating materials, combined with high-speed mixers and multi-step heat treatment processes to ultimately achieve dry coating modification. This process is relatively complex, and the resulting modified lithium cobalt oxide material can only be used at a voltage of 4.5V.

[0004] The background section of this invention may include background information about the problems or environment in which the invention is being developed, and is not necessarily a description of prior art. Therefore, the content included in the background section does not constitute an admission of prior art by the applicant. Summary of the Invention

[0005] To address the technical problem that the coating process used in existing lithium cobalt oxide cathode materials for lithium-ion batteries is complex and the resulting modified lithium cobalt oxide materials can only be used at a voltage of 4.5V, this invention proposes a lithium cobalt oxide cathode material and its preparation method.

[0006] The technical problem of this invention is solved by the following technical solution:

[0007] This invention discloses a lithium cobalt oxide cathode material, comprising a lithium cobalt oxide matrix material obtained by bulk doping with metal elements and a composite coating layer covering the surface of the lithium cobalt oxide matrix material. The composite coating layer comprises a fast ion conductor and a lithium salt material, wherein the fast ion conductor is island-shaped and the lithium salt material serves as a supplementary coating.

[0008] In some embodiments, the metallic element is one or more of the nanoscale oxides corresponding to magnesium, aluminum, titanium, sodium, potassium, calcium, iron, copper, iron, and zinc.

[0009] In some embodiments, the fast ion conductor material is one or more of lithium aluminum germanium phosphate, lithium aluminum titanium phosphate, and lithium lanthanum zirconium niobium oxide.

[0010] In some embodiments, the lithium salt material is one or more selected from phosphate, lithium metaphosphate, lithium nitrate, and lithium sulfate.

[0011] The present invention also illustrates a method for preparing any of the above-described lithium cobalt oxide cathode materials, comprising the following steps:

[0012] S1. Weigh the corresponding materials according to the molar ratio of lithium carbonate, cobalt tetroxide, and metal additives of 1.05:1:(0.001~0.1), grind and mix them evenly, carry out high-temperature solid-state sintering, calcine at 900~1100℃ for 8~14h, cool to room temperature with the furnace, and pulverize to obtain bulk-doped lithium cobalt oxide matrix material.

[0013] S2. Take a certain amount of fast ion conductor and lithium salt material, grind and mix them evenly with the lithium cobalt oxide matrix material prepared in step S1, calcine at 500-900℃ for 2-10 hours, cool to room temperature with the furnace, and pulverize to obtain a novel composite coated modified lithium cobalt oxide cathode material.

[0014] In some embodiments, in step S2, the fast ion conductor accounts for 0.1 to 5 wt% of the weight of the lithium cobalt oxide matrix material, and the lithium salt material accounts for 0.1 to 5 wt% of the weight of the lithium cobalt oxide matrix material.

[0015] In some embodiments, in step S2, the heating rate of the calcination process is 1 to 10 °C / min.

[0016] In some embodiments, in step S2, the gas atmosphere used in the calcination process is air or argon.

[0017] The present invention also discloses a lithium-ion battery comprising the lithium cobalt oxide cathode material described above.

[0018] This invention provides a lithium cobalt oxide cathode material and its preparation method. The lithium cobalt oxide matrix material is obtained by bulk doping with metal elements, and a "fast ion conductor island coating-lithium salt supplementary coating layer" is formed by fast ion conductor and lithium salt materials and wrapped on the surface of the lithium cobalt oxide matrix material. This gives the lithium cobalt oxide cathode material a stable coating layer, thereby enabling the lithium cobalt oxide cathode material to exhibit excellent high voltage cycling performance at room temperature and high temperature.

[0019] The preparation method of this lithium cobalt oxide cathode material does not require a wet chemical environment or the use of an ultra-high-speed mixer for coating and mixing, which greatly simplifies the operation process. The process is simple and easy to control, with low production costs, making it suitable for industrial production.

[0020] Other beneficial effects of the embodiments of the present invention will be further described below. Attached Figure Description

[0021] Figure 1 These are the XRD patterns of lithium cobalt oxide before and after modification in an embodiment of the present invention;

[0022] Figure 2-a Comparative Example 1 - SEM morphology of unmodified lithium cobalt oxide;

[0023] Figure 2-b This is an SEM image of magnesium-doped modified lithium cobalt oxide from Example 1;

[0024] Figure 2-c This is an SEM image of the lithium cobalt oxide material coated with lithium titanium aluminum phosphate, as shown in Example 2.

[0025] Figure 2-d This is an SEM image of lithium cobalt oxide with composite coating of lithium titanium aluminum phosphate / lithium metaphosphate, as shown in Example 5.

[0026] Figure 3-a This is a TEM image of Embodiment 2 of the present invention;

[0027] Figure 3-b yes Figure 3-a TEM topography of region A in the middle;

[0028] Figure 3-c yes Figure 3-a TEM topography of region B in the middle;

[0029] Figure 4-a This is a TEM image of Embodiment 5 of the present invention;

[0030] Figure 4-b yes Figure 4-a TEM topography of region C in the image;

[0031] Figure 4-c yes Figure 4-a TEM topography of region D in the image;

[0032] Figure 5 This refers to the room temperature cycling performance of lithium cobalt oxide in embodiments of the present invention;

[0033] Figure 6 This refers to the high-temperature (45°C) cycling performance of lithium cobalt oxide in the embodiments of the present invention;

[0034] Figure 7 This refers to the room temperature rate performance of lithium cobalt oxide in an embodiment of the present invention;

[0035] Figure 8-a This is the SEM failure diagram of Comparative Example 1 (50 cycles) of the present invention;

[0036] Figure 8-b This is the SEM failure diagram of Embodiment 1 (50 cycles) of the present invention;

[0037] Figure 8-c This is the SEM failure diagram of Comparative Example 2 (50 cycles) of the present invention;

[0038] Figure 8-d This is the SEM failure diagram of Comparative Example 3 (50 cycles) of the present invention;

[0039] Figure 9-a This is the SEM failure diagram of Embodiment 2 (50 cycles) of the present invention;

[0040] Figure 9-b This is the SEM failure diagram of Embodiment 2 (200 cycles) of the present invention;

[0041] Figure 9-c This is the SEM failure diagram of Embodiment 5 (50 cycles) of the present invention;

[0042] Figure 9-d This is the SEM failure diagram of Embodiment 5 (200 cycles) of the present invention. Detailed Implementation

[0043] The embodiments of the present invention will be described in detail below. It should be emphasized that the following description is merely exemplary and not intended to limit the scope and application of the present invention.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of the present invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0045] The technical problem to be solved by the present invention is to provide a novel composite-coated modified high-voltage lithium cobalt oxide cathode material and its preparation method. The method does not involve wet chemical methods, has a wide range of raw material sources, and is simple and controllable. The prepared cathode material can have excellent high-voltage cycling performance at room temperature and high temperature.

[0046] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention that do not depart from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0047] This invention discloses a lithium cobalt oxide cathode material, comprising a lithium cobalt oxide matrix material obtained by bulk doping with metal elements and a composite coating layer covering the surface of the lithium cobalt oxide matrix material. The composite coating layer includes a fast ion conductor and a lithium salt material, wherein the fast ion conductor is island-shaped and the lithium salt material serves as a supplementary coating. The metal elements are one or more nanoscale oxides of magnesium, aluminum, titanium, sodium, potassium, calcium, iron, copper, iron, and zinc. The fast ion conductor material is one or more of lithium aluminum germanium phosphate, lithium aluminum titanium phosphate, and lithium lanthanum zirconium niobium oxide. The lithium salt material is one or more of phosphate, lithium metaphosphate, lithium nitrate, and lithium sulfate.

[0048] The present invention also discloses a lithium-ion battery comprising the above-mentioned lithium cobalt oxide cathode material.

[0049] This invention also illustrates a method for preparing the above-mentioned lithium cobalt oxide cathode material, comprising the following steps:

[0050] S1. Weigh the corresponding materials according to the molar ratio of lithium carbonate, cobalt tetroxide, and metal additives of 1.05:1:(0.001~0.1), grind and mix them evenly, carry out high-temperature solid-state sintering, calcine at 900~1100℃ for 8~14h, cool to room temperature with the furnace, and pulverize to obtain bulk-doped lithium cobalt oxide matrix material.

[0051] S2. Take fast ion conductor and lithium salt material with a coating weight ratio of 1:2 to 2:1, grind and mix them evenly with the lithium cobalt oxide matrix material prepared in step S1, calcine at 500 to 900°C for 2 to 10 hours, cool to room temperature in the furnace, and pulverize to obtain a novel composite coated modified lithium cobalt oxide cathode material.

[0052] In step S2, the fast ion conductor accounts for 0.1–5 wt% of the weight of the lithium cobalt oxide matrix material, and the lithium salt material accounts for 0.1–5 wt% of the weight of the lithium cobalt oxide matrix material. The heating rate during the calcination process is 1–10 °C / min, and the gas atmosphere used during the calcination process is air or argon.

[0053] Example 1:

[0054] S1. Weigh the corresponding materials according to the molar ratio of metal elements in lithium carbonate, cobalt tetroxide, and magnesium oxide, Li:Co:Mg = 1.05:1:0.01, and mix them evenly in an agate mortar. Place the mixed powder in an alumina crucible and calcine it in a muffle furnace at a temperature of 1000℃ in air atmosphere, a heating rate of 5℃ / min, and a holding time of 10h. After cooling to room temperature in the furnace, collect the powder and crush it to obtain magnesium-doped modified lithium cobalt oxide matrix material.

[0055] Example 2:

[0056] S1. Weigh the corresponding materials according to the molar ratio of metal elements in lithium carbonate, cobalt tetroxide, and magnesium oxide, Li:Co:Mg = 1.05:1:0.01, and mix them evenly in an agate mortar. Place the mixed powder in an alumina crucible and calcine it in a muffle furnace at an air atmosphere of 1000℃, a heating rate of 5℃ / min, and a holding time of 10h. After cooling to room temperature in the furnace, collect the powder and crush it to obtain magnesium-doped lithium cobalt oxide matrix material.

[0057] S2. Take 0.99g of the magnesium-doped lithium cobalt oxide matrix material prepared in step S1 and 0.01g of lithium titanium aluminum phosphate, mix them evenly in an agate mortar, place the mixed powder in an alumina crucible and calcine it in a muffle furnace. The calcination temperature is 700℃ in air atmosphere, the heating rate is set to 5℃ / min, the holding time is 5h, and the furnace is cooled to room temperature. Collect the powder and crush it to obtain a single-layer lithium titanium aluminum phosphate coated modified lithium cobalt oxide cathode material.

[0058] Example 3:

[0059] S1. Weigh the corresponding materials according to the molar ratio of metal elements in lithium carbonate, cobalt tetroxide, and magnesium oxide, Li:Co:Mg = 1.05:1:0.01, mix them evenly in an agate mortar, place the mixed powder in an alumina crucible and calcine it in a muffle furnace at an air atmosphere of 1000℃, a heating rate of 5℃ / min, and a holding time of 10h. After cooling to room temperature in the furnace, collect the powder and crush it to obtain magnesium-doped lithium cobalt oxide matrix material.

[0060] S2. Take 1.96g of the magnesium-doped lithium cobalt oxide matrix material prepared in step S1 and 0.02g of lithium titanium aluminum phosphate, mix them evenly in an agate mortar, place the mixed powder in an alumina crucible and calcine it in a muffle furnace. The calcination temperature is 700℃ in air atmosphere, the heating rate is set to 5℃ / min, the holding time is 5h, and the furnace is cooled to room temperature. Collect the powder and crush it to obtain lithium titanium aluminum phosphate coated modified lithium cobalt oxide cathode material.

[0061] In addition, 0.99g of lithium titanium aluminum phosphate-coated modified lithium cobalt oxide cathode material prepared in step S2 and 0.01g of lithium metaphosphate were mixed evenly in an agate mortar. The mixed powder was placed in an alumina crucible and calcined in a muffle furnace at an air atmosphere of 700℃, a heating rate of 5℃ / min, and a holding time of 5h. The mixture was then cooled to room temperature in the furnace, and the powder was collected and pulverized to obtain the double-layer coated modified lithium cobalt oxide cathode material.

[0062] Example 4:

[0063] S1. Weigh the corresponding materials according to the molar ratio of metal elements in lithium carbonate, cobalt tetroxide, and magnesium oxide, Li:Co:Mg = 1.05:1:0.01, mix them evenly in an agate mortar, place the mixed powder in an alumina crucible and calcine it in a muffle furnace. The calcination temperature is 1000℃ in air atmosphere, the heating rate is set to 5℃ / min, the holding time is 10h, and the furnace is cooled to room temperature. The powder is collected and crushed to obtain magnesium-doped lithium cobalt oxide matrix material.

[0064] S2. Take 1.96g of the magnesium-doped lithium cobalt oxide matrix material prepared in step S1 and 0.02g of lithium metaphosphate, mix them evenly in an agate mortar, and place the mixed powder in an alumina crucible for calcination in a muffle furnace. The calcination temperature is 700℃ in air atmosphere, the heating rate is set to 5℃ / min, the holding time is 5h, and the powder is cooled to room temperature in the furnace. Collect the powder and crush it to obtain lithium metaphosphate-coated modified lithium cobalt oxide cathode material.

[0065] In addition, 0.99g of lithium metaphosphate-coated modified lithium cobalt oxide cathode material prepared in step S2 and 0.01g of lithium titanium aluminum phosphate were mixed evenly in an agate mortar. The mixed powder was placed in an alumina crucible and calcined in a muffle furnace at an air atmosphere of 700℃, a heating rate of 5℃ / min, and a holding time of 5h. The mixture was then cooled to room temperature in the furnace, and the powder was collected and pulverized to obtain the double-layer coated modified lithium cobalt oxide cathode material.

[0066] Example 5:

[0067] S1. Weigh the corresponding materials according to the molar ratio of metal elements in lithium carbonate, cobalt tetroxide, and magnesium oxide, Li:Co:Mg = 1.05:1:0.01, and mix them evenly in an agate mortar. Place the mixed powder in an alumina crucible and calcine it in a muffle furnace at a temperature of 1000℃ in air atmosphere, a heating rate of 5℃ / min, and a holding time of 10h. Cool the powder to room temperature in the furnace, collect the powder and crush it to obtain magnesium-doped lithium cobalt oxide matrix material.

[0068] S2. Take 0.985g of the magnesium-doped lithium cobalt oxide matrix material prepared in step S1, 0.01g of lithium titanium aluminum phosphate and 0.005g of lithium metaphosphate, mix them evenly in an agate mortar, put the mixed powder into an alumina crucible and calcine it in a muffle furnace. The calcination temperature is 700℃ in air atmosphere, the heating rate is set to 5℃ / min, the holding time is 5h, and the furnace is cooled to room temperature. The powder is collected and crushed to obtain a novel composite-coated modified lithium cobalt oxide cathode material.

[0069] Comparative Example 1:

[0070] Compared with Example 1, step S1 is changed to:

[0071] Without adding magnesium oxide, and with all other steps remaining unchanged, undoped lithium cobalt oxide cathode material is finally obtained.

[0072] Comparative Example 2:

[0073] Compared with Example 1, step S1 is changed to:

[0074] By replacing magnesium oxide with aluminum oxide while keeping other steps unchanged, aluminum-doped modified lithium cobalt oxide cathode material is finally obtained.

[0075] Comparative Example 3:

[0076] Compared with Example 1, step S1 is changed to:

[0077] By replacing magnesium oxide with titanium oxide while keeping other steps unchanged, titanium-doped modified lithium cobalt oxide cathode material is finally obtained.

[0078] Comparative Example 4:

[0079] Compared with Example 2, step S2 is changed to:

[0080] By replacing lithium titanium aluminum phosphate with lithium metaphosphate while keeping other steps unchanged, a single-layer lithium metaphosphate-coated modified lithium cobalt oxide cathode material is finally obtained.

[0081] Comparative Example 5:

[0082] Compared with Example 5, step S2 is changed to:

[0083] Take 0.98g of the magnesium-doped lithium cobalt oxide matrix material prepared in step 1, 0.01g of lithium titanium aluminum phosphate and 0.01g of lithium metaphosphate, and keep the other steps unchanged.

[0084] Comparative Example 6:

[0085] Compared with Example 5, step S2 is changed to:

[0086] Take 0.97g of the magnesium-doped lithium cobalt oxide matrix material prepared in step 1, 0.01g of lithium titanium aluminum phosphate and 0.02g of lithium metaphosphate, and keep the other steps unchanged.

[0087] Comparative Example 7:

[0088] Compared with Example 5, step S2 is changed to:

[0089] The calcination temperature in air atmosphere is 675℃, and other steps remain unchanged.

[0090] Comparative Example 8:

[0091] Compared with Example 5, step S2 is changed to:

[0092] The calcination temperature in air atmosphere is 725℃, and other steps remain unchanged.

[0093] The following is the approach to exploring the optimal coating methods for lithium titanium aluminum phosphate and lithium metaphosphate:

[0094] Single-layer coating (Example 2, Comparative Example 4), double-layer coating (Example 3, Example 4), novel composite coating (hybrid coating – Example 5)

[0095] For the novel coating layer, with a fixed lithium titanium aluminum phosphate coating amount of 1 wt%, the optimal coating amount of lithium metaphosphate under the novel coating layer was investigated: in Comparative Example 5 (lithium titanium aluminum phosphate: lithium metaphosphate = 1:1), Example 5 (lithium titanium aluminum phosphate: lithium metaphosphate = 2:1), and Comparative Example 6 (lithium titanium aluminum phosphate: lithium metaphosphate = 1:2).

[0096] For the novel coating layer, the optimal coating temperature was investigated: Comparative Example 7 (675℃), Example 5 (700℃), and Comparative Example 8 (725℃).

[0097] Example 1, compared to Comparative Example 1 (undoped and uncoated), was subjected to magnesium doping;

[0098] Example 1 serves as a reference control group compared to Example 2 (coated only with lithium titanium aluminum lithium phosphate), Comparative Example 4 (coated only with lithium metaphosphate), and Example 5 (novel composite coating), which are uncoated (without S2).

[0099] Button cell battery test

[0100] Preparation of lithium cobalt oxide cathode sheet: The lithium cobalt oxide cathode materials obtained in Examples 1-5 and Comparative Examples 1-8 were mixed uniformly with conductive agent acetylene black (Super P) and polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1. The mixture was then prepared into a slurry with N-methylpyrrolidone (NMP), and then uniformly coated on aluminum foil. After vacuum drying, the sheet was cut and weighed to obtain the desired cathode sheet.

[0101] Preparation of lithium-ion half-cells: CR2032 button cells were assembled in the VGB-6 glove box of Microna (China) Co., Ltd. The cells are composed of the above-mentioned positive electrode, lithium negative electrode, separator between the positive and negative electrodes and electrolyte.

[0102] Lithium-ion battery performance test parameter settings: The assembled lithium-ion CR2032 coin cells were tested using a CT-3008-5V-10MA battery tester from Shenzhen Xinwei New Energy Technology Co., Ltd. The test environment was room temperature or a 45℃ constant temperature chamber. Charge and discharge were performed using the rate mode, with the voltage range set to 3.0~4.6V and 1C = 200mAh / g. The coin cells were first activated with a 0.5C current for two cycles, and then cycled using a 1C current.

[0103] Using the undoped lithium cobalt oxide matrix material in Comparative Example 1 as a blank control, and comparing it with Example 1, Comparative Example 2, and Comparative Example 3, as shown in Table 1, the first-cycle discharge specific capacity of Comparative Example 1 (without element doping) is as high as 219.32 mAh / g (0.5C), fully demonstrating the high specific capacity advantage of the 4.6V high-voltage lithium cobalt oxide material. However, after long cycling at 1C, the discharge specific capacity decays rapidly, and the capacity retention rate after 100 cycles is only 29.23%. After bulk metal element doping (Mg, Al, Ti) was performed on Examples 1, 2, and 3, the first-cycle specific capacity of the obtained samples decreased slightly (this is because Mg, Al, Ti, etc. are inactive elements), and the corresponding capacity retention rates after 100 cycles increased to 88.51%, 73.94%, and 65.90%, respectively. In Example 1, the magnesium-doped lithium cobalt oxide material exhibited relatively superior high-voltage cycling performance at room temperature. This is because the radius of the magnesium ion is 0.72 Å, which is close to that of the lithium ion (0.76 Å). Magnesium ions tend to dope into the lithium layer in the lithium cobalt oxide crystal structure, acting as a "pillar ion." After 50 cycles, obvious cracks and "slip steps" (such as...) appeared on the surface of the undoped lithium cobalt oxide particles in Comparative Example 1. Figure 8-a As shown), while the magnesium-doped lithium cobalt oxide material in Example 1 only showed a slight "slip step" (as shown). Figure 8-b As shown in the figure, it exhibits good integrity of lithium cobalt oxide particles.

[0104] Table 1. Room temperature cycling test results of doped modified lithium cobalt oxide materials

[0105]

[0106] The modification effects of monolayer coating with lithium titanium aluminum phosphate and lithium metaphosphate (melting point 656℃) were investigated on magnesium-doped lithium cobalt oxide materials, corresponding to Example 2 and Comparative Example 4, respectively. As shown in Table 2, Example 2 exhibited excellent cycling performance of lithium titanium aluminum phosphate coating: the first-cycle discharge specific capacity reached 208.51 mAh / g, the first-cycle charge-discharge efficiency was 97.53%, and the capacity retention rates after 100 / 200 cycles were 90.22% / 67.57%. This is because lithium titanium aluminum phosphate can react with the lithium cobalt oxide matrix to generate some spinel phases that are beneficial to lithium-ion conduction (such as... Figure 3-c (Regions B1 and B2). The first-cycle discharge specific capacity of Comparative Example 4 was 202.82 mAh / g, with a first-cycle charge-discharge efficiency of 96.14%, and capacity retention of 85.65% / 70.01% after 100 / 200 cycles. This indicates that the single-layer lithium metaphosphate coating significantly enhances cycle stability. This may be due to the fact that lithium metaphosphate melts on the surface of lithium cobalt oxide at a calcination temperature of 700℃, forming a relatively complete coating layer. Due to the excellent lithium-ion conductivity of lithium titanium aluminum phosphate, Example 2 exhibits excellent rate performance: the first-cycle discharge specific capacity at 5C is 149.78 mAh / g, far exceeding that of Comparative Example 1 (53.55 mAh / g) and Example 1 (107.63 mAh / g). The rapid capacity decay after long cycling in Example 2 may be due to the failure of lithium titanium aluminum phosphate to form a complete coating layer on the surface of the lithium cobalt oxide substrate, such as... Figure 3-b As shown in region A.

[0107] Table 2. Room temperature cycling test results of the coated modified lithium cobalt oxide material

[0108]

[0109] Considering the excellent modification effect of Example 2, a combination of lithium titanium aluminum phosphate and lithium metaphosphate for coating was considered. In Example 3, the inner coating layer was lithium titanium aluminum phosphate, and the outer layer was lithium metaphosphate. In Example 4, the inner layer was lithium metaphosphate, and the outer layer was lithium titanium aluminum phosphate. Compared with single-layer coating modification, the discharge specific capacity and cycle retention rate of the lithium cobalt oxide material decreased to varying degrees after double-layer coating modification. This may be because there is a reaction between the lithium titanium aluminum phosphate and the lithium metaphosphate coating layer, or because lithium metaphosphate hinders the reaction between lithium titanium aluminum phosphate and lithium cobalt oxide to form a lithium-ion conductor. To simultaneously combine the effect of lithium titanium aluminum phosphate in improving discharge specific capacity and the effect of lithium metaphosphate in enhancing coating layer integrity, a hybrid coating scheme of lithium titanium aluminum phosphate / lithium metaphosphate was considered, i.e., constructing a lithium titanium aluminum phosphate / lithium metaphosphate coating layer on lithium cobalt oxide particles—a novel composite coating layer structure.

[0110] When performing mixed coating of lithium aluminum titanium phosphate and lithium metaphosphate, the coating ratio of lithium aluminum titanium phosphate was fixed at 1 wt%. The coating amounts of lithium metaphosphate were set to 0.5 wt%, 1 wt%, and 2 wt%, corresponding to Example 5, Comparative Example 5, and Comparative Example 6, respectively. The corresponding test results are shown in Tables 3 and 4.

[0111] Table 3. Room temperature rate test results of modified lithium cobalt oxide materials

[0112]

[0113] Table 4. Results of high-temperature (45℃) cycling test of modified lithium cobalt oxide materials.

[0114]

[0115] Lithium titanium aluminum phosphate and lithium cobalt oxide form an island-shaped spinel phase at 700℃. Figure 4-b In the C1 region), lithium metaphosphate melts on the surface of lithium cobalt oxide particles ( Figure 4-b In the middle D2 region, a novel hybrid coating structure of "island-shaped ionic conductors + uniformly distributed lithium metaphosphate" is formed. Similar to Example 2 (e.g.) Figure 9-a As shown), in Example 5, no obvious grain cracks or "lattice slip" phenomenon were observed after 50 cycles (as shown). Figure 9-c (As shown). After 200 long cycles, Example 2 showed that the coated particles detached, exposing the surface of the lithium cobalt oxide particles (as shown). Figure 9-b As shown). Due to the loss of the protection of the coated particles, the lithium cobalt oxide particles exhibited varying degrees of particle cracking and interlayer slippage. This corresponds to the phenomenon in Example 2 where the specific capacity decayed slowly in the early stages of cycling, but then dropped sharply during subsequent discharge. In contrast, Example 5 did not show any obvious coating particle detachment after 200 cycles (as shown). Figure 9-d (As shown), this is because the low-melting-point lithium metaphosphate forms a more complete coating layer on the surface of lithium cobalt oxide particles, enhancing the bonding between the island-shaped lithium-ion conductors and the lithium cobalt oxide particles. This is thanks to the more complete coating effect of the novel coating layer on the surface of the lithium cobalt oxide particles. In Example 5, the capacity retention rate was 79.24% after 200 cycles at 1C at room temperature and 79.45% after 200 cycles at 1C at 45°C, achieving a significant improvement in both room temperature and high-temperature performance.

[0116] The key point protected by this invention is: a novel composite-coated modified lithium cobalt oxide cathode material.

[0117] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A lithium cobalt oxide cathode material, characterized in that, The lithium cobalt oxide base material is prepared by doping with metal elements, and a composite coating layer is coated on the surface of the lithium cobalt oxide base material, the composite coating layer comprises a fast ion conductor and a lithium salt material, the fast ion conductor is coated in island shape, and the lithium salt material is coated as a supplement.

2. The lithium cobalt oxide cathode material of claim 1, wherein, The metal elements are one or more of nano-sized oxides of magnesium, aluminum, titanium, sodium, potassium, calcium, iron, copper, iron, and zinc.

3. The lithium cobalt oxide cathode material of claim 1, wherein, The fast ion conductor material is one or more of lithium aluminum germanium phosphate, lithium aluminum titanium phosphate, and lithium lanthanum zirconium niobium oxide.

4. The lithium cobalt oxide cathode material of claim 1, wherein, The lithium salt material is one or more of lithium phosphate, lithium metaphosphate, lithium nitrate, and lithium sulfate.

5. The method of producing a lithium cobalt oxide cathode material according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: S1. According to the molar ratio of lithium carbonate, tricobalt tetroxide, and the metal element of the metal additive 1.05:1:(0.001-0.1), the corresponding materials are weighed and uniformly ground and mixed, high-temperature solid-phase sintering is performed, calcination is performed at 900-1100°C for 8-14h, the furnace is cooled to room temperature, and after crushing, a body-phase doped lithium cobalt oxide base material is obtained; S2. The fast ion conductor and the lithium salt material are taken in a coating weight ratio of 1:2-2:1, uniformly ground and mixed with the lithium cobalt oxide base material prepared in step S1, calcination is performed at 500-900°C for 2-10h, the furnace is cooled to room temperature, and after crushing, a composite coating modified lithium cobalt oxide positive electrode material is obtained.

6. The method of claim 5, wherein the lithium cobalt oxide cathode material is prepared by the steps of: mixing cobalt oxide, lithium carbonate, and manganese carbonate; and heating the mixture at a temperature of 700 to 800°C for 10 to 20 hours. In step S2, the weight percentage of the fast ion conductor relative to the lithium cobalt oxide base material is 0.1-5wt%, and the weight percentage of the lithium salt material relative to the lithium cobalt oxide base material is 0.1-5wt%.

7. The method of claim 5, wherein the lithium cobalt oxide cathode material is prepared by the steps of: mixing cobalt oxide and lithium carbonate; and heating the mixture at a temperature of 700 to 800°C for 10 to 20 hours. In step S2, the heating rate of the calcination process is 1-10°C / min.

8. The method for preparing the lithium cobalt oxide cathode material as described in claim 5, characterized in that, In step S2, the gas atmosphere used in the calcination process is air or argon.

9. A lithium-ion battery, characterized by The lithium cobalt oxide positive electrode material as claimed in any one of claims 1-4.

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