Positive electrode material, positive electrode sheet, and battery

Abstract

The present disclosure provides a positive electrode material, and a positive electrode sheet and a battery comprising the positive electrode material. The positive electrode material comprises a core-shell structure, the core of the core-shell structure comprises lithium cobalt oxide, the shell of the core-shell structure comprises lithium cobalt tellurium oxide, the lithium cobalt tellurium oxide has a chemical formula of LiaCobTecA1 dA2 eO6, in which 2≤a≤4, 1≤b≤2, 0<c≤1, 0≤d≤1, 0≤e≤1, A1 comprises at least one of Al, Mg, Ti, Zr, Nb, La, W and Y, and A2 comprises at least one of F, S and P; and the lithium cobalt tellurium oxide has a single-phase structure with a space group of C2 / m, and the shell has a thickness of less than or equal to 200 nm. The positive electrode material of the present disclosure can effectively improve the initial Coulombic efficiency, rate performance and low-temperature performance of the battery, and can also improve the capacity attenuation problem of the battery during the high voltage cycling process.

Description

A positive electrode material, a positive electrode sheet, and a battery Technical Field

[0001] This disclosure relates to the field of battery technology, specifically to a positive electrode material and a positive electrode sheet and battery including the positive electrode material. Background Technology

[0002] Cathode materials play a crucial role in batteries, being one of the core factors determining battery performance. Their performance directly influences the battery's energy density, lifespan, safety, and application areas. Among them, lithium cobalt oxide, as a high-performance cathode material, plays a pivotal role in the battery industry. It boasts advantages such as high specific capacity, a relatively high voltage platform (average output voltage of 3.7V), high safety and reliability, and impact resistance, making it widely used in lithium-ion batteries and a common material in the manufacturing process of small consumer electronics products such as smartphones and laptops.

[0003] However, with the deepening and widespread application of lithium cobalt oxide, the requirements for its energy density are becoming increasingly stringent. This leads to a series of problems with lithium cobalt oxide in high-voltage applications. For example, when the battery is under high-voltage charging, lithium cobalt oxide undergoes a deep delithiation process. The large-scale extraction of lithium ions causes changes in the lattice structure of lithium cobalt oxide. This structural transformation is irreversible and destroys the structural integrity of the material, making subsequent lithium ion insertion and extraction difficult. This, in turn, leads to problems such as battery capacity decay, decreased energy density and cycle performance, and exacerbated side reactions. These problems limit the application and development of lithium cobalt oxide cathode materials in some fields with stringent high-voltage performance requirements.

[0004] Therefore, it is very important to invent a lithium cobalt oxide cathode material that can have high capacity and cycle performance under high voltage. Summary of the Invention

[0005] The purpose of this disclosure is to overcome the problems of capacity decay, structural damage, and decreased cycle performance of lithium cobalt oxide cathode materials under high voltage in the prior art, and to provide a cathode material, a cathode sheet including the cathode material, and a battery. The cathode material of this disclosure includes a core-shell structure, by constructing a lithium cobalt telluride shell layer on the surface of the lithium cobalt oxide core. The lithium cobalt telluride has a single-phase structure with a space group of C2 / m, and the thickness of the shell layer is controlled to be ≤200nm. This can effectively improve the battery's initial efficiency, rate capability, and cycle performance, and improve the capacity decay problem of the battery during high-voltage cycling.

[0006] To achieve the above objectives, the technical solution adopted in this disclosure is as follows:

[0007] The first aspect of this disclosure provides a cathode material comprising a core-shell structure, wherein the core of the core-shell structure comprises lithium cobalt oxide, and the shell layer of the core-shell structure comprises lithium cobalt telluride oxide, wherein the chemical formula of the lithium cobalt telluride oxide is Li. a Co b Te c A 1 d A 2 e O6, where 2≤a≤4, 1≤b≤2, 0<c≤1, 0≤d≤1, 0≤e≤1, A 1 Including at least one of Al, Mg, Ti, Zr, Nb, La, W, and Y, A 2 It includes at least one of F, S and P; the lithium cobalt tellurium oxide has a single-phase structure with space group C2 / m, and the thickness of the shell is ≤200nm.

[0008] This disclosure describes a method for constructing a specific lithium cobalt telluride shell on the surface of lithium cobalt oxide, enabling the cathode material to exist stably under high voltage. This method also improves the battery's initial efficiency and cycle capacity retention to a certain extent, enhances rate performance, and reduces voltage decay, effectively improving the cathode material's performance under high voltage. This is because: First, the shell effectively isolates the cathode material surface from direct contact with the electrolyte, reducing reactive sites and minimizing side reactions. Furthermore, its specific structure interacts with oxygen atoms on the lithium cobalt oxide surface, enhancing the binding force between oxygen atoms and the crystal lattice, reducing oxygen escape from the cathode material surface during charge-discharge cycles, providing a stable environment for transition metal ions, reducing transition metal ion dissolution, maintaining structural stability, and alleviating internal stress accumulated due to volume changes during charge-discharge, further stabilizing the material structure, maintaining stable battery performance, and extending its lifespan. Second, this shell has a higher lithium ratio compared to the bulk-doped Te-Co phase. Since the shell itself can provide additional lithium ions, it reduces the consumption of lithium ions for forming the solid electrolyte interphase (SEI) film during the first charge and discharge cycle, effectively replenishing lithium ions and improving the battery's cycle capacity retention. Furthermore, the specific structure of the shell can optimize the lithium ion transport path to some extent, reduce interfacial impedance, and further improve the battery's rate performance and cycle stability.

[0009] Furthermore, this shell is a stable, single-phase structure with an ordered phase distribution in space group C2 / m. Due to its single-phase characteristics, the shell's composition and structure are relatively uniform, providing a stable crystal structure. This structure can reduce phase transitions in the cathode material during charging and discharging, minimize volume changes in the cathode material, reduce structural collapse caused by stress accumulation, help maintain structural stability, and slow down material degradation during multiple charge-discharge cycles, thereby extending battery life. It can also effectively accommodate lithium-ion insertion and extraction, reducing volume changes in the material during charging and discharging. Moreover, the larger lattice gaps facilitate rapid lithium-ion migration, thereby improving battery charging and discharging efficiency, enabling the battery to operate at high voltages, and improving overall battery performance.

[0010] Furthermore, the fusion of cobalt in the shell and the cobalt on the surface of the lithium cobalt oxide results in a varying thickness on the cathode material surface. This thickness difference significantly increases electrolyte retention, allowing more electrolyte to remain on the material surface. This leads to more thorough contact between the cathode and the electrolyte, greatly improving wetting. Good wetting also accelerates ion transport between the cathode material and the electrolyte, improving battery charge / discharge efficiency, especially at high rates. This results in faster battery response, reduced polarization, and improved overall battery performance, meeting diverse performance requirements in different application scenarios. However, when the shell is too thick (>200nm), the lithium-ion diffusion path becomes longer, increasing diffusion resistance and significantly slowing lithium-ion migration. Due to this hindered lithium-ion diffusion, the active material in the cathode material cannot fully participate in the electrode reaction. During charging and discharging, some positive electrode materials, due to excessively thick shells, cannot effectively contact lithium ions and electrons, resulting in insufficient capacity utilization. This causes the actual specific capacity of the battery to be lower than the theoretical specific capacity, affecting the battery's energy storage capacity and consequently reducing charge-discharge efficiency and rate performance. Therefore, controlling the shell thickness within an appropriate range can further improve the battery's charge-discharge efficiency and rate performance.

[0011] A second aspect of this disclosure provides a positive electrode sheet comprising the positive electrode material described in the first aspect of this disclosure.

[0012] A third aspect of this disclosure provides a battery comprising the positive electrode material described in the first aspect of this disclosure and / or the positive electrode sheet described in the second aspect of this disclosure.

[0013] Compared with the prior art, the present disclosure has at least the following advantages through the above technical solution:

[0014] (1) The cathode material disclosed herein has a stable structure and provides additional lithium ions to improve the charge and discharge efficiency of the battery.

[0015] (2) The positive electrode of this disclosure can slow down the decay of battery capacity.

[0016] (3) The battery disclosed herein has high energy density, good rate performance and cycle stability.

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Attached Figure Description

[0018] Figure 1 shows a scanning electron microscope (SEM) image of the cathode material in an example of this disclosure.

[0019] Figure 2 shows an overall X-ray diffraction pattern of the cathode material in an embodiment and a comparative example of this disclosure.

[0020] Figure 3 shows a partially enlarged X-ray diffraction pattern of the cathode material in one embodiment and comparative example of this disclosure.

[0021] Figure 4 shows a partially enlarged X-ray diffraction pattern of the cathode material in one embodiment and a comparative example of this disclosure.

[0022] Figure 5 shows a partial enlarged view of the X-ray diffraction pattern of the cathode material in one embodiment and comparative example of this disclosure.

[0023] Figure 6 shows a partially enlarged X-ray diffraction pattern of the cathode material in one embodiment and a comparative example of this disclosure.

[0024] Figure 7 shows a scanning electron microscope (SEM) image of lithium cobalt telluride in an example of this disclosure. Detailed Implementation

[0025] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0026] This disclosure provides a cathode material comprising a core-shell structure, wherein the core of the core-shell structure comprises lithium cobalt oxide, and the shell layer comprises lithium cobalt telluride oxide, wherein the chemical formula of the lithium cobalt telluride oxide is Li. a Co b Te c A 1 d A 2 eO6, where 2≤a≤4 (e.g., 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, or 4), 1≤b≤2 (e.g., 1.2, 1.4, 1.6, 1.8, or 2), 0<c≤1 (e.g., 0.01, 0.05, 0.1, 0.2, 0.4, 0.6, 0.8, or 1), 0≤d≤1 (e.g., 0, 0.1, 0.2, 0.4, 0.6, 0.8, or 1), 0≤e≤1 (e.g., 0, 0.1, 0.2, 0.4, 0.6, 0.8, or 1), A 1 Including at least one of Al, Mg, Ti, Zr, Nb, La, W, and Y, A 2 It includes at least one of F, S and P; the lithium cobalt telluride oxide has a single-phase structure with space group C2 / m.

[0027] In this disclosure, the thickness of the shell is ≤200nm, for example, 200nm, 190nm, 180nm, 170nm, 160nm, 150nm, 140nm, 130nm, 120nm, 110nm, 100nm, 90nm, 80nm, 70nm, 60nm, 50nm, 40nm, 30nm, 20nm or 10nm.

[0028] In one instance, the thickness of the shell is ≤100nm, for example, 100nm, 90nm, 80nm, 70nm, 60nm, 50nm, 40nm, 30nm, 20nm or 10nm.

[0029] In one example, the thickness of the shell is 10nm-30nm.

[0030] Figure 1 shows an SEM image of the cathode material in one embodiment of this disclosure. As can be seen from the image, the surface of the cathode material has a nearly uniformly distributed shell layer. This shell layer can orderly and uniformly protect the lithium cobalt oxide surface, effectively isolating the lithium cobalt oxide from direct contact with the electrolyte, reducing the occurrence of side reactions, and thus improving the battery's stability and cycle life. Furthermore, due to the partial fusion of cobalt in the shell layer and the cobalt on the surface of the lithium cobalt oxide, the cathode material surface exhibits varying thicknesses. This thickness difference significantly increases the electrolyte retention, resulting in more electrolyte being retained on the material surface. This leads to more thorough contact between the cathode sheet and the electrolyte, greatly improving the wetting effect. Simultaneously, it also accelerates the transport speed of lithium ions between the cathode material and the electrolyte, improving the battery's charge and discharge efficiency.

[0031] In this disclosure, the thickness of the shell layer is the average thickness of the outer surface shell layer of the lithium cobalt oxide material, which can be measured using conventional methods in the art. For example, the battery can be discharged to 0% SOC, the positive electrode sheet can be disassembled and removed, and its cross-section can be polished using an argon-ion polishing machine to obtain a TEM image; or a TEM image of the positive electrode material can be directly obtained. In the above TEM image, a suitable spherical cross-section is selected, and at least 5 sites on the cross-section are selected to measure the thickness of the shell layer at each site and take the average value.

[0032] In this disclosure, the chemical formula of the lithium cobalt oxide is Li. x Co y M z O2, wherein 0.8 ≤ x ≤ 1.2 (e.g., 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15 or 1.2), 0.8 ≤ y ≤ 1 (e.g., 0.8, 0.85, 0.9, 0.95 or 1), 0 ≤ z ≤ 0.2 (e.g., 0, 0.05, 0.1, 0.15 or 0.2), and M includes at least one of Te, Al, Mg, Ti, Zr, Nb, W, Y and La.

[0033] In one example, the lithium cobalt oxide has a layered rock salt crystal structure.

[0034] In one example, the lithium cobalt telluride oxide comprises the chemical formula Li4CoTeMg. 0.1 O6, Li4CoTeO6 and Li4CoTeMg 0.1 Al 0.1 At least one of O6.

[0035] In one example, the lithium cobalt telluride oxide comprises Li4CoTeO6. The crystal structure of Li4CoTeO6 contains four inequivalent Li atoms. + Site, each Li + All with six O 2 - Atom coordination forms LiO6 octahedra, which are connected to CoO6 and TeO6 octahedra respectively through corner sharing and edge sharing. Different Li + The octahedral tilt angle of the site ranges from 1° to 11°, and the Li-O bond length ranges from [missing value]. to Each Co 4+ With six O 2- Atom coordination forms CoO6 octahedra, which are connected to six LiO6 octahedra through corner sharing and to three TeO6 octahedra through edge sharing. The Co-O bond length ranges from [value missing]. to Each Te 4+ With six O 2-Atom coordination forms TeO6 octahedra, which are connected to six LiO6 octahedra through corner sharing and to three CoO6 octahedra through edge sharing. The Te-O bond length ranges from [value missing]. to This structure can further enhance the bonding force between oxygen atoms and the lattice, reduce oxygen escape from the surface of the cathode material during battery charge and discharge cycles, reduce the dissolution of transition metal ions, maintain structural stability, alleviate the internal stress accumulated by the cathode material due to volume changes during charge and discharge, stabilize the material structure, maintain stable battery performance, and extend its service life.

[0036] In this disclosure, the X-ray diffraction pattern of the cathode material exhibits characteristic diffraction peaks at 18.018°-18.4°, 19.548°-19.71°, 20.42°-20.7°, 22.62°-22.83°, 41.8°-43.93°, and 42.57°-42.68°.

[0037] In this disclosure, the X-ray diffraction pattern of the cathode material has a 003 peak at 2θ = 18.6°-19°, a 006 peak at 38°-38.7°, a 102 peak at 38.8°-39.5°, a 108 peak at 65°-66°, and a 110 peak at 66°-67°.

[0038] In this disclosure, the X-ray diffraction pattern of the cathode material exhibits characteristic diffraction peaks at 18.018°-18.4°, 19.548°-19.71°, 20.42°-20.7°, 22.62°-22.83°, 41.8°-43.93°, and 42.57°-42.68°, indicating that the cathode material includes lithium cobalt tellurium oxide; the X-ray diffraction pattern of the cathode material has 0 at 2θ = 18.6°-19°. The presence of a 03 peak, a 006 peak at 38°-38.7°, a 102 peak at 38.8°-39.5°, a 108 peak at 65°-66°, and a 110 peak at 66°-67° indicates that the cathode material includes lithium cobalt oxide. Furthermore, due to the presence of a lithium cobalt telluride shell on the outer surface of the lithium cobalt oxide, the positions of the 003, 006, 102, 108, and 110 peaks of the cathode material are slightly shifted compared to those of the lithium cobalt oxide in Comparative Preparation Example 3.

[0039] In this disclosure, the average particle size of the lithium cobalt tellurium oxide is ≤200 nm, for example, 200 nm, 180 nm, 150 nm, 130 nm, 100 nm, 80 nm, 50 nm, or 20 nm. The median particle size Dv50 of the lithium cobalt tellurium oxide is ≤200 nm, for example, 200 nm, 180 nm, 150 nm, 130 nm, 100 nm, 80 nm, 50 nm, or 20 nm.

[0040] In one example, the average particle size of the lithium cobalt telluride oxide is 30 nm to 100 nm.

[0041] In one example, the median particle size Dv50 of the lithium cobalt telluride oxide is 30 nm-100 nm.

[0042] Figure 7 shows an SEM image of lithium cobalt telluride oxide in an example of this disclosure. As can be seen from the figure, the shell is a nanoscale single crystal structure with good dispersion and uniform particle size, which is convenient for subsequent coating.

[0043] By controlling the average or median particle size (Dv50) of lithium cobalt telluride oxide within a suitable range, the electron conduction distance can be effectively reduced, the electron transport rate increased, and the battery's output power and cycle life improved. If the particle size of lithium cobalt telluride oxide is too large (e.g., average particle size > 200 nm or Dv50 > 200 nm), the electron conduction distance increases, the electron transport rate decreases, leading to a slower electrode reaction rate and poorer electrochemical performance. This manifests as increased internal resistance, increased voltage drop during high-rate charging / discharging or high-current operation, and decreased output power. Furthermore, excessively large particle size of lithium cobalt telluride oxide can also create uneven stress distribution on the surface of the cathode material. During battery charging and discharging, the positive electrode material undergoes volume changes due to the insertion and extraction of lithium ions. When the lithium cobalt telluride particle size is large, the internal stress is greater, which may lead to cracks or even peeling of the shell. Once the shell is damaged, it loses its protective function for lithium cobalt oxide, exposing the lithium cobalt oxide directly to the electrolyte. This increases the possibility of adverse reactions between the material and the electrolyte, thus affecting the battery's cycle life. Furthermore, internal stress concentration or a mismatch in the coefficient of thermal expansion between the positive electrode material and the internal material may generate more heat, causing the battery temperature to rise and potentially leading to thermal runaway, posing a safety hazard.

[0044] In this disclosure, the particle size Dv50 of the cathode material is 10μm-22μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm or 22μm; Dv90 is 25μm-35μm, for example, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm, 31μm, 32μm, 33μm, 34μm or 35μm; Dv99 ≤ 65μm, for example, 65μm, 62μm, 59μm, 56μm, 53μm, 50μm, 47μm, 44μm, 41μm, 38μm, 35μm or 32μm.

[0045] In one example, the particle size of the cathode material is Dv50 of 14μm-18μm, Dv90 of 26μm-30μm, and Dv99 ≤ 47μm.

[0046] In this disclosure, the average particle size of the lithium cobalt telluride oxide can be obtained by conventional methods in the art. For example, the battery is discharged to 0% SOC, the positive electrode is disassembled and removed, and its cross-section is polished using an argon-ion mill. At least 20 lithium cobalt telluride oxide particles are selected in a TEM image, and the particle size of each particle is measured, with the average value taken. If the lithium cobalt telluride particle appears as a regular circle in the TEM image, then the particle size is the diameter of that circle; if the lithium cobalt telluride particle appears as a non-regular circle in the TEM image, then the particle size is the diameter of an equivalent circle with the same area as the non-regular circle.

[0047] In this disclosure, the median particle size Dv50 of the lithium cobalt telluride oxide and the particle sizes Dv50, Dv90 and Dv99 of the cathode material can be obtained by conventional methods in the art, such as by a laser particle size analyzer.

[0048] In this disclosure, the lithium cobalt telluride oxide has a layered structure, and the interlayer spacing of the lithium cobalt telluride oxide is... For example,

[0049] In one instance, d1 is

[0050] In this disclosure, the interlayer spacing of the lithium cobalt oxide For example,

[0051] When lithium cobalt telluride oxide is sintered and coated onto the surface of lithium cobalt oxide, a layered and lithium-rich superstructure is formed. The interlayer spacing d1 and d2 are determined by analyzing X-ray diffraction patterns using Jade software. Specifically, Figure 2 shows the overall X-ray diffraction pattern of the cathode material in one embodiment and a pair of proportions of this disclosure. Figures 3-6 show enlarged views of the X-ray diffraction patterns of the cathode material in one embodiment and a pair of proportions of this disclosure. Taking the X-ray diffraction pattern of the embodiment as an example, the interlayer spacing is calculated using Bragg's law equation nλ = 2dsinθ, where the horizontal axis (2θ) represents the diffraction angle and the vertical axis (intensity) represents the diffraction intensity. The specific XRD test parameters are: using a Cu target, scanning range 15°-75°, scanning speed 2° / min, n determined by Jade software, and λ is... The interlayer spacing d1 was calculated using the peak position within the range of 18.018°–18.4°; the interlayer spacing d2 was calculated using the 003 peak position (18.6°–19°). The lithium cobalt tellurium oxide disclosed herein has a lithium-rich layered superstructure with a large lithium-ion interlayer spacing, resulting in a high lithium-ion transport rate.

[0052] In this disclosure, the content of lithium cobalt telluride oxide is 3000ppm-30000ppm (e.g., 3000ppm, 5000ppm, 7000ppm, 9000ppm, 11000ppm, 13000ppm, 15000ppm, 17000ppm, 19000ppm, 21000ppm, 23000ppm, 25000ppm, 27000ppm, 29000ppm or 30000ppm) based on the total weight of the cathode material.

[0053] In one example, the content of lithium cobalt telluride was 11,000 ppm to 16,000 ppm.

[0054] In this disclosure, the dielectric constant of the shell is >10.5ε. The dielectric constant of the lithium cobalt telluride oxide is >10.5ε.

[0055] Due to Co in the shell or lithium cobalt telluride structure 4+ and Te 4+ The presence of this material results in a high dielectric constant, which reduces the hindering effect of electrostatic interactions between ions, accelerates lithium-ion transport, and effectively improves the battery's initial efficiency, rate capability, and energy density.

[0056] In this disclosure, the content of lithium cobalt telluride in the cathode material can be tested by conventional methods in the art. For example, the battery is discharged to 0% SOC, the cathode sheet is removed from the battery, the active coating of the cathode is scraped off, and then sintered at 300°C. The remaining material is collected and tested by inductively coupled plasma optical emission spectrometry (ICP-OES). After the sample is digested, the elements in the sample are atomized and excited to emit light. The characteristic spectral wavelength is detected by a spectrophotometer, and the actual content value is calculated by a standard curve.

[0057] In this disclosure, the mass content of Co on the inner surface of the shell is higher than that on the outer surface of the shell; the mass content of Te on the inner surface of the shell is lower than that on the outer surface of the shell. The inner surface of the shell refers to the surface closer to the core, and the outer surface of the shell refers to the surface farther from the core.

[0058] Energy-dispersive X-ray spectroscopy (EDS) revealed a uniform distribution of Te-Co elements on the cathode surface. Due to the partial fusion of cobalt in the shell and the lithium cobalt oxide surface, the mass content of Co differs between the inner and outer surfaces of the shell. Near the outer surface, Co exists as a Li4CoTeO6 compound, while on the inner surface, directly connected to the lithium cobalt oxide, it exists as a compound with a higher Co-Li ratio.

[0059] In this disclosure, the mass content of Co and Te elements on the inner and outer surfaces of the shell can be obtained by conventional methods in the art, such as scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS). In EDS point scanning mode, 5-10 points are selected on the inner and outer surfaces of the shell, and the content of Co and Te elements at each point is measured and the average value is taken.

[0060] In this disclosure, the cathode material includes single crystal and / or polycrystalline.

[0061] In this disclosure, within a voltage range of 3.0V-4.6V, at a charge / discharge rate of 0.1C, the specific capacity of the positive electrode material is 208mAh / g-223mAh / g (e.g., 208mAh / g, 210mAh / g, 212mAh / g, 214mAh / g, 216mAh / g, 218mAh / g, 220mAh / g, or 223mAh / g); at a charge / discharge rate of 0.5C, the specific capacity of the positive electrode material is 203mAh / g-220mAh / g (e.g., 203mAh / g, 205mAh / g, 207mAh / g, 209mAh / g, 211mAh / g, 213mAh / g, 215mAh / g, 217mAh / g, or 220mAh / g).

[0062] The high lithium ratio and lithium-rich layered structure of lithium cobalt telluride oxide (LCO) effectively improve the discharge capacity and cycle capacity retention of batteries. This is due to two main reasons: First, LCO has a higher lithium ratio compared to the bulk-doped Te-Co phase. Since LCO itself provides additional lithium ions, the cathode material contains more lithium ions, reducing the consumption of lithium ions for forming the solid electrolyte interphase (SEI) film during the first charge-discharge cycle, effectively replenishing lithium ions. This means an increased number of lithium ions participating in electrochemical reactions during charge-discharge, resulting in a greater charge throughput per unit time, directly increasing the battery's discharge capacity, improving cycle capacity retention, and ultimately increasing energy density. Second, the formed lithium-rich layered structure provides additional capacity compared to conventionally coated lithium cobalt oxide. This is because this structure provides a faster transport path for lithium ions, reducing the resistance to lithium ion migration within the cathode material, making the insertion and extraction processes smoother during charge-discharge, thereby improving the lithium ion diffusion coefficient and transport efficiency. This means that more lithium ions can participate in the charge-discharge reaction within the same time frame, thereby increasing the battery's charge-discharge capacity. Simultaneously, a well-defined layered structure can increase the specific surface area of ​​the cathode material, allowing more lithium ions to contact and react with the electrode material, further contributing additional capacity.

[0063] This disclosure also provides a method for preparing the cathode material, comprising at least the following steps:

[0064] S1. Mix the cobalt-containing precursor and the first lithium source, and perform the first sintering;

[0065] S2, combine the second lithium source, tellurium source, cobalt source, and optional element A. 1 Source and element A 2 Source mixing;

[0066] S3. Perform a second sintering on the material obtained in step S2;

[0067] S4. Mix the materials obtained in step S1 and step S3, and perform the third sintering.

[0068] In this disclosure, in step S1, the cobalt-containing precursor includes, for example, Co3O4. The first lithium source includes, for example, lithium carbonate. The molar ratio of the first lithium source (calculated as Li) to the cobalt-containing precursor (calculated as Co) is (1.03-1.05):1.

[0069] In this disclosure, in step S1, the first sintering can be performed in sintering equipment conventionally used in the art, such as a muffle furnace. The conditions for the first sintering are: a sintering atmosphere of air, a sintering temperature of 850℃-1200℃, and a sintering time of 6h-15h.

[0070] In this disclosure, step S1 may further include first crushing and first sieving after the first sintering is completed.

[0071] In this disclosure, in step S2, the second lithium source includes, for example, lithium carbonate. The tellurium source includes, for example, tellurium dioxide. The cobalt source includes, for example, cobalt(II) hydroxide.

[0072] In this disclosure, "optional" means that it may include element A. 1 Source and / or element A 2 The source may also exclude element A. 1 Source and / or element A 2 Source. The element A 1 The source, for example, includes element A. 1 Oxides of element A. 2 The source, for example, includes element A. 2 Lithium salts. The element Al includes at least one selected from Al, Mg, Ti, Zr, Nb, and Y. 2 It includes at least one of F, S and P.

[0073] In this disclosure, step S2 further includes at least one of ball milling, drying, and second sieving. The ball milling conditions include: using anhydrous ethanol as the medium for 15-30 hours.

[0074] In this disclosure, in step S3, the second sintering can be performed in sintering equipment conventionally used in the art, such as a muffle furnace. The conditions for the second sintering include: a sintering atmosphere of air; the second sintering comprising a first stage and a second stage; the temperature of the first stage being 500℃-750℃ and the time being 4h-9h; and the temperature of the second stage being 700℃-950℃ and the time being 5h-10h.

[0075] In this disclosure, step S3, after the second sintering, further includes crushing and a third sieving. The third sieving uses a 300-400 mesh sieve.

[0076] In this disclosure, in step S4, the mass ratio of the material obtained in step S1 to the material obtained in step S3 is 100:(0.2-0.8). The third sintering is carried out in sintering equipment conventionally used in the art. The conditions for the third sintering include: a sintering atmosphere of air, a temperature of 750℃-950℃, and a time of 5h-15h.

[0077] A second aspect of this disclosure provides a positive electrode sheet, which may include a positive current collector and a positive active material layer located on at least one side surface of the positive current collector. The positive active material layer may further include a positive conductive agent and a positive binder. The positive conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, carbon nanotubes (including at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes), and carbon fibers. The positive binder may include at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, styrene-butadiene rubber, polytetrafluoroethylene, polyethylene oxide, polyacrylic acid, and derivatives of the above substances. Based on the total weight of the positive electrode active material layer, the content of the positive electrode material can be 80%-96% (e.g., 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, or 96%), the content of the positive electrode conductive agent can be 2%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, or 2%), and the content of the positive electrode binder can be 2%-10% (e.g., 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, or 2%).

[0078] In this disclosure, the compaction density of the positive electrode sheet is 4 g / cm³. 3 -4.8g / cm 3 (For example, 4.0 g / cm³) 3 4.05g / cm 3 4.1g / cm 3 4.15g / cm 3 4.2g / cm 3 4.25g / cm 3 4.3g / cm 3 4.35g / cm 3 4.4g / cm 3 4.45g / cm 3 4.5g / cm 3 4.55g / cm 3 4.6g / cm 3 4.65g / cm 3 4.7g / cm 3 4.75g / cm 3 Or 4.8g / cm 3 ).

[0079] In this disclosure, the compaction density of the positive electrode sheet can be obtained by conventional methods in the art, for example: discharging the battery to 0% SOC, disassembling the battery to remove the positive electrode sheet, soaking it in dimethyl carbonate (DMC) solvent for 12 hours, then rinsing it with DMC to remove the lithium salts attached to the positive electrode sheet, drying it, and then calculating it according to the following formula: (weight of positive electrode sheet - weight of positive electrode current collector) / (area of ​​positive electrode sheet × (thickness of positive electrode sheet - thickness of positive electrode current collector)).

[0080] A third aspect of this disclosure provides a battery comprising the positive electrode material described in the first aspect of this disclosure and / or the positive electrode sheet described in the second aspect of this disclosure.

[0081] In this disclosure, the charging cut-off voltage of the battery is ≥4.53V.

[0082] In this disclosure, the battery is a lithium-ion secondary battery.

[0083] In this disclosure, the components of the battery other than the positive electrode (e.g., negative electrode, separator, electrolyte, etc.) can all be conventional choices in the art.

[0084] In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode material.

[0085] In this disclosure, the negative electrode material can be a conventionally selected material in the art. For example, the negative electrode material is selected from at least one of natural graphite, artificial graphite, petroleum coke, organic pyrolysis carbon, mesophase carbon microspheres, carbon fibers, tin alloys, and silicon-based materials. The silicon-based material includes at least one of silicon-oxygen, silicon-carbon, elemental silicon, and silicon alloys. The silicon-oxygen refers to a material comprising elemental silicon and elemental oxygen. The silicon-carbon includes a material comprising elemental silicon and elemental carbon, for example, comprising a porous carbon matrix and silicon material located within the pores of the porous carbon matrix.

[0086] In this disclosure, the battery assembly method can be carried out in accordance with conventional methods in the art.

[0087] In this disclosure, the battery may be a liquid electrolyte battery, a semi-solid battery, or an all-solid battery.

[0088] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0089] The present disclosure will be described in detail below through embodiments. The embodiments described in this disclosure are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0090] In the following examples, unless otherwise specified, all materials used are commercially available analytical grade.

[0091] The following preparation examples are used to prepare the cathode material of this disclosure.

[0092] Preparation Example 1

[0093] The cathode material was prepared using the following method:

[0094] (1) The precursor Co3O4 and lithium carbonate were mixed evenly according to the molar ratio of Li to Co of 1.035 and placed in a muffle furnace. The mixture was sintered at 1080°C for 10 hours in an air atmosphere. After sintering, the mixture was crushed and sieved.

[0095] (2) Weigh and mix lithium carbonate, tellurium dioxide, cobalt hydroxide and magnesium oxide according to the molar ratio of Li-Co-Te-Mg 4.06:1:1:0.1, ball mill (with anhydrous ethanol as medium) for 20 h, dry, sieve and place in muffle furnace, sinter at 650℃ for 6 h in air atmosphere, and then continue to heat to 800℃ for 7 h.

[0096] (3) The material prepared in step (2) is ground and pulverized by air jet milling and then sieved to obtain lithium cobalt tellurium oxide with a Dv50 of 65 nm. The material prepared in step (1) is mixed evenly at a mass ratio of 0.0046:1. The mixture is heat-treated at 875 °C for 11 hours in air atmosphere and then sieved to obtain a cathode material with a core-shell structure, wherein the core is lithium cobalt oxide, and the chemical formula of lithium cobalt oxide is Li. 0.99 Co 0.9982 Te 0.0018 O2, with a shell of lithium cobalt telluride, the chemical formula of which is Li4CoTeMg. 0.1 O6, space group C2 / m, interlayer spacing d1 is d2 is The shell thickness is 20.5 nm. Based on the total weight of the cathode material, the content of lithium cobalt telluride oxide is 15852 ppm. The prepared cathode material is a single crystal. The particle size of the cathode material is Dv50 of 15.994 μm, Dv90 of 27.391 μm, and Dv99 of 36.052 μm.

[0097] Preparation Example 2

[0098] The cathode material was prepared using the following method:

[0099] (1) The precursor Co3O4 and lithium carbonate were mixed evenly according to the molar ratio of Li to Co of 1.035 and placed in a muffle furnace. The mixture was sintered at 1080°C for 10 hours in an air atmosphere. After sintering, the mixture was crushed and sieved.

[0100] (2) Weigh and mix tellurium dioxide, lithium carbonate and cobalt hydroxide according to the Li-Co-Te chemical element molar ratio of 4.06:1:1, ball mill (with anhydrous ethanol as medium) for 24 hours, dry, sieve and place in a muffle furnace, sinter at 650℃ for 6 hours in air atmosphere, and then continue to heat to 800℃ for 6 hours.

[0101] (3) The material prepared in step (2) is ground and pulverized by an air jet mill, and then sieved to obtain lithium cobalt telluride oxide with a Dv50 of 31 nm. The same material prepared in step (1) is mixed evenly at a mass ratio of 0.0046:1. The mixture is heat-treated at 875°C for 12 hours in air atmosphere, and then sieved to obtain a cathode material with a core-shell structure, wherein the core is lithium cobalt oxide, and the chemical formula of lithium cobalt oxide is LiCo. 0.998 Te 0.002 O2, the shell is lithium cobalt telluride oxide, the chemical formula of which is Li4CoTeO6, space group C2 / m, and the interlayer spacing d1 is... d2 is The shell thickness is 10.2 nm. Based on the total weight of the cathode material, the content of lithium cobalt telluride oxide is 11096 ppm. The prepared cathode material is a single crystal. The particle size of the cathode material is Dv50 of 16.255 μm, Dv90 of 27.745 μm, and Dv99 of 36.518 μm.

[0102] Preparation Example 3

[0103] The cathode material was prepared using the following method:

[0104] (1) The precursor Co3O4 and lithium carbonate were mixed evenly according to the molar ratio of Li to Co of 1.035 and placed in a muffle furnace. The mixture was sintered at 1080°C for 10 hours in an air atmosphere. After sintering, the mixture was crushed and sieved.

[0105] (2) Tellurium dioxide, lithium carbonate, cobalt hydroxide, magnesium oxide and aluminum oxide were weighed according to the chemical element molar ratio of Li-Co-Te-Mg-Al 4.06:1:1:0.1:0.1, ball-milled (with anhydrous ethanol as medium) for 18 hours, dried, sieved and placed in a muffle furnace, sintered at 650℃ for 6 hours in air atmosphere, and then the temperature was raised to 800℃ for 10 hours.

[0106] (3) The material prepared in step (2) is ground and pulverized by an air jet mill, and then sieved to obtain lithium cobalt telluride oxide with a Dv50 of 98 nm. The same material prepared in step (1) is mixed evenly at a mass ratio of 0.0046:1. The mixture is heat-treated at 875°C for 10 hours in air atmosphere, and then sieved to obtain a cathode material with a core-shell structure, wherein the core is lithium cobalt oxide, and the chemical formula of lithium cobalt oxide is Li. 1.01 Co 0.9983 Te 0.0017 O2, with a shell of lithium cobalt telluride, the chemical formula of which is Li4CoTeMg. 0.1 Al 0.1 O6, space group C2 / m, interlayer spacing d1 is d2 is The shell thickness is 29.8 nm. Based on the total weight of the cathode material, the content of lithium cobalt telluride oxide is 13102 ppm. The prepared cathode material is a single crystal. The particle size of the cathode material is Dv50 of 16.073 μm, Dv90 of 27.41 μm, and Dv99 of 35.999 μm.

[0107] The particle sizes of the cathode materials in the other preparation examples all satisfy the following: Dv50 is 10μm-22μm, Dv90 is 25μm-35μm, and Dv99 ≤ 65μm.

[0108] Preparation Example 4

[0109] The preparation was carried out in accordance with Example 1, except that the chemical formula of lithium cobalt telluride oxide was controlled by changing the types and stoichiometric ratios of the added raw materials, as detailed below:

[0110] Preparation Example 4a: Tellurium dioxide, lithium carbonate, cobalt hydroxide, titanium oxide, and lithium fluoride were weighed according to the Li-Co-Te-Ti-F molar ratio of 4.06:1:1:0.5:0.2. The mixture was ball-milled (using anhydrous ethanol as the medium) for 20 hours, dried, sieved, and then sintered in a muffle furnace at 650°C for 6 hours in air, followed by further heating to 800°C and sintering for another 7 hours. The resulting shell-shell lithium cobalt tellurium oxide with the chemical formula Li₄CoTeTi was prepared. 0.5 F 0.2 O6, the chemical formula of the core lithium cobalt oxide is LiCo 0.9981 Te 0.0018 Ti 0.0001 O2.

[0111] Preparation Example 4b: Tellurium dioxide, lithium carbonate, cobalt hydroxide, zirconium oxide, and lithium sulfide were weighed according to the Li-Co-Te-Zr-S molar ratio of 4.06:1:1:0.5:0.2. The mixture was ball-milled (using anhydrous ethanol as the medium) for 20 hours, dried, sieved, and then sintered in a muffle furnace at 650°C for 6 hours in air, followed by further heating to 800°C and sintering for another 7 hours. The resulting shell-shell lithium cobalt tellurium oxide with the chemical formula Li4CoTeZr was prepared. 0.5 S 0.2 O6, the chemical formula of the core lithium cobalt oxide is LiCo 0.9981 Te 0.0018 Zr 0.0001 O2.

[0112] In Preparation Example 4c, tellurium dioxide, lithium carbonate, cobalt hydroxide, and lithium fluoride were weighed according to the Li-Co-Te-F molar ratio of 4.06:1:1:0.2. The mixture was ball-milled (using anhydrous ethanol as the medium) for 20 hours, dried, sieved, and then sintered in a muffle furnace at 650°C for 6 hours in air, followed by further heating to 800°C and sintering for another 7 hours. The resulting shell-shell lithium cobalt tellurium oxide with the chemical formula Li₄CoTeF₂ was prepared. 0.2 O6, the chemical formula of the core lithium cobalt oxide is LiCo 0.9982 Te 0.0018 O2.

[0113] In preparation example 4d, tellurium dioxide, lithium carbonate, cobalt hydroxide, and niobium oxide were weighed according to the Li-Co-Te-Nb molar ratio of 4.06:1:1:0.5. The mixture was ball-milled (using anhydrous ethanol as the medium) for 20 h, dried, sieved, and then sintered in a muffle furnace at 650 °C for 6 h in air, followed by further heating to 800 °C and sintering for another 7 h. The resulting shell-shell lithium cobalt tellurium oxide with the chemical formula Li₄CoTeNb was prepared. 0.5 O6, the chemical formula of the core lithium cobalt oxide is LiCo 0.9985 Te 0.0015 Nb 0.0001 O2.

[0114] Preparation Example 5

[0115] The preparation examples in this group were carried out in accordance with Preparation Example 1, except that the shell thickness was controlled by changing the heat treatment time in step (3), as follows:

[0116] Preparation Example 5a: Heat treatment at 875℃ for 7.5 hours resulted in a shell thickness of 51.4 μm; the core lithium cobalt oxide had the chemical formula LiCo. 0.9985 Te 0.0015 O2.

[0117] Preparation Example 5b: Heat treatment at 875℃ for 7 hours resulted in a shell thickness of 70.6 μm; the core lithium cobalt oxide has the chemical formula LiCo.0.9987 Te 0.0013 O2.

[0118] Preparation Example 5c: Heat treatment at 875℃ for 6.5 hours resulted in a shell thickness of 98.8 μm; the core lithium cobalt oxide has the chemical formula LiCo. 0.999 Te 0.001 O2.

[0119] Preparation Example 6

[0120] The preparation examples in this group were carried out in accordance with Preparation Example 1. The difference was that the average particle size of the lithium cobalt tellurium oxide was controlled by changing the ball milling time and sintering time in step (2), as follows:

[0121] Preparation Example 6a: Ball milling (using anhydrous ethanol as the medium) for 24 h, sintering at 650 °C for 6 h in air atmosphere, followed by further heating to 800 °C and sintering for 5.5 h; the Dv50 of lithium cobalt telluride was 23 nm; the chemical formula of the core lithium cobalt oxide was LiCo. 0.9981 Te 0.0019 O2.

[0122] Preparation Example 6b: Ball milling (using anhydrous ethanol as the medium) for 12 hours, sintering at 650°C for 6 hours in air atmosphere, followed by further heating to 800°C and sintering for another 12 hours; the Dv50 of lithium cobalt telluride was 198 nm; the chemical formula of the core lithium cobalt oxide was LiCo. 0.9984 Te 0.0016 O2.

[0123] Preparation Example 7

[0124] The preparation examples in this group were carried out in accordance with Preparation Example 1, except that the content of the shell layer and the interlayer spacing were controlled by changing the mass ratio of lithium cobalt telluride oxide and lithium cobalt oxide, as detailed below:

[0125] Preparation Example 7a: The lithium cobalt telluride oxide prepared in step (2) was mixed with lithium cobalt oxide in step (1) at a mass ratio of 0.0022:1; wherein the shell content was 3100 ppm and the interlayer spacing of the shell was [missing information]. The chemical formula of the core lithium cobalt oxide is LiCo. 0.9999 Te 0.0001 O2.

[0126] Preparation Example 7b: The lithium cobalt telluride oxide prepared in step (2) was mixed with lithium cobalt oxide in step (1) at a mass ratio of 0.0009:1; wherein the shell content was 813 ppm and the interlayer spacing of the shell was [missing information]. The chemical formula of the core lithium cobalt oxide is LiCo. 0.9999 Te 0.0001 O2.

[0127] Preparation Example 7c: The lithium cobalt telluride oxide prepared in step (2) is mixed with lithium cobalt oxide in step (1) at a mass ratio of 0.0080:1; wherein the shell content is 29948 ppm and the interlayer spacing of the shell is... The chemical formula of the core lithium cobalt oxide is LiCo. 0.996 Te 0.004 O2.

[0128] Preparation Example 8

[0129] The preparation was carried out in accordance with Example 1, except that the crystal structure of the cathode material was controlled by changing the sintering temperature during the preparation of lithium cobalt oxide, as follows: The cathode material prepared by sintering at 900°C for 10 hours in air atmosphere in step (1) is polycrystalline; the chemical formula of the core lithium cobalt oxide is LiCo 0.9982 Te 0.0018 O2.

[0130] Comparative Preparation Example 1

[0131] The preparation was carried out in accordance with Preparation Example 1, except that in step (3), the mixture was heat-treated at 875°C for 4 hours in an air atmosphere, wherein the thickness of the shell layer was 300 nm.

[0132] Comparative Preparation Example 2

[0133] The preparation was carried out in accordance with Example 1, except that steps (2) and (3) were omitted. The material prepared in step (1) is the positive electrode material.

[0134] Comparative preparation example 3

[0135] The preparation was carried out in accordance with Example 1, except that the shell contained different substances. That is, step (2) was omitted, and step (3) was carried out directly. Alumina, titanium oxide, zirconium oxide, yttrium oxide and lanthanum oxide were mixed with lithium cobalt oxide prepared in step (1) in a mass ratio of 0.001:0.001:0.0005:0.001:0.0005:1. After heat treatment at 900°C for 8 hours, the chemical formula of the resulting shell was Al. 0.1 Ti 0.1 Zr 0.05 Y 0.1 La 0.05 O2, space group Fm-3m.

[0136] Comparative preparation example 4

[0137] The preparation was carried out in accordance with Example 1, except that the shell contained a different substance. That is, step (2) was omitted, and step (3) was carried out directly. The solid electrolyte lithium titanium aluminum phosphate and the lithium cobalt oxide prepared in step (1) were mixed at a mass ratio of 0.002:1 and heat-treated at 900°C for 8 hours. The resulting shell had the chemical formula Li. 1.5 Al0.5 Ti 1.5 (PO4)3, space group 1a-3d.

[0138] Test Case I

[0139] (1) XRD test

[0140] XRD tests were performed on the cathode materials prepared in Preparation Examples 1-8 and Comparative Preparation Example 3. Figure 2 shows the XRD diffraction patterns of the cathode materials prepared in Preparation Example 1 and Comparative Preparation Example 3. It can be seen from the figure that the cathode material prepared in Preparation Example 1 has characteristic diffraction peaks at 2θ = 18.143°, 19.642°, 20.505°, 22.833°, 41.854°, and 42.634°. It also has a 003 peak at 2θ = 18.827, a 006 peak at 2θ = 38.386, a 102 peak at 2θ = 39.057, a 108 peak at 2θ = 65.421, and a 110 peak at 2θ = 66.329. The interlayer spacing d1 was calculated to be... d2 is Compared to the cathode material prepared in the comparative example, the peaks (003), (006), and (102) at 2θ = 18.908°, 38.342°, and 2θ = 38.991°, and the peaks (108) and (110) at 2θ = 65.293° and 2θ = 66.186° have larger splitting intervals, and the interlayer spacing calculated by the Bragg equation nλ = 2dsinθ is also larger (the interlayer spacing d2 in the comparative example is...). Larger interlayer spacing provides more spacious diffusion channels for lithium ions, enhancing their diffusion rate. During battery charging and discharging, lithium ions can be inserted and extracted more quickly into the cathode material, reducing transport resistance. This allows more lithium ions to participate in the reaction promptly during high-rate charging and discharging, thereby improving the battery's power performance and enabling it to output larger currents in a short time, meeting the needs of high-power applications. Furthermore, increased interlayer spacing can also improve battery energy density. Larger interlayer spacing is more conducive to accommodating more lithium ions, thus increasing the reversible lithium intercalation capacity of the cathode material. This allows it to store more energy with the same electrode mass, further improving the battery's energy density.

[0141] The remaining preparation examples all exhibit characteristic diffraction peaks at 2θ = 18.018°-18.4°, 2θ = 19.548°-19.710°, 2θ = 20.420°-20.700°, 2θ = 22.620°-22.830°, 2θ = 41.800°-43.930°, and 2θ = 42.570°-42.680°; and have a 003 peak at 2θ = 18.6°-19°, a 006 peak at 2θ = 38°-38.7°, a 102 peak at 2θ = 38.8°-39.5°, a 108 peak at 2θ = 65°-66°, and a 110 peak at 2θ = 66°-67°.

[0142] (2) Element content test

[0143] The elemental content of the inner and outer surfaces of the positive electrode material shell prepared in the preparation examples was tested. The results showed that the mass content of Co on the inner surface of the shell of the positive electrode material prepared in all preparation examples was higher than that on the outer surface of the shell; the mass content of Te on the inner surface of the shell was lower than that on the outer surface of the shell.

[0144] (3) Button test

[0145] The cathode material prepared in the example was subjected to coin cell testing. The specific method is as follows:

[0146] The positive electrode material, conductive agent acetylene black, and binder PVDF were mixed in 10 ml at a mass ratio of 80:10:10. In N-methylpyrrolidone, a slurry was formed by thorough stirring, then coated onto the surface of aluminum foil using a coating machine. After drying, it was cut into appropriate sizes. Using lithium foil as the negative electrode and lithium hexafluorophosphate solution as the electrolyte, coin cells were assembled in an argon-protected glove box using a 2032-type coin cell casing. Under room temperature (25℃) conditions, within a voltage range of 3.0V-4.6V, the cells were charged at a constant current and constant voltage of 0.1C to 4.6V (cutoff current 0.025C). After standing for 2 minutes, the cells were discharged at a current of 0.1C to 3.0V. The specific capacity at 0.1C and the first efficiency were recorded in Table 1. After standing for 2 minutes, the cells were charged at a constant current and constant voltage of 0.5C to 4.6V (cutoff current 0.025C). After standing for 2 minutes, the cells were discharged at a current of 0.5C to 3.0V. The cells were cycled for 100T, and the capacity at 0.5C and the cycle retention rate at 100T were recorded in Table 1.

[0147] Table 1

[0148] As can be seen from the comparison between Preparation 1 and Comparative Preparation 2 in Table 1, the presence of the shell layer is crucial for improving the specific capacity of the cathode material, and the specific capacity can be increased by approximately 19 mAh / g to 27.4 mAh / g depending on the shell layer content. Specifically, in Preparation 1, within a voltage range of 3.0V-4.6V and a charge / discharge rate of 0.1C, the battery specific capacity reached 222.8 mAh / g, with an initial efficiency of 96.60%. After 100 cycles at 0.5C, its specific capacity reached 219.5 mAh / g. In Comparative Preparation 2, within a voltage range of 3.0V-4.6V and a charge / discharge rate of 0.1C, the battery specific capacity reached 203.8 mAh / g, with an initial efficiency of 92.60%. After 100 cycles at 0.5C, its specific capacity was 192.1 mAh / g.

[0149] The following examples illustrate the battery of this disclosure.

[0150] Example 1

[0151] The battery is prepared according to the following method:

[0152] (1) Preparation of positive electrode sheet

[0153] The cathode material prepared in Example 1 (wherein the average particle size of lithium cobalt telluride oxide is 65 nm), acetylene black, carbon nanotubes, and polyvinylidene fluoride were mixed in a mass ratio of 98.2:0.4:0.6:0.8. N-methylpyrrolidone was added, and the mixture was stirred under vacuum until homogeneous to obtain a cathode slurry with a solid content of 75%. The cathode slurry was uniformly coated on both sides of an aluminum foil, and after baking, rolling, and slitting, a cathode sheet was obtained, wherein the compaction density of the cathode sheet was 4.21 g / cm³. 3 .

[0154] (2) Preparation of negative electrode sheet

[0155] Artificial graphite, single-walled carbon nanotubes, multi-walled carbon nanotubes, styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed evenly in a mass ratio of 96.1:0.25:0.15:2.9:0.6. Ethylene carbonate, accounting for 1% of the total mass of the above materials, was added, followed by deionized water, to obtain a negative electrode slurry with a solid content of 45%. The negative electrode slurry was uniformly coated onto a high-strength carbon-coated copper foil with a thickness of 6 μm, and then dried, rolled, die-cut, and sheeted to obtain a negative electrode sheet.

[0156] (3) Battery fabrication

[0157] The positive electrode sheet, separator (polyethylene film with a thickness of 8 μm) prepared in step (1) and the negative electrode sheet prepared in step (2) are stacked in sequence to ensure that the separator is between the positive and negative electrode sheets to play a role in isolation. Then, the bare cell is obtained by winding. The bare cell is placed in an aluminum-plastic film shell, and the electrolyte (a mixed solution of lithium hexafluorophosphate dissolved in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) and 5 vol.% fluoroethylene carbonate, wherein the concentration of lithium hexafluorophosphate is 1 mol / L) is injected into the dried bare cell. After vacuum sealing, standing, formation, shaping and sorting, a lithium-ion battery is obtained.

[0158] Examples 2-8 and Comparative Examples 1-4 were prepared in accordance with Example 1, except that the cathode material was prepared by replacing the same mass of the preparation example 1, as shown in Table 2.

[0159] Example 9 group

[0160] This set of examples is used to verify the impact of changes in the "positive electrode compaction density".

[0161] This set of embodiments is based on Embodiment 1, except that the compaction density of the positive electrode sheet is adjusted by changing the pressure of the control rollers, as detailed below:

[0162] Example 9a: The compaction density of the positive electrode sheet is 4.02 g / cm³. 3 ;

[0163] In Example 9b, the compaction density of the positive electrode sheet was 4.73 g / cm³. 3 .

[0164] Example 10

[0165] The procedure was carried out in accordance with Example 1, except that the negative electrode active material was changed. Specifically, artificial graphite was replaced with a combination of artificial graphite and silicon carbon of the same mass, wherein the mass ratio of artificial graphite to silicon carbon was 93:7.

[0166] Test Case II

[0167] (1) Lithium-ion diffusion coefficient

[0168] After allowing the battery to rest for 2 hours, discharge it to 5mV using a constant current density of 0.1C. After resting for 10 minutes, discharge it again to 5mV using a current density of 0.01C. After resting for another 10 minutes, charge it to 1.5V using a constant current density of 0.05C. After resting for another 10 minutes, repeat the process of discharging at a constant current density of 0.1C for 30 minutes and then resting for 30 minutes until the battery voltage drops below 0.1V. After resting for another 30 minutes, record the voltage E1 at this point. Then discharge it at a constant current density of 0.1C for 30 minutes, recording the voltage E2 at 10 seconds and the voltage E3 at the discharge cutoff. After resting for 60 minutes, record the voltage E4 after 60 minutes. Then, according to the formula...

[0169] The lithium-ion diffusion coefficient (in cm⁻¹) of the cathode material at a potential of 0.1V (vs Li⁺ / Li) can then be obtained. 2 / s), where τ is the relaxation time, i.e., τ = 3600s; n is the number of moles of the positive electrode material, V is the molar volume of the positive electrode material, n×V is the volume of the positive electrode material used in the test, which can be calculated based on the mass w of the coating in the positive electrode sheet and the true density ρ of the positive electrode material, n×V = 0.965×w / ρ; S is the geometric area of ​​the positive electrode sheet, i.e., S = 1.13cm². 2 Record the results in Table 2.

[0170] (2) Loop Test

[0171] The lithium-ion batteries prepared in the examples and comparative examples were subjected to cycle tests. The specific test methods are as follows:

[0172] At 45℃, the battery was charged at a constant current density of 1.2C to 4.30V, then charged at a constant voltage density of 4.30V with a cutoff current of 0.8C. After resting for 1 minute, it was charged at a constant current density of 0.8C to 4.53V, then charged at a constant voltage density of 4.53V with a cutoff current of 0.05C. After resting for 10 minutes, the thickness of the battery at this point was recorded as the initial thickness. The battery was then discharged at a current density of 0.5C to 3.0V, and then rested for 10 minutes. The discharge capacity of the battery at this point was recorded as the initial capacity. The above charge and discharge process was repeated until the 500th cycle of constant voltage charging was completed. After resting for 10 minutes, the thickness of the battery was measured and recorded as the thickness after the cycle. The battery was then discharged at a current density of 0.5C to 3.0V, and then rested for 10 minutes. The discharge capacity of the battery at this point was recorded as the capacity after the cycle. The cycle capacity retention rate = capacity after cycling × 100% / initial capacity, and the thickness expansion rate = (thickness after cycling - initial thickness) × 100% / initial thickness. The cycle capacity retention rate and thickness expansion rate are recorded in Table 2.

[0173] (3) Energy density test

[0174] The batteries prepared in the examples and comparative examples were charged at 0.2C to the upper limit voltage (4.53V), cut off at 0.02C, and discharged at 0.2C to the lower limit voltage (3.0V). The output discharge capacity and operating voltage were measured. The mass of the battery was measured using a balance. The gravimetric energy density was calculated using the formula: Energy density = Discharge capacity × Operating voltage / Mass. The results are recorded in Table 2.

[0175] Table 2

[0176] As can be seen from Table 2, the battery disclosed herein has a higher lithium-ion diffusion coefficient compared with the comparative example, which can balance high energy density and cycle stability, and has a high capacity recovery rate and low thickness expansion rate after high temperature storage.

[0177] The preferred embodiments of this disclosure have been described in detail above; however, this disclosure is not limited thereto. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this disclosure and are all within the protection scope of this disclosure.

Claims

A positive electrode material, characterized in that, The cathode material comprises a core-shell structure, wherein the core of the core-shell structure comprises lithium cobalt oxide, and the shell layer comprises lithium cobalt telluride oxide, the chemical formula of which is Li. a Co b Te c A 1 d A 2 e O6, where 2≤a≤4, 1≤b≤2, 0<c≤1, 0≤d≤1, 0≤e≤1, A 1 Including at least one of Al, Mg, Ti, Zr, Nb, La, W, and Y, A 2 It includes at least one of F, S and P; the lithium cobalt tellurium oxide has a single-phase structure with space group C2 / m, and the thickness of the shell is ≤200nm. The positive electrode material according to claim 1, wherein A 1 comprising Mg and / or Al; and / or, the lithium cobalt oxide has a chemical formula of Li x Co y M z O2, wherein 0.8≤x≤1.2, 0.8≤y≤1, 0≤z≤0.2, M includes at least one of Te, Al, Mg, Ti, Zr, Nb, W, Y, and La; And / or, the X-ray diffraction pattern of the cathode material exhibits characteristic diffraction peaks at 18.018°-18.4°, 19.548°-19.71°, 20.42°-20.7°, 22.62°-22.83°, 41.8°-43.93°, and 42.57°-42.68°. The positive electrode material according to claim 1 or 2, wherein, The X-ray diffraction pattern of the cathode material has a 003 peak at 18.6°-19°, a 006 peak at 38°-38.7°, a 102 peak at 38.8°-39.5°, a 108 peak at 65°-66°, and a 110 peak at 66°-67°. The positive electrode material according to any one of claims 1 to 3, wherein The thickness of the shell layer is ≤100nm; And / or, the average particle size of the lithium cobalt tellurium oxide is ≤200 nm; And / or, the particle size of the positive electrode material is Dv50 of 10μm-22μm; Dv90 of 25μm-35μm; and Dv99 ≤ 65μm. The positive electrode material according to any one of claims 1 to 4, wherein The thickness of the shell layer is 10nm-30nm; And / or, the average particle size of the lithium cobalt telluride oxide is 30nm-100nm; And / or, the particle size of the positive electrode material is Dv50 of 14μm-18μm; Dv90 of 26μm-30μm; and Dv99 of ≤47μm. The positive electrode material according to any one of claims 1 to 5, wherein The lithium cobalt tellurium oxide has a layered structure, and an interlayer distance of the lithium cobalt tellurium oxide is and / or the interlayer distance of the lithium cobalt oxide The positive electrode material according to claim 6, wherein d1 is The positive electrode material according to any one of claims 1 to 7, wherein Based on the total weight of the cathode material, the content of the lithium cobalt telluride oxide is 3000ppm-30000ppm; And / or, the dielectric constant of the shell is >10.5ε. The positive electrode material according to claim 8, wherein Based on the total weight of the cathode material, the content of the lithium cobalt telluride oxide is 11,000 ppm to 16,000 ppm. The positive electrode material according to any one of claims 1-9, wherein The mass content of Co on the inner surface of the shell is higher than the mass content of Co on the outer surface of the shell. And / or, the mass content of Te element on the inner surface of the shell is lower than the mass content of Te element on the outer surface of the shell. The positive electrode material according to any one of claims 1-10, wherein The cathode material includes monocrystalline and / or polycrystalline materials. The positive electrode material according to any one of claims 1-11, wherein Within a voltage range of 3.0V-4.6V, at a charge / discharge rate of 0.1C, the specific capacity of the positive electrode material is 208mAh / g-223mAh / g; And / or, within a voltage range of 3.0V-4.6V, at a charge / discharge rate of 0.5C, the specific capacity of the positive electrode material is 203mAh / g-220mAh / g. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 12; preferably, the positive electrode sheet has a compacted density of 4 g / cm 3 - 4.8 g / cm 3 . A battery characterized by The battery comprises the positive electrode material according to any one of claims 1-12 and / or the positive electrode sheet according to claim 13. A battery according to claim 14, wherein The charging cutoff voltage of the battery is ≥4.53V.

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