Positive electrode material, electrochemical device and electronic device

Abstract

Provided in the present application are a positive electrode material, an electrochemical device and an electronic device. The positive electrode material of the present application comprises a substrate and a surface layer located on a surface of the substrate, wherein the substrate has a layered structure; the surface layer comprises a first region and a second region; the first region contains a spinel phase, and the second region contains a rock salt phase; and the first region and the second region are separately located on the surface of the substrate. The positive electrode material and lithium metal are assembled into a button cell. When the button cell is charged and discharged at a current of 0.04 C in a voltage range of 2.8 V to 4.5 V, the obtained differential capacity (dQ / dV) curve thereof has a first oxidation peak and a first reduction peak in a voltage range of 4.2 V to 4.5 V. In the present application, a surface layer in which a spinel phase and a rock salt phase coexist is constructed on the surface of a lithium-nickel-manganese composite oxide having oxygen defects; therefore, while the stability of the bulk phase and the surface layer of the positive electrode material is improved, the ion conduction rate of the surface layer of the positive electrode material is also improved, thereby enhancing the safety and cycle performance of the electrochemical device under high-temperature and high-voltage conditions.

Description

Cathode materials, electrochemical devices and electronic devices Technical Field

[0001] This application belongs to the field of electrochemistry, specifically relating to cathode materials, electrochemical devices, and electronic devices. Background Technology

[0002] With the increasing popularity of new energy vehicles, the requirements for their batteries are becoming more and more stringent. Lithium-ion batteries have already occupied a mainstream position in the market due to their advantages such as high energy density, good safety, no memory effect, and long service life. To meet people's demand for high energy density, low cost, and long cycle life of lithium-ion batteries, nickel-manganese-based layered oxide cathode materials have always been considered one of the preferred cathode materials for lithium-ion batteries due to their high discharge specific capacity, relatively low cost, and low toxicity. In pursuit of higher energy density, nickel-manganese-based layered oxide cathode materials have been continuously developed towards increasing Ni content and charging voltage. Under high Ni content and high voltage conditions, the problems of surface oxygen release and structural phase transition of nickel-manganese-based layered oxide cathode materials have also been fully exposed, leading to problems such as battery cycle failure, gas generation, and thermal runaway. Summary of the Invention

[0003] In view of the above-mentioned problems in the prior art, this application provides a cathode material, an electrochemical device, and an electronic device to improve the safety and cycle performance of an electrochemical device using nickel-manganese-based basal oxide as the cathode material under high temperature and high voltage conditions.

[0004] In a first aspect, this application provides a cathode material comprising a lithium nickel manganese composite oxide; the cathode material comprises a substrate and a surface layer located on the surface of the substrate, the substrate having a layered structure; the surface layer comprises a first region and a second region; the first region contains a spinel phase, and the second region contains a rock salt phase; the first region and the second region are respectively located on the surface of the substrate; the cathode material is assembled with lithium metal into a coin cell, and when the coin cell is charged and discharged at a current of 0.04C in the voltage range of 2.8V to 4.5V, the obtained capacity-voltage differential dQ / dV curve has a first oxidation peak and a first reduction peak in the range of 4.2V to 4.5V.

[0005] The cathode material of this application, on the one hand, creates oxygen defects in the lithium nickel manganese composite oxide, resulting in a significantly increased reversible charge-discharge capacity in the high voltage range of 4.2V to 4.5V. This significantly improves the charge-discharge capacity of the cathode material while maintaining good structural stability and kinetic performance at high voltage. On the other hand, a dual-phase structure of spinel and rock salt phases is formed on the substrate surface through surface-induced phase transition. The spinel phase stabilizes highly active metal ions and oxygen ions on the substrate surface and provides a faster ion transport channel in the high voltage range, while the rock salt phase has higher structural stability, further improving the stability of the cathode material's surface structure. The combined effect of these two phases significantly improves the stability of the cathode material's surface structure and further enhances the ion conduction rate of the cathode material's surface structure in the high voltage range, thereby improving the storage, gas generation, and cycling performance of the electrochemical device under high temperature and high voltage conditions.

[0006] In some embodiments, the molar percentage c of Mn element in the matrix is ​​determined based on the total molar amount of Ni and Mn elements in the matrix. Mn The proportion is 40% to 60%. Thus, during the surface-induced phase transition, the appropriate proportion of Mn can better promote the formation of the spinel phase in the surface layer, thereby further improving the ion conduction rate of the surface structure in the high-voltage range and improving the cycle performance of the electrochemical device under high-voltage conditions.

[0007] In some embodiments, the cathode material includes an element Q, which includes at least one of Mo, W, Nb, Ta, Si, or Sb; the molar percentage of the element Q in the surface layer is c based on the total molar amount of Ni and Mn elements in the surface layer. 1Q Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Q element in the matrix is ​​c. 2Q ; Satisfies: c 1Q >c 2Q The relatively high concentration of Q element in the surface layer can better induce surface phase transition during the synthesis of cathode materials, promote the formation of spinel and rock salt phases in the surface layer, and act as a doping cation to further improve the structural stability of the spinel phase in the surface layer in the high temperature and high voltage range, thereby further improving the storage gas generation and cycle performance of electrochemical devices under high temperature and high voltage conditions.

[0008] In some implementations, c 1Q It ranges from 0.4% to 5%.

[0009] In some implementations, c 2Q It ranges from 0.05% to 0.5%.

[0010] In some embodiments, the cathode material includes element R, which includes at least one of F, Cl, Br, I, P, or N; based on the total molar amount of Ni and Mn elements in the surface layer, the molar percentage of element R in the surface layer is c. 1R Based on the total molar amounts of Ni and Mn elements in the matrix, the molar percentage of R element in the matrix is ​​c. 2R ; Satisfies: c 1R >c 2R The relatively high R element concentration in the surface layer can better induce surface phase transition during the synthesis of cathode materials, promote the formation of spinel and rock salt phases in the surface layer, and act as a dopant anion to stabilize active oxygen in the surface layer, further improving the structural stability of the surface layer in the high temperature and high voltage range, thereby further improving the storage, gas generation, and cycling performance of the electrochemical device under high temperature and high voltage conditions.

[0011] In some implementations, c 1R It ranges from 1% to 5%.

[0012] In some implementations, c 2R It ranges from 0.1% to 0.5%.

[0013] In some embodiments, scanning transmission electron microscopy reveals a lattice coupling between the spinel phase and the matrix. Thus, the spinel phase better stabilizes highly active metal and oxygen ions on the matrix surface, while also providing a better ion transport channel for lithium ion insertion / extraction in the matrix during high-voltage conditions, thereby improving the storage, gas generation, and cycling performance of the electrochemical device under high-temperature and high-voltage conditions.

[0014] In some embodiments, scanning transmission electron microscopy reveals a lattice coupling between the rock salt phase and the matrix. This allows the rock salt phase to bond more firmly to the matrix surface, thereby better stabilizing highly reactive metal and oxygen ions on the matrix surface, and ultimately improving the storage, gas generation, and circulation performance of the electrochemical device under high temperature and high voltage conditions.

[0015] In some embodiments, scanning transmission electron microscopy reveals a eutectic coupling between the spinel phase and the rock salt phase. This allows for a more robust bond between the spinel and rock salt phases, better suppressing cracking between them during high-voltage cycling. This further enhances the stability of the cathode material's surface structure, thereby improving the storage, gas generation, and cycling performance of the electrochemical device under high-temperature and high-voltage conditions.

[0016] In some embodiments, the thickness of the spinel phase is from 2 nm to 80 nm.

[0017] In some embodiments, the thickness of the rock salt phase is from 2 nm to 80 nm.

[0018] In some embodiments, the cathode material includes Na; based on the total molar amount of Ni and Mn in the surface layer, the molar percentage of Na in the surface layer is c. 1Na Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Na element in the matrix is ​​c. 2Na Satisfying: c 1Na >c 2Na Thus, the surface layer of the cathode material is rich in Na, and Na-containing compounds can further stabilize the surface of the cathode material, thereby further improving the storage, gas generation, and cycle performance of the electrochemical device under high temperature and high voltage conditions.

[0019] In some implementations, c 1Na The percentage is 3% to 15%. Thus, compounds containing Na can better protect the surface of the cathode material, thereby further improving the storage, gas generation, and cycling performance of electrochemical devices under high temperature and high voltage conditions.

[0020] In some implementations, c 2Na The amount is 0.5% to 10%. Thus, the presence of an appropriate amount of Na in the cathode material matrix can further improve the lattice stability of the internal matrix after delithiation, thereby further improving the storage gas generation and cycle performance of the electrochemical device under high temperature and high voltage conditions.

[0021] In some implementations, 1.1 ≤ c 1Na / c 2Na ≤10.

[0022] In some embodiments, based on the mass of the cathode material, the peak intensity of the first oxidation peak is greater than or equal to 1200 mAh / g / V. Thus, the cathode material can exhibit high charging capacity and kinetics in the high-voltage range, thereby improving the cycle performance of the electrochemical device under high-voltage conditions.

[0023] In some embodiments, based on the mass of the cathode material, the peak intensity of the first reduction peak is greater than or equal to 1200 mAh / g / V. Thus, the cathode material can exhibit higher discharge capacity and kinetics in the high-voltage range, thereby improving the cycle performance of the electrochemical device under high-voltage conditions.

[0024] In some embodiments, the peak voltage of the first oxidation peak is Vo1, and the peak voltage of the first reduction peak is Vr1, satisfying |Vo1-Vr1|≤0.12V. This results in better reversibility of the cathode material in the high-voltage range, thereby further improving the cycle performance of the electrochemical device under high-voltage conditions.

[0025] In some embodiments, when the coin cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve of the obtained capacity-voltage curve exhibits a plateau in the 4.2V to 4.5V range. The capacity of the discharge curve in the 4.2V to 4.5V range is Q1, and the capacity of the discharge curve in the 3.0V to 4.5V range is Qt, satisfying: 0.2 ≤ Q1 / Qt ≤ 0.35. Thus, the cathode material can possess a high reversible charge-discharge capacity in the high-voltage range, thereby significantly improving the energy density of the electrochemical device.

[0026] In some embodiments, the capacity-voltage differential dQ / dV curve exhibits a second oxidation peak and a second reduction peak in the 3.6V to 4.0V range.

[0027] In some embodiments, the molar percentage of Ni in the cathode material is greater than or equal to 40%, based on the total molar amount of Ni and Mn elements in the cathode material.

[0028] In some embodiments, the molar percentage of Mn in the cathode material is 30% to 60%, based on the total molar amount of Ni and Mn elements in the cathode material.

[0029] In some embodiments, the molar percentage of Li in the cathode material is 90% to 105%, based on the total molar amount of Ni and Mn elements in the cathode material.

[0030] In some embodiments, the cathode material includes a Q element, which includes at least one of Mo, W, Nb, Ta, Si, or Sb; the molar percentage of the Q element in the cathode material is 0.1% to 5% based on the total molar amount of Ni and Mn elements in the cathode material.

[0031] In some embodiments, the cathode material includes element R, which includes at least one of F, Cl, Br, I, P or N; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of element R in the cathode material is 0.1% to 5%.

[0032] In some embodiments, the cathode material includes Na, and the molar percentage of Na in the cathode material is 0.5% to 10% based on the total molar amount of Ni and Mn elements in the cathode material.

[0033] In some embodiments, the cathode material includes element M, which includes at least one selected from Mg, Al, K, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, In, Sn, Ba, La, Ce, Hf, Pb, Bi, B, or S; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of element M in the cathode material is 0.1% to 5%.

[0034] In some embodiments, the positive electrode material includes: Li x1 Na x2 Ni y1 Mn y2 Q y3 M y4 O 2±z R n Wherein, Q includes at least one of Mo, W, Nb, Ta, Si, or Sb; M includes at least one of Mg, Al, K, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, In, Sn, Ba, La, Ce, Hf, Pb, Bi, B, or S; R includes at least one of F, Cl, Br, I, P, or N; 0.9≤x1≤1.05, 0.005≤x2≤0.1, 0.4≤y1≤1, 0.3≤y2≤0.6, 0.001≤y3≤0.05, 0.001≤y4≤0.05, 0≤z≤0.2, 0≤n≤0.2.

[0035] In some embodiments, the X-ray diffraction pattern of the cathode material exhibits diffraction peaks in the ranges of 2θ: 17° to 20°, 35° to 38°, and 42° to 46°.

[0036] In some embodiments, the cell parameter α of the cathode material satisfies

[0037] In some embodiments, the cell parameter c of the cathode material satisfies

[0038] In some embodiments, the cathode material contains a layered crystal structure belonging to the R-3m space group.

[0039] Secondly, this application provides an electrochemical device including a positive electrode, the positive electrode including a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer including the aforementioned positive electrode material.

[0040] Thirdly, this application provides an electronic device including the aforementioned electrochemical device. Attached Figure Description

[0041] Figure 1 is an X-ray diffraction pattern of the cathode material prepared in Example 1 and Comparative Example 1 of this application.

[0042] Figure 2 is a scanning electron microscope image of the cathode material prepared in Comparative Example 1 of this application at 3000x magnification.

[0043] Figure 3 is a scanning electron microscope image of the cathode material prepared in Example 1 of this application at 3000x magnification.

[0044] Figure 4 is a scanning transmission electron microscope image of the positive electrode material prepared in Example 1 of this application.

[0045] Figure 5 shows the specific capacity-voltage curves of the coin cells assembled with the cathode materials prepared in Example 1 and Comparative Example 1 of this application during the first charge and discharge at a current density of 0.04C.

[0046] Figure 6 shows the capacity-voltage differential dQ / dV curves of the coin cells assembled with the cathode materials prepared in Comparative Example 1 and Example 1 of this application during the first charge and discharge at a current density of 0.04C. Detailed Implementation

[0047] To better illustrate the purpose, technical solution, and advantages of this application, the technical solution of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. Furthermore, the embodiments of this application should not be construed as limiting this application.

[0048] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0049] In this description, unless otherwise stated, "above" and "below" include the stated number. Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art. In this description, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items.

[0050] To improve the safety and cycle performance of electrochemical devices using nickel-manganese layered oxides as cathode materials under high temperature and high voltage conditions, this application provides a cathode material comprising a lithium nickel-manganese composite oxide. The cathode material includes a matrix and a surface layer located on the surface of the matrix, the matrix having a layered structure. The surface layer includes a first region and a second region. The first region contains a spinel phase, and the second region contains a rock salt phase. The first region and the second region are respectively located on the surface of the matrix. When the cathode material is assembled with lithium metal to form a coin cell, and the coin cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the obtained capacity-voltage differential dQ / dV curve exhibits a first oxidation peak and a first reduction peak in the 4.2V to 4.5V range.

[0051] The cathode material of this application, on the one hand, creates oxygen defects in the lithium nickel manganese composite oxide, resulting in a significantly increased reversible charge-discharge capacity in the high voltage range of 4.2V to 4.5V. This significantly improves the charge-discharge capacity of the cathode material while maintaining good structural stability and kinetic performance at high voltage. On the other hand, a dual-phase structure of spinel and rock salt phases is formed on the substrate surface through surface-induced phase transition. The spinel phase stabilizes highly active metal ions and oxygen ions on the substrate surface and provides a faster ion transport channel in the high voltage range, while the rock salt phase has higher structural stability, further improving the stability of the cathode material's surface structure. The combined effect of these two phases significantly improves the stability of the cathode material's surface structure and further enhances the ion conduction rate of the cathode material's surface structure in the high voltage range, thereby improving the storage, gas generation, and cycling performance of the electrochemical device under high temperature and high voltage conditions.

[0052] In some embodiments, the molar percentage c of Mn element in the matrix is ​​determined based on the total molar amount of Ni and Mn elements in the matrix. MnThe proportion is 40% to 60%. Thus, during the surface-induced phase transition, a suitable proportion of Mn can better promote the formation of the spinel phase in the surface layer, thereby further enhancing the ion conduction rate of the surface structure in the high-voltage range and improving the cycling performance of the electrochemical device under high-voltage conditions. Specifically, c Mn It can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, or a range of any two of these values.

[0053] In some embodiments, the cathode material includes an element Q, which includes at least one of Mo, W, Nb, Ta, Si, or Sb; the molar percentage of the element Q in the surface layer is c based on the total molar amount of Ni and Mn elements in the surface layer. 1Q Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Q element in the matrix is ​​c. 2Q ; Satisfies: c 1Q >c 2Q The relatively high concentration of Q element in the surface layer can better induce surface phase transition during the synthesis of cathode materials, promote the formation of spinel and rock salt phases in the surface layer, and act as a doping cation to further improve the structural stability of the spinel phase in the surface layer in the high temperature and high voltage range, thereby further improving the storage gas generation and cycle performance of electrochemical devices under high temperature and high voltage conditions.

[0054] In some implementations, c 1Q The concentration is 0.4% to 5%. This allows for better induction of surface phase transitions during cathode material synthesis, promoting the formation of spinel and rock salt phases in the surface layer. Specifically, c 1Q It can be 0.4%, 0.6%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of these values.

[0055] In some implementations, c 2Q It ranges from 0.05% to 0.5%. Specifically, c 2Q It can be 0.05%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or a range of any two of these values.

[0056] In some embodiments, the cathode material includes element R, which includes at least one of F, Cl, Br, I, P, or N; based on the total molar amount of Ni and Mn elements in the surface layer, the molar percentage of element R in the surface layer is c. 1RBased on the total molar amounts of Ni and Mn elements in the matrix, the molar percentage of R element in the matrix is ​​c. 2R ; Satisfies: c 1R >c 2R The relatively high R element concentration in the surface layer can better induce surface phase transition during the synthesis of cathode materials, promote the formation of spinel and rock salt phases in the surface layer, and act as a dopant anion to stabilize active oxygen in the surface layer, further improving the structural stability of the surface layer in the high temperature and high voltage range, thereby further improving the storage, gas generation, and cycling performance of the electrochemical device under high temperature and high voltage conditions.

[0057] In some implementations, c 1R The percentage is 1% to 5%. This allows for better induction of surface phase transitions during cathode material synthesis, promoting the formation of spinel and rock salt phases in the surface layer. Specifically, c 1R It can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range of any two of these values.

[0058] In some implementations, c 2R It ranges from 0.1% to 0.5%. Specifically, c 2R It can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, or a range of any two of these values.

[0059] In some embodiments, scanning transmission electron microscopy reveals a lattice coupling between the spinel phase and the matrix. Thus, the spinel phase better stabilizes highly active metal ions and oxygen ions on the matrix surface, while also providing a better ion transport channel for lithium ion insertion / extraction in the matrix during high-voltage conditions, thereby improving the storage, gas generation, and cycling performance of the electrochemical device under high-temperature and high-voltage conditions. In this application, "lattice coupling" refers to an angle of less than or equal to 10° between the orientations of the transition metal atoms in the two materials. Specifically, this can be observed using scanning transmission electron microscopy to determine the orientation of the transition metal atoms in each of the two materials.

[0060] In some embodiments, scanning transmission electron microscopy reveals a lattice coupling between the rock salt phase and the matrix. This allows the rock salt phase to bond more firmly to the matrix surface, thereby better stabilizing highly reactive metal and oxygen ions on the matrix surface, and ultimately improving the storage, gas generation, and circulation performance of the electrochemical device under high temperature and high voltage conditions.

[0061] In some embodiments, scanning transmission electron microscopy reveals a eutectic coupling between the spinel phase and the rock salt phase. This allows for a more robust bond between the spinel and rock salt phases, better suppressing cracking between them during high-voltage cycling. This further enhances the stability of the cathode material's surface structure, thereby improving the storage, gas generation, and cycling performance of the electrochemical device under high-temperature and high-voltage conditions.

[0062] In some embodiments, the thickness of the spinel phase is from 2 nm to 80 nm. Specifically, the thickness of the spinel phase may be 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, or any combination of these values.

[0063] In some embodiments, the thickness of the rock salt phase is from 2 nm to 80 nm. Specifically, the thickness of the rock salt phase may be 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, or any combination of these values.

[0064] In some embodiments, the cathode material includes Na; based on the total molar amount of Ni and Mn in the surface layer, the molar percentage of Na in the surface layer is c. 1Na Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Na element in the matrix is ​​c. 2Na Satisfying: c 1Na >c 2Na Thus, the surface layer of the cathode material is rich in Na, and Na-containing compounds can further stabilize the surface of the cathode material, thereby further improving the storage, gas generation, and cycle performance of the electrochemical device under high temperature and high voltage conditions.

[0065] In some implementations, c 1Na It ranges from 3% to 15%. Specifically, c 1Na It can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range of any two of these values.

[0066] In some implementations, c 1Na It ranges from 5% to 10%.

[0067] In some implementations, c 2Na It ranges from 0.5% to 10%. Specifically, c 2Na It can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any two of these values.

[0068] In some implementations, c 2Na It ranges from 3% to 8%.

[0069] In some implementations, 1.1 ≤ c 1Na / c 2Na ≤10. Specifically, c 1Na / c 2Na The value can be 1.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or a range of any two of these values.

[0070] In some implementations, 3≤c 1Na / c 2Na ≤8.

[0071] In some embodiments, based on the mass of the cathode material, the peak intensity of the first oxidation peak is greater than or equal to 1200 mAh / g / V. Thus, the cathode material can exhibit high charging capacity and kinetics in the high-voltage range, thereby improving the cycle performance of the electrochemical device under high-voltage conditions.

[0072] Furthermore, in some embodiments, based on the mass of the cathode material, the peak intensity of the first oxidation peak is from 1500 mAh / g / V to 2500 mAh / g / V. More specifically, the peak intensity of the first oxidation peak may be 1500 mAh / g / V, 1600 mAh / g / V, 1700 mAh / g / V, 1800 mAh / g / V, 1900 mAh / g / V, 2000 mAh / g / V, 2100 mAh / g / V, 2200 mAh / g / V, 2300 mAh / g / V, 2400 mAh / g / V, 2500 mAh / g / V, or a range of any two of these values.

[0073] In some embodiments, based on the mass of the cathode material, the peak intensity of the first reduction peak is greater than or equal to 1200 mAh / g / V. Thus, the cathode material can exhibit higher discharge capacity and kinetics in the high-voltage range, thereby improving the cycle performance of the electrochemical device under high-voltage conditions.

[0074] Furthermore, in some embodiments, based on the mass of the cathode material, the peak intensity of the first reduction peak is from 1500 mAh / g / V to 2500 mAh / g / V. More specifically, the peak intensity of the first oxidation peak may be 1500 mAh / g / V, 1600 mAh / g / V, 1700 mAh / g / V, 1800 mAh / g / V, 1900 mAh / g / V, 2000 mAh / g / V, 2100 mAh / g / V, 2200 mAh / g / V, 2300 mAh / g / V, 2400 mAh / g / V, 2500 mAh / g / V, or a range of any two of these values.

[0075] In some embodiments, the peak voltage of the first oxidation peak is Vo1, and the peak voltage of the first reduction peak is Vr1, satisfying |Vo1-Vr1|≤0.12V. The smaller the voltage difference |Vo1-Vr1| between the first oxidation peak and the first reduction peak, the better the electrochemical reversibility of the cathode material and the smaller the electrochemical polarization. In this application, the cathode material has |Vo1-Vr1|≤0.12V, indicating good reversibility in the high-voltage range, which further improves the cycle performance of the electrochemical device under high-voltage conditions. The value of |Vo1-Vr1| can be 0V, 0.025V, 0.05V, 0.075V, 0.1V, 0.12V, or any combination of these values.

[0076] In some implementations, Vo1 is 4.3V to 4.4V, specifically 4.30V, 4.31V, 4.32V, 4.33V, 4.34V, 4.35V, 4.36V, 4.37V, 4.38V, 4.39V, 4.4V, or a range of any two of these values.

[0077] In some embodiments, when the coin cell is charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve of the obtained capacity-voltage curve exhibits a plateau in the 4.2V to 4.5V range. The capacity of the discharge curve in the 4.2V to 4.5V range is Q1, and the capacity of the discharge curve in the 3.0V to 4.5V range is Qt, satisfying: 0.2 ≤ Q1 / Qt ≤ 0.35. Thus, the cathode material can possess a high reversible charge-discharge capacity in the high-voltage range, thereby significantly improving the energy density of the electrochemical device. The value of Q1 / Qt can be 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.33, 0.35, or any combination of these values.

[0078] In some implementations, Q1 is from 10 mAh / g to 70 mAh / g, specifically 10 mAh / g, 20 mAh / g, 30 mAh / g, 40 mAh / g, 50 mAh / g, 60 mAh / g, 70 mAh / g, or a range of any two of these values.

[0079] In some implementations, Qt is from 100 mAh / g to 230 mAh / g, specifically 100 mAh / g, 130 mAh / g, 160 mAh / g, 190 mAh / g, 220 mAh / g, 230 mAh / g, or a range of any two of these values.

[0080] In some embodiments, the capacity-voltage differential dQ / dV curve exhibits a second oxidation peak and a second reduction peak in the 3.6V to 4.0V range.

[0081] In some embodiments, based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Ni element in the cathode material is greater than or equal to 40%. Specifically, it can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range of two of these values. In some embodiments, the molar percentage of Ni element in the cathode material is between 45% and 70%.

[0082] In some embodiments, based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage content of Mn element in the cathode material is 30% to 60%. Specifically, it can be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, or a range of any two of these values. In some embodiments, the molar percentage content of Mn element in the cathode material is 40% to 50%.

[0083] In some embodiments, based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Li element in the cathode material is 90% to 105%, specifically, it can be 90%, 92%, 94%, 96%, 98%, 100%, 102%, 105%, or any combination of these values.

[0084] In some embodiments, the cathode material includes an element Q, which includes at least one of Mo, W, Nb, Ta, Si, or Sb; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of the element Q in the cathode material is from 0.1% to 5%, specifically, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of these values.

[0085] In some embodiments, the cathode material includes element R, which includes at least one of F, Cl, Br, I, P, or N; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of element R in the cathode material is from 0.1% to 5%, specifically, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of these values.

[0086] In some embodiments, the cathode material includes Na element, and the molar percentage of Na element in the cathode material is 0.5% to 10% based on the total molar amount of Ni and Mn elements in the cathode material. Specifically, it can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any combination of these values.

[0087] In some embodiments, the cathode material includes an element M, which includes at least one of Mg, Al, K, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, In, Sn, Ba, La, Ce, Hf, Pb, Bi, B, or S; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of element M in the cathode material is 0.1% to 5%, specifically, it can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any combination of these values.

[0088] In some embodiments, the positive electrode material includes: Li x1 Na x2 Ni y1 Mn y2 Q y3 M y4 O 2±z R nWherein, Q includes at least one of Mo, W, Nb, Ta, Si, or Sb; M includes at least one of Mg, Al, K, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, In, Sn, Ba, La, Ce, Hf, Pb, Bi, B, or S; R includes at least one of F, Cl, Br, I, P, or N; 0.9≤x1≤1.05, 0.005≤x2≤0.1, 0.4≤y1≤1, 0.3≤y2≤0.6, 0.001≤y3≤0.05, 0.001≤y4≤0.05, 0≤z≤0.2, 0≤n≤0.2.

[0089] In some embodiments, the X-ray diffraction pattern of the cathode material exhibits diffraction peaks in the 2θ ranges of 17° to 20°, 35° to 38°, and 42° to 46°. The diffraction peaks in the 2θ ranges of 17° to 20°, 35° to 38°, and 42° to 46° in the X-ray diffraction pattern of the cathode material are attributed to characteristic peaks of the (003), (101), and (104) crystal planes of the layered lithium nickel manganese composite oxide, respectively.

[0090] In some embodiments, the cell parameter α of the cathode material satisfies Specifically, it can be for Or a range consisting of any two of these values.

[0091] In some embodiments, the cell parameter c of the cathode material satisfies Specifically, it can be for Or a range consisting of any two of these values.

[0092] The cell parameters of the cathode material in this application are larger than those of traditional cathode materials, which is more conducive to improving lithium-ion transport dynamics and further achieving the goal of improving the cycle performance of the battery under high voltage conditions.

[0093] In some embodiments, the cathode material contains a layered crystal structure belonging to the R-3m space group.

[0094] In some embodiments, the method for preparing the positive electrode material includes the following steps:

[0095] S1: Dissolve the nickel source and manganese source in water to obtain a first solution. Mix the first solution with a precipitant and a complexing agent and react to obtain a nickel-manganese-based precursor.

[0096] S2: The nickel-manganese-based precursor is mixed with a sodium source and an optional M element source, and then calcined once under a first atmosphere to obtain the first product.

[0097] S3: The first product is mixed with an R element source and / or a Q element source, and then calcined twice under a second atmosphere. After cooling, the second product is obtained; the second atmosphere is a reducing atmosphere.

[0098] S4: The second product and the lithium source are mixed and calcined three times under a third atmosphere, and then quenched to obtain the cathode material; the third atmosphere is an inert atmosphere.

[0099] In the preparation method of the cathode material of this application, the introduction of anion and cation (R element and / or Q element ions) doping into the surface layer of the first product is beneficial to constructing structural defects. Combined with the sintering assisted by a reducing atmosphere, a disordered phase in which spinel phase and rock salt phase coexist is induced to form on the surface layer of the first product. During the reaction to form the cathode material matrix in step S4, the disordered phase in which spinel phase and rock salt phase coexist is maintained, and finally constitutes the surface layer of the cathode material of this application.

[0100] In some embodiments, in step S1, the nickel source comprises a nickel salt. In some embodiments, the nickel salt comprises at least one of a nickel sulfate, a nickel nitrate, or a nickel acetate.

[0101] In some embodiments, in step S1, the manganese source comprises a manganese salt. In some embodiments, the manganese salt comprises at least one of manganese sulfate, manganese nitrate, or manganese acetate.

[0102] In some embodiments, the precipitant in step S1 comprises an alkaline solution. In some embodiments, the alkaline solution comprises a sodium hydroxide solution.

[0103] In some embodiments, in step S1, the complexing agent includes ammonia.

[0104] In some embodiments, in step S1, the atmosphere of the reaction is an inert atmosphere.

[0105] In some embodiments, the temperature of the reaction in step S1 is between 25°C and 100°C.

[0106] In some implementations, the reaction time in step S1 is 12 hours to 60 hours.

[0107] In some embodiments, in step S1, the pH value of the reaction system is 10 to 13.

[0108] In some embodiments, the temperature of the first calcination in step S2 is 650°C to 900°C.

[0109] In some embodiments, the heating rate to the primary calcination temperature is 2°C / min to 8°C / min. In some embodiments, the primary calcination time is 10h to 48h. In some embodiments, after the primary calcination is completed, the temperature is lowered to room temperature at a cooling rate of 2°C / min to 8°C / min.

[0110] In some embodiments, in step S2, the first atmosphere is an oxygen-containing atmosphere. In some embodiments, the oxygen-containing atmosphere is selected from at least one of an air atmosphere, an oxygen atmosphere, or a mixture of air and oxygen.

[0111] In some embodiments, in step S2, the sodium source includes at least one of a sodium salt, a sodium hydroxide, or a sodium oxide. In some embodiments, the sodium salt includes at least one of a sodium sulfate, a sodium nitrate, a sodium carbonate, or a sodium acetate.

[0112] In some embodiments, in step S2, the source of element M includes at least one of element M, a salt containing element M, a hydroxide containing element M, or an oxide containing element M. In some embodiments, the salt containing element M includes at least one of a nitrate containing element M, an acetate containing element M, or a carbonate containing element M.

[0113] In some embodiments, the temperature of the secondary calcination in step S3 is 600°C to 900°C. In some embodiments, the heating rate to the secondary calcination temperature is 2°C / min to 8°C / min. In some embodiments, the duration of the secondary calcination is 2 hours to 24 hours.

[0114] In some embodiments, in step S3, the reducing atmosphere is selected from at least one of a hydrogen atmosphere and a mixed atmosphere of hydrogen and an inert gas.

[0115] In some embodiments, in step S3, the cooling rate is 5°C / min to 10°C / min.

[0116] In some embodiments, in step S3, the source of element R includes at least one of a salt containing element R or an organic compound containing element R. In some embodiments, the source of element R includes at least one of ammonium fluoride, ammonium chloride, ammonium bromide, ammonium iodide, ammonium dihydrogen phosphate, sodium hydrogen phosphite, urea, or thiourea.

[0117] In some embodiments, in step S3, the Q element source includes at least one of a Q-containing salt, a Q-containing hydroxide, or a Q-containing oxide. In some embodiments, the Q-containing salt includes at least one of a Q-containing nitrate, a Q-containing acetate, or a Q-containing carbonate.

[0118] In some embodiments, in step S4, the lithium source includes at least one of lithium salt, lithium hydroxide, or lithium oxide. In some embodiments, the lithium source includes at least one of lithium hydroxide, lithium oxide, lithium nitrate, lithium fluoride, lithium chloride, lithium acetate, or lithium carbonate.

[0119] In some embodiments, the temperature of the three calcinations in step S4 is between 200°C and 500°C. In some embodiments, the heating rate to the three calcination temperatures is between 2°C / min and 5°C / min. In some embodiments, the duration of the three calcinations is between 0.5 h and 12 h. In some embodiments, the inert atmosphere includes at least one of nitrogen, argon, and helium.

[0120] In some embodiments, in step S4, the cooling rate of the quenching is from 30°C / min to 70°C / min.

[0121] In some embodiments, step S4 further includes the following post-processing steps: washing with water, drying, and sieving.

[0122] In a second aspect, this application provides an electrochemical device including a positive electrode, the positive electrode including a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer including the positive electrode material described in the first aspect of this application.

[0123] In some embodiments, the positive electrode active material layer further includes an adhesive and a conductive agent.

[0124] In some embodiments, the adhesive includes at least one of styrene-butadiene rubber (SBR), waterborne acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA), or polyvinyl alcohol (PVA), and is not limited to the above types. The adhesive can be selected according to actual needs.

[0125] In some embodiments, the mass percentage of the adhesive is less than or equal to 5% based on the total mass of the positive electrode active material layer.

[0126] In some embodiments, the conductive agent includes at least one of graphite, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, or carbon nanofibers, but is not limited to the above-mentioned types. The conductive agent can be selected according to actual needs.

[0127] In some embodiments, the mass percentage of the conductive agent is 1% to 3% based on the total mass of the positive electrode active material layer.

[0128] In some embodiments, the positive current collector includes a sheet of metal material, such as aluminum, nickel, silver, titanium, or aluminum foil, but is not limited thereto.

[0129] The positive electrode can be prepared by conventional methods in the art. For example, the preparation method of the positive electrode includes the following steps: mixing a solvent, a conductive agent, a binder, and a positive electrode material to obtain a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and then drying and cold pressing to obtain the positive electrode.

[0130] In some embodiments, the solvent may include N-methylpyrrolidone (NMP), but is not limited thereto.

[0131] In some embodiments, the electrochemical device further includes a negative electrode, which comprises a negative electrode active material layer and a negative electrode current collector.

[0132] In some embodiments, the negative electrode active material includes at least one of graphite, mesophase carbon microspheres, hard carbon, soft carbon, silicon, silicon-carbon materials, silicon-oxygen materials, Li alloys, and metallic lithium, but is not limited thereto.

[0133] In some embodiments, the negative current collector can be a sheet of metal such as copper, nickel, stainless steel or titanium, for example, copper foil, but is not limited thereto.

[0134] In some embodiments, the electrochemical device further includes a separator membrane located between the positive and negative electrodes. In some embodiments, the separator membrane comprises a porous sheet-like or nonwoven resin, the resin comprising, but not limited to, at least one of, polyolefins, aromatic polyamides, polytetrafluoroethylene, or polyethersulfone.

[0135] In some embodiments, the electrochemical device also includes an electrolyte.

[0136] In some embodiments, the electrolyte may include organic solvents, lithium salts, and additives. This application does not impose specific limitations on the types of organic solvents and lithium salts; they can be selected according to actual needs.

[0137] In some embodiments, the organic solvent may be at least one of methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), or diethyl sulfone (ESE).

[0138] In some embodiments, the lithium salt may be at least one of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium difluorophosphate (LiPO2F2), lithium difluorodioxophosphate (LiDFOP), lithium tetrafluorooxophosphate (LiTFOP), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxophosphate borate (LiDFOB), or lithium dioxophosphate borate (LiBOB).

[0139] In some embodiments, the additives are not specifically limited and can be selected according to actual needs; for example, the additives may include nitrile compounds.

[0140] In some embodiments, the nitrile compound includes at least one of butadionitrile, glutaronitrile, adiponitrile, or 1,3,6-hexanetrionitrile.

[0141] The electrochemical device of this application can be prepared according to conventional methods in the art; such preparation methods may specifically include the following steps: stacking the above-mentioned positive electrode, separator and negative electrode in sequence, with the separator between the positive electrode and the negative electrode, and then winding them to obtain an electrode assembly; placing the electrode assembly in a packaging shell, injecting electrolyte and sealing it to obtain the electrochemical device.

[0142] Thirdly, this application provides an electronic device, including the electrochemical device described in the second aspect of this application. The electrochemical device of this application can be used in various fields such as electronic products, energy storage, and electric vehicles powered by batteries, including mobile phones, laptops, power tools, video recorders, backup power supplies, electric vehicles, electric motorcycles, game consoles, cameras, and drones.

[0143] The technical solution of this application will be described below with reference to specific embodiments and comparative examples. Unless otherwise specified, the materials, reagents, equipment, etc. used can all be obtained commercially.

[0144] Example 1

[0145] S1: Prepare a first aqueous solution containing NiSO4 and MnSO4 according to the molar ratio of Ni:Mn = 50:50. In a nitrogen atmosphere, mix the first aqueous solution with the precipitant NaOH solution and the complexing agent ammonia water to react. Control the concentration of ammonia water in the reaction system to be 1 mol / L and the pH of the reaction system to be 12.5. The total reaction time is 48 hours. After the reaction is completed, filter, wash with water and dry to obtain the nickel-manganese-based precursor.

[0146] S2: According to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Na element, TM(Ni+Mn):Na=1:1.05, the nickel-manganese-based precursor and sodium carbonate are ground and mixed evenly, and then heated to 800℃ at a rate of 5℃ / min in air atmosphere, and calcined for 15h. Then, the temperature is cooled to room temperature at a rate of 5℃ / min to obtain the first product.

[0147] S3: According to the ratio of the total molar amount of Ni and Mn to the molar amount of Mo and F, TM(Ni+Mn):Mo:F=1:0.005:0.005, the first product is ground and mixed evenly with molybdenum trioxide and ammonium fluoride. A mixed atmosphere with Ar and H2 volume percentages of 95% and 5% is introduced, and then the temperature is raised to 700℃ at a rate of 3℃ / min for secondary calcination. After holding at the temperature for 5 hours, it is cooled to room temperature at a rate of 5℃ / min to obtain the second product.

[0148] S4: According to the ratio of the total molar amount of Ni and Mn to the molar amount of Li, TM(Ni+Mn):Li=1:3, the second product and the lithium source (the lithium source is a mixture of lithium hydroxide, lithium chloride and lithium nitrate with a molar ratio of 1:1:1) are thoroughly mixed, heated to 400℃ at a rate of 3℃ / min under a nitrogen atmosphere, and calcined three times for 5h. Then, the mixture is cooled to room temperature at a rate of 50℃ / min. Finally, the cathode material is obtained by washing with deionized water, drying and sieving.

[0149] Example 2

[0150] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with tungsten trioxide and ammonium fluoride according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of W element and the molar amount of F element as TM(Ni+Mn):W:F=1:0.005:0.005, and the rest of the process is the same.

[0151] Example 3

[0152] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with niobium pentoxide and ammonium fluoride according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Nb elements and the molar amount of F elements as TM(Ni+Mn):Nb:F=1:0.005:0.005, and the rest of the process is the same.

[0153] Example 4

[0154] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with tantalum pentoxide and diammonium hydrogen phosphate according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Ta and P elements as TM(Ni+Mn):Ta:P=1:0.005:0.005. The rest of the process is the same.

[0155] Example 5

[0156] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with silicon dioxide and diammonium hydrogen phosphate according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Si elements and the molar amount of P elements as TM(Ni+Mn):Si:P=1:0.005:0.005, and the rest of the process is the same.

[0157] Example 6

[0158] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with antimony dioxide and urea according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Sb elements and the molar amount of N elements as TM(Ni+Mn):Sb:N=1:0.005:0.005, and the rest of the process is the same.

[0159] Example 7

[0160] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with molybdenum trioxide and ammonium fluoride according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Mo and F elements as TM(Ni+Mn):Mo:F=1:0.001:0.001, and the rest of the process is the same.

[0161] Example 8

[0162] The difference between this embodiment and embodiment 1 is that in step S3 of this embodiment, the first product is ground and mixed evenly with molybdenum trioxide and ammonium fluoride according to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Mo and F elements as TM(Ni+Mn):Mo:F=1:0.01:0.01, and the rest of the process is the same.

[0163] Example 9

[0164] The difference between this embodiment and Embodiment 1 is that in step S1 of this embodiment, a first aqueous solution containing NiSO4 and MnSO4 is prepared according to the molar ratio of Ni to Mn of Ni:Mn = 60:40, and the rest of the process is the same.

[0165] Example 10

[0166] The difference between this embodiment and Embodiment 1 is that in step S1 of this embodiment, a first aqueous solution containing NiSO4 and MnSO4 is prepared according to the molar ratio of Ni to Mn of Ni:Mn = 40:60, and the rest of the process is the same.

[0167] Comparative Example 1

[0168] S1: Same as Example 1;

[0169] S2: According to the ratio of the total molar amount of Ni and Mn elements to the molar amount of Li element, TM(Ni+Mn):Li=1:1.05, the nickel-manganese-based precursor and lithium carbonate are ground and mixed evenly. Then, the mixture is heated to 800℃ at a rate of 5℃ / min in air atmosphere and calcined for 15h. After that, it is cooled to room temperature at a rate of 5℃ / min. Finally, the cathode material is obtained by washing with deionized water, drying and sieving.

[0170] Comparative Example 2

[0171] S1: Same as Example 1;

[0172] S2: Same as Example 1;

[0173] S3: According to the ratio of the total molar amount of Ni and Mn to the molar amount of Li (Ni and Mn):Li = 1:3, the first product and the lithium source (a mixture of lithium hydroxide, lithium chloride and lithium nitrate with a molar ratio of 1:1:1) are thoroughly mixed, heated to 400℃ at a rate of 3℃ / min under a nitrogen atmosphere, calcined for 5h, and then cooled to room temperature at a rate of 50℃ / min. Finally, the cathode material is obtained by washing with deionized water, drying and sieving.

[0174] Methods for manufacturing button cells:

[0175] (1) Add the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) to N-methylpyrrolidone (NMP), mix them evenly, and prepare a positive electrode slurry with a solid content of 45wt%, wherein the weight ratio of the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) is 90:5:5.

[0176] (2) The positive electrode slurry is uniformly coated on aluminum foil, with a single-sided coating thickness of 40 μm; after drying, it is rolled to form the desired electrode, wherein the areal density of the positive electrode active layer is 14 mg / cm³. 2 The positive electrode sheet is obtained by drying and then punched into 14mm round sheets;

[0177] (3) The separator (using a porous polyethylene film as the separator) is punched into 18mm round pieces, and the negative electrode is a lithium metal sheet with a diameter of 18mm; LiPF6 is added to a solvent in which propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) are mixed in a weight ratio of 1:1:1, and the mixture is stirred evenly to obtain an electrolyte; the mass concentration of LiPF6 is 12.5% ​​based on the mass of the electrolyte; the positive electrode, separator, negative electrode, electrolyte, battery case and other accessories are moved into a glove box (the water content must be less than 11ppm);

[0178] (4) Assemble the batteries in a stacking order from bottom to top and inject electrolyte. Then, seal them on a packaging machine to obtain button cells.

[0179] Methods for preparing lithium-ion batteries:

[0180] Preparation of the positive electrode:

[0181] (1) Add the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) to N-methylpyrrolidone (NMP), mix them evenly, and prepare a positive electrode slurry with a solid content of 70wt%, wherein the weight ratio of the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) is 96∶2∶2.

[0182] (2) The positive electrode slurry is uniformly coated on one side of the aluminum foil, with a single-sided coating thickness of 40 μm. After drying, the above steps are repeated on the other side of the aluminum foil to obtain a double-sided coated positive electrode sheet. Then, the sheet is rolled, cut, and the tabs are welded to obtain the desired positive electrode. The areal density of the positive electrode active layer on one side is 14 mg / cm³. 2 .

[0183] Preparation of the negative electrode:

[0184] (1) Artificial graphite, styrene-butadiene rubber and sodium carboxymethyl cellulose (CMC) are mixed with deionized water at a mass ratio of 96:2:2 and stirred evenly to obtain negative electrode slurry.

[0185] (2) The negative electrode slurry is uniformly coated on one side of the copper foil. After drying, the above steps are repeated on the other side of the copper foil to obtain a double-coated negative electrode sheet. After cold pressing, cutting, and welding of the tabs, the negative electrode is obtained.

[0186] Electrolyte preparation:

[0187] In a dry argon atmosphere, LiPF6 was added to a solvent consisting of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1, and the mixture was stirred until homogeneous to obtain an electrolyte. The mass concentration of LiPF6 was 12.5% ​​based on the mass of the electrolyte.

[0188] Preparation of the separating membrane:

[0189] Polyethylene (PE) porous film is used as the separator.

[0190] The fabrication of lithium-ion batteries:

[0191] (1) Stack the positive electrode, separator, and negative electrode in sequence, with the separator in the middle of the positive and negative electrodes to provide isolation, and then wind them to obtain the electrode assembly.

[0192] (2) The electrode assembly is placed in the outer packaging aluminum-plastic film, the electrolyte is injected, and it is sealed. The lithium-ion battery is obtained through processes such as formation, degassing, and edge trimming.

[0193] Testing methods for lithium-ion batteries:

[0194] (1) Thickness expansion rate test:

[0195] The lithium-ion battery was charged at a constant current rate of 1.5C to 4.35V at 25℃, and then charged at a constant voltage rate of 0.05C at 4.35V to achieve a fully charged state. The fully charged lithium-ion battery was then stored in a constant temperature chamber at 85℃ for 24 hours. The thickness change of the lithium-ion battery was measured with a micrometer. The initial thickness of the lithium-ion battery before storage was defined as H0, and the thickness after storage was defined as H1. The thickness expansion rate was: (H1-H0) / H0×100%.

[0196] (2) 45℃ Cyclic Capacity Retention Rate Test

[0197] The lithium-ion battery was placed in a 45°C constant temperature chamber and charged at a constant current rate of 1.5C to 4.35V. Then, it was charged at a constant voltage rate of 4.35V to a current of 0.05C. Finally, it was discharged at a constant current rate of 4C to 3.0V. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to 500 charge-discharge cycles in the above manner. The discharge capacity of the lithium-ion battery in the first cycle and the discharge capacity in the 500th cycle were recorded. The cycle capacity retention rate = discharge capacity in the 500th cycle / discharge capacity in the first cycle × 100%.

[0198] Button cell battery testing:

[0199] In an environment of 25℃, the coin cell was charged at a constant current of 0.04C to 4.5V within a voltage range of 2.8V to 4.5V, and then charged at a constant voltage of 4.5V until the current reached 50uA. The charging capacity of the coin cell was recorded. Then, it was discharged at a constant current of 0.04C until the lower limit voltage reached 2.8V. The capacity-voltage relationship curve and the capacity-voltage differential dQ / dV curve were recorded. Based on the capacity-voltage relationship curve, the capacity Q1 in the 4.2 to 4.5V voltage range and the capacity Qt in the 3.0V to 4.5V voltage range can be obtained. Based on the capacity-voltage differential dQ / dV curve, the peak intensity and peak voltage Vo1 of the first oxidation peak and the peak intensity and peak voltage Vr1 of the first reduction peak can be obtained. Wherein, the specific capacity of the positive electrode material is equal to the charging capacity of the coin cell divided by the mass of the positive electrode material.

[0200] Cathode material testing:

[0201] (1) X-ray diffraction test:

[0202] The cathode material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE). The target material was Cu Kα, the voltage and current were 40 kV / 40 mA, and the scanning angle range was 10° to 80°. The XRD patterns of the cathode material obtained from the test were matched with crystals to obtain the crystal phase structure and unit cell parameter information of the cathode material.

[0203] (2) Scanning electron microscopy test:

[0204] The cathode material sample was tested under a scanning electron microscope, and images of the cathode material were taken at a magnification of 3000.

[0205] (3) Scanning transmission electron microscopy (STEM) test:

[0206] The cathode material was observed using a scanning transmission electron microscope, and the phase composition (lattice fringes) and thickness of the cathode material matrix and surface were observed.

[0207] (4) Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) Test:

[0208] The contents of Na, Li, Ni, Mn, Q, and M elements in the cathode material were tested using ICP-OES.

[0209] (5) X-ray photoelectron spectroscopy (XPS) test:

[0210] The content of R element in cathode material particles at different etching depths was determined by X-ray photoelectron spectroscopy.

[0211] (6) Electron probe microanalysis (EPMA) test:

[0212] The electrode sheet containing the positive electrode material is cut with a three-ion beam to obtain a flat cross-section exposing the internal structure of the positive electrode material. For any selected cross-section of the positive electrode material particle, the content of Ni, Mn, Na, Q, and M elements in the matrix and surface layer of the particle is tested using an EPMA (JXA-8230). The surface layer of the positive electrode material extends inward from the surface of the particle up to 10 nm.

[0213] The partial test results of the cathode materials, coin cells, and lithium-ion batteries of Examples 1-10 and Comparative Examples 1-2 are shown in Table 1-2 and Figure 1-6.

[0214] Based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Li element in the cathode materials of Examples 1-10 and Comparative Examples 1-2 (C Li ), molar percentage of Na (C Na The molar percentage of Na in the surface layer of the cathode material is c. 1Na (Based on the total molar amount of Ni and Mn elements in the surface layer of the cathode material), the molar percentage of Na element in the cathode material matrix is ​​c. 2Na (Based on the total molar amount of Ni and Mn elements in the cathode material matrix), c 1Na / c 2Na The value of Q and the molar percentage of Q element in the surface layer of the cathode material are c. 1Q (Based on the total molar amount of Ni and Mn elements in the surface layer of the cathode material), the molar percentage of Q element in the cathode material matrix is ​​c. 2Q (Based on the total molar amount of Ni and Mn elements in the cathode material matrix), the molar percentage of R element in the surface layer of the cathode material is c. 1R (Based on the total molar amount of Ni and Mn elements in the surface layer of the cathode material), the molar percentage of R element in the cathode material matrix is ​​c. 2R The total molar amount of Ni and Mn elements in the cathode material matrix and the crystal structure and thickness of the surface layer are shown in Table 1.

[0215] Table 1

[0216] Figure 1 shows the X-ray diffraction patterns of the cathode materials prepared in Example 1 and Comparative Example 1 of this application. The cell parameters of the cathode materials in Examples 1-10 and Comparative Examples 1-2 are shown in Table 2. According to the XRD pattern analysis of the cathode material in Example 1, the diffraction peaks in the X-ray diffraction patterns of the cathode material of this application, with 2θ values ​​in the ranges of 17° to 20°, 35° to 38°, and 42° to 46°, belong to the characteristic peaks of the (003), (101), and (104) crystal planes of lithium nickel manganese composite oxide, respectively, and belong to the layered crystal structure of the R-3m space group. Among them, the half-width at half-maximum (WHM) of the characteristic peaks of the cathode material of this application is relatively wide, indicating that the size of the primary grains of the cathode material of this application is relatively small. In addition, according to Table 2, compared with the conventional cathode material of Comparative Example 1, the cell parameters of the cathode material of this application are larger, which is more conducive to improving the lithium-ion transport kinetics and further achieving the goal of improving the cycle performance of lithium-ion batteries under high voltage conditions.

[0217] Table 2

[0218] Figure 2 is a scanning electron microscope (SEM) image of the cathode material prepared in Comparative Example 1 at 3000x magnification. Figure 3 is a SEM image of the cathode material prepared in Example 1 at 3000x magnification. Figure 4 is a high-magnification scanning transmission electron microscope (STEM) image of the cathode material prepared in Example 1. As can be seen from Figures 2-4, the morphology of the conventional lithium nickel manganese composite oxide cathode material in Comparative Example 1 is approximately equiaxed, with primary nanocrystals tightly packed together to form spherical secondary micron particles; the morphology of the lithium nickel manganese composite oxide cathode material in Example 1 is slender, primary nanocrystals loosely packed together to form spherical secondary micron particles, and the cathode material of this application is porous and loose. As shown in Figure 4, the matrix region of this cathode material has a layered structure. Within its surface layer, there exists a first region containing a spinel phase and a second region containing a rock salt phase. Both the spinel and rock salt phases are cationic disordered phases relative to the matrix, with a thickness of approximately 12.6 nm. The layered structure of the spinel, rock salt, and matrix is ​​coupled through a commensurate lattice, effectively suppressing structural strain and lattice oxygen loss during deep charge-discharge processes under high temperature and high voltage conditions, thus improving the structural stability of the cathode material. Simultaneously, the cationic disordered phase on the surface can inhibit direct corrosion of the cathode active particles by the electrolyte, alleviate interfacial side reactions between the cathode material and the electrolyte, suppress microcracks and surface degradation during cycling, and improve interfacial stability. Therefore, the cathode material of this application exhibits good structural and interfacial stability under high temperature and high voltage conditions, reducing gas generation during battery storage under these conditions, thereby improving the battery's cycle performance and safety performance.

[0219] Figures 5 and 6 show the specific capacity-voltage curves and the capacity-voltage differential dQ / dV curves of the coin cells assembled with the cathode materials prepared in Comparative Example 1 and Example 1, respectively, at a current density of 0.04C during the first charge-discharge cycle. As shown in Figure 5, when the conventional cathode material and lithium metal assembled into a coin cell in Comparative Example 1 are charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve in the obtained capacity-voltage curve does not show a plateau in the 4.2V to 4.5V range. However, when the cathode material and lithium metal assembled into a coin cell in Example 1 are charged and discharged at a current of 0.04C within a voltage range of 2.8V to 4.5V, the discharge curve in the obtained capacity-voltage curve shows a plateau in the 4.2V to 4.5V range. Meanwhile, compared to the conventional cathode material in Comparative Example 1, the capacity-voltage differential dQ / dV curve of the coin cell composed of the cathode material in Example 1 under these conditions shows a first oxidation peak and a first reduction peak in the range of 4.2V to 4.5V, and a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V. In contrast, the capacity-voltage differential dQ / dV curve corresponding to Comparative Example 1 does not show oxidation peaks and reduction peaks in the range of 4.2V to 4.5V.

[0220] The discharge curves of the coin cells assembled with the cathode materials of Examples 1-10 and Comparative Examples 1-2, and the ratio of their capacities Q1 in the 4.2V to 4.5V range to Qt in the 3.0V to 4.5V range, are shown in Table 3. The peak intensities of the first oxidation peak, the first reduction peak, the peak voltage Vo1 of the first oxidation peak, and the absolute value of the difference between Vo1 and Vr1 of the first reduction peak (|Vo1-Vr1|) for Examples 1-10 and Comparative Example 2 are also shown in Table 3. The thickness expansion rate and 45℃ cycle capacity retention rate of the lithium-ion batteries assembled with the cathode materials of Examples 1-10 and Comparative Examples 1-2 are also shown in Table 3.

[0221] Table 3

[0222] Examples 1-10 are lithium nickel manganese composite oxide cathode materials with a dual-phase structure of spinel and rock salt phases on the surface layer and oxygen defects in the matrix, as described in this application. Comparative Example 1 is a traditional layered lithium nickel manganese composite oxide cathode material, and Comparative Example 2 is a lithium nickel manganese composite oxide cathode material without a dual-phase structure of spinel and rock salt phases on the surface layer and oxygen defects in the matrix. According to Table 3, the coin cell assembled from the traditional layered cathode material of Comparative Example 1 has no oxidation or reduction peaks in the 4.2V to 4.5V range, and its corresponding lithium-ion battery has a high thickness expansion rate, low Q1 / Qt value, and low cycle capacity retention. In Comparative Example 2, the coin cell assembled from the cathode material with oxygen-containing defects in the matrix exhibits a first oxidation peak and a second reduction peak in the 4.2V to 4.5V range. Although the thickness expansion rate and cycle capacity retention of the corresponding lithium-ion battery are improved to some extent, the improvement effect is far inferior to that of the lithium nickel manganese composite oxide cathode material with a dual-phase coexistence structure of spinel phase and rock salt phase on the surface layer in Examples 1-10 of this application. This is because this application forms a dual-phase coexistence structure of spinel phase and rock salt phase on the matrix surface through surface-induced phase transition. The spinel phase stabilizes the highly active metal ions and oxygen ions on the matrix surface while providing a faster ion transport channel in the high-voltage range, while the rock salt phase has higher structural stability, which can further improve the stability of the cathode material surface structure. The two work together to significantly improve the stability of the cathode material surface structure and further improve the ion conduction rate of the surface structure in the high-voltage range, thereby improving the storage gas generation and cycle performance of the lithium-ion battery under high temperature and high voltage conditions.

[0223] Among them, the coin cells composed of cathode materials in Examples 1-10 have peak intensities of 1500 mAh / g / V to 2200 mAh / g / V for the first oxidation peak and 1800 mAh / g / V to 2500 mAh / g / V for the first reduction peak, while satisfying |Vo1-Vr1|≤0.12V, and the discharge curve of the coin cell satisfies 0.2≤Q1 / Qt≤0.35.

[0224] As can be seen from Table 1 and Table 3, the Mn content of the cathode material in Examples 9, 1 and 10 gradually increases, the thickness of its spinel phase and rock salt phase increases, and the structure and interface stability of the cathode material are further enhanced. Therefore, compared with Examples 1 and 9, the lithium-ion battery of Example 10 has a lower degree of gas generation during high-temperature storage and better high-temperature cycle performance.

[0225] In Examples 7, 1, and 8, the contents of R and Q elements gradually increase, the thickness of the spinel phase and rock salt phase increases, and the interfacial stability of the cathode material is further enhanced. Therefore, compared with Examples 1 and 7, the lithium-ion battery in Example 8 has a lower degree of gas generation during high-temperature storage. However, as the thickness of the surface layer increases, the kinetics of lithium-ion insertion and extraction during charging and discharging will decrease accordingly, resulting in lower cycle performance of the lithium-ion battery in Example 8 compared with Example 1.

[0226] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, The cathode material includes a lithium-nickel-manganese composite oxide; The cathode material includes a matrix and a surface layer located on the surface of the matrix. The matrix has a layered structure. The surface layer includes a first region and a second region. The first region contains a spinel phase, and the second region contains a rock salt phase. The first region and the second region are respectively located on the surface of the matrix. The positive electrode material is assembled with lithium metal to form a coin cell. When the coin cell is charged and discharged at a current of 0.04C in the voltage range of 2.8V to 4.5V, the obtained capacity-voltage differential dQ / dV curve has a first oxidation peak and a first reduction peak in the range of 4.2V to 4.5V.

2. The cathode material as described in claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Mn element in the matrix is ​​c. Mn It ranges from 40% to 60%; (2) The cathode material includes element Q, which includes at least one of Mo, W, Nb, Ta, Si, or Sb; based on the total molar amount of Ni and Mn elements in the surface layer, the molar percentage of element Q in the surface layer is c. 1Q Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Q element in the matrix is ​​c. 2Q ; Satisfies: c 1Q >c 2Q ; (3) The positive electrode material includes element R, which includes at least one of F, Cl, Br, I, P, or N; based on the total molar amount of Ni and Mn elements in the surface layer, the molar percentage of element R in the surface layer is c. 1R Based on the total molar amounts of Ni and Mn elements in the matrix, the molar percentage of R element in the matrix is ​​c. 2R ; Satisfies: c 1R >c 2R .

3. The cathode material as described in claim 2, characterized in that, The cathode material satisfies at least one of the following conditions: (1)c 1Q It ranges from 0.4% to 5%; (2)c 2Q It ranges from 0.05% to 0.5%; (3)c 1R It ranges from 1% to 5%; (4)c 2R It ranges from 0.1% to 0.5%.

4. The positive electrode material as described in claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) Scanning transmission electron microscopy revealed that the spinel phase and the matrix were co-latticeally coupled. (2) Scanning transmission electron microscopy revealed that the rock salt phase and the matrix were co-latticeally coupled. (3) Scanning transmission electron microscopy revealed that the spinel phase and the rock salt phase were co-lattice coupled. (4) The thickness of the spinel phase is 2 nm to 80 nm; (5) The thickness of the rock salt phase is 2 nm to 80 nm.

5. The positive electrode material as described in claim 1, characterized in that, The cathode material includes Na; based on the total molar amount of Ni and Mn in the surface layer, the molar percentage of Na in the surface layer is c. 1Na Based on the total molar amount of Ni and Mn elements in the matrix, the molar percentage of Na element in the matrix is ​​c. 2Na ; Satisfies: c 1Na >c 2Na .

6. The cathode material as described in claim 5, characterized in that, The cathode material satisfies at least one of the following conditions: (1)c 1Na The percentage ranges from 3% to 15%. (2)c 2Na It ranges from 0.5% to 10%; (3)1.1≤c 1Na / c 2Na ≤10。 7. The positive electrode material as described in claim 1, characterized in that, The cathode material satisfies at least one of the following conditions: (1) Based on the mass of the cathode material, the peak intensity of the first oxidation peak is greater than or equal to 1200 mAh / g / V; (2) Based on the mass of the cathode material, the peak intensity of the first reduction peak is greater than or equal to 1200 mAh / g / V; (3) The peak voltage of the first oxidation peak is Vo1, and the peak voltage of the first reduction peak is Vr1, satisfying: |Vo1-Vr1|≤0.12V; (4) When the button cell is charged and discharged at a current of 0.04C in the voltage range of 2.8V to 4.5V, the discharge curve in the obtained capacity-voltage curve has a plateau in the range of 4.2V to 4.5V. The capacity of the discharge curve in the range of 4.2V to 4.5V is Q1, and the capacity of the discharge curve in the range of 3.0V to 4.5V is Qt, satisfying: 0.2≤Q1 / Qt≤0.35; (5) The capacity-voltage differential dQ / dV curve has a second oxidation peak and a second reduction peak in the range of 3.6V to 4.0V.

8. The cathode material according to any one of claims 1 to 7, characterized in that, The cathode material satisfies at least one of the following conditions: (1) Based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Ni element in the cathode material is greater than or equal to 40%; (2) Based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Mn element in the cathode material is 30% to 60%; (3) Based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Li element in the cathode material is 90% to 105%; (4) The cathode material includes a Q element, which includes at least one of Mo, W, Nb, Ta, Si or Sb; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Q element in the cathode material is 0.1% to 5%. (5) The cathode material includes element R, which includes at least one of F, Cl, Br, I, P or N; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of element R in the cathode material is 0.1% to 5%. (6) The cathode material includes Na element, and based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of Na element in the cathode material is 0.5% to 10%; (7) The cathode material includes element M, which includes at least one of Mg, Al, K, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, In, Sn, Ba, La, Ce, Hf, Pb, Bi, B or S; based on the total molar amount of Ni and Mn elements in the cathode material, the molar percentage of element M in the cathode material is 0.1% to 5%; (8) The cathode material includes: Li x1 Na x2 Ni y1 Mn y2 Q y3 M y4 O 2±z R n Wherein, Q includes at least one of Mo, W, Nb, Ta, Si, or Sb; M includes at least one of Mg, Al, K, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Ge, Sr, Y, Zr, Ag, In, Sn, Ba, La, Ce, Hf, Pb, Bi, B, or S; R includes at least one of F, Cl, Br, I, P, or N; 0.9≤x1≤1.05, 0.005≤x2≤0.1, 0.4≤y1≤1, 0.3≤y2≤0.6, 0.001≤y3≤0.05, 0.001≤y4≤0.05, 0≤z≤0.2, 0≤n≤0.2; (9) The X-ray diffraction pattern of the cathode material has diffraction peaks in the ranges of 2θ from 17° to 20°, 35° to 38° and 42° to 46°. (10) The cell parameter a of the cathode material satisfies (11) The cell parameter c of the cathode material satisfies (12) The cathode material contains a layered crystal structure belonging to the R-3m space group.

9. An electrochemical device comprising a positive electrode, said positive electrode comprising a positive electrode current collector and a positive electrode active material layer, characterized in that, The positive electrode active material layer comprises the positive electrode material according to any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

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