Positive electrode material, electrochemical device, and electric device

Abstract

The present application provides a positive electrode material, an electrochemical device, and an electric device. The positive electrode material of the present application comprises secondary particles each formed by agglomeration of a plurality of primary grains. Each primary grain comprises a layered lithium-nickel composite oxide. Each secondary particle comprises a first primary grain and a second primary grain adjacent to the first primary grain, wherein a grain boundary region is provided between the first primary grain and the second primary grain, a first surface of the first primary grain comprises a first region connected to the grain boundary region, and a second surface of the second primary grain comprises a second region connected to the grain boundary region. Each secondary particle further comprises a first nickel- and strontium-containing oxide that is located at an included angle formed by the corresponding first region, the corresponding second region and the corresponding grain boundary region and connects the first region and the second region. The positive electrode material of the present application can achieve significantly improved cycle stability and high-temperature safety.

Description

Positive electrode materials, electrochemical devices and electrical devices Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a cathode material, an electrochemical device, and an electrical device. Background Technology

[0002] With the increasing popularity of electric vehicles, the requirements for their batteries are becoming more stringent. Lithium-ion batteries, with their outstanding advantages such as high energy density, good safety, no memory effect, and long service life, have already occupied a mainstream position in the market. To meet the demands of high energy density, low cost, and long cycle life for electric vehicle lithium-ion batteries, layered lithium nickel composite oxide cathode materials have long 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 even higher energy density, layered lithium nickel composite oxide cathode materials have been continuously developed towards increasing Ni content, charging voltage, and the amount of lithium stripping. However, under high Ni content, high charging voltage, and high lithium stripping, the problems of oxygen release and structural phase transition on the surface of layered lithium nickel composite oxide cathode materials are also fully exposed, leading to issues such as battery cycle degradation, gas generation, and thermal runaway. Summary of the Invention

[0003] In view of this, this application provides a cathode material, an electrochemical device, and an electrical device to improve the cycle performance and high-temperature safety of the electrochemical device.

[0004] The first aspect of this application provides a cathode material comprising secondary particles formed by the agglomeration of multiple primary grains. The primary grains comprise layered lithium-nickel composite oxides. The secondary particles comprise adjacent first and second primary grains, with a grain boundary region between the first and second primary grains. The first surface of the first primary grain includes a first region connected to the grain boundary region, and the second surface of the second primary grain includes a second region connected to the grain boundary region. The secondary particles also include a first nickel- and strontium-containing oxide located at the angle formed by the first region, the second region, and the grain boundary region, and connecting the first and second regions.

[0005] The cathode material of this application connects the surfaces of the primary grains at the angles between them by setting nickel and strontium oxides, which can effectively suppress cracking between the primary grains during charge-discharge cycles, thereby reducing side reactions on the cathode material surface and improving the cycle performance of the electrochemical device. At the same time, the nickel and strontium oxides on the surface of the primary grains can isolate the electrolyte and reduce the corrosion of the cathode material surface by the electrolyte. This can effectively reduce the oxygen release phase transition on the cathode material surface and the decomposition and gas generation of the electrolyte under high temperature conditions, thereby improving the high-temperature safety of the electrochemical device.

[0006] In any of the above optional embodiments, the first nickel and strontium-containing oxide includes a first connection region connected to a first region and a second connection region connected to a second region; the first nickel-containing transition metal layer in the first connection region has a first orientation, and the second nickel-containing transition metal layer in the second connection region has a second orientation.

[0007] In any of the above optional embodiments, the third nickel-containing transition metal layer in the first primary grain has a third orientation, and the angle α between the first orientation and the third orientation is ≤10°.

[0008] In any of the above optional embodiments, the fourth nickel-containing transition metal layer in the second primary grain has a fourth orientation, and the included angle β between the second orientation and the fourth orientation is ≤10°.

[0009] Thus, the first connecting region on the surface of the first primary grain and / or the second connecting region on the surface of the second primary grain can be epitaxially grown well. On the one hand, this can enhance the connection between the first primary grain and / or the second primary grain and the first nickel and strontium-containing oxide, thereby better suppressing cracking between primary grains during charge-discharge cycles. On the other hand, it can improve the coordination environment of lattice oxygen on the surface of the primary grain, alleviate the volumetric strain and structural stress caused by the H2-H3 phase transition, and improve the structural stability of lattice oxygen under deep charge-discharge conditions, thereby further suppressing cracking between primary grains and oxygen release phase transition on the material surface, and improving the cycle performance and high-temperature safety of the electrochemical device.

[0010] In any of the above optional embodiments, the first connection region is connected to the second connection region, and the included angle γ between the first orientation and the second orientation is ≤10°. Thus, the connection reliability between the first and second connection regions within the first nickel and strontium-containing oxide is higher, which can suppress cracking under stress between primary grains, thereby better suppressing cracking between primary grains during charge-discharge cycles and improving the cycle performance of the electrochemical device.

[0011] In any of the above-mentioned optional embodiments, the molar ratio of Sr to Ni in the first nickel and strontium-containing oxide ranges from 0.8 to 3.

[0012] In any of the above-mentioned optional embodiments, the first nickel and strontium-containing oxide has space group P321.

[0013] In any of the above optional embodiments, the first nickel and strontium-containing oxide has (112) and / or (300) characteristic crystal planes.

[0014] In any of the above-mentioned optional embodiments, the grain boundary region includes a second nickel- and strontium-containing oxide. Thus, primary grains can be firmly connected through the second nickel- and strontium-containing oxide, thereby further suppressing cracking between primary grains during charge-discharge cycles and improving the cycle performance of the electrochemical device.

[0015] In any of the above-mentioned alternative embodiments, the second nickel and strontium-containing oxide has space group P321.

[0016] In any of the above optional embodiments, the molar ratio of Sr to Ni in the second nickel and strontium-containing oxide ranges from 0.8 to 3.

[0017] In any of the above optional embodiments, the second nickel and strontium-containing oxide has (112) and / or (300) characteristic crystal planes.

[0018] In any of the above optional embodiments, the layered lithium-nickel composite oxide includes Ni and M elements, wherein the M element includes at least one of Co, Mn, Al, Mg, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, or Bi; the molar amount of Ni element in the layered lithium-nickel composite oxide is nNi, and the molar amount of M element is nM.

[0019] In any of the above optional embodiments, the first primary grain includes a first surface region within 50 nm of the grain boundary region. Based on the total molar amount of Ni and M elements in the first surface region, the molar percentage of Sr elements in the first surface region, c1Sr, satisfies: 0.1% ≤ c1Sr ≤ 2%.

[0020] In any of the above optional embodiments, the second primary grain includes a second surface region within 50 nm of the grain boundary region. Based on the total molar amount of Ni and M elements in the second surface region, the molar percentage of Sr elements in the second surface region, c2Sr, satisfies: 0.1% ≤ c2Sr ≤ 2%.

[0021] When the molar percentage of Sr in the primary grain surface region is within the above range, the structural stability of the primary grain surface region during charge-discharge cycles can be further improved, the volumetric strain and structural stress of the primary grains during charge-discharge cycles can be alleviated, thereby further suppressing cracking between primary grains and oxygen release phase transition on the material surface, and improving the cycle performance and high-temperature safety of the electrochemical device.

[0022] In any of the above optional embodiments, the layered lithium-nickel composite oxide further contains Na, and the molar amount of Na in the layered lithium-nickel composite oxide is nNa, satisfying: 0.001≤nNa / (nNi+nM)≤0.01. By doping the layered lithium-nickel composite oxide with Na, the lattice structure of the primary grains during charge-discharge cycles can be further stabilized, alleviating the volumetric strain and structural stress of the primary grains during charge-discharge cycles, thereby further suppressing cracking between primary grains and oxygen release phase transition on the material surface, improving the cycle performance and high-temperature safety of the electrochemical device.

[0023] In any of the above optional embodiments, 0.6≤nNi / (nNi+nM)≤1, 0≤nM / (nNi+nM)≤0.4.

[0024] In any of the above optional embodiments, the first primary grain includes a first core region at a distance of more than 200 nm from the surface of the first primary grain. Based on the total molar amount of Ni and M elements in the first core region, the molar percentage content of Sr element d1Sr in the first core region satisfies: c1Sr / d1Sr≥10.

[0025] In any of the above optional embodiments, the second primary grain includes a second core region at a distance of more than 200 nm from the surface of the second primary grain. Based on the total molar amount of Ni and M elements in the second core region, the molar percentage content of Sr element d2Sr in the second core region satisfies: c2Sr / d2Sr≥10.

[0026] The surface region of the primary grain is rich in Sr compared to the core region, which can improve the stability of the surface region of the primary grain while reducing the impact on the capacity of the cathode material.

[0027] In any of the above optional embodiments, the cathode material includes Li, Ni and M elements, wherein the M element includes at least one of Co, Mn, Al, Mg, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb or Bi.

[0028] In any of the above optional embodiments, the molar percentage of Sr in the cathode material is 0.1% to 5% based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0029] In any of the above optional embodiments, the molar percentage of Li in the cathode material is 90% to 105% based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0030] In any of the above optional embodiments, the molar percentage of Ni in the cathode material is greater than or equal to 60%, based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0031] In any of the above optional embodiments, based on the sum of the molar amounts of Ni and M elements in the cathode material, the molar percentage of M element in the cathode material is less than or equal to 40%.

[0032] In any of the above optional embodiments, the cathode material further includes Na element, and the molar percentage content of Na element in the cathode material is 0.1% to 10% based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0033] In any of the above optional embodiments, the layered lithium-nickel composite oxide has a layered crystal structure belonging to the R-3m space group.

[0034] In any of the above optional embodiments, the X-ray diffraction spectrum of the cathode material shows characteristic peaks for 2θ in the ranges of 28.5° to 30.5° and 31.5° to 34.0°.

[0035] In any of the above optional embodiments, the X-ray photoelectron spectroscopy spectrum of the cathode material shows a Sr 3d characteristic peak in the range of 125 eV to 140 eV.

[0036] In any of the above-mentioned optional embodiments, the cathode material is assembled with lithium metal to form a coin cell. When the coin cell is charged to 4.5V, the X-ray diffraction spectrum of the cathode material shows only one (003) characteristic peak in the range of 17.0° to 21.0° for 2θ. Thus, the cathode material exhibits only the H3 phase at high voltage, which can alleviate the structural distortion and random orientation stress caused by phase inhomogeneity within the cathode material particles, thereby suppressing the formation of primary intergranular cracks and improving the cycle performance of the electrochemical device. Simultaneously, the cathode material can also possess superior kinetic performance.

[0037] In any of the above optional embodiments, the cathode material is assembled with lithium metal into a coin cell. When the coin cell is charged to 4.1V and 4.5V respectively, the difference between the 2θ value of the (003) characteristic peak at 4.5V and the 2θ value of the (003) characteristic peak at 4.1V in the X-ray diffraction spectrum of the cathode material is less than or equal to 0.75°. The cathode material corresponds to the H2-H3 phase transition between 4.1V and 4.5V. The smaller the shift of the 2θ value of the (003) characteristic peak during this phase transition, the smaller the volumetric stress it suffers. Therefore, the difference between the 2θ values ​​of the (003) characteristic peak at 4.5V and 4.1V of the cathode material of this application is less than or equal to 0.75°, which is beneficial to a more stable crystal structure. This can suppress the stress and strain caused by random orientation during the H2-H3 phase transition, alleviate the formation of primary intergranular cracks, and thus improve the cycle performance of the electrochemical device.

[0038] In any of the above-mentioned optional embodiments, the cathode material and lithium metal are assembled into a coin cell. When the coin cell is charged and discharged at a current of 0.1C within a voltage range of 2.7V to 4.5V, the obtained discharge capacity-voltage differential dQ / dV curve shows a first reduction peak in the 4.1V to 4.5V range; the peak intensity of the first reduction peak is less than or equal to 840mAh / g / V. Thus, the irreversible capacity loss of the cathode material during charging is significantly suppressed, and the structural stability is significantly improved, thereby improving the cycle performance of the electrochemical device.

[0039] A second aspect of 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 of the first aspect of this application.

[0040] A third aspect of this application provides an electrical device, including the electrochemical device of the second aspect of this application. Attached Figure Description

[0041] Figure 1 is an X-ray diffraction pattern of the cathode material prepared in Comparative Example 1 and Example 3 of this application;

[0042] Figure 2 is a scanning electron microscope image of the cathode material prepared in Comparative Example 1 of this application;

[0043] Figure 3 is a scanning electron microscope image of the positive electrode material prepared in Example 3 of this application;

[0044] Figure 4 is a transmission electron microscope image of the positive electrode material prepared in Example 3 of this application;

[0045] Figure 5 is a diagram showing the Sr and Ni elemental distribution of the cathode material prepared in Example 3 of this application;

[0046] Figure 6 shows the X-ray diffraction patterns of the (003) diffraction peak of the cathode material prepared in Comparative Example 1 of this application in the initial state and after the prepared coin cell was charged to 4.1V and 4.5V, respectively.

[0047] Figure 7 shows the X-ray diffraction patterns of the (003) diffraction peak of the cathode material prepared in Example 3 of this application in the initial state and after the prepared coin cell is charged to 4.1V and 4.5V, respectively.

[0048] Figure 8 shows the first specific capacity-voltage curve of the coin cell prepared with the cathode material obtained in Comparative Example 1 and Example 3 of this application at a current density of 0.1C.

[0049] Figure 9 is a graph showing the first discharge capacity-voltage differential dQ / dV curve of the coin cell prepared with the cathode material obtained in Comparative Example 1 and Example 3 of this application at a current density of 0.1C.

[0050] Figure 10 is a graph showing the specific capacity of lithium-ion batteries prepared from the cathode materials obtained in Comparative Example 1 and Example 3 of this application after 200 cycles at a current density of 1C.

[0051] Attached image descriptions: 1 - First region; 2 - Second region. Detailed Implementation

[0052] The present application will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely to enable those skilled in the art to better understand the present application and are not intended to limit the present application.

[0053] The first aspect of the application provides a cathode material comprising secondary particles formed by the agglomeration of multiple primary grains. The primary grains comprise layered lithium-nickel composite oxides. The secondary particles comprise adjacent first and second primary grains, with a grain boundary region between the first and second primary grains. The first surface of the first primary grain includes a first region connected to the grain boundary region, and the second surface of the second primary grain includes a second region connected to the grain boundary region. The secondary particles also include a first nickel- and strontium-containing oxide located at the angle formed by the first region, the second region, and the grain boundary region, and connecting the first and second regions.

[0054] The cathode material of this application connects the surfaces of the primary grains at the angles between them by setting nickel and strontium oxides, which can effectively suppress cracking between the primary grains during charge-discharge cycles, thereby reducing side reactions on the cathode material surface and improving the cycle performance of the electrochemical device. At the same time, the nickel and strontium oxides on the surface of the primary grains can isolate the electrolyte and reduce the corrosion of the cathode material surface by the electrolyte. This can effectively reduce the oxygen release phase transition on the cathode material surface and the decomposition and gas generation of the electrolyte under high temperature conditions, thereby improving the high-temperature safety of the electrochemical device.

[0055] It should be noted that a grain boundary region is the connecting region between two single crystals. In secondary grains, due to the different orientations of the primary grains, there are boundaries between them. The grain boundary region connects primary grains with different orientations, transitioning from one orientation to another. Therefore, the local atomic arrangement in the grain boundary region may be irregular. Simultaneously, the grain boundary region may contain heterogeneous material, that is, material with a crystal structure different from that of the primary grains, which connects adjacent primary grains.

[0056] In some alternative embodiments, the first nickel and strontium-containing oxide includes a first connection region connected to a first region and a second connection region connected to a second region.

[0057] In some optional embodiments, the first nickel-containing transition metal layer in the first connection region has a first orientation, and the third nickel-containing transition metal layer in the first primary grain has a third orientation, wherein the angle α between the first orientation and the third orientation is ≤10°. Exemplarily, α is 10°, 9°, 8°, 7°, 6°, 5°, 4°, 2°, 1°, 0°, or a range of any two of the above values.

[0058] In some optional embodiments, the second nickel-containing transition metal layer in the second connection region has a second orientation, and the fourth nickel-containing transition metal layer in the second primary grain has a fourth orientation, wherein the included angle β between the second orientation and the fourth orientation is ≤10°. Exemplarily, β is 10°, 9°, 8°, 7°, 6°, 5°, 4°, 2°, 1°, 0°, or a range of any two of the above values.

[0059] Thus, the first connecting region on the surface of the first primary grain and / or the second connecting region on the surface of the second primary grain can be epitaxially grown well. On the one hand, this can enhance the connection between the first primary grain and / or the second primary grain and the first nickel and strontium-containing oxide, thereby better suppressing cracking between primary grains during charge-discharge cycles. On the other hand, it can improve the coordination environment of lattice oxygen on the surface of the primary grain, alleviate the volumetric strain and structural stress caused by the H2-H3 phase transition, and improve the structural stability of lattice oxygen under deep charge-discharge conditions, thereby further suppressing cracking between primary grains and oxygen release phase transition on the material surface, and improving the cycle performance and high-temperature safety of the electrochemical device.

[0060] In some optional embodiments, the first connection region is connected to the second connection region, and the angle γ between the first orientation and the second orientation is ≤10°. This results in higher connection reliability between the first and second connection regions within the first nickel and strontium-containing oxide, suppressing cracking under stress between primary grains, thereby better suppressing cracking between primary grains during charge-discharge cycles and improving the cycle performance of the electrochemical device. Exemplarily, γ is 10°, 9°, 8°, 7°, 6°, 5°, 4°, 2°, 1°, 0°, or a range consisting of any two of the above values.

[0061] In some alternative embodiments, the molar ratio of Sr to Ni in the first nickel- and strontium-containing oxide ranges from 0.8 to 3. Exemplarily, the molar ratio of Sr to Ni in the first nickel- and strontium-containing oxide is 0.8, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, or a range consisting of any two of the above values.

[0062] In some alternative embodiments, the first nickel and strontium-containing oxide has space group P321.

[0063] In some alternative embodiments, the first nickel and strontium-containing oxide has (112) and / or (300) characteristic crystal planes.

[0064] In some alternative embodiments, the grain boundary region comprises a second nickel- and strontium-containing oxide. Thus, primary grains can be firmly bonded together via the second nickel- and strontium-containing oxide, thereby further suppressing cracking between primary grains during charge-discharge cycles and improving the cycle performance of the electrochemical device.

[0065] In some alternative embodiments, the second nickel and strontium-containing oxide has space group P321.

[0066] In some optional embodiments, the molar ratio of Sr to Ni in the second nickel- and strontium-containing oxide ranges from 0.8 to 3. Exemplarily, the molar ratio of Sr to Ni in the second nickel- and strontium-containing oxide is 0.8, 1, 1.25, 1.5, 1.75, 2, 2.25, 2.5, 2.75, 3, or a range consisting of any two of the above values.

[0067] In some alternative embodiments, the second nickel and strontium-containing oxide has (112) and / or (300) characteristic crystal planes.

[0068] In some optional embodiments, the layered lithium-nickel composite oxide includes Li, Ni and M elements, wherein the M element includes at least one of Co, Mn, Al, Mg, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb or Bi.

[0069] In some optional embodiments, the first primary grain includes a first surface region within 50 nm of the grain boundary region. Based on the total molar amount of Ni and M elements in the first surface region, the molar percentage of Sr element c1Sr in the first surface region satisfies: 0.1% ≤ c1Sr ≤ 2%. Exemplarily, c1Sr is 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 1%, 1.4%, 1.8%, 2%, or a range of any two of the above values. Further, in some optional embodiments, 0.2% ≤ c1Sr ≤ 0.5%.

[0070] In some optional embodiments, the second primary grain includes a second surface region within 50 nm of the grain boundary region. Based on the total molar amount of Ni and M elements in the second surface region, the molar percentage of Sr element c₂Sr in the second surface region satisfies: 0.1% ≤ c₂Sr ≤ 2%. Exemplarily, c₂Sr is 0.1%, 0.2%, 0.3%, 0.5%, 0.7%, 1%, 1.4%, 1.8%, 2%, or a range of any two of the above values. Further, in some optional embodiments, 0.2% ≤ c₂Sr ≤ 0.5%.

[0071] When the molar percentage of Sr in the primary grain surface region is within the above range, the structural stability of the primary grain surface region during charge-discharge cycles can be further improved, the volumetric strain and structural stress of the primary grains during charge-discharge cycles can be alleviated, thereby further suppressing cracking between primary grains and oxygen release phase transition on the material surface, and improving the cycle performance and high-temperature safety of the electrochemical device.

[0072] In some optional embodiments, the first primary grain includes a first core region at a distance of more than 200 nm from the surface of the first primary grain. Based on the total molar amount of Ni and M elements in the first core region, the molar percentage content of Sr element d1Sr in the first core region satisfies: c1Sr / d1Sr≥10. For example, c2Sr / d2Sr is 10, 20, 30, 40, 50, 60, 70, 80, or a range consisting of any two of the above values. Further, in some optional embodiments, 10≤c1Sr / d1Sr≤80.

[0073] In some optional embodiments, the second primary grain includes a second core region at a distance of more than 200 nm from the surface of the second primary grain. Based on the total molar amount of Ni and M elements in the second core region, the molar percentage of Sr element d2Sr in the second core region satisfies: c2Sr / d2Sr ≥ 10. For example, c2Sr / d2Sr is 10, 20, 30, 40, 50, 60, 70, 80, or a range consisting of any two of the above values. Further, in some optional embodiments, 10 ≤ c2Sr / d2Sr ≤ 80.

[0074] The surface region of the primary grain is rich in Sr compared to the core region, which can improve the stability of the surface region of the primary grain while reducing the impact on the capacity of the cathode material.

[0075] In some optional embodiments, the molar amount of Ni in the layered lithium-nickel composite oxide is nNi and the molar amount of M is nM, satisfying: 0.6≤nNi / (nNi+nM)≤1, 0≤nM / (nNi+nM)≤0.4.

[0076] In some optional embodiments, the layered lithium-nickel composite oxide further contains Na, satisfying: 0.001 ≤ nNa / (nNi+nM) ≤ 0.01. By doping the layered lithium-nickel composite oxide with Na, the lattice structure of the primary grains during charge-discharge cycles can be further stabilized, alleviating the volumetric strain and structural stress of the primary grains during charge-discharge processes. This further suppresses cracking between primary grains and oxygen release phase transitions on the material surface, improving the cycle performance and high-temperature safety of the electrochemical device.

[0077] In some optional embodiments, the molar percentage of Sr in the cathode material is 0.1% to 5%, based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0078] In some optional embodiments, the molar percentage of Li in the cathode material is 90% to 105%, based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0079] In some optional embodiments, the molar percentage of Ni in the cathode material is greater than or equal to 60%, based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0080] In some optional embodiments, the molar percentage of element M in the cathode material is less than or equal to 40%, based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0081] In some optional embodiments, the cathode material further includes Na, and the molar percentage of Na in the cathode material is 0.1% to 10% based on the sum of the molar amounts of Ni and M elements in the cathode material.

[0082] In some alternative embodiments, the layered lithium-nickel composite oxide has a layered crystal structure belonging to the R-3m space group.

[0083] In some optional embodiments, the X-ray diffraction spectrum of the cathode material shows characteristic peaks for 2θ in the ranges of 28.5° to 30.5° and 31.5° to 34.0°, respectively. These peaks correspond to Sr5Ni4O. 11 Characteristic peaks of the (112) and (300) crystal planes.

[0084] In some alternative embodiments, the X-ray photoelectron spectroscopy spectrum of the cathode material shows a Sr 3d characteristic peak in the range of 125 eV to 140 eV.

[0085] In some optional embodiments, the cathode material is assembled with lithium metal into a coin cell. When the coin cell is charged to 4.5V, the X-ray diffraction spectrum of the cathode material shows only one (003) characteristic peak at 2θ in the range of 17.0° to 21.0°. Thus, the cathode material exhibits only the H3 phase at high voltage, which can alleviate structural distortion and stress caused by phase inhomogeneity within the cathode material particles, thereby suppressing the formation of primary intergranular cracks and improving the cycle performance of the electrochemical device. Simultaneously, the cathode material can also possess superior kinetic performance.

[0086] In some optional embodiments, the cathode material is assembled with lithium metal into a coin cell. When the coin cell is charged to 4.1V and 4.5V respectively, the difference between the 2θ value of the (003) characteristic peak at 4.5V and the 2θ value of the (003) characteristic peak at 4.1V in the X-ray diffraction spectrum of the cathode material is less than or equal to 0.75°. The cathode material corresponds to the H2-H3 phase transition between 4.1V and 4.5V. The smaller the shift of the 2θ value of the (003) characteristic peak during this phase transition, the smaller the volumetric stress it suffers. Therefore, the difference between the 2θ values ​​of the (003) characteristic peak at 4.5V and 4.1V of the cathode material of this application is less than or equal to 0.75°, which is beneficial to a more stable crystal structure. This can suppress the stress and strain caused by random orientation during the H2-H3 phase transition, alleviate the formation of primary intergranular cracks, and thus improve the cycle performance of the electrochemical device.

[0087] For example, the difference between the above 2θ values ​​is 0.75°, 0.7°, 0.65°, 0.6°, 0.55°, 0.5°, 0.45°, 0.4°, 0.35°, 0.3°, 0.25°, or a range consisting of any two of the above values. Further, in some optional embodiments, the difference between the above 2θ values ​​is less than or equal to 0.4°.

[0088] In some optional embodiments, the cathode material is assembled with lithium metal to form a coin cell. When the coin cell is charged and discharged at a current of 0.1C within a voltage range of 2.7V to 4.5V, the obtained discharge capacity-voltage differential dQ / dV curve exhibits a first reduction peak in the 4.1V to 4.5V range; the peak intensity of the first reduction peak is less than or equal to 840 mAh / g / V. Thus, the irreversible capacity loss of the cathode material during charging is significantly suppressed, and the structural stability is significantly improved, thereby improving the cycle performance of the electrochemical device.

[0089] For example, the peak intensity of the first reduction peak is 840 mAh / g / V, 800 mAh / g / V, 700 mAh / g / V, 600 mAh / g / V, 550 mAh / g / V, 500 mAh / g / V, 450 mAh / g / V, 400 mAh / g / V, or a range of any two of the above values. Further, in some optional embodiments, the peak intensity of the first reduction peak is less than or equal to 700 mAh / g / V.

[0090] The second aspect of this application provides a method for preparing the above-mentioned cathode material, comprising the following steps: S1: according to a preset element molar ratio, a nickel-containing precursor, a lithium source, a strontium source, an optional sodium source, and an optional element M source are placed in a mixed solvent prepared by mixing alcohol and water and stirred, and the solvent is evaporated at a first temperature to obtain a first product; S2: the first product is heated to a second temperature under a first atmosphere for a pre-calcination treatment for a first duration, and then heated to a third temperature for a calcination treatment for a second duration, and after calcination is completed, it is cooled to room temperature to obtain the cathode material.

[0091] In some optional embodiments, in step S1, the stirring rate is 50-500 rpm / min.

[0092] In some alternative embodiments, in step S1, the first temperature is 50°C to 150°C.

[0093] In some optional embodiments, in step S2, the second temperature is 500°C to 600°C, and the first duration is 3h to 7h.

[0094] In some optional embodiments, in step S2, the third temperature is 700°C to 850°C, and the second duration is 10h to 20h.

[0095] In some alternative embodiments, in step S2, the first atmosphere is any one of an air atmosphere, a pure oxygen atmosphere, or a mixture of air and oxygen.

[0096] In some optional embodiments, in step S1, the volume percentage of alcohol in the mixed solution is 0.1 to 0.9.

[0097] In some optional embodiments, in step S1, the nickel-containing precursor includes at least one hydroxide or carbonate of Ni element and optionally M' element, wherein M' element includes at least one of Co, Mn or Al.

[0098] In some optional embodiments, in step S1, the lithium source includes at least one of lithium hydroxide, lithium nitrate, lithium acetate, or lithium carbonate.

[0099] In some optional embodiments, in step S1, the strontium source includes at least one of strontium nitrate, strontium acetate, strontium oxide, strontium hydroxide, and strontium carbonate.

[0100] In some optional embodiments, in step S1, the element source M includes at least one of an oxide, hydroxide, nitrate, or carbonate of element M.

[0101] In some optional embodiments, in step S2, the cooling rate is from 3°C / min to 10°C / min.

[0102] In some optional embodiments, in step S1, the total molar amount of Ni and M' elements is used as the base number a, and the molar ratio of Sr element to a is 0.005 to 0.05:1.

[0103] In some optional embodiments, in step S1, the total molar amount of Ni and M' elements is used as the base number a, and the molar ratio of Na to a is 0.001 to 0.01:1.

[0104] A third aspect of this application provides an electrochemical device including a positive electrode. The positive electrode includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer includes the positive electrode material provided in any embodiment of the first aspect of this application, or includes the positive electrode material prepared by the positive electrode material preparation method provided in any embodiment of the second aspect of this application.

[0105] This application does not impose any particular limitation on the positive electrode current collector, as long as it achieves the purpose of this application. For example, the positive electrode current collector may include a metal foil, such as aluminum foil. The positive electrode active material layer of this application may also include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the positive electrode conductive agent and the positive electrode binder, as long as it achieves the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, carbon materials, metals, etc. Carbon materials may include at least one of conductive carbon black, carbon nanotubes, carbon fibers, or graphene. Metals may include metal powder or metal fibers. The positive electrode binder may include, but is not limited to, at least one of polyacrylic acid, polyacrylate, acrylate polymers, polyimide, polyvinyl alcohol, carboxymethyl cellulose or its salts, or polyvinylidene fluoride.

[0106] In this application, the electrochemical device may further include a negative electrode. This application does not impose any particular limitation on the negative electrode, as long as it achieves the purpose of this application. For example, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. This application does not impose any particular limitation on the negative electrode current collector, as long as it achieves the purpose of this application. For example, the negative electrode current collector may comprise a metal foil, such as copper foil. In this application, the negative electrode active material layer includes a negative electrode active material. This application does not impose any particular limitation on the type of negative electrode active material; any negative electrode active material known in the art can be used, as long as it achieves the purpose of this application. For example, the negative electrode active material may comprise at least one of natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon materials, silicon-oxygen materials, Li alloys, or metallic lithium. The negative electrode active material layer of this application may also include a negative electrode binder. This application does not impose any particular limitation on the negative electrode binder, as long as it achieves the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber, polyacrylic acid, polyacrylate, acrylate polymers, carboxymethyl cellulose or its salts, polyimide, or polyvinyl alcohol. The negative electrode active material layer of this application may also contain a negative electrode conductive agent. This application does not particularly limit the type of negative electrode conductive agent, as long as it can achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, carbon materials, metals, etc. Carbon materials may include at least one of conductive carbon black, carbon nanotubes, carbon fibers, or graphene. Metals may include metal powder or metal fibers.

[0107] In this application, the electrochemical device may further include a separator membrane located between the positive and negative electrodes. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the separator membrane may include a porous membrane. The resin forming the porous membrane may include, but is not limited to, at least one of polyolefins, polyamides, polyacrylates, or polyimides.

[0108] In this application, the electrochemical device may further include an electrolyte, which includes lithium salts and non-aqueous solvents. This application does not particularly limit the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may include, but is not limited to, LiPF6. This application does not particularly limit the content of lithium salt in the electrolyte, as long as it achieves the purpose of this application. This application does not particularly limit the non-aqueous solvent, as long as it achieves the purpose of this application. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds or carboxylic acid ester compounds. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds or cyclic carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate, propylene carbonate, or butylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate.

[0109] A fourth aspect of this application provides an electrical device, including the electrochemical device of the third aspect of this application. The electrical device of this application is not particularly limited and can be any electrical device known in the prior art. In some embodiments, the electrical device may include, but is not limited to, mobile phones, laptops, drones, electric vehicles, etc.

[0110] [Specific Implementation Examples]

[0111] The following specific embodiments and comparative examples illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0112] I. Preparation of cathode materials in each embodiment and comparative example:

[0113]

Example 1

[0114] The cathode material preparation steps in Example 1 include:

[0115] S1: Prepare a mixed aqueous solution containing NiSO4 and MnSO4 according to the elemental molar ratio Ni∶Mn=95∶5. Mix it with a precipitant (NaOH aqueous solution) and a complexing agent (ammonia water) and react them. Control the reaction time to be 50 hours, the ammonia water concentration to be 1 mol / L and the pH of the reaction system to be 12.5 to obtain a precursor TM(OH)2 (TM=Ni+Mn) with an average particle size Dv50 of 10 μm.

[0116] S2: Based on the elemental molar ratio Li / Sr / TM = 1.05:0.003:1, the precursor TM(OH)2, strontium nitrate and lithium hydroxide from S1 were weighed as raw materials and placed in a mixed solvent of alcohol and water with a volume ratio of 5:5 to obtain a mixed solution. The mass ratio of the mixed solvent to the raw materials was 10:1. The mixed solution was then stirred at 500 rpm / min and the solvent was evaporated at 80°C to obtain the first product.

[0117] S3: The first product in S2 is placed in a pure oxygen atmosphere and pre-calcined at 550°C for 5 hours at a rate of 3°C / min, and then calcined at 750°C for 15 hours. Finally, it is cooled to room temperature at a rate of 3°C / min to obtain the cathode material.

[0118]

Example 2

[0119] The difference between the cathode material preparation steps in Example 2 and Example 1 is that in step S2, the precursor TM(OH)2, strontium nitrate, and lithium hydroxide from S1 are weighed according to the elemental molar ratio Li / Sr / TM = 1.05:0.005:1. The remaining steps and parameters are the same as in Example 1.

[0120]

Example 3

[0121] The difference between the cathode material preparation steps in Example 3 and Example 1 is that in step S2, the precursor TM(OH)2, strontium nitrate, and lithium hydroxide from S1 are weighed according to the elemental molar ratio Li / Sr / TM = 1.05:0.01:1. The remaining steps and parameters are the same as in Example 1.

[0122]

Example 4

[0123] The difference between the cathode material preparation steps in Example 4 and Example 1 is that in step S2, the precursor TM(OH)2, strontium nitrate, and lithium hydroxide from S1 are weighed according to the elemental molar ratio Li / Sr / TM = 1.05:0.03:1. The remaining steps and parameters are the same as in Example 1.

[0124]

Example 5

[0125] The difference between the cathode material preparation steps in Example 5 and Example 1 is that in step S2, the precursor TM(OH)2, strontium nitrate, and lithium hydroxide from S1 are weighed according to the elemental molar ratio Li / Sr / TM = 1.05:0.05:1. The remaining steps and parameters are the same as in Example 1.

[0126]

Example 6

[0127] The difference between the cathode material preparation steps in Example 6 and Example 3 is that the calcination temperature in step S3 is 700°C.

[0128]

Example 7

[0129] The difference between the cathode material preparation steps in Example 7 and Example 3 is that the calcination temperature in step S3 is 800°C.

[0130]

Example 8

[0131] The difference between the cathode material preparation steps in Example 8 and Example 3 is that the calcination time in step S3 is 10 hours.

[0132]

Example 9

[0133] The difference between the cathode material preparation steps in Example 9 and Example 3 is that the calcination time in step S3 is 20 hours.

[0134]

Example 10

[0135] The difference between the cathode material preparation steps in Example 10 and those in Example 3 is as follows:

[0136] In step S2, the precursor TM(OH)2, sodium hydroxide, strontium nitrate, and lithium hydroxide from S1 are weighed as raw materials according to the elemental molar ratio Li / Na / Sr / TM = 1.05:0.001:0.003:1. The remaining steps and parameters are the same as in Example 3.

[0137]

Example 11

[0138] The difference between the cathode material preparation steps in Example 11 and those in Example 3 is as follows:

[0139] In step S2, the precursor TM(OH)2, sodium hydroxide, strontium nitrate, and lithium hydroxide from S1 are weighed as raw materials according to the elemental molar ratio Li / Na / Sr / TM = 1.05:0.003:0.003:1. The remaining steps and parameters are the same as in Example 3.

[0140]

Example 12

[0141] The difference between the cathode material preparation steps in Example 12 and those in Example 3 is as follows:

[0142] In step S2, the precursor TM(OH)2, sodium hydroxide, strontium nitrate, and lithium hydroxide from S1 are weighed as raw materials according to the elemental molar ratio Li / Na / Sr / TM = 1.05:0.005:0.003:1. The remaining steps and parameters are the same as in Example 3.

[0143]

Example 13

[0144] The difference between the cathode material preparation steps in Example 13 and those in Example 3 is as follows:

[0145] In step S2, the precursor TM(OH)2, sodium hydroxide, strontium nitrate, and lithium hydroxide from S1 are weighed as raw materials according to the elemental molar ratio Li / Na / Sr / TM = 1.05:0.007:0.003:1. The remaining steps and parameters are the same as in Example 3.

[0146]

Example 14

[0147] The difference between the cathode material preparation steps in Example 14 and those in Example 3 is as follows:

[0148] In step S2, the precursor TM(OH)2, sodium hydroxide, strontium nitrate, and lithium hydroxide from S1 are weighed as raw materials according to the elemental molar ratio Li / Na / Sr / TM = 1.05:0.01:0.003:1. The remaining steps and parameters are the same as in Example 3.

[0149] Comparative Example 1

[0150] The difference between the cathode material preparation steps in Comparative Example 1 and Example 1 is that:

[0151] The raw materials in step S2 contain only TM(OH)2 and lithium hydroxide, and no strontium nitrate is added.

[0152] Comparative Example 2

[0153] The cathode material preparation steps in Comparative Example 2 include:

[0154] S1': Weigh the positive electrode material from Comparative Example 1 and strontium nitrate according to the element molar ratio Sr / TM = 0.01:1 and place them in a mixed solvent of alcohol and water with a volume ratio of 5:5 to obtain a mixed solution, wherein the mass ratio of the mixed solvent to the raw material is 10:1; then stir at 500 rpm / min and evaporate the solvent at 80°C to obtain the first product;

[0155] S2': The first product in S1' is placed in a pure oxygen atmosphere and calcined at 750°C for 15 hours at a rate of 3°C / min; finally, it is cooled to room temperature at a rate of 3°C / min to obtain the cathode material.

[0156] II. Preparation method of button cell battery

[0157] (1) A positive electrode slurry is prepared by mixing the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) in a weight ratio of 90:5:5 with N-methylpyrrolidone (NMP) until homogeneous.

[0158] (2) The mixed positive electrode slurry is uniformly coated onto aluminum foil to a thickness of 40 μm, with single-sided coating; after drying, it is rolled to form the desired electrode, wherein the electrode surface density is 14 mg / cm². 2The positive electrode is obtained by drying and then punched into a circular sheet with a diameter of 14 mm.

[0159] (3) The porous polyethylene separator is punched into a circular piece with a diameter of 18 mm; the negative electrode used is a lithium metal sheet with a diameter of 18 mm; LiPF6 is added to a solvent made of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1 and mixed evenly to obtain an electrolyte, wherein the mass concentration of LiPF6 is 12.5%; the positive electrode, separator, negative electrode (lithium sheet), electrolyte, battery case and other accessories are moved into a glove box (the water content should be less than 11 ppm).

[0160] (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.

[0161] III. Preparation Methods of Lithium-ion Batteries

[0162] 3.1 Preparation of the positive electrode

[0163] (1) A positive electrode slurry was prepared by mixing the positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) in a weight ratio of 96:2:2 with N-methylpyrrolidone (NMP) and mixing them evenly.

[0164] (2) The mixed 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 electrode sheet. Then, the electrode tabs are rolled, cut, and welded to obtain the desired positive electrode.

[0165] 3.2 Preparation of the negative electrode

[0166] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed with deionized water in a mass ratio of 96:2:2 and stirred until homogeneous to obtain a negative electrode slurry. This negative electrode slurry was coated onto one side of a copper foil, and after drying, the above steps were repeated on the other side of the copper foil to obtain a double-sided coated electrode. Subsequently, the electrode was rolled, cut, and had tabs welded to obtain the desired negative electrode.

[0167] 3.3 Preparation of Lithium-ion Batteries

[0168] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to obtain a bare cell. The bare cell is placed in an outer aluminum-plastic film packaging, electrolyte is injected, and it is sealed. After processes such as formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0169] IV. Testing Methods

[0170] 4.1 Thickness Expansion Rate Test

[0171] The lithium-ion battery was charged at 25°C with a constant current rate of 1C to 4.35V, and then charged at 4.35V with a constant voltage until the current reached 0.05C, thus achieving a fully charged state. The fully charged lithium-ion battery was then stored at 85°C for 12 hours, and the thickness change of the lithium-ion battery was measured using 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 calculated according to the following formula I.

[0172] Thickness expansion rate = (H1-H0) / H0×100% Formula I.

[0173] 4.2 25℃ Cyclic Capacity Retention Test

[0174] The lithium-ion battery was placed in a 25°C constant temperature chamber and charged at a constant current rate of 1C 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 1C to 3.0V. This constitutes one charge-discharge cycle. The lithium-ion battery was subjected to the above charge-discharge cycle 200 times. The discharge capacity of the lithium-ion battery in the first cycle and the discharge capacity in the 200th cycle were recorded. The cycle capacity retention rate = discharge capacity in the 200th cycle / discharge capacity in the first cycle × 100%.

[0175] 4.3 Button cell charge / discharge cycle test

[0176] At 25°C, the button cell was charged and discharged at a current of 0.1C within a voltage range of 2.7V to 4.5V to obtain the voltage-capacity curve and the capacity-voltage differential dQ / dV curve.

[0177] 4.4 X-ray diffraction test

[0178] The cathode material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with Cu Kα as the target material; the voltage and current were 40 kV / 40 mA, and the scanning angle range was 10° to 80°.

[0179] 4.5 Scanning Electron Microscopy (SEM) Characterization

[0180] The cathode material sample was tested under a scanning electron microscope, and photographs of the cathode material were taken at magnification.

[0181] 4.6 Transmission Electron Microscopy (TEM) Characterization

[0182] The cathode material was observed using transmission electron microscopy, and the lattice fringes of the grains and surface coatings in the tested cathode material were examined. The molar ratio of Sr to Ni in the first nickel- and strontium-containing oxide was determined using energy dispersive spectroscopy.

[0183] 4.7 Electron Probe Microscopy (EPMA) Characterization

[0184] The electrode containing the positive electrode material is cut with a polyion beam to obtain a flat cross-section that exposes the internal structure of the positive electrode material. Select any cross-section of the positive electrode material particle and use an electron probe microanalyzer (EPMA, JXA-8230) to test the content of elements such as Ni, Mn, Sr, and Na in the first surface region within 50 nm of the grain boundary in the first primary grain, the second surface region within 50 nm of the grain boundary in the second primary grain, the first core region more than 200 nm away from the surface of the first primary grain, the second core region more than 200 nm away from the surface of the second primary grain, and the second nickel and strontium-containing oxide.

[0185] V. Characterization and Test Result Analysis

[0186] 5.1 Characterization Results

[0187] Table 1 is a summary table of various parameters and characterization parameters of the cathode material preparation process in each embodiment and comparative example.

[0188] Figure 1 shows the X-ray diffraction patterns of Comparative Example 1 and Example 3. As can be seen from Figure 1, the cathode materials of Comparative Example 1 and Example 3 both have a layered structure, corresponding to space group R-3m. Notably, some new characteristic peaks appeared after Sr modification, corresponding to Sr5Ni4O. 11 Phase, proving that Sr5Ni4O was formed. 11 The interface phase belongs to space group P321 and has (112) and (300) characteristic crystal planes.

[0189] Figure 2 shows a scanning electron microscope (SEM) image of the cathode material prepared in Comparative Example 1. Figure 3 shows a SEM image of the cathode material prepared in Example 3. As can be seen from Figures 2 and 3, the morphology of the cathode materials prepared in Comparative Example 1 and Example 3 are both secondary micron-sized particles formed by the close packing and assembly of primary nanocrystals. Furthermore, comparing Figures 2 and 3 reveals that the primary grain morphology of the cathode material in Example 3 has changed, with a significantly larger grain size, indicating that the addition of Sr modification can promote primary grain growth.

[0190] Figure 4 is a transmission electron microscope image of the cathode material prepared in Example 3. Figure 4 shows that the first surface of the first primary grain includes a first region 1 connected to the grain boundary region, and the second surface of the second primary grain includes a second region 2 connected to the grain boundary region. The first region 1, the second region 2, and the grain boundary region form an angle. Sr5Ni4O 11 The first connection region connected to the first region 1 is specifically Sr5Ni4O 11The lattice fringe region near the first region 1 is marked by two dashed lines. Sr5Ni4O 11 The second connection region connected to the second region 2 is specifically Sr5Ni4O 11 The lattice fringe region near the second region 2 is marked by two dashed lines.

[0191] As can be seen from Figure 4, Sr5Ni4O was formed at the intergranular angle of the primary grains in the cathode material of Example 3. 11 The interface phase tightly connects adjacent primary grains, which can effectively suppress intergranular cracks and electrolyte corrosion on the surface of primary grains during cycling, improve the mechanical stability and interface stability of the cathode material, and thus enhance cycle stability and high-temperature storage performance.

[0192] Figure 5 shows the Sr and Ni element distribution of the cathode material prepared in Example 3. As can be seen from Figure 5, the Sr element in the cathode material of Example 3 is enriched in the primary grain boundary region and on the surface, proving the formation of the nickel and strontium oxide interface phase.

[0193] Figures 6 and 7 show the X-ray diffraction patterns of the (003) diffraction peaks of the cathode materials prepared in Comparative Example 1 and Example 3 in their initial state, and after the prepared coin cells were charged to 4.1V and 4.5V, respectively. As can be seen from Figure 6, the (003) diffraction peak of the cathode material in Comparative Example 1 at 4.5V is shifted to a higher angle by 0.97° compared to that at 4.1V. As can be seen from Figure 7, the (003) diffraction peak of the cathode material in Example 3 at 4.5V is shifted to a higher angle by 0.39° compared to that at 4.1V. This proves that Sr modification can suppress the lattice c-axis contraction under high voltage, thereby improving the structural stability and cycle stability of the cathode material. Furthermore, the cathode material of Comparative Example 1 splits into two peaks at (003) diffraction peak when charged to 4.5V, while the cathode material of Example 3 still has only one peak, proving that the cathode material of this application modified with Sr can suppress H2 / H3 phase separation under high voltage, and thus has better structural stability and kinetic performance.

[0194] Figure 8 shows the charge-discharge curves of the coin cells of Comparative Example 1 and Example 3. As can be seen from Figure 8, the coulombic efficiency of the coin cell of Example 3 is increased compared to Comparative Example 1, demonstrating that the Sr-modified cathode material of this application can suppress irreversible capacity loss.

[0195] Figure 9 shows the discharge capacity-voltage differential dQ / dV curves of the coin cells of Comparative Example 1 and Example 3. As can be seen from Figure 9, the intensity of the first reduction peak in the 4.1V to 4.5V range of the capacity-voltage differential dQ / dV curve of the coin cell of Example 3 is significantly reduced compared to that of the coin cell of Comparative Example 1 in the same range. This further demonstrates that the Sr-modified cathode material of this application can suppress the H2-H3 phase transition and lattice c-axis contraction under high voltage, thereby improving the structural stability and cycle stability of the cathode material.

[0196] Figure 10 shows the specific capacity curves of lithium-ion batteries prepared with the cathode materials obtained in Comparative Example 1 and Example 3 after 200 cycles at a current density of 1C. As can be seen from Figure 10, the capacity retention rate of the lithium-ion battery in Example 3 after 200 cycles is significantly higher than that in Comparative Example 1, proving that the Sr-modified cathode material of this application can improve cycle stability.

[0197] Coin cells and lithium-ion batteries were prepared using the cathode materials of Comparative Examples 1-2 and Examples 1-14. Charge-discharge cycle tests were performed on the coin cells, and thickness expansion rate and 25°C cycle capacity retention rate tests were performed on the lithium-ion batteries. Table 2 shows the first reduction peak intensity, first discharge specific capacity, and coulombic efficiency of the coin cells of Comparative Examples 1-2 and Examples 1-14, as well as the test results of high-temperature storage thickness expansion rate and 25°C cycle capacity retention rate of the lithium-ion batteries of Comparative Examples 1-2 and Examples 1-14.

[0198] Table 2

[0199] As shown in Table 2, the embodiments of this application introduce nickel and strontium-containing oxides at the angle formed by adjacent primary grains and grain boundaries of the cathode material, which significantly improves the first coulombic efficiency and weakens the intensity of the first reduction peak of the prepared coin cell. This indicates that the irreversible capacity loss of the cathode material modified by strontium during the charging process is significantly suppressed and the structural stability is significantly improved.

[0200] As shown in Table 2, when the cathode materials of Examples 1-14 satisfy the following conditions: 0.1% ≤ c1Sr ≤ 2%, 10 ≤ c1Sr / d1Sr ≤ 80, the design of the Sr element gradient distribution improves the stability of the surface interface structure and reduces the interfacial reaction activity between surface oxygen and electrolyte. Therefore, the lithium-ion batteries of Examples 1-14 have improved high-temperature storage gas generation and excellent cycle performance. Compared with Comparative Example 2, the cathode material in this application embodiment is sintered after coating the precursor with a strontium source, which is beneficial to promote the epitaxial growth of Sr and Ni elements in the precursor on the surface of the primary grains to form a eutectic nickel and strontium oxide on the surface of the primary grains. In contrast, the cathode material in Comparative Example 2 is sintered after coating the surface of the cathode material with a strontium source that has already formed primary grains, which can only form a non-eutectic strontium oxide coating. Therefore, its effect on suppressing intergranular cracks and stabilizing the surface of the cathode material during cycling is far less than that of the cathode material in this application embodiment.

[0201] A comparison of Examples 10-14 with Example 3 shows that by further introducing Na element doping into the cathode material, the high-temperature storage gas generation and cycle performance of lithium-ion batteries can be further improved.

[0202] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A cathode material comprising secondary particles formed by the agglomeration of multiple primary grains, wherein the primary grains comprise layered lithium-nickel composite oxide, and the secondary particles comprise adjacent first and second primary grains, wherein a grain boundary region exists between the first and second primary grains, wherein a first surface of the first primary grain comprises a first region connected to the grain boundary region, and a second surface of the second primary grain comprises a second region connected to the grain boundary region. The secondary particles also include a first nickel- and strontium-containing oxide located at the angle formed by the first region, the second region and the grain boundary region, and connecting the first region and the second region.

2. The cathode material according to claim 1, wherein the first nickel- and strontium-containing oxide comprises a first connection region connected to the first region and a second connection region connected to the second region; the first nickel-containing transition metal layer in the first connection region has a first orientation, and the second nickel-containing transition metal layer in the second connection region has a second orientation, satisfying at least one of the following conditions: (1) The third nickel-containing transition metal layer in the first primary grain has a third orientation, and the angle α between the first orientation and the third orientation is ≤10°; (2) The fourth nickel-containing transition metal layer in the second primary grain has a fourth orientation, and the angle β between the second orientation and the fourth orientation is ≤10°; (3) The first connection region is connected to the second connection region, and the angle γ between the first orientation and the second orientation is ≤10°.

3. The cathode material according to claim 1, wherein at least one of the following conditions is met: (1) The molar ratio of Sr to Ni in the first nickel and strontium-containing oxide ranges from 0.8 to 3; (2) The first nickel and strontium-containing oxide has space group P321; (3) The first nickel and strontium-containing oxide has (112) and / or (300) characteristic crystal planes.

4. The cathode material according to claim 1, wherein the grain boundary region comprises a second nickel- and strontium-containing oxide, and the second nickel- and strontium-containing oxide satisfies at least one of the following conditions: (1) The second nickel and strontium-containing oxide has space group P321; (2) The molar ratio of Sr to Ni in the second nickel and strontium oxide ranges from 0.8 to 3; (3) The second nickel and strontium oxide has (112) and / or (300) characteristic crystal planes.

5. The cathode material according to claim 1, wherein the layered lithium-nickel composite oxide comprises Ni and M elements, wherein the M element comprises at least one of Co, Mn, Al, Mg, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, or Bi; the molar amount of Ni in the layered lithium-nickel composite oxide is nNi, and the molar amount of M is nM, satisfying at least one of the following conditions: (1) The first primary grain includes a first surface region within 50 nm of the grain boundary region. Based on the total molar amount of Ni and M elements in the first surface region, the molar percentage of Sr elements in the first surface region, c1Sr, satisfies: 0.1% ≤ c1Sr ≤ 2%. (2) The second primary grain includes a second surface region within 50 nm of the grain boundary region. Based on the total molar amount of Ni and M elements in the second surface region, the molar percentage of Sr elements in the second surface region, c2Sr, satisfies: 0.1% ≤ c2Sr ≤ 2%. (3) The layered lithium-nickel composite oxide also contains Na element, and the molar amount of Na element in the layered lithium-nickel composite oxide is nNa, which satisfies: 0.001≤nNa / (nNi+nM)≤0.01; (4)0.6≤nNi / (nNi+nM)≤1, 0≤nM / (nNi+nM)≤0.

4.

6. The cathode material according to claim 5, wherein at least one of the following conditions is met: (1) The first primary grain includes a first core region at a distance of more than 200 nm from the surface of the first primary grain. Based on the total molar amount of Ni and M elements in the first core region, the molar percentage of Sr elements d1Sr in the first core region satisfies: c1Sr / d1Sr≥10. (2) The second primary grain includes a second core region at a distance of more than 200 nm from the surface of the second primary grain. Based on the total molar amount of Ni and M elements in the second core region, the molar percentage of Sr elements d2Sr in the second core region satisfies: c2Sr / d2Sr≥10.

7. The cathode material according to any one of claims 1 to 6, wherein the cathode material comprises Li, Ni, and M, and the M element comprises at least one of Co, Mn, Al, Mg, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Hf, Ta, W, Pb, or Bi, and satisfies at least one of the following conditions: (1) Based on the sum of the molar amounts of Ni and M elements in the cathode material, the molar percentage of Sr element in the cathode material is 0.1% to 5%; (2) Based on the sum of the molar amounts of Ni and M elements in the cathode material, the molar percentage of Li element in the cathode material is 90% to 105%. (3) Based on the sum of the molar amounts of Ni and M elements in the cathode material, the molar percentage of Ni in the cathode material is greater than or equal to 60%. (4) Based on the sum of the molar amounts of Ni and M elements in the cathode material, the molar percentage of M element in the cathode material is less than or equal to 40%. (5) The cathode material also includes Na element, and the molar percentage of Na element in the cathode material is 0.1% to 10% based on the sum of the molar amounts of Ni and M elements in the cathode material; (6) The layered lithium-nickel composite oxide has a layered crystal structure belonging to the R-3m space group; (7) In the X-ray diffraction spectrum of the cathode material, 2θ has characteristic peaks in the ranges of 28.5° to 30.5° and 31.5° to 34.0°; (8) In the X-ray photoelectron spectrum of the cathode material, there is a Sr 3d characteristic peak in the range of 125eV to 140eV.

8. The cathode material according to any one of claims 1 to 6, satisfying at least one of the following conditions: (1) The positive electrode material is assembled with lithium metal into a button cell. When the button cell is charged to 4.5V, the X-ray diffraction spectrum of the positive electrode material shows that 2θ has only one (003) characteristic peak in the range of 17.0° to 21.0°. (2) The positive electrode material is assembled with lithium metal into a button cell. When the button cell is charged to 4.1V and 4.5V respectively, the difference between the 2θ value of the characteristic peak of (003) at 4.5V and the 2θ value of the characteristic peak of (003) at 4.1V is less than or equal to 0.75° in the X-ray diffraction spectrum of the positive electrode material. (3) The positive electrode material is assembled with lithium metal to form a button cell. When the button cell is charged and discharged at a current of 0.1C in the voltage range of 2.7V to 4.5V, the obtained discharge capacity voltage differential dQ / dV curve has a first reduction peak in the range of 4.1V to 4.5V. The peak intensity of the first reduction peak is less than or equal to 840mAh / g / V.

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

10. An electrical device comprising the electrochemical device of claim 9.

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