Positive electrode material, electrochemical apparatus, and electronic device

Abstract

The present application provides a positive electrode material, an electrochemical apparatus, and an electronic device. The positive electrode material comprises a lithium transition metal composite oxide, the lithium transition metal composite oxide comprises an element T, and the element T comprises an Ni element, wherein the valence VNi1 of the Ni element on the grain surface of the positive electrode material, the valence VNi2 of the Ni element at a depth of 50±2 nm from the grain surface, and the valence VNi3 of the Ni element at a depth of 100±2 nm from the grain surface satisfy: 2≤VNi1<VNi2<VNi3≤2.52. The positive electrode material has good cycling stability and higher capacity.

Description

Cathode materials, electrochemical devices and electronic equipment Technical Field

[0001] This application relates to the field of battery technology, and more specifically, to a cathode material, an electrochemical device, and an electronic device. Background Technology

[0002] With the widespread adoption of consumer electronics such as laptops, mobile phones, tablets, power banks, and drones, and the continuous growth of the electric vehicle market, there is a huge demand for advanced lithium-ion batteries (LIBs) with high power and high energy density, leading to increasingly stringent requirements for their electrochemical devices. In pursuit of higher energy density, lithium-ion batteries have been continuously developing towards increasing voltage and thus increasing the amount of lithium removed. However, at high voltages and high lithium removal rates, the cycle stability of the cathode material is poor. Therefore, it is necessary to improve the cycle stability of the cathode material. Summary of the Invention

[0003] This application provides a cathode material, an electrochemical device, and an electronic device, designed to improve the cycle stability of the cathode material.

[0004] In a first aspect, a cathode material is provided, the cathode material comprising a lithium transition metal composite oxide, the lithium transition metal composite oxide comprising element T, the element T comprising element Ni, wherein the valence V of the Ni element on the grain surface of the cathode material is V. Ni1 The valence V of Ni at a depth of 50±2nm from the grain surface Ni2 The valence V of Ni element at a depth of 100±2nm from the grain surface Ni3 Satisfy: 2≤V Ni1 <V Ni2 <V Ni3 ≤2.52. Based on this application, the oxidation state of Ni in the cathode material is related to the grain depth. The oxidation state of Ni on the grain surface is low, while that inside the grain is high, showing a gradient change. The oxidation state of Ni on the grain surface is closer to +2, which can reduce the side reactions between the cathode material and the electrolyte. At the same time, the oxidation state of Ni inside the grain is closer to +3, which can reduce the mixing of lithium and nickel in the layered structure and improve the capacity of the cathode material. Therefore, the cathode material has good cycle stability and higher capacity.

[0005] In some embodiments, element T further includes element Mn, wherein the valence V of the Mn element on the grain surface of the cathode material is... Mn1 The valence V of Mn element at a depth of 50±2nm from the grain surface Mn2 The valence V of Mn element at a depth of 100±2nm from the grain surface Mn3 Satisfy: 3.8 ≥ VMn1 >V Mn2 >V Mn3 ≥3.2.

[0006] In some of the above embodiments, the Mn element in the cathode material can improve the cycle stability of the cathode material. In addition, the oxidation state of Mn does not exceed 3.8. This is because the cathode material introduces oxygen defects, allowing Mn to participate in redox reactions and generate capacity simultaneously. At the same time, the oxidation state of Mn on the grain surface is higher, while that inside the grain is lower, showing a gradient distribution. The oxidation state of surface Mn is closer to +4, which can improve the oxygen resistance of the grain surface and further reduce the side reactions of the electrolyte. Moreover, the oxidation state of internal Mn is lower, which can generate higher capacity. Therefore, the cycle stability of the cathode material is better.

[0007] In some embodiments, element T further includes element Mn, wherein the average valence V of Ni and Mn elements on the grain surface of the cathode material is... Ni+Mn1 The average oxidation state V of Ni and Mn elements at a depth of 50±2 nm from the grain surface Ni+Mn2 The average valence V of Ni and Mn elements at a depth of 100±2 nm from the grain surface Ni+Mn3 Satisfies: 2.995 ≥ V Ni+Mn1 >V Ni+Mn2 >V Ni+Mn3 ≥2.74.

[0008] In some of the above embodiments, the oxidation states of Ni and Mn elements in the cathode material are below +3. This is because the cathode material introduces oxygen defects, which reduces the average oxidation state of both elements. This can activate the redox properties of the transition metals, thereby simultaneously generating capacity, increasing the additional charge and discharge voltage platform, and improving the capacity of the cathode material. At the same time, the average oxidation state of both elements shows a gradient distribution from large to small from the surface to the interior. The average oxidation state on the surface is closer to +3, which can further improve the cycle stability of the cathode material.

[0009] In some embodiments, the voltage-capacity differential curve of the button cell made of the positive electrode material relative to the lithium sheet, when charged and discharged at a rate of 0.04C in the voltage range of 2.8V to 4.5V, shows a first oxidation peak and a first reduction peak in the range of 3.6V to 4.0V, and a second oxidation peak and a second reduction peak in the range of 4.2V to 4.5V.

[0010] In some of the above embodiments, the cathode material has two redox peaks in the voltage ranges of 3.6V to 4.0V and 4.2V to 4.5V, respectively. This is because the cathode material introduces oxygen defects, which can increase the reversible charge and discharge capacity, thereby giving the cathode material a higher capacity.

[0011] In some embodiments, the peak height of the second oxidation peak is from 587 mAh / g / V to 3698 mAh / g / V. This indicates that the cathode material has a high capacity in the voltage range of 4.2V to 4.5V, resulting in a higher energy density.

[0012] 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|≤0.214V. This indicates that the cathode material exhibits low polarization and good reversibility during charging and discharging in the voltage range of 3.6V to 4.0V, demonstrating good cycle stability.

[0013] In some embodiments, the peak voltage of the second oxidation peak is Vo2, and the peak voltage of the second reduction peak is Vr2, satisfying |Vo2-Vr2|≤0.247V. This indicates that the cathode material exhibits low polarization and good reversibility during charging and discharging in the voltage range of 4.2V to 4.5V, demonstrating good cycle stability.

[0014] The small difference in peak voltage between the two sets of redox peaks is due to the introduction of oxygen defects into the cathode material, which can improve the conductivity of lithium ions and electrons, enhance the kinetic performance of the cathode material, thereby reducing polarization and improving the cycle stability of the cathode material.

[0015] In some embodiments, the positive electrode material is used to charge and discharge a coin cell made of lithium foil at a rate of 0.04C within a voltage range of 2.8V to 4.5V to obtain a voltage-capacity curve. The discharge curve in the voltage-capacity curve exhibits a plateau in the 4.2V to 4.5V voltage range. The capacity of the discharge curve in the 4.2V to 4.5V voltage range is Q1, and the capacity in the 2.8V to 4.5V voltage range is Q. t The condition is satisfied that: 0.112 ≤ Q1 / Q t ≤0.269. Based on the above implementation method, the cathode material has a higher capacity ratio in the high voltage range of 4.2V to 4.5V, thus the cathode material has a higher energy density.

[0016] In some embodiments, the X-ray diffraction pattern of the cathode material exhibits diffraction peaks in the ranges of 16° to 20°, 34° to 38°, and 42° to 46°. This indicates that the cathode material has layered or spinel-type characteristics.

[0017] In some embodiments, the cell parameter 'a' of the cathode material satisfies: At this point, the structure of the cathode material exhibits good stability.

[0018] In some embodiments, the cell parameter c of the cathode material satisfies: At this point, the cathode material is more prone to lithium ion insertion / extraction, thus having a higher capacity.

[0019] In some implementations, 4 ≤ c / a ≤ 5. In this case, the cathode material exhibits good cycle stability and capacity.

[0020] In some embodiments, the lithium transition metal composite oxide includes element M, which includes at least one of Na, K, or Y. Doping the lithium layer with element M, which has a high ionic radius, can increase the lithium-oxygen interlayer spacing, thereby improving the kinetic performance of the cathode material.

[0021] In some embodiments, the mass percentage of Li element is greater than 5% based on the total mass of the lithium transition metal composite oxide.

[0022] In some implementations, the molar ratio of Li to T is 0.5 to 2.

[0023] In some embodiments, the molar percentage of Ni is 40% to 60% based on the total molar amount of element T. In some embodiments, the molar percentage of Mn is 40% to 60% based on the total molar amount of element T.

[0024] In some embodiments, element T further includes element Co, and the molar percentage of element Co is 10% to 30% based on the total molar amount of element T.

[0025] In some embodiments, the molar percentage of element M is 1% to 10% based on the total molar amount of element T; preferably 2% to 8%.

[0026] In some embodiments, the lithium transition metal composite oxide further includes element M', which includes at least one of Ca, Al, Ti, Zr or Sr; the molar percentage of element M' is 0.5% to 10% based on the total molar amount of element T; preferably, element M' is at least one of Ca and Zr.

[0027] In some embodiments, the lithium transition metal composite oxide further includes element M", which includes at least one of F and Cl; the molar percentage of element M" is 0.05% to 5% based on the total molar amount of element T; preferably F.

[0028] In a second aspect, this application provides an electrochemical device including a positive electrode and an electrolyte, wherein the positive electrode includes a positive electrode film layer, and the positive electrode film layer includes a positive electrode material according to any embodiment of the first aspect.

[0029] According to this application, the positive electrode film layer of the positive electrode in the electrochemical device includes the positive electrode material of the first aspect, thus the electrochemical device has good cycle performance and high energy density.

[0030] In some embodiments, the electrolyte includes a compound having at least two cyano groups. In this case, the compound with at least two cyano groups in the electrolyte, in conjunction with the aforementioned cathode material, can enable the electrochemical device to have better cycle performance.

[0031] Thirdly, this application provides an electronic device including an electrochemical device according to any embodiment of the second aspect. Attached Figure Description

[0032] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0033] Figure 1 shows the variation of Ni valence with grain depth in Comparative Example 1 and Example 12.

[0034] Figure 2 shows the variation of Mn element valence with grain depth in Comparative Example 1 and Example 12.

[0035] Figure 3 shows the variation of the average valence of Ni and Mn elements with grain depth in Comparative Example 1 and Example 12.

[0036] Figure 4 shows the capacity-voltage differential curves of the coin half-cells of Comparative Example 1 and Example 12.

[0037] Figure 5 shows the charge-discharge curves of the coin half-cells of Comparative Example 1 and Example 12.

[0038] Figure 6 illustrates the specific capacity Q1 of the coin half-cells of Comparative Example 1 and Example 12 at a plateau of 4.2V to 4.5V and a specific capacity Q1 at 2.8V to 4.5V. t The ratio of . Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the art to which this application pertains; the terminology used in the specification of this application is only for the purpose of describing specific embodiments and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or accompanying drawings of this application are used to distinguish different objects, not to describe a specific order or primary / secondary relationship.

[0040] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0041] In this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, in this application, the character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0042] It is generally believed that the capacity of ternary cathode materials is mainly generated by the valence changes of nickel and cobalt. Their charge / discharge capacity is related to the nickel content; the higher the nickel content, the higher the capacity. Mn, in its +4 valence state, primarily provides support for the layered structure of the ternary material and does not contribute capacity during charge / discharge, further limiting the material's energy density. Furthermore, the low electrochemical activity of manganese leads to poor material kinetics. Under deep delithiation, the high activity of oxygen ions on the material surface easily leads to side reactions with the electrolyte, resulting in increased interfacial impedance or gas generation. Finally, the low lithium-oxygen interlayer spacing in ternary materials typically hinders lithium-ion diffusion at the end of discharge, causing sluggish material kinetics and lower capacity.

[0043] This application introduces oxygen defects into the ternary material by controlling the synthesis and sintering process, altering the oxidation states of Ni and Mn in the bulk phase. This reduces the overall average oxidation state of Ni and Mn, activating the redox properties of the transition metals, increasing the charge-discharge voltage plateau, and significantly improving the material's energy density. Simultaneously, the reduced oxidation state of Mn in the bulk phase, contrary to conventional understanding, means that Mn no longer simply maintains a +4 oxidation state during charge-discharge; the change in Mn's oxidation state simultaneously generates capacity, significantly increasing the material's capacity. Furthermore, a valence gradient material is constructed through surface treatment, reducing the oxidation state of Ni and increasing the oxidation state of Mn on the grain surface. This enhances the material's oxidation resistance, reduces side reactions with the electrolyte, and avoids the impact of increased surface inactivity on capacity, achieving improved cycle performance without deteriorating capacity. At the same time, the oxygen vacancies formed on the surface reduce the activity of oxygen on the material surface, stabilizing the oxygen ions on the outer layer of the cathode material and preventing oxygen release and gas generation during high-temperature cycling.

[0044] cathode materials

[0045] In a first aspect, this application provides a cathode material comprising a lithium transition metal composite oxide, wherein the lithium transition metal composite oxide comprises element T, and element T includes element Ni, wherein the valence V of the Ni element on the grain surface of the cathode material is... Ni1 The valence V of Ni at a depth of 50±2nm from the grain surface Ni2 The valence V of Ni element at a depth of 100±2nm from the grain surface Ni3 Satisfy: 2≤V Ni1 <V Ni2 <V Ni3 ≤2.52.

[0046] Based on this application, the valence of Ni in the cathode material is related to the grain depth. The valence of Ni is low at the grain surface and high inside, exhibiting a gradient change. The valence of Ni at the grain surface is closer to +2, which can reduce side reactions between the cathode material and the electrolyte. At the same time, the valence of Ni inside the grain is closer to +3, which can reduce lithium-nickel mixing in the layered structure and improve the capacity of the cathode material. Therefore, this cathode material has good cycle stability and higher capacity. As an example, Figure 1 shows the valence of Ni at different grain depths in a cathode material of one embodiment. It can be seen that the valence of Ni increases with the increase of grain depth, and the valence is between 2 and 2.52. Figure 1 also shows the valence of Ni at different grain depths in a general cathode material, where the valence of Ni at different grain depths is 2.

[0047] For example, V Ni1 VNi2 V Ni3 It can be 2, 2.11, 2.2, 2.23, 2.27, 2.3, 2.31, 2.35, 2.37, 2.4, 2.44, 2.47, 2.51, 2.52, or any of the above values, and satisfies V Ni1 <V Ni2 <V Ni3 In some embodiments, element T further includes Mn, wherein the valence V of the Mn element on the grain surface of the cathode material is... Mn1 The valence V of Mn element at a depth of 50±2nm from the grain surface Mn2 The valence V of Mn element at a depth of 100±2nm from the grain surface Mn3 Satisfy: 3.8 ≥ V Mn1 >V Mn2 >V Mn3 ≥3.2. In some of the above embodiments, the Mn element in the cathode material can improve the cycle stability of the cathode material. In addition, the oxidation state of Mn does not exceed 3.8. This is because the cathode material introduces oxygen defects, allowing Mn to participate in redox reactions and generate capacity simultaneously. At the same time, the oxidation state of Mn on the grain surface is higher, while that inside the grain is lower, showing a gradient distribution. The oxidation state of Mn on the surface is closer to +4, which can improve the oxygen resistance of the grain surface and further reduce the side reactions of the electrolyte. Moreover, the lower oxidation state of Mn inside the grain can generate higher capacity, thus resulting in better cycle stability of the cathode material. As an example, Figure 2 shows the oxidation state of Mn at different depths of the cathode material in one embodiment. It can be seen that the oxidation state of Ni decreases with the increase of grain depth, and the oxidation state is between 3.2 and 3.8. Figure 2 also shows the oxidation state of Mn at different depths of the grains of a general cathode material, where the oxidation state of Mn at different grain depths is 4.

[0048] For example, V Mn1 V Mn2 V Mn3 It can be 3.2, 3.24, 3.27, 3.3, 3.36, 3.39, 3.42, 3.46, 3.5, 3.56, 3.59, 3.65, 3.69, 3.7, 3.74, 3.78, 3.8, or any of the above values, and satisfies V. Mn1 >V Mn2 >V Mn3 .

[0049] In some embodiments, the cathode material includes Mn, wherein the average valence V of Ni and Mn elements on the grain surface of the cathode material is... Ni+Mn1The average oxidation state V of Ni and Mn elements at a depth of 50±2 nm from the grain surface Ni+Mn2 The average valence V of Ni and Mn elements at a depth of 100±2 nm from the grain surface Ni+Mn3 Satisfies: 2.995 ≥ V Ni+Mn1 >V Ni+Mn2 >V Ni+Mn3 ≥2.74.

[0050] In some of the above embodiments, the oxidation states of Ni and Mn in the cathode material are below +3. This is because the introduction of oxygen defects into the cathode material lowers the average oxidation state of both elements, which can activate the redox properties of the transition metal, thereby simultaneously generating capacity, increasing the additional charge-discharge voltage platform, and improving the capacity of the cathode material. Simultaneously, the average oxidation state of both elements exhibits a gradient distribution from the surface to the interior, with the average oxidation state at the surface being closer to +3, further improving the cycle stability of the cathode material. The lower average oxidation state at the interior further enhances the capacity of the cathode material. As an example, Figure 3 shows the average oxidation states of Ni and Mn at different depths in the grains of a cathode material in one embodiment. It can be seen that the average oxidation states of Ni and Mn decrease with increasing grain depth, and the oxidation states are between 2.6 and 3. Figure 3 also shows the average oxidation states of Ni and Mn at different depths in a typical cathode material, where the oxidation state of Mn is 3 at all grain depths.

[0051] For example, V Ni+Mn1 V Ni+Mn2 V Ni+Mn3 It can be 2.74, 2.76, 2.78, 2.80, 2.83, 2.84, 2.86, 2.87, 2.89, 2.90, 2.91, 2.93, 2.94, 2.97, 2.99, 2.995, or any of the above values, and satisfies V Ni+Mn1 >V Ni+Mn2 >V Ni+Mn3 .

[0052] It should be noted that the Ni and Mn elements, as well as the average valence of Ni and Mn elements at various locations within the grains of the cathode material, were detected using the following method:

[0053] Ion beam etching was used to etch the material surface layer at different depths, followed by quantitative analysis of the elemental composition and valence state distribution of the material surface using X-ray photoelectron spectroscopy (XPS). The X-ray source used was aluminum K2. α Micro-focused monochromator with an energy range of 0–1400 eV and a vacuum level of 10. -9The energy resolution was 0.5 eV, and the analytical spectrum was recorded using a 180° dual-focusing hemispherical analyzer with a 128-channel detector. The Ni elemental oxidation state was determined using the XPSpeak41 peak-splitting software. 2+ Ni 3+ Ni 4+ The corresponding XPS energy dispersive spectral peaks were fitted for quantification, and the equivalent valence of Ni was calculated based on the molar ratio of each valence. The valence of Mn was determined using the XPSpeak41 peak-splitting software. 3+ Mn 4+ The corresponding XPS energy dispersive spectroscopy peaks were fitted for quantitative analysis, and the equivalent valence of Mn was converted based on the molar ratio of each valence element. The fitted valences of Ni and Mn were then used to calculate the average valence of (Ni+Mn) element based on the molar ratio of Ni and Mn elements in the material.

[0054] In some embodiments, the voltage-capacity differential curve of a button cell made of positive electrode material relative to lithium sheet, obtained by charging and discharging at a rate of 0.04C in the voltage range of 2.8V to 4.5V, shows a first oxidation peak and a first reduction peak in the range of 3.6V to 4.0V, and a second oxidation peak and a second reduction peak in the range of 4.2V to 4.5V.

[0055] In some of the above embodiments, the cathode material exhibits two redox peaks within the voltage ranges of 3.6V to 4.0V and 4.2V to 4.5V, respectively. This is because the cathode material introduces oxygen defects, which can increase the reversible charge-discharge capacity, thus giving the cathode material a higher capacity. As an example, Figure 4 shows the voltage-capacity differential curve of the cathode material in one embodiment. It can be seen that it has a first oxidation peak and a first reduction peak in the 3.6V to 4.0V range, and a second oxidation peak and a second reduction peak in the 4.2V to 4.5V range. Figure 4 also shows the voltage-capacity differential curve of a typical cathode material, which only has redox peaks in the 3.6V to 4.0V range.

[0056] In some embodiments, the peak height of the second oxidation peak is between 587 mAh / g / V and 3698 mAh / g / V. This indicates that the cathode material has a higher capacity in the voltage range of 4.2V to 4.5V, resulting in a higher energy density. For example, the peak height of the second oxidation peak can be 587 mAh / g / V, 823 mAh / g / V, 1057 mAh / g / V, 1201 mAh / g / V, 1633 mAh / g / V, 1916 mAh / g / V, 2099 mAh / g / V, 2484 mAh / g / V, 2802 mAh / g / V, 2966 mAh / g / V, 3405 mAh / g / V, 3616 mAh / g / V, 3698 mAh / g / V, or any range of the above values.

[0057] 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|≤0.214V. This indicates that the cathode material exhibits low polarization and good reversibility during charging and discharging in the voltage range of 3.6V to 4.0V, demonstrating good cycle stability. For example, |Vo1-Vr1| can be 0.01V, 0.02V, 0.03V, 0.07V, 0.09V, 0.11V, 0.13V, 0.16V, 0.17V, 0.20V, 0.22V, 0.214V, or any range of the above values.

[0058] In some embodiments, the peak voltage of the second oxidation peak is Vo2, and the peak voltage of the second reduction peak is Vr2, satisfying |Vo2-Vr2|≤0.247V. This indicates that the cathode material exhibits low polarization and good reversibility during charging and discharging in the voltage range of 4.2V to 4.5V, demonstrating good cycle stability. For example, |Vo2-Vr2| can be 0.01V, 0.02V, 0.03V, 0.07V, 0.09V, 0.11V, 0.13V, 0.16V, 0.17V, 0.20V, 0.22V, 0.247V, or any value within the range described above.

[0059] The small difference in peak voltage between the two sets of redox peaks is due to the introduction of oxygen defects into the cathode material, which can improve the conductivity of lithium ions and electrons, enhance the kinetic performance of the cathode material, thereby reducing polarization and improving the cycle stability of the cathode material.

[0060] In some embodiments, the button cell made of positive electrode material relative to lithium sheet is charged and discharged at a rate of 0.04C within a voltage range of 2.8V to 4.5V to obtain a voltage-capacity curve. The discharge curve in the voltage-capacity curve shows a plateau in the 4.2V to 4.5V voltage range. The capacity of the discharge curve in the 4.2V to 4.5V voltage range is Q1, and the capacity in the 2.8V to 4.5V voltage range is Q. t The condition is satisfied that: 0.112 ≤ Q1 / Q t ≤0.269. Based on the above implementation method, the cathode material has a higher capacity ratio in the high voltage range of 4.2V to 4.5V, thus exhibiting a higher energy density. For example, Q1 / Q t It can be 0.112, 0.13, 0.14, 0.16, 0.19, 0.24, 0.26, 0.269, or any of the above values.

[0061] As an example, Figure 5 shows the voltage-capacity curve of the cathode material in one embodiment. It can be seen that the discharge curve exhibits plateaus at 3.6V to 4.0V and 4.2V to 4.5V, respectively. Figure 5 also shows the voltage-capacity curve of a typical cathode material, where the discharge curve only exhibits plateaus in the 3.6V to 4.0V range. Figure 6 shows the capacity ratio of the cathode material in one embodiment of this application and a typical cathode material at the 4.2V to 4.5V high-voltage plateau. It can be seen that the capacity ratio of the cathode material in this embodiment at the 4.2V to 4.5V high-voltage plateau is significantly higher than that of the typical cathode material, thus exhibiting a higher energy density.

[0062] It should be noted that the voltage-capacity curve and voltage-capacity differential curve of the button battery prepared by the positive electrode material relative to the lithium sheet can be obtained by charging and discharging at a rate of 0.04C in the voltage range of 2.8V to 4.5V in the following ways: (1) Add a certain weight ratio (90∶5∶5) of positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (Super P) to N-methylpyrrolidone (NMP) to prepare a positive electrode slurry;

[0063] (2) Adjust the viscosity of the positive electrode slurry to 3000 mPa·s to 6000 mPa·s, and uniformly coat the mixed slurry onto aluminum foil with a coating thickness of 40 μm, coating one side only; after drying, roll press to form the required electrode. The humidity of the electrode processing and transportation environment is 45%. The areal density of the coated electrode is 14 mg / cm³. 2 After drying, a positive electrode sheet is obtained, and then a circular sheet with a diameter of 14 mm is punched out;

[0064] (3) Cut the separator into 18mm round pieces; the negative electrode used is a lithium metal sheet with a diameter of 18mm; add LiPF6 to a solvent made of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio 1:1:1) and mix evenly to obtain an electrolyte, wherein the mass concentration of LiPF6 is 12.5%; move the positive electrode, separator, negative electrode (lithium sheet), electrolyte, battery case and other accessories into a glove box (the water content must be less than 11ppm);

[0065] (4) Assemble the batteries in a stacking order from bottom to top and inject electrolyte. Then encapsulate them on a packaging machine to obtain button cells.

[0066] (5) At 25°C, the button cell was charged and discharged at a current of 0.04C within the voltage range of 2.8V to 4.5V to obtain the voltage-capacity curve and the voltage-capacity differential dQ / dV curve.

[0067] In some embodiments, the X-ray diffraction pattern of the cathode material exhibits diffraction peaks in the ranges of 16° to 20°, 34° to 38°, and 42° to 46°. This indicates that the cathode material has layered or spinel-type characteristics.

[0068] In some implementations, the cell parameter 'a' of the cathode material satisfies: At this point, the structure of the cathode material exhibits good stability.

[0069] In some implementations, the cell parameter c of the cathode material satisfies: At this point, the cathode material is more prone to lithium ion insertion / extraction, thus having a higher capacity.

[0070] In some implementations, 4 ≤ c / a ≤ 5. In this case, the cathode material exhibits good cycle stability and capacity.

[0071] It should be noted that the X-ray diffraction pattern, unit cell parameters a and c of the cathode material can be obtained in the following way: The cathode material is tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), with Cu Kα as the target material; the voltage and current are 40KV / 40mA, and the scanning angle range is 10° to 70°. The X-ray diffraction pattern of the cathode material is obtained, and the values ​​of unit cell parameters a and c can be calculated.

[0072] In some embodiments, the lithium transition metal composite oxide includes element M, which includes at least one of Na, K, or Y. Doping the lithium layer with element M, which has a high ionic radius, can increase the lithium-oxygen interlayer spacing, thereby improving the kinetic performance of the cathode material.

[0073] In some embodiments, based on the total mass of the lithium transition metal composite oxide, the mass percentage of Li element is greater than 5%.

[0074] In some embodiments, the molar ratio of Li element to element T is 0.5 to 2.

[0075] In some embodiments, based on the total molar amount of element T, the molar percentage of Ni element is 40% to 60%.

[0076] In some embodiments, based on the total molar amount of element T, the molar percentage of Mn element is 40% to 60%.

[0077] In some embodiments, based on the total molar amount of element T, the molar percentage of Co element is 10% to 30%.

[0078] In some embodiments, based on the total molar amount of element T, the molar percentage of element M is 1% to 10%; preferably 2% to 8%.

[0079] In some embodiments, the lithium transition metal composite oxide further comprises element M', wherein element M' comprises at least one of Ca, Al, Ti, Zr or Sr; based on the total molar amount of element T, the molar percentage of element M' is 0.5% to 10%; preferably, element M' is at least one of Ca and Zr.

[0080] In some embodiments, the lithium transition metal composite oxide further comprises element M'', wherein element M'' comprises at least one of F and Cl; based on the total molar amount of element T, the molar percentage of element M'' is 0.5% to 5%; preferably F. In some embodiments, the positive electrode material satisfies the general formula Li x M y (Ni a Co b Mn c M' d )O e M'' f , 0 < x + y ≤ 2, 0 ≤ a, b, c, d ≤ 1, and a, b, c, d are not 0 at the same time, 0 < e ≤ 3, 0 ≤ f < 1, M is at least one of Na, K and Y, M' is at least one of Ca, Al, Ti, Zr or Sr, and M'' is at least one of F and Cl.

[0081] In some embodiments, the preparation method of the cathode material includes the following steps: 1) under a first atmosphere, calcining the precursor with a lithium source, an element M source, an optional element M' source, and an optional element M” source at a first temperature for a first time; 2) cooling to a second temperature and maintaining it under a second atmosphere for a second time; 3) finally cooling to room temperature. The first atmosphere is selected from air, oxygen, or a mixture of air and oxygen; the precursor contains element T, which includes at least one of Ni, Co, or Mn; the element M includes at least one of Na, K, or Y; the element M' includes at least one of Ca, Al, Ti, Zr, or Sr; the element M” includes at least one of F and Cl; the second atmosphere is selected from at least one of an inert atmosphere or a mixture of inert gas and reducing gas. This application introduces oxygen defects into the cathode material by introducing an inert gas or a mixture of inert gas and reducing gas during the cooling process after calcination and maintaining the temperature for a period of time, thereby changing the valence of the transition metal in the cathode material and obtaining a cathode material with a gradient distribution of transition metal valence. The reducing gas may include ammonia and / or hydrogen.

[0082] In some embodiments, the first temperature is 700°C to 1200°C; the first time is 10h to 48h. In some embodiments, the first temperature can be 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, or any range of the above values. In some embodiments, the first time can be 10h, 12h, 16h, 14h, 18h, 24h, 36h, 48h, or any range of the above values.

[0083] In some embodiments, the second temperature is 350°C to 600°C; the second time is 4 hours to 24 hours. In some embodiments, the second temperature can be 350°C, 400°C, 450°C, 500°C, 550°C, 600°C, or any range of the above values. In some embodiments, the second time can be 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 16 hours, 18 hours, 24 hours, or any range of the above values.

[0084] In some embodiments, the inert gas is selected from at least one of N2, Ar, or He.

[0085] In some embodiments, the cooling rate in step 3) is greater than or equal to 50°C / min.

[0086] In some embodiments, based on the total volume of the inert gas and H2 mixture, the volume percentage of H2 in the mixture is less than or equal to 10%. In some embodiments, based on the total volume of the inert gas and H2 mixture, the volume percentage of H2 in the mixture can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range of any of the above values, such as 1% to 3%, 5% to 10%, etc.

[0087] In some embodiments, the precursor comprises a hydroxide of element T.

[0088] In some embodiments, the lithium source includes at least one of lithium carbonate or lithium hydroxide.

[0089] In some embodiments, the source of element M includes at least one of the carbonates or hydroxides of element M.

[0090] In some embodiments, the source of element M' includes an oxide of element M'.

[0091] In some embodiments, the source of element M” includes at least one of an ammonium salt or a lithium salt of element M”.

[0092] In some embodiments, the molar percentage of Ni is 40% to 60% based on the total molar amount of element T.

[0093] In some embodiments, the molar percentage of Mn is 40% to 60% based on the total molar amount of element T.

[0094] In some embodiments, the molar percentage of Co is 10% to 30% based on the total molar amount of element T.

[0095] In some embodiments, the molar percentage of element M is 1% to 10% based on the total molar amount of element T.

[0096] In some embodiments, the molar percentage of element M' is 0.5% to 10% based on the total molar amount of element T.

[0097] In some embodiments, the molar percentage of element M” is 0.5% to 20% based on the total molar amount of element T. A preferred range is 0.5% to 5%.

[0098] Electrochemical device

[0099] In a second aspect, this application provides an electrochemical device including a positive electrode and an electrolyte, wherein the positive electrode includes a positive electrode film layer, and the positive electrode film layer includes a positive electrode material according to any embodiment of the first aspect.

[0100] According to this application, the positive electrode film layer of the positive electrode in the electrochemical device includes the positive electrode material of the first aspect, thus the electrochemical device has good cycle performance and high energy density.

[0101] Typically, electrochemical devices also include a negative electrode and a separator.

[0102]

Positive Electrode

[0103] In some embodiments, the positive electrode film layer further includes an adhesive. The adhesive improves the bonding between the positive electrode material particles and also improves the bonding between the positive electrode material and the positive electrode current collector.

[0104] 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), but is not limited thereto; the adhesive may be selected according to actual needs.

[0105] In some embodiments, the weight percentage of the binder is less than or equal to 5.0% based on the total weight of the positive electrode film. In some embodiments, the weight percentage of the binder is 5.0%, 4.0%, 3.0%, 2.0%, 1.5%, 1.0%, 0.5%, 0.3%, 0.1%, or any of the above values, based on the total weight of the positive electrode film.

[0106] In some embodiments, the positive electrode film layer further includes a conductive agent, which includes at least one of graphite, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers, but is not limited thereto. The conductive agent can be selected according to actual needs.

[0107] In some embodiments, the weight percentage of the conductive agent is greater than or equal to 0.5% based on the total weight of the positive electrode film. In some embodiments, the weight percentage of the conductive agent is greater than or equal to 1.0% or greater than or equal to 1.5% based on the total weight of the positive electrode film.

[0108] In some embodiments, the positive current collector may be a metal foil or a porous metal plate, such as a foil or porous plate of metals or alloys thereof, such as aluminum foil, copper, nickel, titanium or silver, but not limited thereto.

[0109] In some embodiments, the thickness of the positive current collector is from 5 μm to 20 μm, for example, 5 μm, 6 μm, 7 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm or any of the above values.

[0110] In some embodiments, the positive electrode sheet can be prepared by methods known in the art. For example, the positive electrode sheet can be obtained by mixing a positive electrode material, a conductive agent, and a binder in a solvent to prepare a positive electrode slurry, coating the positive electrode slurry onto a positive electrode current collector, and obtaining the positive electrode sheet through processes such as drying and cold pressing. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone (NMP).

[0111] [Negative electrode plate]

[0112] In some embodiments, the negative electrode sheet may be a lithium metal sheet, or it may include a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector. In some embodiments, the negative electrode film layer includes a negative electrode material, and optionally includes a conductive agent and a binder.

[0113] In some embodiments, the negative electrode material may include one or more of natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Li-Al alloy, and metallic lithium.

[0114] In some embodiments, the conductive agent may include one or more of acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0115] In some embodiments, the adhesive may be one or more of styrene-butadiene rubber, polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, waterborne acrylic resin, or carboxymethyl cellulose.

[0116] The negative electrode in the electrochemical device of this application is not limited to the above materials. Other materials that can be used as negative electrode materials, conductive agents, binders and thickeners in lithium-ion batteries may also be used.

[0117] The negative electrode current collector can be made of materials such as metal foil or porous metal plate, for example, using metals or alloys of them such as copper, nickel, titanium or iron, or porous plates such as copper foil.

[0118] The negative electrode sheet can be prepared according to conventional methods in the art. Typically, the negative electrode material and optional conductive agent and binder are dispersed in a solvent, such as N-methylpyrrolidone or water, to form a uniform negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing.

[0119]

Isolation Film

[0120] The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0121] In some embodiments, the material of the separator can be selected from one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these. Optionally, the material of the separator may include polyethylene and / or polypropylene. The separator can be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating may also be provided on the separator.

[0122] Electrolyte

[0123] The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The electrolyte used in the electrochemical device of this application can be any electrolyte known in the prior art.

[0124] In some embodiments, the electrolyte may include an organic solvent, an electrolyte salt, and optional additives. The types of organic solvents, lithium salts, and additives are not specifically limited and can be selected as needed.

[0125] In some embodiments, the electrochemical device is a lithium-ion battery, and the electrolyte salt may include a lithium salt. As examples, the lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium dicoxalate borate), LiPO2F2 (lithium difluorophosphate), LiDODFP (lithium difluorodioxalate phosphate), and LiOTFP (lithium tetrafluorooxalate phosphate). One of the above lithium salts may be used alone, or two or more may be used simultaneously.

[0126] In some embodiments, as examples, the organic solvent includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). One of the above organic solvents may be used alone, or two or more may be used simultaneously. Optionally, two or more of the above organic solvents may be used simultaneously.

[0127] In some embodiments, the additive includes a compound having at least two cyano groups. In this case, the compound with at least two cyano groups in the electrolyte, in conjunction with the aforementioned cathode material, can enable the electrochemical device to have better cycle performance.

[0128] In some embodiments, the additive may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0129] As an example, the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0130] The electrolyte can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials; for example, the electrolyte salt and optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte; or, the electrolyte salt can be added to the organic solvent first, and then the optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte.

[0131] electronic devices

[0132] Thirdly, this application provides an electronic device including an electrochemical device according to any embodiment of the second aspect.

[0133] Since the electronic device includes the electrochemical device of any embodiment of the second aspect, it has the beneficial effects of the second aspect.

[0134] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0135] The following are embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0136] Comparative Example 1

[0137] The positive electrode material is manufactured as follows:

[0138] 1) Prepare a mixed solution containing NiSO4 and MnSO4 according to the elemental molar ratio Ni:Mn = 50:50. Mix this solution with a precipitant (NaOH solution) and a complexing agent (ammonia water) and react them. Control the reaction time to be 60 h, the ammonia water concentration to be 1 mol / L, and the pH to be 12.2 to obtain the ternary precursor Ni0. .5 Mn 0.5 (OH)2;

[0139] 2) Grind and mix the precursor and lithium carbonate in the above steps at a molar ratio of 1.02 until uniform, calcine at 800°C in air for 20 hours, cool to room temperature at a rate of 10°C / min, and finally crush and sieve to obtain the cathode material.

[0140] Comparative Example 2

[0141] The positive electrode material is manufactured as follows:

[0142] 1) Ternary precursor Ni 0.5 Mn 0.5(OH)2 is the same as in Comparative Example 1;

[0143] 2) Grind the precursor, lithium carbonate and sodium carbonate in the above steps according to the molar ratio of Li: element T (Ni / Co / Mn) of 1.02 and the doping concentration of Na (the molar percentage of Na to element T) of 0.1% until uniformly mixed. Calcinate at 800℃ in air for 20h, cool to room temperature at a rate of 10℃ / min, and finally crush and sieve to obtain the cathode material.

[0144] Examples 1-10:

[0145] The positive electrode material is manufactured as follows:

[0146] Ternary precursor Ni 0.5 Mn 0.5 (OH)2 is the same as in Comparative Example 1;

[0147] The precursor and lithium carbonate from the above steps were ground and mixed evenly at a molar ratio of 1.05. The mixture was calcined at 800°C in an air atmosphere for 20 hours. The temperature was then reduced to the surface treatment temperature in Table 1 at a rate of 10°C / min. During the annealing and holding process, a certain proportion of N2, NH3, and H2 mixed gas was introduced according to Table 1. After maintaining the surface treatment time as shown in Table 1 under these conditions, the mixture was quenched to room temperature in an oxygen atmosphere at the cooling rate shown in Table 1. Finally, the cathode material was obtained by crushing and sieving.

[0148] Examples 11 to 15:

[0149] The positive electrode material is manufactured as follows:

[0150] Ternary precursor Ni 0.5 Mn 0.5 (OH)2 is the same as in Comparative Example 1;

[0151] The precursor and lithium carbonate from the above steps were ground and mixed uniformly at a molar ratio of 1.05. The carbonate of element M was then mixed uniformly with the precursor and lithium carbonate according to the M doping concentration (molar percentage of M to element T) in Table 1. The mixture was calcined at 800℃ in air for 20 hours, then cooled to the surface treatment temperature in Table 1 at a rate of 10℃ / min. During the annealing and holding process, a mixture of N2, NH3, and H2 in a certain proportion was introduced according to Table 1. After maintaining the surface treatment time as shown in Table 1 under these conditions, the mixture was quenched to room temperature in an oxygen atmosphere at the cooling rate shown in Table 1. Finally, the cathode material was obtained by crushing and sieving.

[0152] Examples 16-17:

[0153] The positive electrode material is manufactured as follows:

[0154] Ternary precursor Ni 0.5 Mn 0.5(OH)2 is the same as in Comparative Example 1;

[0155] The precursor and lithium carbonate from the above steps were ground and mixed uniformly at a molar ratio of 1.05. Na element was added to the precursor and lithium carbonate at a doping concentration (molar percentage of Na to element T) of 5%, and ground and mixed uniformly. The ammonium salt of element M” was added to the precursor and lithium carbonate at the doping concentration (molar percentage of M” to element T) in Table 1, and ground and mixed uniformly. The mixture was calcined at 800℃ in air for 20 hours, then cooled to the surface treatment temperature in Table 1 at a rate of 10℃ / min. During the annealing and holding process, a certain proportion of N2, NH3, and H2 mixed gas was introduced according to Table 1. After maintaining the surface treatment time as shown in Table 1 under these conditions, the mixture was quenched to room temperature in an oxygen atmosphere at the cooling rate shown in Table 1. Finally, the cathode material was obtained by crushing and sieving.

[0156] Examples 18 to 22:

[0157] The positive electrode material is manufactured as follows:

[0158] Ternary precursor Ni 0.5 Mn 0.5 (OH)2 is the same as in Comparative Example 1;

[0159] The precursor and lithium carbonate from the above steps were ground and mixed uniformly at a molar ratio of 1.05. Na element was added to the precursor and lithium carbonate at a doping concentration (molar percentage of Na to element T) of 5%, and ground and mixed uniformly. The oxide of element M' was added to the precursor and lithium carbonate at a doping concentration (molar percentage of M' to element T) of 5% as shown in Table 1, and ground and mixed uniformly. The mixture was calcined at 800℃ in air for 20 hours, then cooled to the surface treatment temperature in Table 1 at a rate of 10℃ / min. During the annealing and holding process, a mixture of N2, NH3, and H2 in a certain proportion was introduced according to Table 1. After maintaining the surface treatment time as shown in Table 1 under these conditions, the mixture was quenched to room temperature in an oxygen atmosphere at the cooling rate shown in Table 1. Finally, the cathode material was obtained by crushing and sieving.

[0160] Methods for preparing pouch cells:

[0161] (1) A positive electrode slurry is prepared by adding a certain weight ratio (96∶2∶2) of positive electrode material, polyvinylidene fluoride (PVDF) and conductive carbon black (SuperP) to N-methylpyrrolidone (NMP);

[0162] (2) Adjust the viscosity of the positive electrode slurry to 3000 mPa·s to 6000 mPa·s, and uniformly coat the mixed slurry onto aluminum foil. The coating thickness on one side is 40 μm, and double-sided coating is also possible. After drying, roll-press the slurry to form the desired electrode. The humidity of the electrode processing and transportation environment is 45%. The surface density of the coated electrode is 14 mg / cm³.2 .

[0163] Preparation of negative electrode

[0164] Artificial graphite, styrene-butadiene rubber, and sodium carboxymethyl cellulose (CMC) were mixed with deionized water at a mass ratio of 96:2:2 and stirred until homogeneous to obtain a negative electrode slurry. This negative electrode slurry was then coated onto a 12 μm thick copper foil. After drying and cold pressing, the foil was cut and tabs were welded to obtain the negative electrode.

[0165] The electrolyte was prepared under a dry argon atmosphere by adding LiPF6 and succinate to a solvent composed of propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) in a weight ratio of 1:1:1, and mixing thoroughly to obtain the electrolyte. The mass concentration of LiPF6 was 12.5%, and the mass concentration of succinate was 1%.

[0166] Test section

[0167] 1. Thickness expansion rate test:

[0168] A lithium-ion battery was charged to 4.35V at 85℃ and stored for 24 hours. 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 as (H1-H0) / H0×100%.

[0169] 2. Cyclic capacity retention test:

[0170] The lithium-ion battery was placed in a 45°C constant temperature chamber and charged at a constant current rate of 1C to 4.35V. Then, it was charged at a constant voltage 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 1000 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 1000th cycle were recorded. The cycle capacity retention rate = discharge capacity in the 1000th cycle / discharge capacity in the first cycle × 100%.

[0171] Table 1

[0172] Continued from Table 1

[0173] Table 2 shows the Ni, Mn, average valence, plateau peak height, voltage plateau capacity ratio, plateau polarization |Vo-Vr|, cell parameters, pouch cell cycle retention rate, and expansion rate of the cathode materials obtained in the above embodiments and comparative examples at different grain depths.

[0174] Table 2

[0175] Continued from Table 2

[0176] Continued from Table 2

[0177] As shown in Table 2, the valence of Ni at different depths of the cathode materials prepared in each embodiment of this application exhibits a gradient distribution, with lower valence at the surface and higher valence inside. The valence of Ni at the surface is closer to +2, which can reduce side reactions between the cathode material and the electrolyte. Simultaneously, the valence of Ni inside the grains is closer to +3, which can reduce lithium-nickel mixing in the layered structure and improve the capacity of the cathode material. The valence of Mn does not exceed 3.8. This is because the cathode material introduces oxygen defects, allowing Mn to participate in redox reactions and simultaneously generate capacity. Furthermore, the valence of Mn is higher at the surface and lower inside the grains, exhibiting a gradient distribution. The oxidation state of Mn on the surface is closer to +4, which can improve the oxygen resistance of the grain surface and further reduce the side reactions of the electrolyte. Moreover, the oxidation state of Mn inside is lower, which can generate higher capacity. The oxidation states of Ni and Mn in the cathode material are below +3. This is because the cathode material introduces oxygen defects, which reduces the average oxidation state of both elements. This can activate the redox properties of the transition metals, thereby generating capacity simultaneously, increasing the additional charge and discharge voltage platform, and improving the capacity of the cathode material. At the same time, the average oxidation state of both elements shows a gradient distribution from the surface to the interior, with the average oxidation state on the surface being closer to +3, which can further improve the cycle stability of the cathode material.

[0178] The voltage-capacity differential curves of the cathode materials prepared in the various embodiments of this application show a second oxidation peak and a second reduction peak in the range of 4.2V to 4.5V, indicating that the cathode material has reversible charge-discharge capacity in the aforementioned high voltage range, and has a higher specific capacity compared to the comparative example; at the same time, the discharge curve satisfies Q1 / Q t The range of 0.13 to 0.5 indicates that the cathode material has a high capacity within the aforementioned high voltage range, thus resulting in a higher energy density. Furthermore, the pouch cell prepared using this cathode material exhibits a lower cycle expansion rate and a higher cycle capacity retention rate compared to the comparative example, indicating that the cathode material also possesses high cycle stability.

[0179] In each embodiment, the difference between the peak oxidation voltage and the peak reduction voltage of the cathode material in the two voltage ranges is no greater than 0.3V, indicating that the cathode material has good kinetic performance and low polarization during the charging and discharging process.

[0180] In each embodiment, the cell parameters a and c of the cathode material satisfy the following: 4≤c / a≤5 indicates that the cathode material has good cycle stability and capacity.

[0181] Figure 1 shows the valence of Ni at different depths of the cathode material in Example 12. It can be seen that the valence of Ni increases with the increase of grain depth, and the valence is between 2.2 and 2.7. Figure 1 also shows the valence of Ni at different depths of the cathode material in Comparative Example 1, where the valence of Ni at different grain depths is 2.

[0182] Figure 2 shows the valence of Mn at different depths of the cathode material in Example 12. It can be seen that the valence of Ni decreases with increasing grain depth, and the valence is between 3.2 and 3.8. Figure 2 also shows the valence of Mn at different depths of the cathode material in Comparative Example 1, where the valence of Mn at different grain depths is 4.

[0183] Figure 3 shows the average valence of Ni and Mn elements at different depths of the cathode material in Example 12. It can be seen that the average valence of Ni and Mn elements decreases with the increase of grain depth, and the valence is between 2.6 and 3. At the same time, Figure 3 also shows the average valence of Ni and Mn elements at different depths of the cathode material in Comparative Example 1. The valence of Mn at different grain depths is 3.

[0184] Figure 4 shows the voltage-capacity differential curve of the cathode material in Example 12. It can be seen that there are first oxidation peaks and first reduction peaks in the range of 3.6V to 4.0V, and second oxidation peaks and second reduction peaks in the range of 4.2V to 4.5V. Figure 4 also shows the voltage-capacity differential curve of the cathode material in Comparative Example 1, which has redox peaks only in the range of 3.6V to 4.0V.

[0185] Figure 5 shows the voltage-capacity curves of the cathode material in Example 12. It can be seen that the discharge curves exhibit plateaus at 3.6V to 4.0V and 4.2V to 4.5V, respectively. Figure 5 also shows the voltage-capacity curves of the cathode material in Comparative Example 1, where the discharge curves only exhibit plateaus in the 3.6V to 4.0V range. Figure 6 shows the capacity percentage of the cathode material in Example 12 and the cathode material in Comparative Example 1 at the 4.2V to 4.5V high-voltage plateau. It can be seen that the capacity percentage of the cathode material in Example 12 at the 4.2V to 4.5V high-voltage plateau is significantly higher than that of the cathode material in Comparative Example 1, thus exhibiting a higher energy density.

[0186] In particular, the aforementioned cathode material, in conjunction with the succinic acid material in the electrolyte, can synergistically improve the battery's cycle performance.

[0187] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0188] 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 them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A cathode material, said cathode material comprising a lithium transition metal composite oxide, said lithium transition metal composite oxide comprising element T, said element T comprising element Ni. in, The oxidation state V of Ni on the grain surface of the cathode material Ni1 The valence V of Ni at a depth of 50±2nm from the grain surface Ni2 The valence V of Ni element at a depth of 100±2nm from the grain surface Ni3 Satisfy: 2≤V Ni1 <V Ni2 <V Ni3 ≤2.

52.

2. The cathode material according to claim 1, wherein, The element T also includes the element Mn. The oxidation state V of the Mn element on the grain surface of the cathode material is... Mn1 The valence V of Mn element at a depth of 50±2nm from the grain surface Mn2 The valence V of Mn element at a depth of 100±2nm from the grain surface Mn3 Satisfy: 3.8 ≥ V Mn1 >V Mn2 >V Mn3 ≥3.

2.

3. The cathode material according to claim 1 or 2, wherein, The element T also includes the element Mn. The average valence V of Ni and Mn elements on the grain surface of the cathode material is described above. Ni+Mn1 The average oxidation state V of Ni and Mn elements at a depth of 50±2 nm from the grain surface Ni+Mn2 The average valence V of Ni and Mn elements at a depth of 100±2 nm from the grain surface Ni+Mn3 Satisfies: 2.995 ≥ V Ni+Mn1 >V Ni+Mn2 >V Ni+Mn3 ≥2.

74.

4. The cathode material according to any one of claims 1 to 3, wherein, The voltage-capacity differential curve of the button cell made of the positive electrode material relative to the lithium sheet, obtained by charging and discharging at a rate of 0.04C in the voltage range of 2.8V to 4.5V, shows a first oxidation peak and a first reduction peak in the range of 3.6V to 4.0V, and a second oxidation peak and a second reduction peak in the range of 4.2V to 4.5V.

5. The cathode material according to claim 4, wherein, The peak height of the second oxidation peak ranges from 587 mAh / g / V to 3698 mAh / g / V.

6. The cathode material according to claim 4 or 5, wherein, The peak voltage of the first oxidation peak is Vo1, and the peak voltage of the first reduction peak is Vr1. It satisfies: |Vo1-Vr1|≤0.214V.

7. The cathode material according to any one of claims 4 to 6, wherein, The peak voltage of the second oxidation peak is Vo2, and the peak voltage of the second reduction peak is Vr2. It satisfies: |Vo2-Vr2|≤0.247V.

8. The cathode material according to any one of claims 1 to 7, wherein, The button cell made of the positive electrode material relative to the lithium sheet was charged and discharged at a rate of 0.04C within a voltage range of 2.8V to 4.5V to obtain a voltage-capacity curve. The discharge curve in the voltage-capacity curve has a plateau in the voltage range of 4.2V to 4.5V. The discharge curve shows a capacity of Q1 in the 4.2V to 4.5V voltage range and a capacity of Q in the 2.8V to 4.5V voltage range. t The condition is satisfied that: 0.112 ≤ Q1 / Q t ≤0.

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9. The cathode material according to any one of claims 1 to 8, wherein, The X-ray diffraction pattern of the cathode material shows diffraction peaks in the ranges of 16° to 20°, 42° to 46°, and 34° to 38°.

10. The cathode material according to any one of claims 1 to 9, wherein, The cell parameters a and c of the cathode material satisfy at least one of the following conditions: (1) (2) (3) 4≤c / a≤5.

11. The cathode material according to any one of claims 1 to 10, wherein, The lithium transition metal composite oxide includes element M, which includes at least one of Na, K, or Y, and the lithium transition metal composite oxide satisfies at least one of the following conditions: (1) Based on the total mass of the lithium transition metal composite oxide, the mass percentage of Li element is greater than 5%; (2) The molar ratio of Li to T is 0.5 to 2; (3) Based on the total molar amount of element T, the molar percentage of Ni is 40% to 60%; (4) The element T also includes the element Mn, and based on the total molar amount of the element T, the molar percentage of the element Mn is 40% to 60%; (5) The element T also includes the element Co, and the molar percentage of the element Co is 10% to 30% based on the total molar amount of the element T. (6) Based on the total molar amount of element T, the molar percentage of element M is 1% to 10%; preferably 2% to 8%; (7) The lithium transition metal composite oxide further includes element M', which includes at least one of Ca, Al, Ti, Zr or Sr; the molar percentage of element M' is 0.5% to 10% based on the total molar amount of element T; preferably, element M' is at least one of Ca and Zr. (8) The lithium transition metal composite oxide further includes element M”, which includes at least one of F and Cl; based on the total molar amount of element T, the molar percentage of element M” is 0.05% to 10%; preferably F.

12. An electrochemical device comprising a positive electrode and an electrolyte, wherein the positive electrode comprises a positive electrode film layer comprising a positive electrode material according to any one of claims 1 to 11.

13. The electrochemical device according to claim 12, wherein, The electrolyte comprises a compound having not less than two cyano groups.

14. An electronic device comprising the electrochemical device according to claim 12 or 13.

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