Positive electrode sheet, secondary battery, electric device, positive electrode material, and preparation method

Abstract

The present disclosure provides a positive electrode sheet, a secondary battery, an electric device, a positive electrode material, and a preparation method. The positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer located on at least one surface of the positive electrode current collector; the positive electrode film layer comprises a positive electrode material; the positive electrode material at least comprises a sodium-containing layered oxide; the sodium-containing layered oxide comprises at least two phases; a first phase and a second phase form a phase interface; the first phase is an O3 phase layered oxide, and the second phase is a P2 phase layered oxide; and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide.

Description

Positive electrode sheet, secondary battery, electrical device, positive electrode material and its preparation method

[0001] Cross-references to related applications

[0002] This disclosure is based on and claims priority to Chinese Patent Application No. 202411026834.X, filed on July 29, 2024, entitled "Positive Electrode Sheet, Secondary Battery, Electrical Device, Positive Electrode Material and Preparation Method Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, and in particular to a positive electrode sheet, a secondary battery, an electrical device, a positive electrode material, and a method for preparing the same. Background Technology

[0004] In recent years, with the increasingly wide range of applications, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, and many other fields. Due to the significant development of secondary batteries, higher requirements have been placed on their capacity and cycle stability.

[0005] As a crucial component of secondary batteries, the performance of the positive electrode significantly impacts the overall performance of the battery. Currently, layered oxides with an O3 phase are commonly used as positive electrode materials. However, using layered oxides with an O3 phase as a positive electrode material cannot simultaneously achieve good cycle performance and high capacity. Summary of the Invention

[0006] This disclosure is made in view of the above-mentioned problems, and its object is to provide a positive electrode, a secondary battery, an electrical device, a positive electrode material, and a method for preparing the same. The secondary battery using this positive electrode can achieve both excellent cycle performance and high capacity.

[0007] To achieve the above objectives, a first aspect of this disclosure provides a positive electrode sheet, including a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode material, wherein the positive electrode material includes at least a sodium-containing layered oxide, the sodium-containing layered oxide including at least two phases, wherein a first phase and a second phase form a phase interface; the first phase is an O3 phase layered oxide, the second phase is a P2 phase layered oxide, and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide.

[0008] In this disclosure, the cathode material includes a P2-phase layered oxide and an O3-phase layered oxide. Since the P2-phase layered oxide possesses high structural stability, its introduction can improve the cycle performance of the cathode material. Furthermore, because the P2-phase and O3-phase layered oxides form a phase interface in the cathode material, the presence of this interface can alleviate stress accumulation caused by structural changes in the two phases during charge and discharge. In other words, the presence of the phase interface can disperse stress during charge and discharge, thereby suppressing structural degradation of the cathode material and improving its cycle stability during charge and discharge. Based on this, by setting the mass of the O3-phase layered oxide in the cathode material to be greater than the mass of the P2-phase layered oxide, the capacity of the cathode material can be improved, thus achieving a balance between excellent cycle performance and high capacity.

[0009] In some embodiments, the primary particles containing sodium-containing layered oxides include near-single-crystal particles, at least some of which comprise O3-phase layered oxides and P2-phase layered oxides. This facilitates the formation of a symbiotic structure of O3-phase and P2-phase layered oxides, thereby achieving a balance between cycle performance and capacity.

[0010] In some embodiments, the O3 phase layered oxide and the P2 phase layered oxide are in contact through the ab plane of the unit cell. This alleviates the structural stress caused by the slippage of the transition metal layer along the ab plane, suppresses the slippage of the transition metal layer, thereby suppressing phase transition and improving the stability of the cathode material.

[0011] In some embodiments, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(5-9). This is advantageous for balancing excellent cycle performance and high capacity.

[0012] In some embodiments, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(6-8). This is beneficial for further balancing excellent cycle performance and high capacity.

[0013] In some embodiments, the average grain size of the O3 phase layered oxide is smaller than that of the P2 phase layered oxide. This results in a better lattice matching between the P2 and O3 phase layered oxides, promoting the formation of the cathode material and thus improving its stability, which in turn enhances the cycle stability of the battery.

[0014] In some embodiments, during charging, the O3 phase layered oxide transforms into the P3 phase layered oxide at 3.0V to 3.2V, and at 4.0V to 4.2V, the P3 phase layered oxide transforms into the OP2 phase layered oxide. This reflects the high stability of the cathode material, which is beneficial to the cycle stability of the battery.

[0015] In some implementations, the voltage plateau of the positive electrode material during discharge is 3.05V to 3.35V. This reflects that the secondary battery has a high capacity.

[0016] In some implementations, the voltage plateau of the positive electrode material during discharge cycles of up to 100 cycles is 2.95V to 3.2V. This indicates that the secondary battery has a high capacity.

[0017] In some implementations, the voltage plateau of the positive electrode material during discharge cycles up to 500 times is 2.85V to 3.15V. This indicates that the secondary battery has a high capacity.

[0018] In some implementations, the voltage plateau of the cathode material during discharge cycles up to 1000 times is 2.75V to 3.05V. This indicates that the secondary battery has a high capacity.

[0019] In some embodiments, the XRD diffraction pattern of the cathode material includes a first diffraction peak with a 2θ between 15.9° and 16.3° and a second diffraction peak with a 2θ between 16.3° and 16.7°; the full width at half maximum (FWHW) of the first diffraction peak is... (002) The full width at half maximum (FWHW) of the second diffraction peak (003) Satisfies: 1.0 ≤ FWHW (003) / FWHW (002) ≤1.5. This makes the lattice matching of P2 phase layered oxide and O3 phase layered oxide on the ab plane more complete, promoting the formation of cathode material, thereby improving the stability of cathode material and thus improving the cycle stability of battery.

[0020] In some implementations, 1.05 ≤ FWHW (003) / FWHW (002) ≤1.4. This is more conducive to improving the cycle stability of the battery.

[0021] In some implementations, the peak intensity I of the first diffraction peak (002) Peak intensity I of the second diffraction peak (003) Satisfy: 0.1≤I (002) / [I (002) +I (003) ≤0.2. This is beneficial for increasing battery capacity.

[0022] In some implementations, the peak intensity I of the first diffraction peak (002) Peak intensity I of the second diffraction peak (003) Satisfy: 0.11≤I (002) / [I (002) +I (003)≤0.17. This is more conducive to increasing battery capacity.

[0023] In some embodiments, the cathode material includes nickel-iron-manganese sodium oxide.

[0024] In some embodiments, the cathode material includes Na. x [M a W b Y c O2, 0.8≤x<1.0, 0.9<a<1.0, 0<b<0.1, 0≤c<0.1, a+b+c=1.0; M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co; W includes one or more alkali metal elements or alkaline earth metal elements with radii larger than transition metal elements; Y includes any metal element other than M and W. Since the above cathode material includes element W with a radius larger than transition metal elements, a two-phase symbiotic cathode material can be obtained, which is beneficial to improving the stability of the cathode material and the cycle performance of the battery.

[0025] In some implementations, W includes Li and / or Mg.

[0026] In some implementations, M includes one or more of Ti, Ni, Fe, and Mn.

[0027] In some implementations, Y includes one or more of Ca, Al, and F.

[0028] In some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the cathode material is 1.1 to 1.3. This is beneficial for improving both battery capacity and cycle performance.

[0029] In some embodiments, the powder compaction density of the cathode material at 3t is 3.2 g / cc to 3.4 g / cc. This is beneficial for improving the volumetric energy density of the battery.

[0030] A second aspect of this disclosure provides a secondary battery including the positive electrode sheet of the first aspect described above.

[0031] A third aspect of this disclosure provides an electrical device including the secondary battery described in the second aspect.

[0032] A fourth aspect of this disclosure provides a cathode material comprising a sodium-containing layered oxide, the sodium-containing layered oxide comprising at least two phases, wherein a first phase and a second phase form a phase interface; the first phase is an O3 phase layered oxide, the second phase is a P2 phase layered oxide, and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide.

[0033] In this disclosure, the cathode material includes a P2-phase layered oxide and an O3-phase layered oxide. Since the P2-phase layered oxide possesses high structural stability, its introduction can improve the cycle performance of the cathode material. Furthermore, because the P2-phase and O3-phase layered oxides form a phase interface in the cathode material, the presence of this interface can alleviate stress accumulation caused by structural changes in the two phases during charge and discharge. In other words, the presence of the phase interface can disperse stress during charge and discharge, thereby suppressing structural degradation of the cathode material and improving its cycle stability during charge and discharge. Based on this, by setting the mass of the O3-phase layered oxide in the cathode material to be greater than the mass of the P2-phase layered oxide, the capacity of the cathode material can be improved, thus achieving a balance between excellent cycle performance and high capacity.

[0034] In some embodiments, the primary particles containing sodium-containing layered oxides include near-single-crystal particles, at least some of which comprise O3-phase layered oxides and P2-phase layered oxides. This facilitates the formation of a symbiotic structure of O3-phase and P2-phase layered oxides, thereby achieving a balance between cycle performance and capacity.

[0035] In some embodiments, the O3 phase layered oxide and the P2 phase layered oxide are in contact through the ab plane of the unit cell. This alleviates the structural stress caused by the slippage of the transition metal layer along the ab plane, suppresses the slippage of the transition metal layer, thereby suppressing phase transition and improving the stability of the cathode material.

[0036] In some embodiments, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(5-9). This is advantageous for balancing excellent cycle performance and high capacity.

[0037] In some embodiments, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(6-8). This is beneficial for further balancing excellent cycle performance and high capacity.

[0038] In some embodiments, the average grain size of the O3 phase layered oxide is smaller than that of the P2 phase layered oxide. This results in a better lattice matching between the P2 and O3 phase layered oxides, promoting the formation of the cathode material and thus improving its stability, which in turn enhances the cycle stability of the battery.

[0039] In some embodiments, during charging, the O3 phase layered oxide transforms into the P3 phase layered oxide at 3.0V to 3.2V, and at 4.0V to 4.2V, the P3 phase layered oxide transforms into the OP2 phase layered oxide. This reflects the high stability of the cathode material, which is beneficial to the cycle stability of the battery.

[0040] In some implementations, the voltage plateau of the positive electrode material during discharge is 3.05V to 3.35V. This indicates that the secondary battery has a high capacity.

[0041] In some implementations, the voltage plateau of the positive electrode material during discharge cycles of up to 100 cycles is 2.95V to 3.2V. This indicates that the secondary battery has a high capacity.

[0042] In some implementations, the voltage plateau of the positive electrode material during discharge cycles up to 500 times is 2.85V to 3.15V. This indicates that the secondary battery has a high capacity.

[0043] In some implementations, the voltage plateau of the cathode material during discharge cycles up to 1000 times is 2.75V to 3.05V. This indicates that the secondary battery has a high capacity.

[0044] In some embodiments, the XRD diffraction pattern of the cathode material includes a first diffraction peak with a 2θ between 15.9° and 16.3° and a second diffraction peak with a 2θ between 16.3° and 16.7°; the full width at half maximum (FWHW) of the first diffraction peak is... (002) The full width at half maximum (FWHW) of the second diffraction peak (003) Satisfies: 1.0 ≤ FWHW (003) / FWHW (002) ≤1.5. This makes the lattice matching of P2 phase layered oxide and O3 phase layered oxide on the ab plane more complete, promoting the formation of cathode material, thereby improving the stability of cathode material and thus improving the cycle stability of battery.

[0045] In some implementations, 1.05 ≤ FWHW (003) / FWHW (002) ≤1.4. This is more conducive to improving the cycle stability of the battery.

[0046] In some implementations, the peak intensity I of the first diffraction peak (002) Peak intensity I of the second diffraction peak (003) Satisfy: 0.1≤I (002) / [I (002) +I (003) ≤0.2. This is beneficial for increasing battery capacity.

[0047] In some implementations, the peak intensity I of the first diffraction peak (002) Peak intensity I of the second diffraction peak (003) Satisfy: 0.11≤I (002) / [I (002) +I (003)≤0.17. This is more conducive to increasing battery capacity.

[0048] In some embodiments, the cathode material includes nickel-iron-manganese sodium oxide.

[0049] In some embodiments, the cathode material includes Na. x [M a W b Y c O2, 0.8≤x<1.0, 0.9<a<1.0, 0<b<0.1, 0≤c<0.1, a+b+c=1.0; M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co; W includes one or more alkali metal elements with radii larger than transition metal elements; Y includes any metal element other than M and W or an alkaline earth metal element. Since the above cathode material includes element W with a radius larger than transition metal elements, a two-phase symbiotic cathode material can be obtained, which is beneficial to improving the stability of the cathode material and the cycle performance of the battery.

[0050] In some implementations, W includes Li and / or Mg.

[0051] In some implementations, M includes one or more of Ti, Ni, Fe, and Mn.

[0052] In some implementations, Y includes one or more of Ca, Al, and F.

[0053] In some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the cathode material is 1.1 to 1.3. This is beneficial for improving both battery capacity and cycle performance.

[0054] In some embodiments, the powder compaction density of the cathode material at 3t is 3.2 g / cc to 3.4 g / cc. This is beneficial for improving the volumetric energy density of the battery.

[0055] The fifth aspect of this disclosure provides a method for preparing a cathode material, including a mixing step and a heat treatment step; the mixing step includes mixing a sodium source and a metal source to obtain a cathode precursor; wherein the metal source includes at least a W source, W includes one or more alkali metal elements or alkaline earth metal elements with radii larger than transition metal elements, and in the cathode precursor, the molar ratio of sodium source to W source is greater than 16:1 based on the molar amounts of sodium and W elements; the heat treatment step includes heat treating the cathode precursor to obtain the cathode material.

[0056] In this disclosure, by introducing a W source into a metal source, a cathode material comprising a P2-phase layered oxide and an O3-phase layered oxide can be prepared, with a phase interface existing between the P2-phase and O3-phase layered oxides. Furthermore, by controlling the molar ratio of the Na source to the W source in the cathode precursor to be within the aforementioned range, a cathode material with a greater mass of O3-phase layered oxide than P2-phase layered oxide can be prepared, thereby achieving both excellent cycle performance and high capacity.

[0057] In some implementations, W includes Li and / or Mg.

[0058] In some embodiments, the molar ratio of sodium source to W source in the cathode precursor is (22–90):1, based on the molar amounts of sodium and W. In other embodiments, the molar ratio of sodium source to W source in the cathode precursor is (25–45):1, based on the molar amounts of sodium and W. This facilitates the formation of cathode materials with suitable P2 and O3 phase mass ratios, thereby further achieving a balance between excellent cycle performance and high capacity.

[0059] In some embodiments, the molar ratio of Na source to metal source in the cathode precursor is (0.8–1.0):1, based on the molar amounts of sodium and metal elements. This is beneficial for forming a cathode material with a uniform elemental distribution.

[0060] In some embodiments, during the mixing step, the metal source further includes an M source and a Y source; in the positive electrode precursor, M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co; and Y includes any metal element other than M and W.

[0061] In some embodiments, in the cathode precursor, the molar ratio of M source, W source, and Y source, based on the molar amounts of M, W, and Y elements, is (0.9–1.0):(0–0.1):(0–0.1). This helps to maintain the valence state balance of the material and preserve the overall structural stability of the material.

[0062] In some embodiments, the volumetric particle size distribution D of the sodium source V The nanometer size is 2μm to 10μm. Therefore, a cathode material with a uniform sodium element distribution can be obtained.

[0063] In some embodiments, the heat treatment step includes a pre-sintering step of pre-sintering the cathode precursor and a sintering step of secondary sintering the product of the pre-sintering step. This is beneficial for increasing the compaction density of the powder forming the cathode material, thereby increasing the volumetric energy density of the battery.

[0064] In some embodiments, the pre-sintering step includes at least one of the following features: (1) being carried out at 650°C to 950°C; (2) lasting for 5 h to 20 h; (3) being carried out in at least one atmosphere selected from air, argon, and oxygen. Pre-sintering can remove some of the gases generated during the heat treatment process, which is beneficial for improving the compaction density of the powder after pre-sintering.

[0065] In some embodiments, the sintering step includes at least one of the following features: (1) being carried out at 600°C to 1000°C; (2) lasting for 5 h to 20 h; (3) being carried out in at least one atmosphere selected from air, argon, and oxygen. The sintering step helps to further increase the powder compaction density of the cathode material, thereby improving the volumetric energy density of the battery. Attached Figure Description

[0066] Figure 1 is a crystal structure diagram of the P2 phase layered oxide.

[0067] Figure 2 is a crystal structure diagram of the O3 phase layered oxide.

[0068] Figure 3 is a schematic diagram of a battery cell according to one embodiment of the present disclosure.

[0069] Figure 4 is an exploded view of a battery cell according to an embodiment of the present disclosure shown in Figure 3.

[0070] Figure 5 is a schematic diagram of a battery module according to one embodiment of the present disclosure.

[0071] Figure 6 is a schematic diagram of a battery pack according to one embodiment of the present disclosure.

[0072] Figure 7 is an exploded view of a battery pack according to an embodiment of the present disclosure, as shown in Figure 6.

[0073] Figure 8 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of the present disclosure.

[0074] Figure 9 is a scanning electron microscope image of the positive electrode material prepared in Embodiment 1 of this disclosure.

[0075] Figure 10 is a spherical aberration electron microscope image of the positive electrode material prepared in Embodiment 1 of this disclosure.

[0076] Figure 11 is the X-ray diffraction pattern of the cathode material prepared in Example 1 of this disclosure.

[0077] Figure 12 is the X-ray diffraction pattern of the cathode material prepared in Comparative Example 3 of this disclosure.

[0078] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0079] The following detailed description, with appropriate reference to the accompanying drawings, provides specific embodiments of the positive electrode sheet, secondary battery, electrical device, positive electrode material, and method for preparing the present disclosure. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of providing a full understanding of the present disclosure by those skilled in the art and are not intended to limit the subject matter of the claims.

[0080] The "range" disclosed in this disclosure is defined by a lower limit and an upper limit, whereby a given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this disclosure, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0081] Unless otherwise specified, all embodiments and optional embodiments of this disclosure can be combined to form new technical solutions.

[0082] Unless otherwise specified, all technical features and optional technical features of this disclosure can be combined to form new technical solutions.

[0083] Unless otherwise specified, all steps of this disclosure may be performed sequentially or randomly, preferably sequentially. For example, if a method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if it is mentioned that the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0084] Unless otherwise specified, the terminology used in this disclosure has the common meaning as commonly understood by those skilled in the art.

[0085] Unless otherwise specified, the values ​​of the parameters mentioned in this disclosure can be determined using various test methods commonly used in the art, for example, according to the test methods given in this disclosure.

[0086] In this disclosure, the term "P2 phase layered oxide" has a meaning known in the art. Specifically, the oxygen stacking sequence of the P2 phase is ABBAAB, and the space group is P63 / mmc. In the P2 phase, there are two types of sodium sites: one is that which is in contact with the face of the upper and lower MO6 octahedra, which is Na. f Another type of site is the Na site, which is connected to the edges of the upper and lower MO6 octahedra. e Sites. Figure 1 shows the crystal structure of P2 phase layered oxides. As shown in Figure 1, in the P2 phase, sodium ions occupy prismatic sites and are transported via adjacent prismatic sites. Here, "P" represents prismatic. P2 phase layered oxides generally have high structural stability.

[0087] In this disclosure, the term "O3 phase layered oxide" has a meaning known in the art; specifically, the oxygen stacking sequence of the O3 phase is ABCABC, and the space group is [insert space group here]. Figure 2 shows the crystal structure of layered oxides in the O3 phase. As shown in Figure 2, in the O3 phase, sodium is located at the octahedral sites of O3, connected to the edges of the upper and lower MO6 octahedra. Here, "O" represents octahedral. Layered oxides in the O3 phase typically have high capacity.

[0088] In this disclosure, the terms "a-axis", "b-axis", and "c-axis" refer to the a-axis, b-axis, and c-axis of the unit cell, respectively. For details, please refer to the "a-axis", "b-axis", and "c-axis" shown in Figure 1 or Figure 2.

[0089] In this disclosure, the term "ab plane" refers to the plane formed by the a-axis and b-axis of the unit cell.

[0090] In this disclosure, the term "voltage window" refers to the range of the highest and lowest voltages that a battery can withstand during charging and discharging.

[0091] In this disclosure, the term "primary particle" refers to the smallest solid particle that is not aggregated and can exist independently, often also referred to as a single particle or a primitive particle. Primary particles typically have a small particle size and may be monocrystalline or polycrystalline.

[0092] In this disclosure, the term "quasi-single crystal" refers to a structure with a relatively regular and ordered microstructure, that is, a structure similar to single crystal particles. Quasi-single crystal is not actually a single crystal.

[0093] In this disclosure, the term "symbiotic structure" refers to a structure in which two different phases (such as crystalline phase, amorphous phase, or phases with different chemical compositions) influence and restrict each other during the growth process within a material, ultimately forming a structure with specific morphology and properties and grain boundaries.

[0094] Because O3-phase layered oxides have high capacity, they are commonly used as positive electrode materials for secondary batteries. To further improve the capacity of O3-phase layered oxides, the inventors expanded the voltage window of O3-phase layered oxides (such as nickel-iron-manganese ternary materials) to 4.2V. However, after expanding the voltage window, the inventors found that O3-phase layered oxides are prone to structural degradation (e.g., crystal destruction, phase transition) during charge and discharge, severely affecting the cycle stability of the battery.

[0095] In related technologies, on the one hand, the stability of O3 phase layered oxides is adjusted by doping with metal or non-metal elements, thereby reducing their structural degradation and improving the electrochemical performance of the materials; on the other hand, the cycle stability of the battery is improved by compositing P2 phase layered oxides with higher stability into O3 phase layered oxides.

[0096] However, the doping process reduces the capacity of O3-phase layered oxides, meaning that doping cannot simultaneously improve capacity and cycle stability. Composite P2-phase layered oxides are typically materials that physically blend P2-phase and O3-phase layered oxides or form a symbiotic structure where P2-phase and O3-phase layered oxides are in contact along the c-axis of the unit cell. In the case of a blend of P2-phase and O3-phase layered oxides, the P2-phase layered oxides cannot influence the structural changes of the O3-phase layered oxides during charge and discharge, thus failing to improve the structural stability of the O3-phase layered oxides. Similarly, materials with a symbiotic structure where P2-phase and O3-phase layered oxides are in contact along the c-axis also suffer from poor structural stability; during sodium removal, the transition metal layer slides along the ab-plane, easily inducing a phase transition reaction in the O3-phase layered oxides. Therefore, related technologies have failed to address the problem of the transition metal layer sliding along the ab-plane during active ion insertion / extraction.

[0097] Based on this, this disclosure provides a new positive electrode sheet, a secondary battery, an electrical device, a positive electrode material, and a method for preparing the same. The secondary battery using this positive electrode sheet can achieve both excellent cycle performance and high capacity.

[0098] Positive electrode sheet

[0099] The first aspect of this disclosure provides a positive electrode sheet, including a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer includes a positive electrode material, wherein the positive electrode material includes at least a sodium-containing layered oxide, the sodium-containing layered oxide including at least two phases, wherein a first phase and a second phase form a phase interface; the first phase is an O3 phase layered oxide, the second phase is a P2 phase layered oxide, and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide.

[0100] In this disclosure, the cathode material includes a P2-phase layered oxide and an O3-phase layered oxide. Since the P2-phase layered oxide possesses high structural stability, its introduction can improve the cycle performance of the cathode material. Furthermore, because the P2-phase and O3-phase layered oxides form a phase interface in the cathode material, the presence of this interface can alleviate stress accumulation caused by structural changes in the two phases during charge and discharge. In other words, the presence of the phase interface can disperse stress during charge and discharge, thereby suppressing structural degradation of the cathode material and improving its cycle stability during charge and discharge. Based on this, by setting the mass of the O3-phase layered oxide in the cathode material to be greater than the mass of the P2-phase layered oxide, the capacity of the cathode material can be improved, thus achieving a balance between excellent cycle performance and high capacity.

[0101] In some embodiments, the primary particles containing sodium-containing layered oxides include near-single-crystal particles, at least some of which comprise O3-phase layered oxides and P2-phase layered oxides. This facilitates the formation of a symbiotic structure of O3-phase and P2-phase layered oxides, thereby achieving a balance between cycle performance and capacity.

[0102] In some embodiments, the O3 phase layered oxide and the P2 phase layered oxide are in contact through the ab plane of the unit cell. This contact between the O3 phase layered oxide and the P2 phase layered oxide can alleviate the structural stress caused by the slippage of the transition metal layer along the ab plane, suppress the slippage of the transition metal layer, thereby suppressing phase transition and improving the stability of the cathode material.

[0103] It should be noted that the contact between the O3 phase layered oxide and the P2 phase layered oxide through the ab plane of the unit cell includes contact along the a axis of the unit cell, contact along the b axis of the unit cell, and contact along any direction within the ab plane of the unit cell.

[0104] In some embodiments, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(5-9), and optionally, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(6-8). By controlling the mass ratio of P2 phase layered oxide to O3 phase layered oxide within the above range, it is beneficial to further balance excellent cycle performance and high capacity.

[0105] In some embodiments, the average grain size of the O3 phase layered oxide is smaller than that of the P2 phase layered oxide. This configuration allows for a better lattice matching between the P2 and O3 phase layered oxides, promoting the formation of the cathode material and thus improving its stability, ultimately enhancing the cycle stability of the battery.

[0106] In some embodiments, during charging, the O3 phase layered oxide transforms into the P3 phase layered oxide at 3.0V to 3.2V, and at 4.0V to 4.2V, the P3 phase layered oxide transforms into the OP2 phase layered oxide. The symbiotic structure of the cathode material in this disclosure exhibits fewer phase transitions during charging, reflecting high stability of the cathode material and thus contributing to the cycle stability of the battery.

[0107] In some embodiments, the voltage plateau of the positive electrode material during discharge is 3.05V to 3.35V. The positive electrode material in this disclosure has a relatively high voltage plateau, thus reflecting a high capacity in the secondary battery.

[0108] In some embodiments, the voltage plateau of the positive electrode material during discharge cycles up to 100 cycles is 2.95V to 3.2V. In some embodiments, the voltage plateau of the positive electrode material during discharge cycles up to 500 cycles is 2.85V to 3.15V. In some embodiments, the voltage plateau of the positive electrode material during discharge cycles up to 1000 cycles is 2.75V to 3.05V. A higher voltage plateau during cycling indicates a higher capacity in the secondary battery.

[0109] In some embodiments, the XRD diffraction pattern of the cathode material includes a first diffraction peak with a 2θ between 15.9° and 16.3° and a second diffraction peak with a 2θ between 16.3° and 16.7°, wherein the full width at half maximum (FWHW) of the first diffraction peak is... (002) The full width at half maximum (FWHW) of the second diffraction peak (003) Satisfies: 1.0 ≤ FWHW (003) / FWHW (002) ≤1.5, optionally, 1.05≤FWHW (003) / FWHW (002) ≤1.4. For example, FWHW (003) / FWHW (002) The values ​​are within the range of 1.03, 1.04, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, or any two of these values. The full width at half maximum (FWHM) of the P2-phase layered oxide and the O3-phase layered oxide respectively reflect the grain size of the P2-phase layered oxide and the O3-phase layered oxide. Since the unit cell of the P2-phase layered oxide has two transition metal (M element) layers on the ab plane, and the unit cell of the O3-phase layered oxide has three transition metal layers on the ab plane, a smaller FWHM of the P2-phase layered oxide reflects a larger grain size of the corresponding phase. Controlling the FWHM within the above range allows for better lattice matching between the P2-phase layered oxide and the O3-phase layered oxide on the ab plane, promoting the formation of the cathode material, thereby improving the stability of the cathode material and ultimately enhancing the cycle stability of the battery.

[0110] In some implementations, the peak intensity I of the first diffraction peak (002) Peak intensity I of the second diffraction peak (003) Satisfy: 0.1≤I (002) / [I (002) +I (003) ]≤0.2, optionally, 0.11≤I (002) / [I (002) +I (003) ]≤0.17, for example, I (002) / [I (002) +I (003)[I] represents a value within a range of 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, or any two values. (002) / [I (002) +I (003) Within the above range, it reflects that the O3 phase has a high proportion in the cathode material, which is beneficial to improving the battery capacity.

[0111] In some embodiments, the cathode material includes nickel-iron-manganese sodium oxide.

[0112] In some embodiments, the cathode material includes Na. x [M a W b Y c O2, 0.8≤x<1.0, 0.9<a<1.0, 0<b<0.1, 0≤c<0.1, a+b+c=1.0, the values ​​of x, a, b, and c satisfy charge balance; M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co, optionally, M includes one or more of Ti, Ni, Fe, and Mn; W includes one or more alkali metal elements or alkaline earth metal elements with radii larger than transition metal elements, optionally, W includes Li and / or Mg; Y includes any metal element other than M and W, optionally, Y includes one or more of Ca, Al, and F. Since the above cathode material includes the element W with a radius larger than transition metal elements, a two-phase symbiotic cathode material can be obtained, which is beneficial to improving the stability of the cathode material and the cycle performance of the battery.

[0113] In this disclosure, because the ionic radii of Li or Mg are larger than those of ordinary transition metals, the introduction of Li or Mg readily forms a two-phase structure. Furthermore, due to the lower valence states of Li or Mg, and considering charge compensation, the Na content in the resulting substance is lower, thus favoring the formation of the P2 phase. Further, since the main structure of this disclosure is the O3 phase, a symbiotic P2 phase is formed on this basis.

[0114] In some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the cathode material is 1.1 to 1.3, and optionally, (Dv90-Dv10) / Dv50 is 1.2 to 1.3. Exemplarily, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the cathode material is a value between 1.1, 1.2, 1.3, or any two of these values. A volumetric particle size distribution (Dv90-Dv10) / Dv50 within the above range reflects that the cathode material has a suitable particle size distribution, which is beneficial for improving both battery capacity and cycle performance.

[0115] In some embodiments, the powder compaction density of the cathode material at 3t is 3.2 g / cc to 3.4 g / cc. A compaction density of the cathode material within this range is beneficial for improving the volumetric energy density of the battery.

[0116] In some embodiments, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0117] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0118] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0119] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0120] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive electrode material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0121] In this disclosure, the phase interface, O3 phase layered oxide, and P2 phase layered oxide in the positive electrode material can be reversed through contact at the ab plane of the unit cell. Specifically, the battery is disassembled to obtain the positive electrode sheet. The positive electrode material is peeled off from the positive electrode current collector, and the peeled-off positive electrode material is ultrasonically dispersed in N,N-dimethylformamide (DMF) to form a suspension. A small amount of the suspension is then dropped onto an ultrathin carbon film. After the carbon film is vacuum-dried, it is placed on a sample holder and sent to a spherical aberration electron microscope for testing in HAADF-STEM mode to obtain a spherical aberration electron microscope image. A spherical aberration electron microscope image refers to a microstructure image obtained by testing along any direction of the a-axis, b-axis, or ab plane of the unit cell. The "horizontal" direction in the spherical aberration electron microscope image is any direction within the ab plane of the unit cell (including the a-axis and b-axis directions), and the "vertical" direction in the spherical aberration electron microscope image is the c-axis direction of the unit cell. By observing spherical aberration electron microscopy (SEM) images, it can be seen that the cathode material simultaneously comprises P2-phase layered oxides and O3-phase layered oxides, thus confirming the presence of a phase interface. Furthermore, the alignment direction of the P2-phase and O3-phase layered oxides in the SEM images can be analyzed. If the P2-phase and O3-phase layered oxides are aligned along the a-axis (or b-axis, or any direction within the ab-plane) of the unit cell, then it can be determined that the P2-phase and O3-phase layered oxides are in contact through the ab-plane of the unit cell.

[0122] In this disclosure, the mass and mass ratio of the P2-phase layered oxide to the O3-phase layered oxide in the cathode material can be reversed in the following manner. Specifically, the battery is disassembled to obtain the cathode electrode, and the cathode material is peeled off from the cathode current collector. X-ray diffraction (XRD) patterns are obtained from the peeled cathode material. The XRD patterns are then refined using the FULLPROF software. The mass of the P2-phase layered oxide can be obtained from the diffraction peaks of the refined P2-phase layered oxide, and the mass of the O3-phase layered oxide can be obtained from the diffraction peaks of the refined O3-phase layered oxide. Therefore, the mass ratio of the P2-phase layered oxide to the O3-phase layered oxide can be further obtained.

[0123] In this disclosure, the phase transition process of the cathode material during charging can be detected by in-situ XRD. The test conditions are: voltage window 1.5–4.2 V, current 10 mA / g, Bruker D8 Discover X-ray diffractometer, in-situ battery mold assembly, CuKα rays as radiation source, copper target as anode target, voltage 40 kV, current 40 mA, anti-scattering slit 1 mm, scanning 2θ angle range 15°–70°, step size 0.02°, scanning rate 5° / min.

[0124] In this disclosure, the voltage plateau of the cathode material during discharge can be read from the test results of the corresponding charge-discharge curve of the battery. The ratio of discharge energy density to discharge capacity is the discharge voltage plateau. The charge-discharge curve of the battery is tested under the conditions of a voltage window of 1.5V to 4.2V and a current of 10mA / g.

[0125] In this disclosure, the XRD diffraction pattern of the cathode material can be tested using an X-ray diffractometer according to JIS K 0131-1996. The test conditions are as follows: the cathode material is prepared using the flat plate method, with CuKα rays as the radiation source, a copper target as the anode target, a voltage of 40 kV, a current of 40 mA, a 1 mm anti-scattering slit, a scanning 2θ angle range of 20°–80°, a step size of 0.01671°, a step duration of 0.24 s, and a scanning rate of 4° / min. A Bruker D8 Discover X-ray diffractometer can be used as the testing instrument.

[0126] In this disclosure, after obtaining the XRD diffraction pattern of the cathode material, the full width at half maximum (FWHM) of the P2 and O3 phases in the cathode material can be determined in the following way: open the corresponding XRD data using Highscore software, then click the "BG" icon and manually drag the "red dot" in the figure to adjust the baseline; click the "BG" icon again to subtract the background; select the shortcut key marked by the red dotted line, manually select the desired peak, and the area, intensity I, and FWHM data of this peak can be displayed.

[0127] In this disclosure, after obtaining the XRD diffraction pattern of the cathode material, I can be determined based on the peak intensity value of the highest point of the first diffraction peak and the peak intensity value of the highest point of the second diffraction peak. (002) / [I (002) +I (003) ].

[0128] In this disclosure, the volumetric particle sizes Dv50, Dv90, and Dv10 have meanings known in the art, representing the particle sizes corresponding to a cumulative volumetric distribution percentage of 50%, 90%, and 10%, respectively, and can be determined using instruments and methods known in the art. For example, they can be determined using a laser particle size analyzer, referring to GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0129] In this disclosure, powder compaction density has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., a UTM7305 type electronic pressure testing machine) in accordance with GB / T 24533-2009. An exemplary test method is as follows: Weigh 1g of sample powder and add it to a container with a bottom area of ​​1.327cm².2 In the mold, the pressure is increased to 3t, held for 30s, then depressurized and held for 10s. The compaction density of the powder under 3t pressure is then recorded and calculated.

[0130] Secondary batteries

[0131] The second aspect of this disclosure provides a secondary battery, and the secondary battery and power-consuming device of this disclosure will be described below with appropriate reference to the accompanying drawings.

[0132] The term "secondary battery" used in this article refers to a single battery cell, a battery module, or a battery pack. These will be explained separately below.

[0133] Typically, a single secondary battery cell includes, firstly, a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through.

[0134] Negative electrode sheet

[0135] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0136] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0137] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0138] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this disclosure is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0139] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0140] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0141] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0142] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0143] electrolytes

[0144] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This disclosure does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid.

[0145] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0146] In some embodiments, the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonamide, sodium ditrifluoromethanesulfonamide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0147] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0148] In some embodiments, the electrolyte may optionally include additives. For example, additives 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.

[0149] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0150] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0151] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0152] This disclosure does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 shows a square battery cell 5 as an example.

[0153] In some embodiments, referring to FIG4, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0154] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0155] Figure 5 shows a battery module 4 as an example. Referring to Figure 5, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0156] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0157] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0158] Figures 6 and 7 illustrate a battery pack 1 as an example. Referring to Figures 6 and 7, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0159] Electrical appliances

[0160] In addition, a third aspect of this disclosure provides an electrical device, which includes a secondary battery provided by this disclosure. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0161] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0162] Figure 8 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0163] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0164] Currently, O3-phase layered oxides are commonly used as cathode materials for secondary batteries. However, the capacity of O3-phase layered oxides as cathode materials for secondary batteries still has room for improvement. This invention aims to improve the capacity of O3-phase layered oxides (such as nickel-iron-manganese ternary materials) by expanding the voltage window to 4.2V. However, after expanding the voltage window, the inventors found that O3-phase layered oxides are prone to structural degradation (e.g., crystal destruction, phase transition) during charge and discharge, which seriously affects the cycle stability of the battery.

[0165] In related technologies, on the one hand, the stability of O3 phase layered oxides is adjusted by doping with metal or non-metal elements, thereby reducing their structural degradation and improving the electrochemical performance of the materials; on the other hand, the cycle stability of the battery is improved by compositing P2 phase layered oxides with higher stability into O3 phase layered oxides.

[0166] However, the doping process reduces the capacity of O3-phase layered oxides, meaning that doping cannot simultaneously improve capacity and cycle stability. Composite P2-phase layered oxides are typically materials that form blends of P2-phase and O3-phase layered oxides or symbiotic structures where they are in contact along the c-axis of the unit cell. In blends, the P2-phase and O3-phase layered oxides are in physical contact, meaning the P2-phase oxides cannot influence the structural changes of the O3-phase oxides during charge and discharge, thus failing to improve their structural stability. Similarly, symbiotic structures where the P2-phase and O3-phase oxides are in contact along the c-axis also suffer from poor structural stability; during sodium removal, the transition metal layer slides along the ab-plane, easily inducing a phase transition reaction in the O3-phase layered oxide. Therefore, related technologies have failed to address the problem of the transition metal layer sliding along the ab-plane during active ion insertion / extraction.

[0167] Based on this, the present disclosure provides a new cathode material, and a secondary battery using this cathode material can achieve both excellent cycle performance and high capacity.

[0168] cathode materials

[0169] The fourth aspect of this disclosure provides a cathode material, which includes at least a sodium-containing layered oxide, the sodium-containing layered oxide including at least two phases, wherein a first phase and a second phase form a phase interface; the first phase is an O3 phase layered oxide, the second phase is a P2 phase layered oxide, and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide.

[0170] In this disclosure, the cathode material includes a P2-phase layered oxide and an O3-phase layered oxide. Since the P2-phase layered oxide possesses high structural stability, its introduction can improve the cycle performance of the cathode material. Furthermore, because the P2-phase and O3-phase layered oxides form a phase interface in the cathode material, the presence of this interface can alleviate stress accumulation caused by structural changes in the two phases during charge and discharge. In other words, the presence of the phase interface can disperse stress during charge and discharge, thereby suppressing structural degradation of the cathode material and improving its cycle stability during charge and discharge. Based on this, by setting the mass of the O3-phase layered oxide in the cathode material to be greater than the mass of the P2-phase layered oxide, the capacity of the cathode material can be improved, thus achieving a balance between excellent cycle performance and high capacity.

[0171] In some embodiments, the primary particles containing sodium-containing layered oxides include near-single-crystal particles, at least some of which comprise O3-phase layered oxides and P2-phase layered oxides. This facilitates the formation of a symbiotic structure of O3-phase and P2-phase layered oxides, thereby achieving a balance between cycle performance and capacity.

[0172] In some embodiments, the O3 phase layered oxide and the P2 phase layered oxide are in contact through the ab plane of the unit cell. This contact between the O3 phase layered oxide and the P2 phase layered oxide can alleviate the structural stress caused by the slippage of the transition metal layer along the ab plane, suppress the slippage of the transition metal layer, thereby suppressing phase transition and improving the stability of the cathode material.

[0173] In some embodiments, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(5-9), and optionally, the mass ratio of P2 phase layered oxide to O3 phase layered oxide is 1:(6-8). By controlling the mass ratio of P2 phase layered oxide to O3 phase layered oxide within the above range, it is beneficial to further balance excellent cycle performance and high capacity.

[0174] In some embodiments, the average grain size of the O3 phase layered oxide is smaller than that of the P2 phase layered oxide. This configuration allows for a better lattice matching between the P2 and O3 phase layered oxides, promoting the formation of the cathode material and thus improving its stability, ultimately enhancing the cycle stability of the battery.

[0175] In some embodiments, during charging, the O3 phase layered oxide transforms into the P3 phase layered oxide at 3.0V to 3.2V, and at 4.0V to 4.2V, the P3 phase layered oxide transforms into the OP2 phase layered oxide. The symbiotic structure of the cathode material in this disclosure exhibits fewer phase transitions during charging, reflecting high stability of the cathode material and thus contributing to the cycle stability of the battery.

[0176] In some embodiments, the voltage plateau of the positive electrode material during discharge is 3.05V to 3.35V. The positive electrode material in this disclosure has a relatively high voltage plateau, thus reflecting a high capacity in the secondary battery.

[0177] In some embodiments, the voltage plateau of the positive electrode material during discharge cycles up to 100 cycles is 2.95V to 3.2V. In some embodiments, the voltage plateau of the positive electrode material during discharge cycles up to 500 cycles is 2.85V to 3.15V. In some embodiments, the voltage plateau of the positive electrode material during discharge cycles up to 1000 cycles is 2.75V to 3.05V. A higher voltage plateau during cycling indicates a higher capacity in the secondary battery.

[0178] In some embodiments, the XRD diffraction pattern of the cathode material includes a first diffraction peak with a 2θ between 15.9° and 16.3° and a second diffraction peak with a 2θ between 16.3° and 16.7°, wherein the full width at half maximum (FWHW) of the first diffraction peak is... (002) The full width at half maximum (FWHW) of the second diffraction peak (003) Satisfies: 1.0 ≤ FWHW (003) / FWHW (002) ≤1.5, optionally, 1.05≤FWHW (003) / FWHW (002) ≤1.4. For example, FWHW (003) / FWHW (002) The values ​​are within the range of 1.03, 1.04, 1.05, 1.1, 1.2, 1.3, 1.4, 1.5, or any two of these values. The full width at half maximum (FWHM) of the P2-phase layered oxide and the O3-phase layered oxide reflect the grain size of the P2-phase layered oxide and the O3-phase layered oxide, respectively. Since the unit cell of the P2-phase layered oxide has two transition metal (M element) layers on the ab plane, and the unit cell of the O3-phase layered oxide has three transition metal layers on the ab plane, a smaller FWHM of the P2-phase layered oxide reflects a larger grain size of the corresponding phase. Controlling the FWHM within the above range allows for a better lattice matching between the P2-phase layered oxide and the O3-phase layered oxide on the ab plane, promoting the formation of the cathode material, thereby improving the stability of the cathode material and ultimately enhancing the cycle stability of the battery.

[0179] In some implementations, the peak intensity I of the first diffraction peak (002) Peak intensity I of the second diffraction peak (003) Satisfy: 0.1≤I (002) / [I (002) +I (003)]≤0.2, optionally, 0.11≤I (002) / [I (002) +I (003) ]≤0.17, for example, I (002) / [I (002) +I O3(003) [I] represents a value within a range of 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, or any two values. (002) / [I (002) +I (003) Within the above range, it reflects that the O3 phase has a high proportion in the cathode material, which is beneficial to improving the battery capacity.

[0180] In some embodiments, the cathode material includes nickel-iron-manganese sodium oxide.

[0181] In some embodiments, the cathode material includes Na. x [M a W b Y c O2, 0.8≤x<1.0, 0.9<a<1.0, 0<b<0.1, 0≤c<0.1, a+b+c=1.0, the values ​​of x, a, b, and c satisfy charge balance; M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co, optionally, M includes one or more of Ti, Ni, Fe, and Mn; W includes one or more alkali metal elements or alkaline earth metal elements with radii larger than transition metal elements, optionally, W includes Li and / or Mg; Y includes any metal element other than M and W, optionally, Y includes one or more of Ca, Al, and F. Since the above cathode material includes the element W with a radius larger than transition metal elements, a two-phase symbiotic cathode material can be obtained, which is beneficial to improving the stability of the cathode material and the cycle performance of the battery.

[0182] In this disclosure, because the ionic radii of Li or Mg are larger than those of common transition metals, the introduction of W readily forms a two-phase structure. Furthermore, due to the lower valence states of Li or Mg, and considering charge compensation, the Na content in the resulting substance is relatively low, thus favoring the formation of the P2 phase. Further, since the main structure of this disclosure is the O3 phase, a symbiotic P2 phase is formed on this basis.

[0183] In some embodiments, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the cathode material is 1.1 to 1.3, and optionally, (Dv90-Dv10) / Dv50 is 1.2 to 1.3. Exemplarily, the volumetric particle size distribution (Dv90-Dv10) / Dv50 of the cathode material is a value between 1.1, 1.2, 1.3, or any two of these values. A volumetric particle size distribution (Dv90-Dv10) / Dv50 within the above range reflects that the cathode material has a suitable particle size distribution, which is beneficial for improving both battery capacity and cycle performance.

[0184] In some embodiments, the powder compaction density of the cathode material at 3t is 3.2 g / cc to 3.4 g / cc. A compaction density of the cathode material within this range is beneficial for improving the volumetric energy density of the battery.

[0185] Preparation method of positive electrode material

[0186] This disclosure provides a fifth aspect of a method for preparing a cathode material, comprising a mixing step and a heat treatment step. The mixing step includes mixing a sodium source and a metal source to obtain a cathode precursor; wherein the metal source includes at least a W source, and W includes one or more alkali metal elements or alkaline earth metal elements with radii larger than transition metal elements; in the cathode precursor, the molar ratio of sodium source to W source is greater than 16:1, based on the molar amounts of sodium and W elements; the heat treatment step includes heat-treating the cathode precursor to obtain the cathode material.

[0187] In this disclosure, by introducing a W source into a metal source, a cathode material comprising a P2-phase layered oxide and an O3-phase layered oxide can be prepared, with a phase interface existing between the P2-phase and O3-phase layered oxides. Furthermore, by controlling the molar ratio of Na source to W source in the cathode precursor within the aforementioned range, a cathode material with a greater mass of O3-phase layered oxide than P2-phase layered oxide can be obtained.

[0188] In this cathode material, the P2 phase layered oxide exhibits high structural stability; therefore, its introduction can improve the cycle performance of the cathode material. Furthermore, the P2 and O3 phase layered oxides form a phase interface in the cathode material. This interface can alleviate stress accumulation caused by structural changes in the two phases during charge and discharge; that is, the interface can disperse stress during charge and discharge, thereby inhibiting structural degradation of the cathode material and improving its cycle stability. Based on this, by setting the mass of the O3 phase layered oxide in the cathode material to be greater than that of the P2 phase layered oxide, a larger mass fraction of the O3 phase layered oxide in the cathode material can be achieved, ensuring increased capacity and thus balancing excellent cycle performance with high capacity.

[0189] In some embodiments, W includes Li and / or Mg. Since the ionic radii of Li and / or Mg are larger than those of common transition metal elements, the introduction of Li and / or Mg readily forms a two-phase structure.

[0190] In some embodiments, the molar ratio of sodium source to W source in the cathode precursor is (22–90):1, based on the molar amounts of sodium and W elements. Optionally, the molar ratio of sodium source to W source is (25–45):1. By controlling the molar ratio of sodium source to W source in the cathode precursor to be within the above range, a cathode material with a suitable mass ratio of P2 phase to O3 phase can be prepared, thereby further achieving both excellent cycle performance and high capacity.

[0191] In some embodiments, the molar ratio of sodium source to metal source in the cathode precursor is (0.8 to 1.0):1, based on the molar amounts of sodium and metal elements. A molar ratio of sodium source to metal source within the above range is beneficial for forming a cathode material with uniform elemental distribution.

[0192] In some embodiments, during the mixing step, the metal source further includes an M source and a Y source; in the positive electrode precursor, M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co; and Y includes any metal element other than M and W.

[0193] In some embodiments, in the cathode precursor, the molar ratio of M source, W source, and Y source, based on the molar amounts of M metal, W element, and Y metal, is (0.9–1.0):(0–0.1):(0–0.1). Having the molar ratio of M source, W source, and Y source within this range is beneficial for maintaining the valence state balance of the material and preserving the overall structural stability of the material.

[0194] In some embodiments, the sodium source includes one or more of Na2O2, NaOH, Na2CO3, CH3COONa, and NaNO3. Optionally, the sodium source includes Na2CO3 and CH3COONa.

[0195] In some embodiments, the volumetric particle size distribution D of the sodium source V 50 is 2μm to 10μm, and optionally, the volumetric particle size distribution D of the sodium source is... V 50 is 4μm to 6μm. For example, the volumetric particle size distribution D of the sodium source. V 50 represents a value within the range of 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or any two of these values. The volumetric particle size distribution D of the sodium source. V Within the above range, a cathode material with uniform sodium distribution can be obtained.

[0196] In some embodiments, a mixer is used in the mixing step to mix the sodium source, M source, W source, and Y source at high speed. The mixer includes one of the following: an inclined mixer, a high-speed mixer, a V-type mixer, and a plow-blade mixer. Optionally, an inclined mixer is used for mixing.

[0197] In some embodiments, one of zirconium balls, aluminum balls, polyurethane balls, and agate balls is used for mixing in the mixing step. The mixing machine speed is 10 r / min to 100 r / min, optionally 40 r / min to 60 r / min, and optionally, the mixing time is 1 h to 10 h. Mixing under the above conditions can ensure that the components of the cathode precursor are fully mixed, resulting in a cathode precursor with uniform element distribution.

[0198] In some embodiments, the M source includes one or more of nickel oxide, manganese dioxide, ferric oxide, and titanium dioxide; the W source includes one or more of lithium carbonate and magnesium oxide; and the Y source includes one or more of calcium oxide, aluminum oxide, and sodium fluoride.

[0199] In some embodiments, the heat treatment step includes a pre-sintering step of pre-sintering the cathode precursor and a sintering step of secondary sintering the product of the pre-sintering step. By pre-sintering and secondary sintering the cathode precursor, the compaction density of the powder forming the cathode material can be increased, thereby improving the volumetric energy density of the battery.

[0200] In some embodiments, the pre-sintering step includes at least one of the following features: (1) being carried out at 650°C to 950°C; (2) lasting for 5 h to 20 h; (3) being carried out in at least one atmosphere selected from air, argon, and oxygen. Pre-sintering can remove some of the gases generated during the heat treatment process, which is beneficial for improving the compaction density of the powder after pre-sintering.

[0201] In some embodiments, the sintering step includes at least one of the following features: (1) being carried out at 600°C to 1000°C; (2) lasting for 5 h to 20 h; (3) being carried out in at least one atmosphere selected from air, argon, and oxygen. The sintering step helps to further increase the powder compaction density of the cathode material, thereby improving the volumetric energy density of the battery.

[0202] Example

[0203] The following describes embodiments of this disclosure. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure. 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 the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0204] Example 1

[0205] Preparation of cathode materials

[0206] 1) Mixing step: Sodium carbonate, lithium carbonate, nickel oxide, iron oxide, manganese dioxide and titanium dioxide are mixed at high speed in an inclined mixer in a molar ratio of 90:3:54:25:80:10 to obtain the positive electrode precursor. The speed of the mixer is 50 r / min and the mixing time is 4 h.

[0207] 2) Heat treatment steps: a) Pre-sintering step: The mixed positive electrode precursor from step 1) is sintered at 800℃ for 10 hours in air atmosphere, with a heating rate of 5℃ / min; b) Sintering step: The pre-sintered product from step a) is ground, sieved, and then subjected to secondary sintering at 900℃, with a heating rate of 5℃ / min, for 15 hours in air atmosphere, yielding a product with the chemical formula Na. 0.89 Li 0.027 Ni 0.26 Fe 0.258 Mn 0.41 Ti 0.045 The positive electrode material for O2. After excluding testing errors, the subscripts of each element in the chemical formula of the positive electrode material obtained in Example 1 are approximately equal to the amounts of sodium carbonate, lithium carbonate, nickel oxide, iron oxide, manganese dioxide, and titanium dioxide added.

[0208] Parameter testing of cathode materials

[0209] (1) Microscopic morphology test

[0210] The cathode material prepared in Example 1 was observed using a scanning electron microscope (ZEISSSEM) and SEM images were taken. The tests were performed in accordance with JY / T010-1996. Figure 9 shows the SEM image of the cathode material in Example 1 of this disclosure. As shown in Figure 9, the cathode material exhibits a morphological characteristic similar to a single crystal, with single crystal particles in contact and entangled with each other.

[0211] The cathode material was observed using a spherical aberration electron microscopy (Themis Z instrument), and spherical aberration electron micrographs were taken. The HADDF-STEM mode of the spherical aberration electron microscopy was used for testing. Figure 10 shows a spherical aberration electron micrograph of the cathode material in Embodiment 1 of this disclosure. As shown in Figure 10, the cathode material in Embodiment 1 includes an O3 phase layered oxide with oxygen layers (corresponding to oxygen atoms in the figure) arranged in an ABCABC pattern, and a P2 phase layered oxide with oxygen layers arranged in an ABBA pattern. The grain size of the P2 phase layered oxide is... The grain size of the O3 phase layered oxide is In addition, the spherical aberration electron microscopy image also shows that there is a phase interface between the O3 phase layered oxide and the P2 phase layered oxide in Example 1, and the O3 phase layered oxide and the P2 phase layered oxide are arranged in a "horizontal" direction, that is, the O3 phase layered oxide and the P2 phase layered oxide are in contact through the ab plane of the unit cell.

[0212] (2) Phase characterization;

[0213] The cathode material prepared in Example 1 was tested using an X-ray powder diffractometer (instrument model: Bruker D8 Discover) to obtain the XRD pattern of the cathode material.

[0214] Figure 11 shows the XRD pattern of the cathode material in Embodiment 1 of this disclosure. The XRD pattern obtained by the test was refined using the refinement software FULLPROF to obtain a first diffraction peak with a 2θ between 15.9° and 16.3° and a second diffraction peak with a 2θ between 16.3° and 16.7°. The first diffraction peak is the main peak of the P2 phase and the second diffraction peak is the main peak of the O3 phase. Based on the area of ​​the first diffraction peak and the area of ​​the second diffraction peak, the mass ratio of the P2 phase to the O3 phase can be obtained as 1:7. The calculation results are shown in Table 1.

[0215] The XRD patterns obtained from the tests were magnified using Origin software, and the full width at half maximum (FWHW) of the first diffraction peak was obtained using HighScore software. (002) The full width at half maximum (FWHW) of the second diffraction peak is 0.5. (003) It is 0.6, therefore, FWHW (003) / FWHW (002) The value is 1.2, and the calculation results are shown in Table 2.

[0216] Preparation of positive electrode sheet

[0217] The positive electrode material prepared in Example 1, the nano-scale conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 94:3:3. The mixture was then coated onto one side of an aluminum foil with a thickness of 13 μm, dried, and cold-pressed to obtain the positive electrode sheet. The areal density of the coating on one side of the positive electrode sheet was 0.02 g / cm³. 2 .

[0218] Preparation of negative electrode sheet

[0219] Hard carbon (the negative electrode active material), acetylene black (a nano-scale conductive agent), styrene-butadiene rubber (SBR) (a binder), and sodium carboxymethyl cellulose (CMC) (a thickener) were thoroughly mixed in a deionized water solvent system at a weight ratio of 95:2:2:1. The mixture was then coated on both sides of a 6 μm thick copper foil, dried, and cold-pressed to obtain the negative electrode sheet. The areal density of the coating on one side of the negative electrode sheet was 0.012 g / cm³. 2 .

[0220] electrolyte

[0221] An organic solvent was prepared by mixing equal volumes of ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC). NaPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0222] Separating membrane

[0223] Porous polyethylene-based membrane is used as the separator.

[0224] Preparation of secondary batteries

[0225] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. This stacking process yields a bare battery cell. The bare battery cell is then placed in outer packaging, filled with the prepared electrolyte, and sealed to obtain a secondary battery.

[0226] Performance testing of secondary batteries

[0227] 1) Capacity testing

[0228] ① Charge the capacitor to 4.2V at a constant current of 0.33C, then charge it to 0.05C at a constant voltage of 4.2V, and record the charging capacity C1.

[0229] ② Let stand for 30 minutes;

[0230] ③ Discharge at a constant current of 1C to 1.5V and record the discharge capacity D1;

[0231] Initial coulombic efficiency = discharge capacity D1 / charge capacity C1 * 100%.

[0232] 2) Cyclic performance test

[0233] ① Let stand for 5 minutes;

[0234] ② Charge at a constant current of 0.33C to 4.2V, then charge at a constant voltage of 4.2V to a current of 0.05C;

[0235] ③ Let stand for 5 minutes;

[0236] ④ Discharge at a constant current of 1C to 1.5V, and record the discharge capacity D1 of the first cycle;

[0237] ⑤ Repeat steps ① to ④ above 100 times, and record the discharge capacity Dn on the 100th cycle;

[0238] Capacity retention rate after 100 cycles (%) = Discharge capacity Dn of the 100th cycle / Discharge capacity D1 of the first cycle * 100%. The test results are shown in Table 2.

[0239] Comparative Example 1

[0240] The cathode material was prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that the molar ratio of sodium carbonate, lithium carbonate, nickel oxide, iron oxide, manganese dioxide and titanium dioxide was 80:10:40:25:80:10 when preparing the cathode material. For the specific cathode material and secondary battery parameters, please refer to Table 2 below.

[0241] Comparative Example 2

[0242] The cathode material was prepared in a similar manner to that in Example 1 and assembled into a secondary battery. The only difference was that lithium carbonate was not added when preparing the cathode material. That is, the molar ratio of sodium carbonate, lithium carbonate, nickel oxide, iron oxide, manganese dioxide and titanium dioxide was 90:0:60:25:80:10. For the specific cathode material and secondary battery parameters, please refer to Table 2 below.

[0243] Figure 12 shows the X-ray diffraction pattern of the cathode material prepared in Comparative Example 2. As shown in Figure 12, the cathode material in Comparative Example 3 only has the O3 phase and does not have the P2 phase.

[0244] Comparative Example 3

[0245] The cathode material was prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that the molar ratio of sodium carbonate, lithium carbonate, nickel oxide, iron oxide, manganese dioxide and titanium dioxide was 70:10:40:25:80:10 when preparing the cathode material. For the specific cathode material and secondary battery parameters, please refer to Table 2 below.

[0246] Table 1 below shows the molar ratio of each raw material and the chemical formula of the prepared cathode material in Example 1 and Comparative Examples 1-3. Table 2 below shows the parameters for preparing the cathode material in Example 1 and Comparative Examples 1-3 and the performance test parameters of the secondary battery.

[0247] Table 1

[0248] Table 2

[0249] In Table 2, " / " indicates that the symbol does not exist.

[0250] As can be seen from Tables 1 and 2, compared to Comparative Example 1 (where the mass of the P2 phase layered oxide in the cathode material is greater than the mass of the O3 phase layered oxide), Comparative Example 2 (where only the O3 phase exists in the cathode material), and Comparative Example 3 (where only the P2 phase exists in the cathode material), Example 1, by controlling the mass of the O3 phase layered oxide in the cathode material to be greater than the mass of the P2 phase layered oxide, can balance the cycle performance and capacity of the secondary battery. Comparative Examples 1 and 3 show higher cycle retention rates, but their charging capacities are too low.

[0251] Examples 2-7

[0252] The cathode material was prepared in a manner similar to that in Example 1 and assembled into a secondary battery. The only difference was that the molar ratio of sodium carbonate, lithium carbonate, nickel oxide, iron oxide, manganese dioxide and titanium dioxide was adjusted according to Table 3 below when preparing the cathode material. For the specific cathode material and secondary battery parameters, please refer to Table 4 below.

[0253] Table 3 below shows the molar ratio of each raw material and the chemical formula of the prepared cathode material in Examples 2-7. Table 4 below shows the parameters for preparing the cathode material in Examples 2-7 and the performance test parameters of the secondary battery. In addition, for ease of comparison, relevant data from Example 1 are also shown.

[0254] Table 3

[0255] Table 4

[0256] As can be seen from Tables 3 and 4, by controlling the mass ratio of P2 phase layered oxide to O3 phase layered oxide in the cathode material to be 1:(5-9), the cycle performance, charging capacity and discharging capacity of the secondary battery can be balanced.

[0257] It should be noted that this disclosure is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same essential structure and achieving the same effect as the technical concept within the scope of this disclosure are included in the technical scope of this disclosure. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this disclosure without departing from the spirit of this disclosure.

Claims

A positive electrode sheet, comprising a positive electrode current collector and a positive electrode film layer on at least one surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode material, wherein, the positive electrode material comprises at least a sodium-containing layered oxide, the sodium-containing layered oxide comprising at least two phases, wherein a first phase forms a phase interface with a second phase; the first phase is an O3 phase layered oxide, and the second phase is a P2 phase layered oxide, and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide. The positive electrode plate according to claim 1, wherein primary particles of the sodium-containing layered oxide comprise quasi-single crystal particles, at least a portion of the quasi-single crystal particles comprising the O3 phase layered oxide and the P2 phase layered oxide. The positive electrode plate according to claim 1 or 2, wherein the O3 phase layered oxide and the P2 phase layered oxide are in contact through a unit cell ab plane. The positive electrode plate according to any one of claims 1 to 3, wherein the average grain size of the O3 phase layered oxide is smaller than the average grain size of the P2 phase layered oxide. The positive electrode plate according to any one of claims 1 to 4, wherein the mass ratio of the P2 phase layered oxide to the O3 phase layered oxide is 1:(5-9). The positive electrode plate according to any one of claims 1 to 5, wherein the mass ratio of the P2 phase layered oxide to the O3 phase layered oxide is 1:(6-8). The positive electrode plate according to any one of claims 1 to 6, wherein in a charging process, the O3 phase layered oxide is converted into a P3 phase layered oxide at 3.0 V-3.2 V, and the P3 phase layered oxide is converted into an OP2 phase layered oxide at 4.0 V-4.2 V. The positive electrode plate according to any one of claims 1 to 7, wherein the voltage plateau of the positive electrode material in a discharging process is 3.05 V-3.35 V. The positive electrode plate according to any one of claims 1 to 8, wherein the voltage plateau of the positive electrode material in a discharging process within 100 cycles is 2.95 V-3.2 V. The positive electrode plate according to any one of claims 1 to 9, wherein the voltage plateau of the positive electrode material in a discharging process within 500 cycles is 2.85 V-3.15 V. The positive electrode plate according to any one of claims 1 to 10, wherein the voltage plateau of the positive electrode material in a discharging process within 1000 cycles is 2.75 V-3.05 V. The positive electrode plate according to any one of claims 1 to 11, wherein the XRD diffraction pattern of the positive electrode material comprises a first diffraction peak between 2θ of 15.9° and 16.3°, and a second diffraction peak between 2θ of 16.3° and 16.7°; FWHM of the first diffraction peak (002) FWHM of the second diffraction peak (003) satisfies: 1.0 ≤ FWHM of the first diffraction peak (003) FWHM of the second diffraction peak (002) ≤ 1.

5. The positive electrode plate according to claim 12, wherein 1.05 < FWHW (003) FWHW (002) ≤ 1.

4. The positive electrode plate according to claim 12 or 13, wherein a peak intensity I of the first diffraction peak (002) a peak intensity I of the second diffraction peak (003) satisfies: 0.1≤I (002) / [I (002) +I (003) ]≤0.

2. The positive electrode plate according to any one of claims 12 to 14, wherein a peak intensity I of the first diffraction peak (002) a peak intensity I of the second diffraction peak (003) satisfies: 0.11≤I (002) / [I (002) +I (003) ]≤0.

17. The positive electrode plate according to any one of claims 1 to 15, wherein the positive electrode material comprises a nickel-iron-manganese sodium-containing oxide. The positive electrode plate according to any one of claims 1 to 15, wherein The positive electrode material comprises Na x [M a W b Y c ]O2, 0.8≤x<1.0, 0.9 a+b+c=1.0; M comprises one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, Co; W comprises one or more alkali metal elements or alkaline earth metal elements with a larger radius than the transition metal elements; Y comprises any metal element other than the M and the W. The positive electrode plate according to claim 17, wherein the W comprises Li and / or Mg. The positive electrode plate according to claim 17 or 18, wherein the M comprises one or more of Ti, Ni, Fe, Mn. The positive electrode plate according to any one of claims 17 to 19, wherein the Y comprises one or more of Ca, Al, F. The positive electrode plate according to any one of claims 1 to 20, wherein the volume particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode material is 1.1-1.

3. The positive electrode plate according to any one of claims 1 to 21, wherein the powder compaction density of the positive electrode material at 3t is 3.2 g / cc-3.4 g / cc. a secondary battery comprising the positive electrode sheet of any one of claims 1-22. an electric device comprising the secondary battery of claim 23. a positive electrode material, the positive electrode material comprising at least a sodium-containing layered oxide, the sodium-containing layered oxide comprising at least two phases, wherein a first phase forms a phase interface with a second phase; The first phase is an O3 phase layered oxide, and the second phase is a P2 phase layered oxide, and the mass of the O3 phase layered oxide is greater than the mass of the P2 phase layered oxide. The positive electrode material according to claim 25, wherein, The primary particles of the sodium-containing layered oxide include quasi-single crystal particles, and at least part of the quasi-single crystal particles include O3 phase layered oxides and P2 phase layered oxides. The positive electrode material according to claim 25 or 26, wherein The O3 phase layered oxide and the P2 phase layered oxide are in contact through a unit cell ab plane. The positive electrode material according to any one of claims 25 to 27, wherein The average grain size of the O3 phase layered oxide is smaller than the average grain size of the P2 phase layered oxide. The positive electrode material according to claim 25 or 28, wherein The mass ratio of the P2 phase layered oxide to the O3 phase layered oxide is 1:(5-9). The positive electrode material according to any one of claims 25 to 29, wherein The mass ratio of the P2 phase layered oxide to the O3 phase layered oxide is 1:(6-8). The positive electrode material according to any one of claims 25 to 30, wherein During charging, the O3 phase layered oxide is converted into a P3 phase layered oxide at 3.0 V to 3.2 V, and the P3 phase layered oxide is converted into an OP2 phase layered oxide at 4.0 V to 4.2 V. The positive electrode material according to any one of claims 25 to 31, wherein The voltage plateau of the positive electrode material during discharging is 3.05 V to 3.35 V. The positive electrode material according to any one of claims 25 to 32, wherein The voltage plateau of the positive electrode material during discharging within 100 cycles is 2.95 V to 3.2 V. The positive electrode material according to any one of claims 25 to 33, wherein The voltage plateau of the positive electrode material during discharging within 500 cycles is 2.85 V to 3.15 V. The positive electrode material according to any one of claims 25 to 34, wherein The voltage plateau of the positive electrode material during discharging within 1000 cycles is 2.75 V to 3.05 V. The positive electrode material according to any one of claims 25 to 35, wherein The XRD diffraction pattern of the positive electrode material includes a first diffraction peak between 2θ of 15.9° and 16.3° and a second diffraction peak between 2θ of 16.3° and 16.7°. a full width at half maximum FWHM of the first diffraction peak (002) a full width at half maximum FWHM of the second diffraction peak (003) satisfies: 1.0 ≤ FWHM (003) / FWHM (002) ≤ 1.

5. The positive electrode material according to claim 36, wherein 1.05 < FWHW (003) FWHW (002) ≤ 1.

4. The positive electrode material according to claim 36 or 37, wherein a peak intensity I of the first diffraction peak (002) a peak intensity I of the second diffraction peak (003) satisfies: 0.1≤I (002) / [I (002) +I (003) ]≤0.

2. The positive electrode material according to any one of claims 36 to 38, wherein a peak intensity I of the first diffraction peak (002) a peak intensity I of the second diffraction peak (003) satisfies: 0.11≤I (002) / [I (002) +I (003) ]≤0.

17. The positive electrode material according to any one of claims 25 to 39, wherein The positive electrode material includes a nickel-iron-manganese sodium-containing oxide. The positive electrode material according to any one of claims 25 to 39, wherein The positive electrode material comprises Na x [M a W b Y c ]O2, 0.8≤x<1.0, 0.9 a+b+c=1.0, M includes one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, and Co; W includes one or more alkali metal elements or alkaline earth metal elements with a larger radius than the transition metal elements; Y includes any metal element other than M and W. The positive electrode material according to claim 41, wherein, W includes Li and / or Mg. The positive electrode material according to claim 41 or 42, wherein M includes one or more of Ti, Ni, Fe, and Mn. The positive electrode material according to any one of claims 41 to 43, wherein Y includes one or more of Ca, Al, and F. The positive electrode material according to any one of claims 25 to 44, wherein The volume particle size distribution (Dv90-Dv10) / Dv50 of the positive electrode material is 1.1-1.

3. The positive electrode material according to any one of claims 25 to 45, wherein The powder compaction density of the positive electrode material at 3t is 3.2 g / cc-3.4 g / cc. A preparation method of a positive electrode material includes: A mixing step includes mixing a sodium source and a metal source to obtain a positive electrode precursor; wherein the metal source at least includes a W source, the W includes one or more alkali metal elements or alkaline earth metal elements with a larger radius than the transition metal elements, and in the positive electrode precursor, the molar ratio of the sodium source to the W source is greater than 16:1 in terms of the molar amount of sodium elements and W elements; A heat treatment step includes heat treating the positive electrode precursor to obtain the positive electrode material. The method of making of claim 47, wherein, W includes Li and / or Mg. The method of manufacturing according to claim 47 or 48, wherein, In the positive electrode precursor, a molar ratio of the sodium source to the W source is (22-90):1, based on molar amounts of the sodium element and the W element. The method of manufacturing according to any one of claims 47 to 49, wherein, In the positive electrode precursor, a molar ratio of the sodium source to the W source is (25-45):1, based on molar amounts of the sodium element and the W element. The method of making according to any one of claims 47 to 50, wherein, In the positive electrode precursor, a molar ratio of the sodium source to the metal source is (0.8-1.0):1, based on molar amounts of the sodium element and the metal element. The method of making according to any one of claims 47 to 51, wherein, In the mixing step, the metal source further comprises an M source and a Y source; the M comprises one or more of Ti, Ni, Fe, Mn, Cu, Zn, Cr, V, Co; and the Y comprises any metal element other than the M and the W. The method of making of claim 52, wherein, In the positive electrode precursor, a molar ratio of the M source, the W source and the Y source is (0.9-1.0):(0-0.1):(0-0.1), based on molar amounts of the M element, the W element and the Y element. The method of making according to any one of claims 47 to 53, wherein, The volume particle size distribution D of the sodium source V 50 is 2 to 10 μm. The method of making according to any one of claims 47 to 54, wherein, The heat treatment step comprises a pre-sintering step of pre-sintering the positive electrode precursor and a sintering step of secondary sintering a product of the pre-sintering step. The method of making of claim 55, wherein, The pre-sintering step comprises at least one of the following features: (1) being performed at 650-950℃; (2) lasting for 5-20h; (3) being performed under at least one of air, argon, oxygen. The method of manufacturing according to claim 55 or 56, wherein, The sintering step comprises at least one of the following features: (1) being performed at 600-1000℃; (2) lasting for 5-20h; (3) being performed under at least one of air, argon, oxygen.

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