Sodium-ion secondary battery and electric device

Abstract

A sodium-ion secondary battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active material layer; the positive electrode active material layer comprises a positive electrode active material; and the positive electrode active material comprises a sodium iron phosphate-pyrophosphate positive electrode material and an O3-phase layered transition metal oxide, the mass percentage of the O3-phase layered transition metal oxide in the positive electrode active material being greater than 0 and less than 50%, and the volume-based particle size Dv50 of the O3-phase layered transition metal oxide being smaller than the Dv50 of the sodium iron phosphate-pyrophosphate positive electrode material. By mixing the O3-phase layered transition metal oxide with the sodium iron phosphate-pyrophosphate positive electrode material and also controlling the addition amount of the O3-phase layered transition metal oxide and the particle sizes of the two materials, the cycle performance and energy density of the sodium-ion secondary battery are improved.

Description

Sodium-ion secondary batteries and electrical devices

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202411773353.5, filed on December 4, 2024, entitled “Sodium-ion Secondary Battery and Power Consumption Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of batteries, and more particularly to a sodium-ion secondary battery and an electrical device thereof. Background Technology

[0004] Sodium-ion batteries have attracted increasing attention and research due to their high safety, long cycle life, and wide temperature range.

[0005] Although sodium iron pyrophosphate cathode material theoretically has the potential for low-cost, large-scale energy storage, at present, its compaction density and specific capacity are relatively low. Using it as the main cathode material results in low electrode compaction density and low energy density of the battery cell. Furthermore, sodium iron pyrophosphate cathode material itself has low electronic conductivity. Although carbon coating can improve electronic conductivity and lifespan, its cycle capacity needs further improvement.

[0006] In other words, how to improve the energy density and cycle performance of sodium iron pyrophosphate cathode material battery systems is a current research challenge. Summary of the Invention

[0007] This application is made in view of the above-mentioned issues, and its purpose is to provide a sodium-ion secondary battery and power supply device that enables the sodium iron pyrophosphate cathode material battery system to achieve both high energy density and cycle performance.

[0008] The first aspect of this application provides a sodium-ion secondary battery, which includes a positive electrode sheet, the positive electrode sheet including a positive active material layer, the positive active material layer including a positive active material, the positive active material including sodium iron pyrophosphate positive electrode material and O3 phase layered transition metal oxide.

[0009] Among them, the mass percentage of O3 phase layered transition metal oxide in the positive electrode active material is greater than 0 and less than 50%, and the volume particle size distribution Dv50 of O3 phase layered transition metal oxide is smaller than the Dv50 particle size of sodium iron pyrophosphate positive electrode material.

[0010] Therefore, this application utilizes O3-phase layered transition metal oxides to blend with sodium iron pyrophosphate cathode material. By controlling the mass percentage of O3-phase layered transition metal oxides in the cathode active material to be greater than 0 and less than 50%, and using sodium iron pyrophosphate cathode material as the main material, it is beneficial to maintain the working voltage of the sodium-ion secondary battery between 1.5V and 3.85V, improve the stability of O3-phase layered transition metal oxides and sodium iron pyrophosphate cathode material in the working voltage range of the secondary battery after blending, and improve the cycle stability of the secondary battery. Since the blending uses sodium iron pyrophosphate cathode material as the main material, controlling the volumetric particle size distribution (Dv50) of O3-phase layered transition metal oxides to be smaller than that of sodium iron pyrophosphate cathode material helps to shorten the sodium ion diffusion path and bulk diffusion resistance of the cathode active material after blending, reduce the polarization of the cathode active material, improve the capacity performance after blending, and at the same time, it is beneficial to control the overall particle size to be small. By combining the two, the compaction density is increased, which is beneficial to further improve the energy density of the sodium-ion secondary battery.

[0011] Therefore, this application effectively improves the cycle performance and energy density of sodium-ion secondary batteries by mixing O3 phase layered transition metal oxide with sodium iron pyrophosphate cathode material and simultaneously controlling the amount of O3 phase layered transition metal oxide added and the relative size of their Dv50 particle size.

[0012] In any embodiment, the mass percentage of O3-phase layered transition metal oxide in the positive electrode active material is 20%-30.1%. Controlling the mass percentage of O3-phase layered transition metal oxide in the positive electrode active material within the above range is beneficial to improving the energy density and cycle life of sodium-ion secondary batteries.

[0013] In any embodiment, the structural formula of the O3 phase layered transition metal oxide is Na. a Ni b Fe c Mn d A e M f O g The following parameters are given: 0.81≤a≤1, 0<b≤0.4, 0.2≤c≤0.5, 0.3≤d≤0.6, 0≤e≤0.12, 0≤f≤0.08, 1.8≤g≤2; A is Cu or Zn, and M is selected from at least one of V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca. The above-mentioned O3 phase layered transition metal oxides have high compaction density and / or high capacity at operating voltages of 1.5V-3.85V, therefore, their combination is beneficial for improving the energy density of sodium-ion secondary batteries.

[0014] In any embodiment, the O3 phase layered transition metal oxide satisfies at least one of (a1)-(a2):

[0015] (a1) b+c+d < 0.88; By controlling b+c+d < 0.88, it is beneficial to prepare O3 phase layered transition metal oxides.

[0016] (a2) b+c+d+e+f=1. By controlling b+c+d+e+f=1, it is beneficial for the O3 phase layered transition metal oxide to contain a high sodium content, thereby increasing the capacity of the O3 phase layered transition metal oxide and improving the energy density of sodium-ion secondary batteries.

[0017] In any embodiment, in the structural formula of the O3 phase layered transition metal oxide, A is Cu, and 0.04≤e≤0.12, 0≤f≤0.07. By introducing Cu into the O3 phase layered transition metal oxide, it achieves a charge-discharge capacity comparable to or better than that of sodium iron pyrophosphate cathode material under the charge-discharge voltage of sodium-ion secondary battery. This effectively optimizes the morphology and structure of the O3 phase layered transition metal oxide, improves particle sphericity, and increases the powder compaction density of the O3 phase layered transition metal oxide. After physical mixing with sodium iron pyrophosphate cathode material, it increases the occupancy rate of sodium iron pyrophosphate cathode material in the cathode sheet. Furthermore, since the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is smaller than that of the sodium iron pyrophosphate cathode material, the sodium iron pyrophosphate cathode material and small particles of O3 phase layered transition metal oxide can fill the stacking gaps to further increase the occupancy rate of the main material, effectively improving the energy density of sodium-ion secondary battery.

[0018] In any embodiment, the volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is 6 μm-12 μm, and the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is 5 μm-9 μm. Controlling the volumetric particle size distribution Dv50 of both the sodium iron pyrophosphate cathode material and the O3 phase layered transition metal oxide within the above ranges is beneficial for effectively improving the energy density and cycle performance of sodium-ion secondary batteries after mixing.

[0019] In any embodiment, the compacted density of the O3 phase layered transition metal oxide powder under 3T conditions is 3.3 g / cm³. 3 -3.5g / cm 3 The aforementioned O3-phase layered transition metal oxides have high powder compaction density, therefore, blending them with sodium iron pyrophosphate cathode material is beneficial for improving the energy density of sodium-ion secondary batteries.

[0020] In any embodiment, the aspect ratio of the O3 phase layered transition metal oxide is 4:1.5-3:1-3. Controlling the aspect ratio of the O3 phase layered transition metal oxide to 4:1.5-3:1-3 is beneficial for the O3 phase layered transition metal oxide to have a high powder compaction density, which is beneficial for improving the energy density of sodium-ion secondary batteries.

[0021] In any embodiment, A is Zn in the structural formula of the O3-phase layered transition metal oxide, and 0 ≤ e ≤ 0.08. The aforementioned O3-phase layered transition metal oxide has a high specific capacity; therefore, when mixed with sodium iron pyrophosphate cathode material, it effectively improves the energy density of sodium-ion secondary batteries. Simultaneously, the aforementioned O3-phase layered transition metal oxide exhibits stable cycling performance between 1.5V and 3.85V, enhancing the cycle stability of sodium-ion secondary batteries.

[0022] In any embodiment, the volumetric particle size distribution (Dv50) of the sodium iron pyrophosphate cathode material is 6 μm-12 μm, and the volumetric particle size distribution (Dv50) of the O3 phase layered transition metal oxide is 2.8 μm-9 μm. Controlling the Dv50 particle size of the sodium iron pyrophosphate cathode material and the O3 phase layered transition metal oxide within the above range is beneficial for increasing the compaction density of the cathode sheet after mixing, thereby improving the energy density of the sodium-ion secondary battery.

[0023] In any embodiment, the compaction density of the O3 phase layered transition metal oxide powder under 3T conditions is 2.7 g / cm³. 3 -3.2g / cm 3 O3-phase layered transition metal oxides have high powder compaction density, so mixing them with sodium iron pyrophosphate cathode material is beneficial to improving the energy density of sodium-ion secondary batteries.

[0024] In any embodiment, the sodium iron pyrophosphate cathode material includes sodium iron pyrophosphate particles and a carbon coating layer. The carbon coating layer coats the surface of the sodium iron pyrophosphate particles, and the mass content of the carbon coating layer in the sodium iron pyrophosphate cathode material is 1%-3%. By introducing the carbon coating layer and controlling the mass content of the sodium iron pyrophosphate cathode material, it is beneficial to improve the conductivity of the sodium iron pyrophosphate particles, enabling them to achieve both high initial charge capacity and cycle performance.

[0025] In any embodiment, the powder compaction density of the sodium iron pyrophosphate cathode material under 1T conditions is 1.8 g / cm³. 3 -2.1g / cm 3By controlling the powder compaction density of sodium iron pyrophosphate cathode material within the above range under 1T conditions, the sodium iron pyrophosphate cathode material itself has a better energy density, and thus, after being mixed with O3 phase layered transition metal oxides, it is beneficial to improve the energy density of sodium-ion secondary batteries.

[0026] In any embodiment, the compaction density of the positive electrode active material layer is 1.8 g / cm³. 3 -2.1g / cm 3 When the compaction density of the positive electrode active material layer is within the above-mentioned range, it is beneficial to improve the volumetric energy density of the sodium-ion secondary battery, and it also allows for sufficient porosity in the positive electrode active material layer so that the electrolyte can be fully wetted, maintaining the normal kinetic performance of the sodium-ion secondary battery.

[0027] In any embodiment, the thickness of the positive electrode active material layer is 50 μm-120 μm. Controlling its thickness within this range is beneficial for improving the energy density and cycle performance of sodium-ion secondary batteries.

[0028] A second aspect of this application also provides an electrical device comprising the sodium-ion secondary battery provided in the first aspect of this application. Attached Figure Description

[0029] Figure 1 shows the Na provided in Example 1. 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu 0.12 SEM image of O2.

[0030] Figure 2 is a schematic diagram of a battery cell according to one embodiment of this application.

[0031] Figure 3 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 2.

[0032] Figure 4 is a schematic diagram of a battery module according to one embodiment of this application.

[0033] Figure 5 is a schematic diagram of a battery pack according to one embodiment of this application.

[0034] Figure 6 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 5.

[0035] Figure 7 is a schematic diagram of an electrical device using a sodium-ion secondary battery as a power source according to an embodiment of this application.

[0036] Explanation of reference numerals in the attached figures:

[0037] 1-Battery pack; 2-Upper housing; 3-Lower housing; 4-Battery module; 5-Battery cell; 51-Housing; 52-Electrode assembly; 53-Top cover assembly. Embodiments of the present invention

[0038] The embodiments of the sodium-ion secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a 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 included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 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 application, 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.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0042] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the 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 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.

[0043] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0044] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0045] Although sodium iron pyrophosphate cathode material theoretically has the potential for low-cost, large-scale energy storage, at present, its compaction density and specific capacity are relatively low. When used as the main cathode material, the low compaction density of the electrode results in low energy density of the sodium-ion secondary battery. Furthermore, sodium iron pyrophosphate cathode material itself has low electronic conductivity. Although carbon coating can improve electronic conductivity and lifespan, its cycle capacity needs further improvement.

[0046] To improve the energy density and cycle performance of sodium iron pyrophosphate cathode material battery systems, O3 phase layered transition metal oxides can be physically mixed in. However, the actual energy density and cycle performance of sodium iron pyrophosphate cathode material battery systems need further optimization.

[0047] Based on this, the first aspect of the present application provides a sodium-ion secondary battery, which includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive active material, the positive active material includes sodium iron pyrophosphate positive electrode material and O3 phase layered transition metal oxide.

[0048] Among them, the volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is 6μm-12μm, the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is smaller than that of the sodium iron pyrophosphate cathode material, and the mass percentage of the O3 phase layered transition metal oxide in the cathode active material is greater than 0 and less than 50%.

[0049] In this application, O3-phase layered transition metal oxides are also called octahedral transition metal oxides, which refer to a type of transition metal oxide in which octahedrons sharing common edges form transition metal layers, with sodium ions located between the transition metal layers. In O3-phase layered transition metal oxides, O represents the position of sodium ions (O represents octahedron), and the number 3 indicates that the oxygen stacking pattern is ABCABC.

[0050] The testing method for volumetric particle size distribution (Dv50) includes: disassembling the battery to obtain the positive electrode sheet, then cutting it into 6mm*6mm pieces with ceramic scissors, attaching it to a sample stage coated with paraffin wax, and ensuring the sample protrudes slightly (<1mm) from the edge of the sample stage. Appropriate polishing time and voltage are set to perform ion cross-section polishing on the electrode end face. The polished sample is then tested using a scanning electron microscope and energy dispersive spectroscopy (SEM) (equipment model Sigma300), according to JY / T010-1996. O3-phase layered transition metal oxides (e.g., 200 particles) or sodium iron pyrophosphate positive electrode material (e.g., 200 particles) at different locations on the electrode sheet are selected, and Avizo image processing analysis is used to obtain the volumetric particle size distribution (Dv50) of the O3-phase layered transition metal oxides and the sodium iron pyrophosphate positive electrode material.

[0051] The method for testing the mass percentage of O3 phase layered transition metal oxides in positive electrode active materials includes: disassembling the battery to obtain the positive electrode sheet, then cutting it into 6mm*6mm pieces with ceramic scissors, attaching it to a sample stage coated with paraffin, and ensuring the sample protrudes slightly (<1mm) from the edge of the sample stage. Appropriate polishing time and voltage are set to perform ion cross-section polishing on the electrode end face. The polished sample is then tested using a scanning electron microscope and energy dispersive spectroscopy (EDS) for elemental analysis to obtain its composition and corresponding content.

[0052] O3-phase layered transition metal oxides possess high theoretical capacity, but most O3-phase layered transition metal oxides are prone to irreversible phase transformation in the high sodium desodium range above 3.85V, making them susceptible to structural distortion. Therefore, by physically mixing O3-phase layered transition metal oxides with sodium iron pyrophosphate cathode material, and controlling the mass percentage of O3-phase layered transition metal oxides in the cathode active material to be greater than 0 and less than 50%, it is beneficial to the working voltage of sodium-ion secondary batteries, as the O3-phase layered transition metal oxide content is less than 50%, with sodium iron pyrophosphate cathode material as the main material. The voltage is maintained at 1.5V-3.85V, which coincides with the working voltage range of sodium iron pyrophosphate cathode material, thus avoiding affecting the structural stability of sodium iron pyrophosphate cathode material. In addition, O3 phase layered transition metal oxide rarely enters or does not enter the harmful phase region below 3.85V, improving the stability of O3 phase layered transition metal oxide, which is beneficial to improving the cycle performance of sodium-ion secondary batteries. On the other hand, O3 phase layered transition metal oxide has a high compaction density and / or high capacity at a working voltage of 1.5V-3.85V. Therefore, the combination is beneficial to improving the energy density of sodium-ion secondary batteries.

[0053] Since the blending is based on sodium iron pyrophosphate cathode material, controlling the volumetric particle size distribution (Dv50) of the O3 phase layered transition metal oxide to be smaller than that of the sodium iron pyrophosphate cathode material helps to shorten the sodium ion diffusion path and bulk diffusion resistance of the blended cathode active material, reduce the polarization of the cathode active material, improve the capacity utilization after blending, and at the same time help to control the overall particle size to be small. By combining the two, the compaction density can be increased, which is conducive to further improving the energy density of sodium-ion secondary batteries.

[0054] This application improves the cycle performance and energy density of sodium-ion secondary batteries by mixing O3-phase layered transition metal oxides with sodium iron pyrophosphate cathode materials and simultaneously controlling the amount of O3-phase layered transition metal oxides added and the relative Dv50 particle size of the two materials.

[0055] In some embodiments, the O3 phase layered transition metal oxide accounts for 20%-30.1% of the mass percentage in the positive electrode active material.

[0056] Controlling the mass percentage of O3 phase layered transition metal oxides in the positive electrode active material within the above range is beneficial to improving the energy density and cycle life of sodium-ion secondary batteries.

[0057] For example, the mass percentage of O3 phase layered transition metal oxide in the positive electrode active material is any one of 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or 30.1%, or between any two of these values.

[0058] In some embodiments, the structural formula of the O3 phase layered transition metal oxide is Na. a Ni b Fe c Mn d A e M f O g , 0.81≤a≤1, 0<b≤0.4, 0.2≤c≤0.5, 0.3≤d≤0.6, 0≤e≤0.12, 0≤f≤0.08, 1.8≤g≤2; A is Cu or Zn, and M is selected from at least one of V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca.

[0059] It is understandable that in the structural formula of O3 phase layered transition metal oxides, the values ​​of a, b, c, d, e, f, and g must satisfy the above range and the charge balance of the chemical formula must be satisfied.

[0060] The aforementioned O3 phase layered transition metal oxides have high compaction density and / or high capacity at operating voltages of 1.5V-3.85V, thus their combination is beneficial for improving the energy density of sodium-ion secondary batteries.

[0061] It should be noted that sodium-ion secondary batteries experience sodium intercalation / deintercalation and consumption during charging and discharging, resulting in varying molar Na content at different discharge states. In the chemical formula of the positive electrode active material in this application, the molar Na content represents the initial state of the material, i.e., the state before material addition. As the positive electrode active material is applied to the battery system, the molar Na content changes after charge-discharge cycles. The molar O content is only a theoretical value; lattice oxygen release leads to changes in the molar oxygen content, causing fluctuations in the actual molar O content.

[0062] For example, the preparation method of O3 phase layered transition metal oxide includes: mixing sodium source, manganese source, nickel source, iron source, metal A source and metal M source according to the proportions of each element in the chemical formula of the target material, sintering at high temperature, and crushing to obtain the target layered O3 type oxide cathode material. Specific sintering temperatures can be found in relevant technologies.

[0063] In some embodiments, the O3 phase layered transition metal oxide satisfies at least one of (a1)-(a2):

[0064] (a1) b+c+d<0.88;

[0065] Controlling b+c+d < 0.88 is beneficial for the preparation of O3 phase layered transition metal oxides.

[0066] (a2)b+c+d+e+f=1.

[0067] By controlling b+c+d+e+f=1, it is beneficial to have a high sodium content in the O3 phase layered transition metal oxide, thereby increasing the capacity of the O3 phase layered transition metal oxide and improving the energy density of sodium-ion secondary batteries.

[0068] In some embodiments, A is Cu in the structural formula of the O3 phase layered transition metal oxide, and 0.04≤e≤0.12, 0≤f≤0.07.

[0069] That is, the structural formula of the O3 phase layered transition metal oxide is Na. a Ni b Fe c Mn d Cu e M f O g , 0.81≤a≤1, 0<b≤0.4, 0.2≤c≤0.5, 0.3≤d≤0.6, 0.04≤e≤0.12, 0≤f≤0.07, 1.8≤g≤2; M is selected from at least one of V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca.

[0070] By introducing Cu into the O3-phase layered transition metal oxide, the charge-discharge capacity of the O3-phase layered transition metal oxide is made comparable to or better than that of sodium iron pyrophosphate cathode material under the charge-discharge voltage of sodium-ion secondary battery. This effectively optimizes the morphology and structure of the O3-phase layered transition metal oxide, improves the sphericity of the particles, and increases the powder compaction density of the O3-phase layered transition metal oxide. After physical mixing with sodium iron pyrophosphate cathode material, the occupancy rate of sodium iron pyrophosphate cathode material in the cathode sheet is increased. Furthermore, since the volumetric particle size distribution (Dv50) of the O3-phase layered transition metal oxide is smaller than that of the sodium iron pyrophosphate cathode material, the sodium iron pyrophosphate cathode material and the small particles of O3-phase layered transition metal oxide can be used to fill the stacking gaps to further improve the occupancy rate of the main material, effectively improving the energy density of sodium-ion secondary battery.

[0071] It is understandable that when 0 < f ≤ 0.07, the cycling stability of the O3 phase layered transition metal oxide can be further improved by introducing element M doping into the O3 phase layered transition metal oxide with Cu, so that the sodium-ion secondary battery mixed with sodium iron pyrophosphate cathode material can achieve both cycling stability and energy density.

[0072] For example, the O3 phase layered transition metal oxide includes Na 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu0.12 O2, Na 0.88 Mn 0.46 Fe 0.23 Ni 0.2 Cu 0.1 O2, Na 0.88 Mn 0.47 Fe 0.23 Ni 0.23 Cu 0.06 O2 and Na 0.837 Mn 0.40 Fe 0.28 Ni 0.26 Cu 0.04 Zn 0.03 At least one of O2.

[0073] In some embodiments, the volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is 6μm-12μm, and the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is 5μm-9μm.

[0074] Dv50 has a meaning known in the art and can be tested using methods known in the art. For example, it can be measured using a laser diffraction particle size distribution measuring instrument according to the laser diffraction method for particle size distribution (see GB / T19077-2016 for details). Here, Dv50 refers to the particle size at which the cumulative volume starts from the smallest diameter and reaches 50% in particle size distribution measurement by laser scattering.

[0075] By controlling the volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material and the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide within the aforementioned ranges, the mixing of the two not only improves the capacity utilization after mixing but also effectively increases the compaction density of the cathode sheet, achieving high compaction density. This, in turn, enhances the energy density of the sodium-ion secondary battery. Furthermore, the O3 phase layered transition metal oxide within the aforementioned volumetric particle size distribution Dv50 range exhibits superior pressure resistance and is less prone to breakage under high compaction density, thus contributing to improved cycle performance of the sodium-ion secondary battery.

[0076] For example, the volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is any value of 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or between any two values.

[0077] For example, the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is any value of 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, 9.0 μm or between any two values.

[0078] In some embodiments, the compaction density of the O3 phase layered transition metal oxide powder under 3T conditions is 3.3 g / cm³. 3 -3.5g / cm 3 .

[0079] The aforementioned O3 phase layered transition metal oxide has a high powder compaction density, so mixing it with sodium iron pyrophosphate cathode material is beneficial to improving the energy density of sodium-ion secondary batteries.

[0080] For example, the compaction density of O3 phase layered transition metal oxide powder under 3T conditions is 3.30 g / cm³. 3 3.35g / cm 3 3.40 g / cm 3 3.45g / cm 3 3.50g / cm 3 It can be any value in the range or any two values ​​in between.

[0081] In some embodiments, the aspect ratio of the O3 phase layered transition metal oxide is 4:1.5-3:1-3.

[0082] The aspect ratio (ARR) of O3-phase layered transition metal oxides refers to the ratio of the longest diameter along the X-axis to the two longest diameters perpendicular to it (i.e., the width diameter along the Y-axis and the thickness diameter along the Z-axis) within the O3-phase layered transition metal oxide particle. The ARR of O3-phase layered transition metal oxides can be obtained through dynamic particle image analysis (e.g., using a NewPattec QICPIC dynamic particle image analyzer). During the preparation of positive electrode active materials, the ARR of O3-phase layered transition metal oxide materials can be controlled through a grading process. When the ARR of O3-phase layered transition metal oxides is relatively small, the O3-phase layered transition metal oxide particles are elongated. The closer the ARR of O3-phase layered transition metal oxides is to 1, the closer the length, width, and thickness diameters are to each other, meaning the O3-phase layered transition metal oxide particles are closer to a spherical shape.

[0083] Controlling the aspect ratio of the O3 phase layered transition metal oxide within the above range is beneficial for the O3 phase layered transition metal oxide to have a high powder compaction density.

[0084] For example, the aspect ratio of the O3 phase layered transition metal oxide is any one of the following ratios: 4:1.5:1, 4:1.5:2, 4:1.5:3, 4:2:1, 4:2:2, 4:2:3, 4:3:1, or 4:3:3, or between any two ratios.

[0085] In some embodiments, A is Zn in the structural formula of the O3 phase layered transition metal oxide, and 0≤e≤0.08.

[0086] That is, the structural formula of the O3 phase layered transition metal oxide is Na. a Ni b Fe c Mn d Zn e M f O g , 0.81≤a≤1, 0<b≤0.4, 0.2≤c≤0.5, 0.3≤d≤0.6, 0≤e≤0.08, 0≤f≤0.08, 1.8≤g≤2; M is selected from at least one of V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca.

[0087] It is understandable that when 0 < f ≤ 0.08, the cycling stability of the O3 phase layered transition metal oxide can be further improved by introducing element M doping into the O3 phase layered transition metal oxide, so that the sodium-ion secondary battery after being mixed with sodium iron pyrophosphate cathode material can achieve both cycling stability and energy density.

[0088] The specific capacity of the aforementioned O3-phase layered transition metal oxide is within the range of 1.5V-3.85V, with a coin charge capacity ≥134mAh / g and a discharge capacity ≥120mAh / g. In other words, the aforementioned O3-phase layered transition metal oxide has a high specific capacity. Therefore, when it is mixed with sodium iron pyrophosphate cathode material, the energy density of sodium-ion secondary batteries is effectively improved. At the same time, the aforementioned O3-phase layered transition metal oxide is stable in cycling at 1.5V-3.85V, thus improving the cycle stability of sodium-ion secondary batteries.

[0089] For example, the O3 phase layered transition metal oxide includes, but is not limited to, NaNi. 0.4 Fe 0.2 Mn 0.4 O2, NaNi 0.33 Fe 0.33 Mn 0.33 O2, Na 0.92 Ni 0.26 Fe 0.3 Mn 0.36 Zn 0.08 O2 and Na 0.88 Ni 0.22 Fe 0.31 Mn 0.39 Zn 0.05 Al 0.03 At least one of O2.

[0090] In some embodiments, the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is 2.8 μm-9 μm.

[0091] Dv50 has a meaning known in the art and can be tested using methods known in the art. For example, it can be measured using a laser diffraction particle size distribution measuring instrument according to the laser diffraction method for particle size distribution (see GB / T19077-2016 for details). Here, Dv50 refers to the particle size at which the cumulative volume starts from the smallest diameter and reaches 50% in particle size distribution measurement by laser scattering.

[0092] Controlling the volumetric particle size distribution Dv50 of sodium iron pyrophosphate cathode material and the volumetric particle size distribution Dv50 of O3 phase layered transition metal oxide within the above ranges ensures that the mixing of the two not only improves the capacity utilization after mixing, but also helps to increase the compaction density of the cathode sheet, which in turn helps to improve the energy density of sodium-ion secondary batteries.

[0093] Controlling the particle size of the O3 phase layered transition metal oxide within the above range is beneficial for increasing the compaction density of the cathode sheet and improving the energy density of the sodium-ion secondary battery after mixing it with sodium iron pyrophosphate cathode material.

[0094] For example, the volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is any value of 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm or between any two values.

[0095] For example, the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is any value of 2.8 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, 6.5 μm, 7.0 μm, 7.5 μm, 8.0 μm, 8.5 μm, or 9.0 μm, or between any two values.

[0096] In some embodiments, the compaction density of the O3 phase layered transition metal oxide powder under 3T conditions is 2.7 g / cm³. 3 -3.2g / cm 3 .

[0097] O3 phase layered transition metal oxides have high powder compaction density, so mixing them with sodium iron pyrophosphate cathode material is beneficial to improving the energy density of sodium-ion secondary batteries.

[0098] For example, the compaction density of O3 phase layered transition metal oxide powder under 3T conditions is 2.7 g / cm³. 3 2.8g / cm 3 2.9g / cm 3 3.0g / cm 3 3.1g / cm 3 3.2g / cm 3It can be any value in the range or any two values ​​in between.

[0099] Among them, the sodium iron pyrophosphate cathode material can be bare sodium iron pyrophosphate (that is, sodium iron pyrophosphate without a coating layer on its surface) or carbon-coated sodium iron pyrophosphate.

[0100] In some embodiments, the sodium iron pyrophosphate cathode material includes sodium iron pyrophosphate particles and a carbon coating layer, wherein the carbon coating layer coats the surface of the sodium iron pyrophosphate particles, and the mass content of the carbon coating layer in the sodium iron pyrophosphate cathode material is 1%-3%.

[0101] Introducing a carbon coating layer and controlling the mass content of sodium iron pyrophosphate cathode material can improve the conductivity of sodium iron pyrophosphate particles, enabling them to achieve both high initial charge capacity and cycle performance.

[0102] For example, the mass content of the carbon coating layer in the sodium iron pyrophosphate cathode material is any one of 1.0%, 1.2%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0% or between any two values.

[0103] It is understood that sodium iron pyrophosphate in this application includes, but is not limited to, at least one of the following:

[0104] (1) Na x Fe y (PO4)2P2O7, x=3.5-4.5, y=2.75-3.25; for example, the chemical formula of sodium iron pyrophosphate is: Na 4.1 Fe 2.95 (PO4)2P2O7 or Na4Fe3(PO4)2P2O7.

[0105] (2) Na x Fe y P m O n 3.5≤x≤4.5, 2.5≤y≤3.5, 3.7<m<4, 14.5≤n≤15.5; By introducing phosphorus vacancies, it is beneficial for its crystal lattice to grow along the (602) crystal plane, shortening the Na... + The transmission path improves Na + The diffusion rate is beneficial to the rate performance and initial coulombic efficiency of the battery.

[0106] (3) Doped sodium iron pyrophosphate, wherein the doping element includes, but is not limited to, one or more of Mn, Co, Ni, Mg, Cu, Zn, Zr, Ti, V, and Nb. For example, the doped sodium iron pyrophosphate is Na₄Fe₂O₃. 3-2x Vx (PO4)2P2O7, where x takes values ​​in the range of 0 < x < 0.5. For example, the doped sodium iron pyrophosphate is Na. x Fe y Nb m (PO4) n (P2O7); where x is 2-8, y is 1.5-6, m is 0.05-0.3, and n is 1-4.

[0107] It should be noted that sodium iron pyrophosphate may contain some impurities, including but not limited to sodium iron phosphate. The mass content of these impurities in sodium iron pyrophosphate is <8%, ideally 0%, meaning the mass content of the active ingredient is ≥92%. At this point, the impurity content in sodium iron pyrophosphate is low, resulting in higher capacity and better cycle performance for the sodium iron pyrophosphate cathode material.

[0108] For example, the active ingredient in sodium iron pyrophosphate is Na4Fe3(PO4)2P2O7, wherein the mass content of the active ingredient in sodium iron pyrophosphate is ≥92%.

[0109] In some embodiments, the powder compaction density of the sodium iron pyrophosphate cathode material under 1T conditions is 1.80 g / cm³. 3 -2.1g / cm 3 .

[0110] By controlling the powder compaction density of sodium iron pyrophosphate cathode material within the above range under 1T conditions, the sodium iron pyrophosphate cathode material itself has a better energy density, which is beneficial to improving the energy density of sodium-ion secondary batteries after being mixed with O3 phase layered transition metal oxides.

[0111] For example, the powder compaction density of sodium iron pyrophosphate cathode material under 1T conditions is 1.80 g / cm³. 3 1.85g / cm 3 1.90g / cm 3 1.95g / cm 3 2.00g / cm 3 2.05g / cm 3 2.10 g / cm 3 It can be any one of the values ​​or between any two values.

[0112] In some embodiments, the compaction density of the positive electrode active material layer is 1.8 g / cm³. 3 -2.1g / cm 3 .

[0113] The compaction density of the active material layer is a term known in the art and can be tested using methods known in the art. For example, the compaction density of the active material layer = the areal density of the active material layer / the thickness of the active material layer. The areal density of the active material layer is a term known in the art and can be tested using methods known in the art. For example, take an electrode sheet coated on one side and cold-pressed (if it is a double-sided coated electrode sheet, the active material layer on one side can be wiped off first), cut it into a small circular piece with an area of ​​S0, weigh it, and record its weight as M1; then wipe off the active material layer of the weighed electrode sheet, weigh the current collector, and record it as M0. The areal density of the active material layer = (M1 - M0) / S0.

[0114] When the compaction density of the positive electrode active material layer is within the above range, it is beneficial to improve the volumetric energy density of the sodium-ion secondary battery, and also allows for sufficient porosity in the positive electrode active material layer so that the electrolyte can be fully wetted, maintaining the normal kinetic performance of the sodium-ion secondary battery.

[0115] For example, the compaction density of the positive electrode active material layer is 1.80 g / cm³. 3 1.85g / cm 3 1.90g / cm 3 1.95g / cm 3 2.00g / cm 3 2.05g / cm 3 2.10 g / cm 3 It can be any one of the values ​​or between any two values.

[0116] In some embodiments, the thickness of the positive electrode active material layer is 50 μm-120 μm.

[0117] Controlling its thickness within the above range is beneficial to improving the energy density and cycle performance of sodium-ion secondary batteries.

[0118] For example, the thickness of the positive electrode active material layer is any value of 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 92μm, 100μm, 105μm, 110μm, 105μm, 120μm or between any two values.

[0119] The second aspect of this application provides an electrical device that includes the sodium-ion secondary battery provided in the first aspect of this application.

[0120] In addition, the sodium-ion secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0121] Sodium-ion secondary batteries

[0122] Typically, a sodium-ion secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0123] [Positive electrode plate]

[0124] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, as shown in the positive active material layer of the sodium-ion secondary battery provided in the first aspect of this application.

[0125] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0126] 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.).

[0127] In some embodiments, the positive electrode active material 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.

[0128] In some embodiments, the positive electrode active material layer 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.

[0129] 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 active 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.

[0130] [Negative electrode plate]

[0131] In some embodiments, the negative electrode sheet includes a negative current collector and a layer of negative active material disposed on at least one surface of the negative current collector.

[0132] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0133] In some embodiments, the negative electrode 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, copper, copper 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.).

[0134] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The negative electrode active material may be any 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, 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 application 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.

[0135] In some embodiments, the negative electrode active material 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).

[0136] In some embodiments, the negative electrode active material layer 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.

[0137] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0138] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as 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 a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0139] In other embodiments, the current collector of the negative electrode sheet may typically include a current collector body and a base coating. The base coating may be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, but may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot play the role of negative electrode active material.

[0140] [Electrolytes]

[0141] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be selected based on existing sodium-ion secondary batteries.

[0142] In some implementations, the electrolyte comprises an organic solvent and a sodium salt.

[0143] For example, the sodium salt includes, but is not limited to, at least one of NaPF6, NaClO4, NaSO3CF3 or Na(CH3)C6H4SO3.

[0144] For example, the organic solvent is an ester-based solvent, which includes, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), and 1,4-butyrolactone (GBL).

[0145] 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.

[0146] For example, the additive may include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate (DFEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), or tris(trimethylsilane) borate (TMSB).

[0147] [Isolation membrane]

[0148] In some embodiments, the sodium-ion secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0149] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0150] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0151] In some embodiments, the sodium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0152] In some embodiments, the outer packaging of a sodium-ion secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of a sodium-ion secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0153] In this application, a sodium-ion secondary battery can refer to a single battery cell, or it can refer to a single physical module comprising multiple battery cells to provide higher voltage and capacity, and it can take the form of a battery pack, battery module, etc.

[0154] This application 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 2 shows a battery cell 5 as a square structure.

[0155] In some embodiments, referring to FIG3, 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.

[0156] In some embodiments, individual battery cells can be assembled into a battery module, and the number of sodium-ion secondary batteries contained in the battery module 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 module.

[0157] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, 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.

[0158] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0159] 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.

[0160] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, 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 box 2 and a lower box 3, with the upper box 2 covering the lower box 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.

[0161] In addition, this application also provides an electrical device, which includes at least one sodium-ion secondary battery (a battery cell, a battery module, or a battery pack) provided in this application. The sodium-ion 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.

[0162] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0163] Figure 7 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 sodium-ion secondary batteries for this device, a battery pack or battery module can be used.

[0164] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0165] Examples and Comparative Examples

[0166] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0167] I. Battery Preparation

[0168] Preparation of the positive electrode sheet

[0169] O3-phase layered transition metal oxides and sodium iron pyrophosphate cathode material were mixed at the mass ratios shown in Table 1 to obtain the cathode active material. The sodium iron pyrophosphate cathode material was carbon-coated Na4Fe3(PO4)2P2O7, abbreviated as Na4Fe3(PO4)2P2O7 / C. The sodium iron pyrophosphate cathode material had an initial charge specific capacity of 116 mAh / g, an initial discharge specific capacity of 108 mAh / g, a volume particle size distribution (Dv50) of 12 μm, and a 1T powder compaction density of 1.82 g / cm³. 3 .

[0170] The positive electrode active material, binder polyvinylidene fluoride, and conductive agent SP are mixed in a weight ratio of 95:2.5:2.5 and dissolved in the solvent N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. The slurry is then coated onto the current collector aluminum foil, dried, and then cold-pressed, trimmed, cut, and slit to produce the positive electrode sheet.

[0171] Preparation of the negative electrode sheet

[0172] The negative electrode active material hard carbon HC, conductive agent SP, and binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 95:2.5:2.5 and dissolved in deionized water to prepare a negative electrode slurry. The slurry is then coated onto a current collector aluminum foil, dried, and then cold-pressed, trimmed, cut, and slit to produce a negative electrode sheet.

[0173] Preparation of Electrolyte

[0174] The electrolyte was prepared in an argon-atmospheric glove box with a water content of <10 ppm. First, sodium salt NaPF6 was added to the solvent (DEC / EC weight ratio of 4:1), followed by the addition of FEC to complete the electrolyte preparation. The molar concentration of sodium salt was 1 mol / L, and the content of FEC in the electrolyte was 2 wt%.

[0175]

Isolation Film

[0176] Polyethylene film is used as the separation membrane.

[0177] [Preparation of Secondary Batteries]

[0178] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to obtain the electrode assembly. The electrode assembly is placed in the casing, dried, and then injected with electrolyte for sodium-ion batteries. After vacuum sealing, settling, formation, and shaping, a sodium-ion secondary battery is obtained.

[0179]

Preparation of Button Electrodes

[0180] Using a sodium metal sheet as the negative electrode, the prepared positive electrode, separator, and sodium metal sheet are stacked in sequence, with the separator positioned between the positive electrode and the sodium metal sheet to provide isolation. The electrolyte is then injected into the dried cell to assemble a CR2032 button cell.

[0181] Among them, the volumetric particle size distribution Dv50 test: with reference to the standard GB / T19077-2016, the measurement was performed using a laser diffraction scattering particle size analyzer.

[0182] Coin cell initial charge / discharge capacity test: Using LAND testing instruments, the specific test procedure was as follows: Coin cells were prepared using sodium iron pyrophosphate cathode material alone, O3-phase layered transition metal oxide used in each example and comparative example, and cathode active material obtained by combining sodium iron pyrophosphate cathode material and O3-phase layered transition metal oxide in each example, respectively. The coin cells were left to stand for 3 hours, charged at a constant current of 0.1C to 3.85V, and charged at a constant voltage of 50uA to obtain the initial charge capacity of each component. After standing for 5 minutes, the cells were discharged at a constant current of 0.1C to 1.5V, and left to stand for 4 minutes to obtain the initial charge / discharge capacity of each component.

[0183] Among them, the volumetric particle size distribution Dv50 test: with reference to the standard GB / T19077-2016, the measurement was performed using a laser diffraction scattering particle size analyzer.

[0184] Coin cell initial charge / discharge capacity test: Using LAND testing instruments, the specific test procedure was as follows: Coin cells were prepared using sodium iron pyrophosphate cathode material alone, O3-phase layered transition metal oxide used in each example and comparative example, and cathode active material obtained by combining sodium iron pyrophosphate cathode material and O3-phase layered transition metal oxide in each example, respectively. The coin cells were left to stand for 3 hours, charged at a constant current of 0.1C to 3.85V, and charged at a constant voltage of 50uA to obtain the initial charge capacity of each component. After standing for 5 minutes, the cells were discharged at a constant current of 0.1C to 1.5V, and left to stand for 4 minutes to obtain the initial charge / discharge capacity of each component.

[0185] The sodium-ion secondary batteries in each embodiment and comparative example were prepared using the same method as in Example 1, but the composition and parameters of the positive electrode were adjusted. Specifically, the O3-phase layered transition metal oxides in Examples 1-10 and Comparative Examples 2-4 were O3-phase layered transition metal oxides with introduced Cu elements. In Examples 1, 5-10, and Comparative Examples 1 and 3-4, Na... 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu 0.12 O2, the O3 phase layered transition metal oxide used in Example 2 is Na 0.88 Mn 0.46 Fe 0.23 Ni 0.2 Cu 0.1 O2, the O3 phase layered transition metal oxide used in Example 3 is Na 0.88 Mn 0.47 Fe 0.23 Ni 0.23 Cu 0.06O2, the O3 phase layered transition metal oxide used in Example 4 is Na 0.837 Mn 0.40 Fe 0.28 Ni 0.26 Cu 0.04 Zn 0.03 O2.

[0186] Figure 1 shows the Na provided in Example 1. 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu 0.12 The SEM image of O2, as shown in Figure 1, shows that its morphology is relatively regular and the particles have a high degree of sphericity.

[0187] In Examples 11-19 and Comparisons 5-7, the O3-phase layered transition metal oxides were all Cu-free O3-phase layered transition metal oxides. Specifically, in Example 11, the O3-phase layered transition metal oxide was NaNi. 0.4 Fe 0.2 Mn 0.4 O2, the O3 phase layered transition metal oxide in Examples 12, 15-19 and Comparative Examples 5-7 is NaNi. 0.33 Fe 0.33 Mn 0.33 O2, in Example 13, the O3 phase layered transition metal oxide is Na. 0.92 Ni 0.26 Fe 0.3 Mn 0.36 Zn 0.08 O2, in Example 14, the O3 phase layered transition metal oxide is Na. 0.88 Ni 0.22 Fe 0.31 Mn 0.39 Zn 0.05 Al 0.03 O2.

[0188] The only difference between Comparative Example 1 and Example 1 is that the O3 phase layered transition metal oxide Na 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu 0.12 The mass ratio of O2 to sodium iron pyrophosphate cathode material is 1:1, which means that the mass percentage of O3 phase layered transition metal oxide in cathode active material is 50%.

[0189] The only difference between Comparative Example 2 and the various embodiments is that the positive electrode active material in Comparative Example 2 only contains sodium iron pyrophosphate positive electrode material.

[0190] The only difference between Comparative Example 3 and Example 1 is that the positive electrode active material in Comparative Example 3 contains only O3 phase layered transition metal oxide Na. 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu 0.12 O2.

[0191] The only difference between Comparative Example 4 and Example 1 is that in Comparative Example 4, the O3 phase layered transition metal oxide Na... 0.854 Mn 0.44 Fe 0.23 Ni 0.2 Cu 0.12 The volumetric particle size distribution Dv50 of O2 is greater than that of sodium iron pyrophosphate cathode material.

[0192] The only difference between Comparative Example 5 and Example 12 is that the O3 phase layered transition metal oxide NaNi 0.33 Fe 0.33 Mn 0.33 The mass ratio of O2 to sodium iron pyrophosphate cathode material is 1:1, which means that the mass percentage of O3 phase layered transition metal oxide in cathode active material is 50%.

[0193] The only difference between Comparative Example 6 and Example 12 is that the positive electrode active material in Comparative Example 6 contains only O3 phase layered transition metal oxide NaNi. 0.33 Fe 0.33 Mn 0.33 O2.

[0194] The only difference between Comparative Example 7 and Example 12 is that in Comparative Example 7, the O3 phase layered transition metal oxide NaNi 0.33 Fe 0.33 Mn 0.33 The volumetric particle size distribution Dv50 of O2 is greater than that of sodium iron pyrophosphate cathode material.

[0195] The different parameters in each embodiment and comparative example are detailed in Table 1.

[0196] Table 1 Different parameters of the positive electrode sheet

[0197]

[0198] It should be noted that in Table 1, — indicates that no test was conducted, and / indicates that none was performed.

[0199] II. Performance Testing of Positive Electrode and Secondary Battery

[0200] [Compact density test of the positive electrode active material layer]

[0201] The compaction density of the active material layer = the areal density of the active material layer / the thickness of the active material layer. The areal density of the positive electrode active material layer can be obtained by taking the electrode sheet coated on one side and cold-pressed (if it is a double-sided coated electrode sheet, the positive electrode active material layer on one side can be wiped off first), punching it into a small circular piece with an area of ​​S0, weighing it, and recording its weight as M1; then wipe off the positive electrode active material layer of the electrode sheet weighed above, weigh the current collector, and record it as M0. The areal density of the positive electrode active material layer = (M1-M0) / S0.

[0202] [Rechargeable battery energy density and cycle performance cls@90%SOH]

[0203] Under a constant temperature environment of 25℃, the secondary battery is charged at 1C to 3.9V, and then charged at a constant voltage of 3.9V until the current is less than or equal to 0.05mA. After resting for 5 minutes, it is discharged at 1C to 1.5V, and the discharge capacity at this point is recorded as D0. The aforementioned charge-discharge cycle is repeated until the discharge capacity decreases to 90% of D0. The number of cycles completed at this point is recorded, which is the cycle life at 90% SOH.

[0204] Wherein, mass energy density = D0 / mass of secondary battery; (unit of mass energy density: Wh / kg), where D0 is the measured discharge capacity of the cell.

[0205] Positive electrode sheets, secondary batteries, and coin cells for each embodiment and comparative example were prepared according to the above method, and the results are shown in Table 2 below.

[0206] Table 2

[0207]

[0208] As can be seen from Tables 1 and 2, compared with the sodium iron pyrophosphate cathode material alone, the cycle capacity and energy density of Examples 1-19 were improved.

[0209] As can be seen from Examples 1-19 and Comparative Examples 2, 3, and 6, the mixed positive electrode active material provided in this application, compared with the single sodium iron pyrophosphate positive electrode material or the single O3 phase layered transition metal oxide, can significantly improve the cycle performance of the battery while maintaining high energy density.

[0210] As can be seen from Examples 1-10 and Comparative Examples 1 and 3-4, the length, width, and thickness of the O3 phase layered transition metal oxides with introduced Cu are relatively close, and the sphericity of the O3 phase layered transition metal oxide particles is high. Among them, the compaction density of O3 phase layered transition metal oxides with a volume particle size distribution Dv50 of 5μm-9μm under 3T conditions can be greater than 3.3g / cm³. 3 It has a high compaction density.

[0211] As can be seen from Examples 1-4, the length, width, thickness and diameter of the O3 phase layered transition metal oxide with Cu element are relatively close. The O3 phase layered transition metal oxide particles have high sphericity and high compaction density. They can be physically mixed with sodium iron pyrophosphate cathode material to achieve both high cycle performance and high energy density.

[0212] As can be seen from Examples 1, 5-6 and Comparative Example 4, when O3 phase layered transition metal oxide is mixed with sodium iron pyrophosphate cathode material, the volumetric particle size distribution Dv50 of O3 phase layered transition metal oxide is smaller than that of sodium iron pyrophosphate cathode material, which is beneficial for sodium-ion secondary batteries to achieve both high energy density and high cycle life.

[0213] Comparing Examples 1, 7-10, and Comparative Example 1, it can be seen that in the positive electrode active material obtained by mixing sodium iron pyrophosphate cathode material and O3 phase layered transition metal oxide, the mass percentage of O3 phase layered transition metal oxide in the positive electrode active material is greater than 0 and less than 50%, and the volumetric particle size distribution (Dv50) of O3 phase layered transition metal oxide is smaller than that of sodium iron pyrophosphate cathode material. This can effectively improve the cycle performance of the battery and increase the energy density. Specifically, with the mass percentage of O3 phase layered transition metal oxide in the positive electrode active material being 20%-30.1%, the sodium-ion secondary battery achieves a better balance between energy density and cycle life.

[0214] As can be seen from Examples 11-19 and Comparative Examples 5-7, the O3 phase layered transition metal oxide (Na) a Ni b Fe c Mn d Zn e M f O g The coin cell has a high initial charge / discharge capacity, i.e., high capacity, provided that 0.81≤a≤1, 0<b≤0.4, 0.2≤c≤0.5, 0.3≤d≤0.6, 0≤e≤0.08, 0≤f≤0.08, and 1.8≤g≤2; M is selected from at least one of V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, and Ca.

[0215] As can be seen from Examples 11-14, different Cu-free O3 phase layered transition metal oxides all have high capacity and can achieve both high cycle performance and energy density after being physically mixed with sodium iron pyrophosphate cathode material.

[0216] As can be seen from Examples 11, 15-16 and Comparative Example 7, when O3 phase layered transition metal oxide is mixed with sodium iron pyrophosphate cathode material, the volumetric particle size distribution Dv50 of O3 phase layered transition metal oxide is smaller than that of sodium iron pyrophosphate cathode material, which is beneficial for sodium-ion secondary batteries to achieve both high energy density and high cycle life.

[0217] As can be seen from the comparison of Examples 1, 17-19 and Comparative Example 6, in the positive electrode active material obtained by mixing sodium iron pyrophosphate cathode material and O3 phase layered transition metal oxide, the mass percentage of O3 phase layered transition metal oxide in the positive electrode active material is less than 50%, and the volumetric particle size distribution Dv50 of O3 phase layered transition metal oxide is smaller than that of sodium iron pyrophosphate cathode material, which can effectively improve the cycle performance of the battery while also achieving better energy density. Specifically, the mass percentage of O3 phase layered transition metal oxide in the positive electrode active material is 20%-30.1%, resulting in sodium-ion secondary batteries with better energy density and cycle life. It should be noted that this application is not limited to the above embodiments. The above embodiments are merely examples, and embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. 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 application without departing from the spirit of this application.

Claims

1. A sodium-ion secondary battery, wherein, It includes a positive electrode sheet, the positive electrode sheet includes a positive active material layer, the positive active material layer includes a positive active material, the positive active material includes sodium iron pyrophosphate positive electrode material and O3 phase layered transition metal oxide; Wherein, the mass percentage of the O3 phase layered transition metal oxide in the positive electrode active material is greater than 0 and less than 50%, and the volume particle size distribution Dv50 of the O3 phase layered transition metal oxide is smaller than the Dv50 particle size of the sodium iron pyrophosphate positive electrode material.

2. The sodium-ion secondary battery according to claim 1, wherein, The O3 phase layered transition metal oxide accounts for 20%-30.1% of the mass percentage of the positive electrode active material.

3. The sodium-ion secondary battery according to claim 1 or 2, wherein Na a Ni b Fe c Mn d A e M f O g , 0.81≤a≤1, 0 A is Cu or Zn, and M is selected from at least one of V, Cr, Al, Sc, Sn, Sb, Zr, Nb, Ti, Mg, Ru, Ir, Ca.

4. The sodium-ion secondary battery of claim 3, wherein, The O3 phase layered transition metal oxide satisfies at least one of (a1)-(a2): (a1) b+c+d<0.88; (a2)b+c+d+e+f=1.

5. The sodium-ion secondary battery according to claim 3 or 4, wherein In the structural formula of the O3 phase layered transition metal oxide, A is Cu, and 0.04≤e≤0.12, 0≤f≤0.

07.

6. The sodium-ion secondary battery of claim 5, wherein, The volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is 6μm-12μm, and the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is 5μm-9μm.

7. The sodium-ion secondary battery of claim 5, wherein, The powder compaction density of the O3 phase layered transition metal oxide under 3T condition is 3.3 g / cm 3 - 3.5 g / cm 3 .

8. The sodium-ion secondary battery of claim 5, wherein, The aspect ratio of the O3 phase layered transition metal oxide is 4:1.5-3:1-3.

9. The sodium-ion secondary battery according to claim 3 or 4, wherein, In the structural formula of the O3 phase layered transition metal oxide, A is Zn, and 0≤e≤0.

08.

10. The sodium-ion secondary battery of claim 9, wherein, The volumetric particle size distribution Dv50 of the sodium iron pyrophosphate cathode material is 6μm-12μm, and the volumetric particle size distribution Dv50 of the O3 phase layered transition metal oxide is 2.8μm-9μm.

11. The sodium-ion secondary battery of claim 9, wherein, The powder compaction density of the O3 phase layered transition metal oxide under 3T condition is 2.7 g / cm 3 - 3.2 g / cm 3 .

12. The sodium-ion secondary battery according to any one of claims 1-11, wherein, The sodium iron pyrophosphate cathode material includes sodium iron pyrophosphate particles and a carbon coating layer. The carbon coating layer coats the surface of the sodium iron pyrophosphate particles, and the mass content of the carbon coating layer in the sodium iron pyrophosphate cathode material is 1%-3%.

13. The sodium-ion secondary battery according to any one of claims 1-12, wherein, The powder compaction density of the sodium iron phosphate pyrophosphate positive electrode material under 1T condition is 1.8 g / cm 3 -2.1 g / cm 3 .

14. The sodium-ion secondary battery according to any one of claims 1-13, wherein, The compacted density of the positive electrode active material layer is 1.8 g / cm 3 - 2.1 g / cm 3 .

15. The sodium-ion secondary battery according to any one of claims 1-14, wherein, The thickness of the positive electrode active material layer is 50μm-120μm.

16. An electrical appliance, wherein, Includes the sodium-ion secondary battery according to any one of claims 1-15.

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