Sodium secondary battery and electric device

Abstract

A sodium secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; the negative electrode sheet comprises a negative electrode current collector, or comprises a negative electrode current collector and a sodium metal layer arranged on the surface of the negative electrode current collector; the electrolyte comprises colloidal particles, an electrolyte salt and a solvent; the Raman spectrum of the electrolyte comprises a first Raman characteristic peak having a Raman shift ranging from 815 cm-1 to 825 cm-1 and a second Raman characteristic peak having a Raman shift ranging from 845 cm-1 to 855 cm-1, the peak area A1 of the first Raman characteristic peak and the peak area A2 of the second Raman characteristic peak satisfying: (A1+A2) / S1≤30%. In the formula, S1 represents the sum of peak areas of all characteristic peaks appearing in the Raman spectrum and having a Raman shift ranging from 800 cm-1 to 900 cm-1. The sodium secondary battery achieves both high capacity and high safety performance.

Description

Sodium secondary battery and electric device

[0001] Cross Reference to Related Applications

[0002] The present disclosure is based on and claims priority to Chinese Patent Application No. 202411280500.5, filed on September 12, 2024, entitled “Sodium secondary battery and electric device”, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of batteries, and in particular to a sodium secondary battery and an electric device. BACKGROUND

[0004] In recent years, with the application range of secondary batteries becoming more and more extensive, secondary batteries are widely used in energy storage power supply systems such as hydropower, thermal power, wind power and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, aerospace, etc. Due to the great development of secondary batteries, higher requirements are put forward for their service life and safety performance.

[0005] The electrolyte inside the secondary battery is prone to side reactions. Side reactions are usually accompanied by gas generation, affecting the service life of the secondary battery, and in severe cases, can cause safety problems such as fire and explosion. SUMMARY

[0006] The present disclosure is made in view of the above-mentioned problems, and aims to provide a sodium secondary battery and an electric device that balance high capacity and high safety performance.

[0007] To achieve the above-mentioned purpose, the first aspect of the present disclosure provides a sodium secondary battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the negative electrode sheet comprising a negative electrode current collector, or comprising a negative electrode current collector and a sodium metal layer provided on the surface of the negative electrode current collector; the electrolyte comprising colloidal particles, an electrolyte salt, and a solvent; the electrolyte comprising a first Raman characteristic peak with a Raman shift of 815 cm -1 to 825 cm -1 and a second Raman characteristic peak with a Raman shift of 845 cm -1 to 855 cm -1 in a Raman spectrum of the electrolyte, the peak area A1 of the first Raman characteristic peak and the peak area A2 of the second Raman characteristic peak satisfying: (A1+A2) / S1≤30%, wherein S1 represents the area of the Raman spectrum with a Raman shift of 800 cm -1 to 900 cm -1the sum of the peak areas of all Raman characteristic peaks appearing in the range. In the present disclosure, by including the colloidal particles in the electrolyte, the ratio of (A1+A2) / S1 is reduced to below 30%, indicating that the colloidal particles have a high degree of constraint on the solvent, which is conducive to reducing the probability of migration of the solvent to the surface of the electrode material, reducing the side reaction between the solvent and the electrode material, thereby reducing the gas production of the sodium secondary battery, improving the safety performance of the battery, and in addition, the sodium secondary battery also has high capacity.

[0008] In some embodiments, (A1+A2) / S1≤24%. By controlling (A1+A2) / S1 in the above range, it is conducive to further reducing the gas production of the battery.

[0009] In some embodiments, the particle size of the colloidal particles is 1000 nm or less. By controlling the particle size of the colloidal particles in the above range, the risk of agglomeration and sedimentation of the colloidal particles can be reduced, which is conducive to improving the constraint of the colloidal particles on the solvent.

[0010] In some embodiments, the particle size of the colloidal particles is 10 nm to 100 nm. By controlling the particle size of the colloidal particles in the above range, the risk of agglomeration and sedimentation of the colloidal particles can be reduced, which is conducive to improving the constraint of the colloidal particles on the solvent.

[0011] In some embodiments, the colloidal particles include at least one of sodium fluoride, hexagonal boron nitride, sodium carbonate, lithium fluoride, lithium oxide, lithium carbonate, aluminum oxide, titanium oxide, titanium nitride, silicon nitride, silicon carbide, Na 3.3 Zr 1.7 La 0.3 Si2PO 12 The above colloidal particles have a large constraint on the solvent.

[0012] In some embodiments, the colloidal particles include β-aluminum oxide. By selecting colloidal particles including β-aluminum oxide, on the one hand, the constraint of β-aluminum oxide on the solvent can reduce the gas production of the battery, and on the other hand, the high ionic conductivity of β-aluminum oxide can promote the movement of active ions in the electrolyte, thereby improving the kinetic performance of the battery.

[0013] In some embodiments, the colloidal particles include sodium fluoride or hexagonal boron nitride. By selecting sodium fluoride as the colloidal particles, the colloidal particles can reduce the loss of passivation components (e.g., NaF) in the SEI formed in-situ at the interface, thereby further inhibiting side reactions between the solvent and the electrode material. By selecting hexagonal boron nitride as the colloidal particles, the colloidal particles can scavenge free radicals in the solvent, thereby further inhibiting side reactions between the solvent and the electrode material. In some embodiments, the mass content of the colloidal particles in the electrolyte is 1wt% to 10wt%. By controlling the mass content of the colloidal particles in the above range, it is beneficial for the colloidal particles to exert their binding effect on the solvent while reducing the risk of colloidal particle aggregation and sedimentation.

[0014] In some embodiments, the mass content of the colloidal particles in the electrolyte is 3wt% to 5wt%. By controlling the mass content of the colloidal particles in the above range, it is beneficial to further balance the binding effect on the solvent and the risk of sedimentation.

[0015] In some embodiments, the electrolyte further includes an inorganic gel. By adding the inorganic gel, it is beneficial for the colloidal particles to be better dispersed and suspended in the solvent, thereby improving the binding effect of the colloidal particles on the solvent, and further reducing the gas production of the battery.

[0016] In some embodiments, the colloidal particles include at least one of hexagonal boron nitride, β-aluminum oxide, and sodium carbonate. Thereby, it is beneficial to further reduce the gas production of the battery.

[0017] In some embodiments, the electrolyte includes hexagonal boron nitride and an inorganic gel. Thereby, it is beneficial to further reduce the gas production of the battery.

[0018] In some embodiments, the inorganic gel includes fumed silica and / or nanoclay. The viscosity of fumed silica and nanoclay is moderate, and by adding fumed silica and / or nanoclay to the electrolyte, the viscosity of the electrolyte can be moderately increased, which is beneficial for the colloidal particles to be better dispersed and suspended, so that they can fully exert their binding effect on the solvent.

[0019] In some embodiments, the mass content of the inorganic gel in the electrolyte is 15wt% or less. By controlling the mass content of the inorganic gel in the above range, the viscosity of the electrolyte is moderate, which is beneficial for the colloidal particles to be better dispersed and suspended while also maintaining high kinetic performance of the battery

[0020] In some embodiments, the mass ratio of the colloidal particles to the inorganic gel in the electrolyte is (3-0.5):1.

[0021] In some embodiments, the electrolyte has a viscosity of 50 mPa·s to 5000 mPa·s. By controlling the viscosity of the electrolyte in the above range, it is beneficial to suppress the colloidal particle aggregation settlement while also beneficial to maintain high kinetic performance of the battery.

[0022] In some embodiments, the solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, vinyl carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate. By selecting the above solvent, it is beneficial to reduce the dissolution of the sodium metal layer.

[0023] In some embodiments, the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium nitrate, sodium perchlorate, sodium acetate, sodium trifluoroacetate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide.

[0024] In some embodiments, the positive electrode tab includes a positive current collector and a positive film layer disposed on at least one surface of the positive current collector, the positive film layer includes a positive active material, the positive active material includes at least one of a sodium-containing layered oxide, a polyanion sodium ion compound, a Prussian blue sodium ion compound. By selecting the above positive active material, it is beneficial to improve the performance of the battery.

[0025] In some embodiments, the positive active material includes carbon-coated sodium iron pyrophosphate. By selecting sodium iron pyrophosphate as the positive active material, it is beneficial to improve the cycle performance of the battery.

[0026] In some embodiments, the negative electrode tab further includes a coating layer disposed on at least one side surface of the negative current collector, the coating layer includes a sodium-philic material. By disposing the coating layer containing the sodium-philic material on the surface of the negative current collector, the sodium metal deposition overpotential can be reduced, so that the sodium metal is deposited faster and more uniformly, which helps to reduce the heat effect caused by the local current density being too high, thereby further reducing the gas production of the battery.

[0027] In some embodiments, the sodium-philic material includes a carbon material. By selecting a carbon material as the sodium-philic material, it is beneficial for the negative electrode tab to achieve high electronic conductivity.

[0028] In some embodiments, the thickness of the coating layer is 2 μm to 100 μm. By controlling the thickness of the coating layer in the above range, it is beneficial to maintain high capacity of the battery while also beneficial to uniform deposition of the sodium metal.

[0029] A second aspect of the present disclosure provides a power utilization device including the sodium secondary battery of the first aspect. BRIEF DESCRIPTION OF DRAWINGS

[0030] FIG. 1 is a schematic view of a battery cell according to an embodiment of the present disclosure.

[0031] FIG. 2 is an exploded view of the battery cell according to an embodiment of the present disclosure shown in FIG. 1.

[0032] FIG. 3 is a schematic view of a battery module according to an embodiment of the present disclosure.

[0033] FIG. 4 is a schematic view of a battery pack according to an embodiment of the present disclosure.

[0034] FIG. 5 is an exploded view of the battery pack according to an embodiment of the present disclosure shown in FIG. 4.

[0035] FIG. 6 is a schematic view of an electric device using a sodium secondary battery according to an embodiment of the present disclosure as a power source.

[0036] FIG. 7 is a Raman spectrum of ethylene glycol dimethyl ether, Comparative Example 2, Comparative Example 3, Example 9, and Example 13 according to the present disclosure.

[0037] Explanation of Reference Numerals:

[0038] 1: battery pack; 2: upper case; 3: lower case; 4: battery module; 5: battery cell; 51: case; 52: electrode assembly; 53: top cap assembly. DETAILED DESCRIPTION

[0039] Hereinafter, embodiments of a sodium secondary battery and an electric device according to the present disclosure are specifically disclosed while appropriately referring to the accompanying drawings. However, there will be cases where unnecessary detailed explanations are omitted. For example, there will be cases where detailed explanations of matters that are well known, repeated explanations of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following explanations are provided so that those skilled in the art can fully understand the present disclosure, and are not intended to limit the subject matter recited in the claims.

[0040] The ranges disclosed herein are defined by their lower and upper endpoints, and given that a range is defined by selecting a lower endpoint and an upper endpoint, the selected lower and upper endpoints define the boundaries of the particular range. Ranges defined by endpoints can be inclusive or exclusive of the endpoints, and can be arbitrarily combined, i.e., any lower endpoint can be combined with any upper endpoint to form a range. For example, if ranges of 60-120 and 80-110 are listed, it is understood that ranges of 60-110 and 80-120 are also contemplated. 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 contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present disclosure, unless otherwise stated, a numerical range "a-b" indicates a shorthand way of describing all of the individual real combinations of values that are within the range of a to b, where a and b are both real numbers. For example, the numerical range "0-5" indicates that all of the real numbers between 0 and 5 have been listed herein, and "0-5" is merely a shorthand way of describing those numerical combinations. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present disclosure can be combined with each other to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of the present disclosure can be combined with each other to form new technical solutions.

[0043] Unless otherwise specified, all steps of the present disclosure can be performed in sequence or randomly, and preferably in sequence. For example, a method comprising steps (a) and (b) indicates that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, it is mentioned that the method can further comprise step (c), which indicates that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0044] Unless otherwise specified, the terms used in the present disclosure have the commonly understood meanings understood by those skilled in the art.

[0045] Unless otherwise specified, the values of the parameters mentioned in the present disclosure can be measured by various test methods commonly used in the art, for example, can be measured according to the test methods given in the present disclosure.

[0046] The term "secondary battery" mentioned herein refers to a battery cell, a battery module or a battery pack. The following are described respectively.

[0047] Generally, a secondary battery cell includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charging and discharging process of the battery, active ions move back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent the short circuit of the positive and negative electrodes, while allowing the active ions to pass through.

[0048] During the charging and discharging process of the secondary battery, some components (e.g., solvents) of the electrolyte can come into contact with the electrode material (e.g., sodium metal of the anode-free sodium metal battery) and cause side reactions, especially at high temperatures, the side reactions are particularly serious. The side reactions not only exacerbate the gas production of the battery, but also cause irreversible loss of the capacity of the battery. In order to inhibit the side reactions between the electrode material and the solvent of the electrolyte, the current method is to construct a passivation interface to isolate the contact between the solvent and the electrode material, reduce the side reactions, and thus reduce the gas production of the secondary battery.

[0049] For example, it is reported that a solid electrolyte interface (SEI) is formed on the surface of the sodium metal in the anode-free sodium metal battery to reduce the contact between the solvent and the sodium metal, and the SEI includes an in-situ SEI (a passivation layer generated by the decomposition of the electrolyte itself at a low potential) and a non-in-situ SEI (a man-made passivation layer coated or deposited in advance). However, the inventors found in the research that the method of constructing the SEI has the following problems. For the in-situ SEI, it is unstable at high temperatures, especially in the electrolyte system of the ether solvent, some components with passivation function can be dissolved in the ether solvent, resulting in poor passivation effect and serious gas production problem of the battery. In addition, in the anode-free sodium metal battery, since the sodium metal has high chemical activity, it is easy to react with the solvent to generate some gas, and these gases cause some pores to appear in the SEI layer during the formation process, which allows the solvent to pass through, resulting in that the sodium metal cannot be completely passivated, and the battery still has a serious gas production problem. For the non-in-situ SEI, it can be designed to have a dense structure, so that it has good passivation function. However, the introduction of the non-in-situ SEI often inhibits the capacity.

[0050] In addition, there are also reports of a suspension electrolyte, which induces an inorganic-rich SEI film derived from anions by adding suspended particles, so as to inhibit the generation of dendrites in lithium batteries. However, the inventors found in the research that although the addition of suspended particles can form an SEI with passivation function on the surface of the lithium metal, it cannot completely passivate the surface of the sodium metal in the anode-free sodium metal battery.

[0051] Based on this, the present disclosure provides a sodium secondary battery and an electric device. The sodium secondary battery can reduce the amount of gas generated while maintaining high capacity, thereby improving the safety performance of the battery.

[0052] Secondary battery

[0053] The first aspect of the present disclosure provides a sodium secondary battery, comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; the negative electrode sheet comprises a negative electrode current collector, or comprises a negative electrode current collector and a sodium metal layer arranged on the surface of the negative electrode current collector; the electrolyte comprises colloidal particles, an electrolyte salt and a solvent; the Raman spectrum of the electrolyte comprises a first Raman characteristic peak with a Raman shift of 815 cm -1 to 825 cm -1 and a second Raman characteristic peak with a Raman shift of 845 cm -1 to 855 cm -1 , the peak area A1 of the first Raman characteristic peak and the peak area A2 of the second Raman characteristic peak satisfy: (A1+A2) / S1≤30%, wherein S1 represents the sum of the peak areas of all Raman characteristic peaks with a Raman shift in the range of 800 cm -1 to 900 cm -1 in the Raman spectrum.

[0054] The Raman spectrum of the electrolyte comprises a first Raman characteristic peak with a Raman shift of 815 cm -1 to 825 cm -1 and a second Raman characteristic peak with a Raman shift of 845 cm -1 to 855 cm -1 , the first Raman characteristic peak and the second Raman characteristic peak reflect the existence of non-coordinated C-O-C asymmetric stretching vibration in the electrolyte. The peak area of the first Raman characteristic peak is denoted as A1 and the peak area of the second Raman characteristic peak is denoted as A2. The sum of the peak areas of all Raman characteristic peaks with a Raman shift in the range of 800 cm -1 to 900 cm -1 is denoted as S1.

[0055] (A1+A2) / S1 reflects the degree of coordination / binding of colloidal particles to the solvent. A small value of (A1+A2) / S1 indicates that the Raman characteristic peak of the coordinated C-O-C bond in the electrolyte is greatly shifted, i.e., the solvent is greatly coordinated / bound.

[0056] In the present disclosure, by including colloidal particles in the electrolyte, the colloidal particles are dispersed in the solvent in the form of tiny particles, which has little effect on the viscosity of the electrolyte, and these tiny particles have high adsorption capacity and can anchor and bind the solvent of the electrolyte based on their adsorption capacity and electrostatic effect. By making (A1+A2) / S1≤30%, it indicates that the degree of coordination / binding of colloidal particles to the solvent is high, which is conducive to reducing the probability of solvent migration to the surface of the electrode material, reducing the side reaction between the solvent and the electrode material, thereby reducing the gas production of the sodium secondary battery and improving the safety performance of the battery. In some cases, the surface of the colloidal particles may be charged, which can further produce electrostatic effect, which can further enhance the binding of colloidal particles to the solvent.

[0057] In addition, compared with the above-mentioned prior art method of constructing a passivation interface, the present disclosure adds colloidal particles to the solvent of the electrolyte, and the solvent still exists in the form of a continuous phase, which can provide a continuous channel for the transmission of charges or active ions, and the addition of colloidal particles has little negative impact on the capacity of the battery. Therefore, the sodium secondary battery has high capacity and high safety performance.

[0058] In the present disclosure, (A1+A2) / S1 can be tested in the following way. The electrolyte to be tested can be prepared or obtained by disassembling the battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the battery is disassembled to obtain the electrolyte. The electrolyte is sucked into a capillary tube, and then the sample in the capillary tube is analyzed by a Renishaw inVia Qontor Raman spectrometer, the laser wavelength is selected as 633 nm, and the Raman shift range is 600cm -1 to 2000cm -1 , to obtain a Raman spectrum. The Raman spectrum is peak-separated by Origin to obtain Raman characteristic peaks, and then the Raman characteristic peaks are integrated to obtain A1, A2 and S2. (A1+A2) / S1 is calculated.

[0059] In the present disclosure, the colloidal particles include tiny particles dispersed in a continuous phase (e.g., solvent), and the colloidal particles are capable of remaining suspended in the solvent. The colloidal particles have a high adsorption capacity and can anchor and bind the solvent. In some cases, the surface of the colloidal particles can be charged, which can generate an electrostatic effect, and this electrostatic effect can further enhance the binding of the colloidal particles to the solvent, thereby reducing the gas production of the battery. In the present disclosure, the electrolyte including colloidal particles can be tested by the following method. The electrolyte to be tested can be prepared electrolyte or electrolyte obtained by disassembling the battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the battery is disassembled to obtain the electrolyte. The electrolyte is transferred to a gel filtration column (the column filler is usually a porous polymer such as dextran or agarose). The components left on the column are collected. The collected components are measured by a laser particle size analyzer to obtain the particle size of the components. If the particle size of the components is less than 1000 nm, it is determined that the electrolyte includes colloidal particles.

[0060] In the sodium secondary battery of the present disclosure, the negative electrode tab does not include a conventional negative electrode active material layer, and during the charging process, sodium ions are reduced on the surface of the negative electrode current collector and deposited to form a sodium metal layer.

[0061] In the present disclosure, (A1+A2) / S1≤30%, for example, (A1+A2) / S1 is 30%, 25%, 20%, 15%, 10%, 5%, 1%, or a value between any two of the above values. Preferably, (A1+A2) / S1≤24%. By controlling (A1+A2) / S1 in the above range, the gas production of the battery is further reduced.

[0062] In some embodiments, the infrared spectrum of the electrolyte includes an infrared characteristic peak with an infrared wave number ranging from 1120 cm -1 to 1150 cm -1 , and the peak area A3 of the infrared characteristic peak satisfies: A3 / S2≤50%, wherein S2 represents the sum of the peak areas of all infrared characteristic peaks appearing in the infrared spectrum with an infrared wave number ranging from 1050 cm -1 to 1170 cm - 1 . For example, A3 / S2 is 50%, 40%, 30%, 20%, 10%, or a value between any two of the above values. Preferably, A3 / S2≤41%. By controlling A3 / S2 in the above range, the gas production of the sodium secondary battery is further reduced.

[0063] In the present disclosure, the infrared spectrum of the electrolyte includes an infrared characteristic peak with an infrared wave number ranging from 1120 cm -1 to 1150 cm -1The infrared characteristic peak reflects the presence of the non-coordinated C-O-C bond asymmetric stretching vibration in the electrolyte. Moreover, the peak area A3 of the infrared characteristic peak can reflect the intensity of the non-coordinated C-O-C bond asymmetric stretching vibration.

[0064] In the present disclosure, A3 / S2 reflects the degree of binding of the colloidal particles to the solvent. A small A3 / S2 indicates that the intensity of the non-coordinated C-O-C bond asymmetric stretching vibration in the electrolyte is small, the number of free solvents is small, and the number of solvents bound by colloidal particles is large.

[0065] In the present disclosure, A3 / S2 can be tested in the following manner. The electrolyte to be tested can be a prepared electrolyte or an electrolyte obtained by disassembling a battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the battery is disassembled to obtain the electrolyte. The electrolyte is dropped on a glass slide, and then Fourier Transform Infrared Spectroscopy (FTIR) testing is performed using a Thermo Scientific Nicolet iS50 Fourier Transform Infrared Spectrometer. The infrared wave number range for testing is 500 cm -1 to 4000 cm -1 , and the infrared spectrum is obtained. The infrared spectrum is peak-divided using Origin to obtain the infrared characteristic peak, and then the infrared characteristic peak is integrated to obtain A3 and S2. A3 / S2 is calculated.

[0066] In some embodiments, the colloidal particles have a particle size of 1000 nm or less. For example, the colloidal particles have a particle size of 1 nm, 5 nm, 10 nm, 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, 500 nm, 1000 nm, or a value between any two of the above values. Preferably, the colloidal particles have a particle size of 10 nm to 100 nm. By controlling the particle size of the colloidal particles within the above range, the risk of agglomeration and sedimentation of the colloidal particles can be reduced, which is beneficial to improving the binding of the colloidal particles to the solvent.

[0067] In the present disclosure, the particle size of the colloidal particles can be tested by the following method. The electrolyte to be tested can be prepared or obtained by disassembling a battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the battery is disassembled to obtain the electrolyte. The particle size of the colloidal particles can be tested by a laser diffraction scattering particle size analyzer according to the standard GB / T 19077-2016. In some embodiments, the viscosity of the electrolyte is 50 mPa s to 5000 mPa s. For example, the viscosity of the electrolyte is 50 mPa s, 100 mPa s, 1000 mPa s, 2000 mPa s, 3000 mPa s, 4000 mPa s, 5000 mPa s or a value between any two of the above values. Alternatively, the viscosity of the electrolyte is 50 mPa s to 1000 mPa s, and further alternatively, the viscosity of the electrolyte is 50 mPa s to 500 mPa s. By controlling the viscosity of the electrolyte within the above range, it is beneficial to inhibit the agglomeration and sedimentation of the colloidal particles while maintaining high kinetic performance of the battery.

[0068] In the present disclosure, the viscosity of the electrolyte can be tested by the following method. The electrolyte to be tested can be prepared or obtained by disassembling a battery. Hereinafter, the testing process is described by taking the latter as an example. Specifically, the battery is disassembled to obtain the electrolyte. The viscosity of the electrolyte can be tested by a viscometer-rotation method according to the standard GB / T 10247-2008. In some embodiments, the colloidal particles include at least one of sodium fluoride, hexagonal boron nitride, sodium carbonate, lithium fluoride, lithium oxide, lithium carbonate, aluminum oxide, titanium oxide, titanium nitride, silicon nitride, silicon carbide, sodium superionic conductor solid-state electrolyte (e.g., Na 3.3 Zr 1.7 La 0.3 Si2PO 12 The above colloidal particles have a large binding effect on the solvent.

[0069] In some embodiments, the colloidal particles include β-aluminum oxide. By selecting colloidal particles including β-aluminum oxide, on the one hand, the production of gas of the battery can be reduced based on the binding effect of β-aluminum oxide on the solvent, and on the other hand, the movement of active ions in the electrolyte can be promoted based on the high ionic conductivity of β-aluminum oxide, thereby improving the kinetic performance of the battery.

[0070] In some embodiments, the colloidal particles include sodium fluoride and / or hexagonal boron nitride. By selecting sodium fluoride as the colloidal particles, the colloidal particles can reduce the loss of passivation components (e.g., NaF) in the SEI formed in-situ at the interface, thereby further inhibiting side reactions between the solvent and the electrode material. By selecting hexagonal boron nitride as the colloidal particles, the colloidal particles can scavenge free radicals in the solvent, thereby further inhibiting side reactions between the solvent and the electrode material. In some embodiments, the mass content of the colloidal particles in the electrolyte is 1 wt% to 10 wt%. For example, the mass content of the colloidal particles is 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or a value between any two of the foregoing values. By controlling the mass content of the colloidal particles within the foregoing range, the colloidal particles can be facilitated to play their role in binding the solvent while reducing the risk of colloidal particle agglomeration and sedimentation. Preferably, the mass content of the colloidal particles is 3 wt% to 5 wt%.

[0071] In some embodiments, the electrolyte further includes an inorganic gel. By adding the inorganic gel, the colloidal particles can be better dispersed and suspended in the solvent, thereby improving the binding of the colloidal particles to the solvent and further reducing the gas production of the battery. When the inorganic gel is included, the viscosity of the electrolyte is 1000 mPa·s to 5000 mPa·s.

[0072] In some embodiments, the electrolyte includes an inorganic gel, and the colloidal particles include at least one of hexagonal boron nitride, β-aluminum oxide, and sodium carbonate. Thereby, the gas production of the battery can be further reduced. In some embodiments, the electrolyte includes hexagonal boron nitride and an inorganic gel. Thereby, the gas production of the battery can be further reduced.

[0073] In the present disclosure, the inorganic gel is a three-dimensional network structure formed by chemical or physical methods from inorganic substances (e.g., metal oxides, silicates, etc.). When such a three-dimensional network structure of the inorganic gel coexists with the colloidal particles, the colloidal particles can be better dispersed and suspended, thereby facilitating the colloidal particles to fully play their role in binding the solvent.

[0074] In some embodiments, the inorganic gel includes fumed silica and / or nanoclay. The viscosity of fumed silica and nanoclay is moderate, and by adding fumed silica and / or nanoclay to the electrolyte, the viscosity of the electrolyte can be moderately increased, thereby facilitating the colloidal particles to be better dispersed and suspended and to fully play their role in binding the solvent.

[0075] In some embodiments, the inorganic gel includes an inorganic gel that does not react with sodium metal. For example, the inorganic gel includes fumed silica and / or nanoclay.

[0076] In some embodiments, the mass content of the inorganic gel in the electrolyte is 15 wt% or less. For example, the mass content of the inorganic gel is 15 wt%, 12 wt%, 9 wt%, 6 wt%, 3 wt%, 1 wt%, or a value between any two of the recited values. By controlling the mass content of the inorganic gel in the above range, the viscosity of the electrolyte is moderate, which is conducive to better dispersion of the colloidal particles in suspension, while also conducive to maintaining high kinetic performance of the battery.

[0077] In some embodiments, the mass ratio of the colloidal particles to the inorganic gel in the electrolyte is (3-0.5): 1. For example, the mass ratio of the colloidal particles to the inorganic gel is 3:1, 2:1, 1:1, 0.5:1, or a value between any two of the recited values. By controlling the mass ratio of the colloidal particles to the inorganic gel in the above range, the viscosity of the electrolyte is moderate, which is conducive to better dispersion of the colloidal particles in suspension, while also conducive to maintaining high kinetic performance of the battery.

[0078] In some embodiments, the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium nitrate, sodium perchlorate, sodium acetate, sodium trifluoroacetate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium difluorophosphate, sodium difluoroboric oxalate, sodium bisoxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorodioxalate phosphate.

[0079] In some embodiments, the solvent can include at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, vinyl carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluorovinyl carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dimethyl sulfoxide, ethylene carbonate, propylene carbonate, methyl propylene carbonate, ethyl propylene carbonate, butylene carbonate, fluorinated ethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, butyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0080] In some embodiments, the solvent can include at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, vinyl carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluorovinyl carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate. By selecting the above solvent, the stability of the sodium metal layer is improved.

[0081] In some embodiments, the solvent can be selected from at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. By selecting the above-mentioned ether solvents, the dissolution of the sodium metal layer can be further reduced.

[0082] In some embodiments, the electrolyte can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature or low-temperature performance of the battery, etc.

[0083] Negative electrode sheet

[0084] The sodium secondary battery of the present disclosure does not include a conventional negative electrode active material layer, and during charging thereof, sodium ions are reduced on the surface of the negative electrode current collector and deposited as a sodium metal layer.

[0085] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base layer such as a base layer of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0086] In some embodiments, the negative electrode current collector can include a copper foil and a sodium metal layer disposed on the surface of the copper foil, the negative electrode current collector can include a copper foil, the negative electrode current collector can include an aluminum foil and a sodium metal layer disposed on the surface of the aluminum foil, and the negative electrode current collector can include an aluminum foil.

[0087] In some embodiments, the aluminum foil has a thickness of 10 μm to 100 μm. In some embodiments, the negative electrode sheet further includes a negative electrode current collector and a coating layer disposed on at least one side of the negative electrode current collector, the coating layer including a sodium-philic material. By disposing the coating layer including the sodium-philic material on the surface of the negative electrode current collector, the sodium metal deposition overpotential can be reduced, and the sodium metal can be deposited more quickly and uniformly, which helps to reduce the heat effect caused by the excessively high local current density, thereby further reducing the gas generation amount of the battery.

[0088] In the present disclosure, the sodium-philic material refers to a material capable of forming a stable interaction with sodium ions and promoting the transport of sodium ions. The sodium-philic material includes, but is not limited to, at least one of a carbon material, a sodium-containing sulfide, a sodium-containing phosphate, and a sodium-containing oxide.

[0089] In some embodiments, the sodium-philic material comprises a carbon material. By selecting a carbon material as the sodium-philic material, it is beneficial for the negative electrode sheet to achieve high electronic conductivity.

[0090] In some embodiments, the carbon material comprises at least one of single-walled carbon nanotube, amorphous carbon, graphite, graphene, multi-walled carbon nanotube, carbon 60.

[0091] In some embodiments, the thickness of the coating layer is 2 μm to 100 μm. For example, the thickness of the coating layer is 2 μm, 5 μm, 10 μm, 50 μm, 100 μm, or a value between a range consisting of any two of the values. Preferably, the thickness of the coating layer is 2 μm to 5 μm. By controlling the thickness of the coating layer in the above range, it is beneficial for the battery to maintain high capacity while also facilitating uniform deposition of sodium metal.

[0092] Positive electrode sheet

[0093] In some embodiments, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode film layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector can adopt a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be adopted. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer material base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0095] In some embodiments, the positive electrode active material can adopt a positive electrode active material for sodium secondary batteries known in the art.

[0096] In some embodiments, the positive electrode active material can comprise a sodium-containing layered oxide, a polyanion compound, a Prussian blue compound, etc. By selecting the above positive electrode active material, it is beneficial to improve the performance of the battery. For example, by selecting a polyanion compound as the positive electrode active material, it is beneficial to improve the cycle performance of the battery. By selecting a sodium-containing layered oxide as the positive electrode active material, it is beneficial to improve the energy density of the battery.

[0097] In some embodiments, the positive electrode active material comprises NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na(Cu 1 / 9 Ni 2 / 9 Fe1 / 3 Mn 1 / 3 )O2, Na 2 / 3 Ni 1 / 6 Mn 2 / 3 Cu 1 / 9 Mg 1 / 18 O2, NaFePO4, Na3V2(PO4)3, Na 1.9 CoFe(CN)6, Na2NiFe(CN)6, NaMnFe(CN)6.

[0098] In some embodiments, the positive active material can include sodium iron phosphate. By selecting sodium iron phosphate as the positive active material, the cycle performance of the battery can be improved.

[0099] In some embodiments, the surface of the positive active material has a coating layer, the coating layer includes one or more of carbon material, polyaniline, polypyrrole, poly(3,4- ethylenedioxythiophene), aluminum oxide, zinc oxide, titanium oxide, zirconium oxide, magnesium oxide, silicon oxide, lanthanum oxide, sodium fluoride, lithium fluoride, and aluminum fluoride, and the carbon material includes one or more of amorphous carbon, graphite, and graphene.

[0100] In some embodiments, the positive active material includes carbon-coated sodium iron pyrophosphate. By selecting sodium iron pyrophosphate as the positive active material, both excellent cycle stability and cycle life can be achieved, and in addition, carbon coating can improve the electrical conductivity of sodium iron pyrophosphate and reduce polarization, which is more conducive to the overall capacity of the battery and high rate performance.

[0101] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic ester resin.

[0102] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0103] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode tab can be obtained.

[0104] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator film can be made into an electrode assembly through a winding process or a stacking process.

[0105] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte described above.

[0106] In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, or the like. The outer package of the battery cell can also be a soft pack, such as a pouch soft pack. The material of the soft pack can be plastic, and as plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, or the like can be listed.

[0107] The present disclosure does not have a particular limitation on the shape of the battery cell, which can be cylindrical, square, or any other arbitrary shape. For example, FIG. 1 is a battery cell 5 of a square structure as an example.

[0108] In some embodiments, referring to FIG. 2, the outer package can include a housing 51 and a top cover assembly 53. The housing 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can be provided on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be made into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to specific actual needs.

[0109] In some embodiments, the battery cell can be assembled into a battery module, and the number of battery cells contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0110] FIG. 3 is a battery module 4 as an example. Referring to FIG. 3, in the battery module 4, a plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be made. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0111] Optionally, the battery module 4 can also include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0112] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0113] FIGS. 4 and 5 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery case includes an upper case 2 and a lower case 3, and the upper case 2 is capable of being provided on the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery case in any manner.

[0114] Electric device

[0115] In addition, the second aspect of the present disclosure provides an electric device including the sodium secondary battery provided by the present disclosure. The sodium secondary battery can be used as a power source of the electric device, or can be used as an energy storage unit of the electric device. The electric device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0116] As the electric device, the battery cell, the battery module or the battery pack can be selected according to the use requirement thereof.

[0117] FIG. 6 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the sodium secondary battery for the electric device, the battery pack or the battery module can be used.

[0118] As another example of the device, it can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the battery cell can be used as a power source.

[0119] Embodiment

[0120] Hereinafter, an embodiment of the present disclosure will be described. The embodiment described below is exemplary and is only used to explain the present disclosure, and cannot be understood as a limitation of the present disclosure. If a specific technique or condition is not mentioned in the embodiment, it is performed according to the technique or condition described in the literature in the art or according to the product instruction. If the reagent or instrument used is not mentioned by the manufacturer, it is a conventional product that can be obtained by purchase in the market.

[0121] Embodiment 1

[0122] Preparation of the positive electrode tab

[0123] A positive electrode slurry with a solid content of 5% was prepared by mixing carbon-coated sodium iron pyrophosphate (C-coated Na4Fe3(PO4)2P2O7), conductive carbon black, and polyvinylidene fluoride (PVDF) in a mass ratio of 95:3:2 and adding a solvent (N-methylpyrrolidone). The positive electrode slurry was coated on one side of an aluminum foil, and after cold pressing and cutting, a positive electrode sheet was obtained.

[0124] Preparation of negative electrode sheet

[0125] Single-walled carbon nanotubes and sodium carboxymethyl cellulose (CMC) were mixed at a mass ratio of 99:1 and then added to deionized water to prepare a film slurry with a solid content of 4‰. The film slurry was coated on one side of an aluminum foil, and after cold pressing and cutting, a negative electrode sheet was obtained. The negative electrode sheet consists of an aluminum foil and a coating with a thickness of 15 μm.

[0126] Preparation of electrolytes

[0127] Colloidal particles (NaF) with a particle size of 100 nm were added to a 1 mol / L sodium hexafluorophosphate solution in ethylene glycol dimethyl ether to obtain an electrolyte. The mass content of the colloidal particles in the resulting electrolyte was 5 wt%.

[0128] Electrolyte testing

[0129] 1) Raman test

[0130] Electrolytes were drawn into a capillary tube, and the sample in the capillary tube was then analyzed using a Renishaw inVia Qontor Raman spectrometer. The laser wavelength was selected as 633 nm, and the Raman shift range was measured to be 600 cm⁻¹. -1 Up to 2000cm -1 Raman spectra were obtained. Peak separation of the Raman spectra was performed using Origin, yielding Raman shifts around 800 cm⁻¹. -1 Up to 900cm -1 All Raman characteristic peaks that appeared were identified. Linear integration was performed on these Raman characteristic peaks to obtain A1, A2, and S1. Finally, (A1+A2) / S1 was calculated. The test results are recorded in Table 1-1.

[0131] The following uses ethylene glycol dimethyl ether as an example to illustrate the formation process of (A1+A2) / S1.

[0132] Import the Raman spectrum obtained from the test of ethylene glycol dimethyl ether in Figure 7 into Origin software. Then click the “Analysis” control → “Peak Analysis” control → “Fit Peak” control in sequence.

[0133] Next, on the Origin software interface, set the Raman shift range of the first Raman characteristic peak (815 cm⁻¹).-1 -825 cm -1 ), a Raman shift range of a second Raman characteristic peak (845 cm -1 -855 cm -1 ), and a Raman shift range of a third Raman characteristic peak (865 cm -1 -875 cm -1 ).

[0134] Then, the "OK" control is clicked to trigger the Origin software to generate the data after peak separation. The "Analysis" control is clicked, then the "Mathematics" control is clicked, and then the "Integrated" control is clicked to trigger the Origin software to generate the peak area (A1) of the first Raman characteristic peak, the peak area (A2) of the second Raman characteristic peak, and the peak area (A4) of the third Raman characteristic peak based on the data after peak separation.

[0135] Then, the Origin software calculates the sum (S1) of the peak areas of all Raman characteristic peaks appearing in the Raman shift range of 800 cm -1 to 900 cm -1 based on the following formula: S1 = A1 + A2 + A4.

[0136] Finally, the Origin software calculates (A1 + A2) / S1.

[0137] Isolation film

[0138] A polyethylene film with a thickness of 7 μm was used as the isolation film, and an alumina ceramic coating layer with a thickness of 12 μm was coated on the surface of the polyethylene film.

[0139] Preparation of a sodium secondary battery

[0140] The tab was welded on the positive electrode sheet and the negative electrode sheet by electric welding, and then stacked in the order of "negative electrode sheet-isolation film-positive electrode sheet", and then packaged together with the aluminum plastic film. The above electrolyte was injected into the stacked battery, vacuum packaging was performed, and a sodium secondary battery was obtained.

[0141] Performance test of a sodium secondary battery

[0142] 1) Safety performance test

[0143] a) Test of gas production amount during high-temperature storage

[0144] ① After standing for 4 h, the volume V1 of the battery was tested.

[0145] ② After constant current charging at a current of 0.1 C to 3.65 V, constant voltage charging at 3.65 V to a current of 0.02 C, and standing for 5 minutes, the volume V2 of the battery was tested.

[0146] ③ Discharge at 0.1 C to 1.5 V, then rest for 5 minutes and discharge at 0.02 C to 1.5 V.

[0147] ④ Charge at 1 C to 3.65 V, then charge at 3.65 V to 0.02 C and rest for 5 minutes.

[0148] ⑤ Put into 60 °C constant temperature box for 10 days to test the volume V2 of the battery.

[0149] According to the formula: V2-V1, the gas production (ml) of 10 days of storage is obtained, and the test results are recorded in Table 1-2.

[0150] b) Test of gas production during high temperature cycling

[0151] ① Rest for 4h, test the volume V1 of the battery.

[0152] ② Charge at 0.1 C to 3.65 V, then charge at 3.65 V to 0.02 C and rest for 5 minutes.

[0153] ③ Discharge at 0.1 C to 1.5 V, then rest for 5 minutes and discharge at 0.02 C to 1.5 V.

[0154] ④ Charge at 1 C to 3.65 V, then charge at 3.65 V to 0.02 C and rest for 5 minutes.

[0155] ⑤ Discharge at 1 C to 1.5 V, then rest for 5 minutes and discharge at 0.02 C to 1.5 V.

[0156] ⑥ Put into 60 °C temperature-controlled silicone oil, and cyclically perform the above steps ④ and ⑤, and test the volume V3 of the battery after 200 cycles.

[0157] According to the formula: V3-V1, the gas production (ml) of 200 cycles is obtained, and the test results are recorded in Table 1-2.

[0158] 2) Capacity test

[0159] ⑦ Take the battery after 200 cycles out of the 60 °C silicone oil and rest at room temperature for 4 hours.

[0160] ⑧ Charge at 1 / 3 C to 3.65 V, then charge at 3.65 V to 0.02 C and rest for 5 minutes.

[0161] ⑨ Discharge at 1 / 3 C to 1.5 V, and the capacity is recorded as C1, then rest for 5 minutes and discharge at 0.02 C to 1.5 V, and the capacity is recorded as C2, and the capacity of the battery is obtained according to the formula C1+C2. The test results are recorded in Table 1-2.

[0162] Example 2

[0163] A sodium secondary battery was prepared in a similar manner to Example 1, except that NaF was replaced with hexagonal boron nitride according to Table 1-1 when preparing the electrolyte.

[0164] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1, and the sodium secondary battery parameters are shown in Table 1-2.

[0165] Example 3

[0166] A sodium secondary battery was prepared in a similar manner to Example 1, except that NaF was replaced with β-aluminum oxide according to Table 1-1 when preparing the electrolyte.

[0167] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1, and the sodium secondary battery parameters are shown in Table 1-2.

[0168] Example 4

[0169] A sodium secondary battery was prepared in a similar manner to Example 1, except that NaF was replaced with lithium carbonate according to Table 1-1 when preparing the electrolyte.

[0170] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1, and the sodium secondary battery parameters are shown in Table 1-2.

[0171] Example 5

[0172] A sodium secondary battery was prepared in a similar manner to Example 1, except that NaF was replaced with silicon nitride according to Table 1-1 when preparing the electrolyte.

[0173] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1, and the sodium secondary battery parameters are shown in Table 1-2.

[0174] Example 6

[0175] A sodium secondary battery was prepared in a similar manner to Example 1, except that NaF was replaced with Na 3.3 Zr 1.7 La 0.3 Si2PO 12 .

[0176] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1, and the sodium secondary battery parameters are shown in Table 1-2.

[0177] Example 7

[0178] A sodium secondary battery was prepared in a similar manner to Example 1, except that the amount of NaF colloidal particles added was adjusted to 2 wt% when preparing the electrolyte.

[0179] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1 below, and the parameters of the sodium secondary battery are shown in Table 1-2 below.

[0180] Comparative Example 1

[0181] A sodium secondary battery was prepared in a similar manner to Example 1, except that no colloidal particles were added when preparing the electrolyte, but a film-forming additive (fluoroethylene carbonate, FEC) was added to form an SEI film.

[0182] The electrolyte and secondary electrode were tested, and the electrolyte parameters are shown in Table 1-1 below, and the parameters of the sodium secondary battery are shown in Table 1-2 below.

[0183] Comparative Example 2

[0184] A sodium secondary battery was prepared in a similar manner to Example 1, except that no colloidal particles were added when preparing the electrolyte.

[0185] The electrolyte of Comparative Example 2 was sucked into a capillary tube, and Raman testing was performed in the manner described above in Example 1, and the Raman spectrum of Comparative Example 2 is shown as curve 2 in Figure 7. Curve 1 in Figure 7 represents the Raman spectrum obtained by Raman testing of ethylene glycol dimethyl ether under the same conditions.

[0186] The first Raman characteristic peak in Figure 7 is the response signal of the non-coordinated C-O-C bond asymmetric stretching vibration in the solvent, with a Raman shift of 815 cm - 1 to 825 cm -1 , and the peak area is represented as A1. The second Raman characteristic peak is the response signal of the non-coordinated C-O-C bond asymmetric stretching vibration in the solvent, with a Raman shift of 845 cm -1 to 855 cm -1 , and the peak area is represented as A2. The third Raman characteristic peak is the response signal of the coordinated C-O-C bond asymmetric stretching vibration in the solvent, with a Raman shift of 860 cm -1 to 870 cm -1 , and the peak area is represented as A4. All Raman characteristic peaks appearing at a Raman shift of 800 cm -1 to 900 cm -1 are represented as S1, where S1 = A1 + A2 + A4.

[0187] From curve 2 in FIG. 7, it can be read that in the Raman spectrum of Comparative Example 2, (A1+A2) / S1=55%. The electrolyte components of Comparative Example 2 and the parameters of the components are recorded in Table 1-1.

[0188] The performance of the sodium secondary batteries of Example Comparative Example 2 was tested, and the test results are recorded in Table 1-2.

[0189] Table 1-1

[0190] Table 1-2

[0191] From the data in Tables 1-1 to 1-2, it can be seen that, compared with Comparative Example 1 (in which the colloidal particles are replaced with a film-forming additive), and Comparative Example 2 (in which no colloidal particles are added to the electrolyte), the sodium secondary batteries of Examples 1 to 7 have both high capacity and high safety performance.

[0192] Examples 8-15

[0193] Sodium secondary batteries were prepared in a manner similar to Example 1, except that when preparing the electrolyte, the electrolyte was adjusted according to the following Table 2-1.

[0194] The electrolyte of Example 9 was sucked into a capillary tube, and Raman testing was performed in the manner described above for Example 1, and the Raman spectrum of Example 9 is shown as curve 4 in FIG. 7. From curve 4 in FIG. 7, it can be read that in the Raman spectrum of Example 9, (A1+A2) / S1=16%.

[0195] The electrolyte of Example 13 was sucked into a capillary tube, and Raman testing was performed in the manner described above for Example 1, and the Raman spectrum of Example 13 is shown as curve 5 in FIG. 7. From curve 5 in FIG. 7, it can be read that in the Raman spectrum of Example 13, (A1+A2) / S1=12%.

[0196] (A1+A2) / S1of other examples is shown in Table 2-1. The electrolyte components of Examples 8-15 and the parameters of the components are recorded in Table 2-1.

[0197] The performance of the sodium secondary batteries of Examples 8-15 was tested, and the test results are recorded in Table 2-2.

[0198] Comparative Example 3

[0199] Sodium secondary batteries were prepared in a manner similar to Example 13, except that when preparing the electrolyte, no colloidal particles were added.

[0200] The electrolyte of Comparative Example 3 was sucked into a capillary tube, and Raman test was performed in the manner as described in Example 1 above, and the Raman spectrum of Comparative Example 3 is shown as curve 3 in Figure 7. From curve 3 in Figure 7, it can be read that in the Raman spectrum of Comparative Example 3, (A1+A2) / S1=34%.

[0201] The electrolyte components of Comparative Example 3 and the parameters of the components are recorded in Table 2-1.

[0202] The performance of the sodium secondary battery of Comparative Example 3 was tested, and the test results are recorded in Table 2-2.

[0203] Table 2-1

[0204] Table 2-2

[0205] From the data of Example 8-Example 10 in Table 2-1 to Table 2-2, it can be known that when the particle size of the colloidal particles is 10nm to 1000nm, the sodium secondary battery has both high capacity and high safety performance.

[0206] From the data of Example 11 and Example 12 in Table 2-1 to Table 2-2, it can be known that when the mass content of the colloidal particles is 1wt% to 10wt%, the sodium secondary battery has both high capacity and high safety performance.

[0207] Compared with Comparative Example 3 and Example 9, the electrolyte in Example 13 to Example 15 simultaneously includes colloidal particles and inorganic gel, which is beneficial to further reduce the gas production of the sodium secondary battery.

[0208] It should be noted that the present disclosure is not limited to the above-described embodiments. The above-described embodiments are only examples, and embodiments having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solutions of the present disclosure are all included in the technical scope of the present disclosure. In addition, within the scope of the main idea of the present disclosure, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the components of the embodiments are also included in the scope of the present disclosure.

Claims

1. A sodium secondary battery comprising: The positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte, the negative electrode sheet including a negative electrode current collector, or including the negative electrode current collector and a sodium metal layer provided on a surface of the negative electrode current collector; The electrolyte includes colloidal particles, an electrolyte salt, and a solvent; includes a first Raman characteristic peak having a Raman shift of 815 cm -1 to 825 cm -1 and a second Raman characteristic peak having a Raman shift of 845 cm -1 to 855 cm -1 in a Raman spectrum of the electrolyte, a peak area A1 of the first Raman characteristic peak and a peak area A2 of the second Raman characteristic peak satisfy: (A1+A2) / S1≤30%, In the formula, S1 represents the sum of peak areas of all Raman characteristic peaks appearing in the Raman spectrum with Raman shift in the range of 800 cm -1 to 900 cm -1 .

2. The sodium secondary battery according to claim 1, wherein (A1+A2) / S1≤24%.

3. The sodium secondary battery according to claim 1 or 2, wherein, The particle size of the colloidal particles is 1000 nm or less.

4. The sodium secondary battery according to any one of claims 1 to 3, wherein The particle size of the colloidal particles is 10 nm to 100 nm.

5. The sodium secondary battery according to any one of claims 1 to 4, wherein, The colloidal particles include at least one of sodium fluoride, hexagonal boron nitride, sodium carbonate, lithium fluoride, lithium oxide, lithium carbonate, aluminum oxide, titanium oxide, titanium nitride, silicon nitride, silicon carbide, Na 3.3 Zr 1.7 La 0.3 Si2PO 12 Si2PO 6. The sodium secondary battery according to claim 5, wherein, The colloidal particles include β-aluminum oxide.

7. The sodium secondary battery according to claim 5, wherein, The colloidal particles include sodium fluoride or hexagonal boron nitride.

8. The sodium secondary battery according to any one of claims 1 to 7, wherein, The mass content of the colloidal particles in the electrolyte is 1 wt% to 10 wt%.

9. The sodium secondary battery according to any one of claims 1 to 8, wherein, The mass content of the colloidal particles in the electrolyte is 3 wt% to 5 wt%.

10. The sodium secondary battery according to any one of claims 1 to 5, wherein, The electrolyte further includes an inorganic gel.

11. The sodium secondary battery according to claim 10, wherein The colloidal particles include at least one of hexagonal boron nitride, β-aluminum oxide, and sodium carbonate.

12. The sodium secondary battery according to claim 10 or 11, wherein, The electrolyte includes hexagonal boron nitride and an inorganic gel.

13. The sodium secondary battery according to any one of claims 10 to 12, wherein, The inorganic gel includes fumed silica and / or nanoclay.

14. The sodium secondary battery according to any one of claims 10 to 13, wherein, The mass content of the inorganic gel in the electrolyte is 15 wt% or less.

15. The sodium secondary battery according to any one of claims 10 to 14, wherein, The mass ratio of the colloidal particles to the inorganic gel in the electrolyte is (3-0.5):

1.

16. The sodium secondary battery according to any one of claims 1 to 15, wherein, The viscosity of the electrolyte is 50 mPa·s to 5000 mPa·s.

17. The sodium secondary battery according to any one of claims 1 to 16, wherein, The solvent includes at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, vinyl carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate, and dipropyl carbonate.

18. The sodium secondary battery according to any one of claims 1 to 17, wherein, The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium nitrate, sodium perchlorate, sodium acetate, sodium trifluoroacetate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.

19. The sodium secondary battery according to any one of claims 1 to 18, wherein, The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer provided on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material, the positive electrode active material including at least one of a sodium-containing layered oxide, a polyanion sodium ion compound, and a Prussian blue sodium ion compound.

20. The sodium secondary battery according to claim 19, wherein, The positive electrode active material includes carbon-coated sodium iron pyrophosphate.

21. The sodium secondary battery according to any one of claims 1 to 20, wherein, The negative electrode sheet further includes a coating layer provided on at least one side surface of the negative electrode current collector, the coating layer including a sodiumophilic material.

22. The sodium secondary battery according to claim 21, wherein, The sodiumophilic material includes a carbon material.

23. The sodium secondary battery according to claim 21 or 22, wherein, The thickness of the coating layer is 2 μm to 100 μm.

24. An electric device including the sodium secondary battery of any one of claims 1 to 23.

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