A sodium-ion battery

Abstract

The present invention discloses a sodium-ion battery, which includes a positive electrode, a negative electrode and a non-aqueous electrolyte. The non-aqueous electrolyte includes a first additive and a second additive. The first additive includes at least one of tris(trimethylsilyl) phosphate or tris(trimethylsilyl) borate. The second additive includes at least one of 1,3-propane sultone or vinylene sulfate. The mass percentage content a% of the first additive in the non-aqueous electrolyte is 0.1% to 3%, and the mass percentage content b% of the second additive in the non-aqueous electrolyte is 1% to 5%. The median particle size D 50 of the positive electrode active material in the positive electrode has a value c of 2 to 10 μm. By performing cyclic voltammetry tests, the current difference between the oxidation peak and the reduction peak of the positive electrode is 0.002 to 0.008 A / g. The sodium-ion battery of the present invention improves the cycle performance of the sodium-ion battery, increases the initial efficiency, and inhibits gas generation in the battery by regulating the content of the additives and the median particle size of the positive electrode active material.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage devices, and in particular, to a sodium-ion battery. Background Art

[0002] The principle and structure of sodium-ion batteries are similar to those of lithium-ion batteries. Compared with lithium-ion batteries, sodium-ion batteries have abundant resources, low cost, small fluctuations, and have the properties of a wide temperature range and high safety, and have broad development space in the field of energy storage. With the continuous progress of technology, sodium-ion batteries will occupy an important position in China's energy system. Developing high-performance and low-cost sodium-ion batteries is a decisive factor in determining whether they can be industrialized.

[0003] During the first charge and discharge process of sodium-ion batteries, the electrode material reacts with the electrolyte at the solid-liquid phase interface to form a passivation layer covering the surface of the electrode material. This passivation layer is an interface layer with the characteristics of a solid electrolyte, and this passivation film is called a solid electrolyte interface film, abbreviated as the interface film. The performance of sodium-ion batteries is closely related to the quality of the interface film. At present, sodium-ion batteries have problems such as low initial efficiency, insufficient cycle performance, and battery gas generation. Therefore, it is necessary to study and improve sodium-ion batteries to improve the initial efficiency and cycle performance of sodium-ion batteries, and at the same time be able to inhibit battery gas generation. Summary of the Invention

[0004] The present invention is based on the inventor's discovery and recognition of the following facts and problems: At present, sodium-ion batteries have problems such as low initial efficiency, insufficient cycle performance, and large battery gas generation. Therefore, it is necessary to improve sodium-ion batteries to improve the initial efficiency and cycle performance of sodium-ion batteries, and at the same time be able to inhibit battery gas generation.

[0005] The present invention aims to solve at least one of the technical problems in the related art to some extent. For this purpose, the present invention provides a sodium-ion battery, including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein,

[0006] The non-aqueous electrolyte includes a solvent, an electrolyte salt, and an additive. The additive includes a first additive and a second additive. The first additive includes at least one of tris(trimethylsilyl) phosphate (TMSP) or tris(trimethylsilyl) borate (TMSB). The second additive includes at least one of 1,3-propane sultone (RPS) or vinylene sulfate (DTD). The mass percentage content a% of the first additive in the non-aqueous electrolyte is 0.1% to 3%, and the mass percentage content b% of the second additive in the non-aqueous electrolyte is 1% to 5%;

[0007] The positive electrode includes a positive electrode active material, and the median particle size D 50 of the positive electrode active material has a value c of 2 to 10 μm;

[0008] Cyclic voltammetry (CV) tests were carried out using an electrochemical workstation. The test voltage was 1.5 - 4.0 V, and the scanning rate was 0.1 - 1 mV / s. The current difference corresponding to the oxidation peak and reduction peak of the positive electrode was 0.002 - 0.008 A / g.

[0009] Optionally, the sodium-ion battery satisfies the following condition: 0.19 ≤ (a + b) / c ≤ 2.67;

[0010] Where a% is the mass percentage of the first additive in the non-aqueous electrolyte, with the unit of %;

[0011] b% is the mass percentage of the second additive in the non-aqueous electrolyte, with the unit of %;

[0012] c is the median particle size D 50 of the positive electrode active material, with the unit of μm.

[0013] Optionally, the sodium-ion battery satisfies the following condition: 0.3 ≤ (a + b) / c ≤ 2.0.

[0014] Optionally, the mass percentage a% of the first additive in the non-aqueous electrolyte is 0.2 - 1.5%; the mass percentage b% of the second additive in the non-aqueous electrolyte is 1% - 3%.

[0015] Optionally, the median particle size D 50 of the positive electrode active material has a value c of 3 - 7 μm.

[0016] Optionally, the positive electrode active material is selected from at least one of layered metal oxides, polyanion compounds, Prussian compounds, phosphate compounds, and sulfate compounds.

[0017] Optionally, the chemical formula of the layered metal oxide is Na x M y O z , 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V. Preferably, the layered metal oxide is NaNi m Fe n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or NaNi m Co n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or at least one of them;

[0018] The molecular formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, where M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20. Preferably, the Prussian compound is Na x Mn[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20), or at least one of them;

[0019] The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, and M is selected from at least one of Al, V, Ge, Fe, and Ga. Preferably, the phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F; alternatively, the chemical formula of the phosphate compound is Na2MPO4F, and M is selected from at least one of Fe and Mn. Preferably, the phosphate compound is at least one of Na2FePO4F or Na2MnPO4F;

[0020] The chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0021] Optionally, the solvent includes at least one of C3 - C8 carbonates, C2 - C6 carboxylates, and C4 - C10 ethers; the mass percentage of the solvent in the non-aqueous electrolyte is 70% - 92%;

[0022] Preferably, the C3 - C8 carbonates are selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC); the mass percentage of the cyclic carbonate in the non-aqueous electrolyte is not less than 30%.

[0023] Optionally, the electrolyte salt is selected from at least one of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]), or sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]).

[0024] Optionally, the additive further includes fluorinated carbonate. Preferably, the fluorinated carbonate includes at least one of fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC).

[0025] For the sodium-ion battery provided by the present invention, trimethylsilyl phosphate (TMSP) and / or trimethylsilyl borate (TMSB) are added as the first additive, and r-Propane sultone (RPS) and / or 1,3,4-Dithiadiazole-2,5-disulfide (DTD) are added as the second additive in the non-aqueous electrolyte. The two can decompose on the surface of the positive electrode to form an interfacial film during the battery formation stage. The interfacial film can effectively maintain the structural stability of the positive electrode active material. Through a large number of studies, the inventor found that by controlling the content a of the first additive, the content b of the second additive, and the median particle size D 50 value c of the positive electrode active material, it is beneficial to improve the film-forming quality of the interfacial film. The film-forming quality of the interfacial film affects the magnitude of the current difference corresponding to the oxidation peak and the reduction peak in the cyclic voltammetry (CV) test of the positive electrode. When the current difference is too low or too high, the battery cycle reversibility is poor, the irreversible capacity in the first cycle increases, and the battery performance deteriorates. The inventor found that by controlling the current difference corresponding to the oxidation peak and the reduction peak in the CV test of the positive electrode within the range of 0.002 - 0.008 A / g, the initial efficiency and cycle performance of the battery can be effectively improved. It is speculated that the median particle size of the positive electrode active material affects the wetting degree of the non-aqueous electrolyte on the positive electrode and the shuttle of sodium ions in the positive electrode. When the content of the first additive is 0.1 - 3 wt%, the content of the second additive is 1 - 5 wt%, and the median particle size D 50 of the positive electrode active material is 2 - 10 μm, the three can achieve a better cooperation effect, improve the cycle performance of the sodium-ion battery, increase the initial efficiency, and inhibit gas generation in the battery; In particular, when the sodium-ion battery satisfies the condition 0.19 ≤ (a + b) / c ≤ 2.67, the sodium-ion battery has the best battery performance. Detailed Embodiment

[0026] The embodiments of the present invention will be described in detail below. The embodiments are exemplary and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0027] A sodium-ion battery according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. Among them,

[0028] The non-aqueous electrolyte includes a solvent, an electrolyte salt, and an additive. The additive includes a first additive and a second additive. The first additive includes at least one of tris(trimethylsilyl) phosphate or tris(trimethylsilyl) borate. The second additive includes at least one of r-Propane sultone or vinyl sulfate. The mass percentage content a% of the first additive in the non-aqueous electrolyte is 0.1% - 3%, and the mass percentage content b% of the second additive in the non-aqueous electrolyte is 1% - 5%;

[0029] The positive electrode includes a positive electrode active material, and the median particle size D of the positive electrode active material 50 has a value c of 2 to 10 μm;

[0030] Cyclic voltammetry testing is performed using an electrochemical workstation, the test voltage is 1.5 to 4.0 V, the scanning rate is 0.1 to 1 mV / s, and the current difference corresponding to the oxidation peak and reduction peak of the positive electrode is 0.002 to 0.008 A / g.

[0031] The first additive and the second additive will form a stable interfacial film at the positive electrode interface, and the film-forming quality of this interfacial film will affect the magnitude of the current difference corresponding to the oxidation peak and reduction peak of the positive electrode in the CV test, thereby affecting the initial efficiency, cycle performance, and gas generation of the battery. The film-forming quality of this interfacial film is mainly related to the median particle size D of the positive electrode active material 50 size, the mass percentage contents of the first additive and the second additive, and the film-forming quality of the interfacial film can also be finely adjusted through different formation conditions. During the formation process, for batteries at different formation potentials, the quality of the interfacial film formed is different, and as the formation potential increases, the growth of the film layer tends to be complete. At the same time, the formation current, formation time, and formation temperature, etc. will also affect the quality of the interfacial film.

[0032] In some embodiments, the formation conditions of the sodium-ion battery include the following operating steps: performing constant-current charging formation on the sodium-ion battery, charging the sodium-ion battery at a rate of 0.03 to 0.1C for 2 to 4 h, then charging at a constant current of 0.1 to 0.3C until the charging stops when reaching 3.0 to 3.8 V, and then aging the sodium-ion battery at 25 to 50 °C, optionally 30 to 50 °C for 5 to 30 min, and performing secondary vacuum sealing; continuing to charge and form the sodium-ion battery at a rate of 0.1 to 0.3C, stopping charging when the formation potential reaches 3.5 to 4.0 V, and then aging the sodium-ion battery at 25 to 50 °C, optionally 30 to 50 °C for 10 - 48 h, and continuing to charge and form the sodium-ion battery at a rate of 0.3 to 0.5C until reaching 100% SOC. To form a specific interfacial film on the positive electrode surface, so that the current difference corresponding to the oxidation peak and reduction peak of the positive electrode is between 0.002 and 0.008 A / g.

[0033] In a specific embodiment, the sodium-ion battery satisfies the following conditions:

[0034] 0.19 ≤ (a + b) / c ≤ 2.67;

[0035] where a% is the mass percentage content of the first additive in the non-aqueous electrolyte, with the unit of %;

[0036] b% is the mass percentage content of the second additive in the non-aqueous electrolyte, with the unit of %;

[0037] c is the median particle size D of the positive electrode active material 50 , with the unit of μm.

[0038] The sodium-ion battery uses TMSP and / or TMSB as the first additive and RPS and / or DTD as the second additive to participate in the formation of the interfacial film on the positive electrode surface. The inventors found through research that when the content a% of the first additive, the content b% of the second additive, and the median particle size D of the positive electrode active material 50 The value c satisfies the condition 0.19 ≤ (a + b) / c ≤ 2.67, the obtained sodium-ion battery has excellent initial efficiency and cycling performance. It is speculated that by controlling the median particle size D of the positive electrode active material 50 , the electrolyte can be fully infiltrated into the positive electrode interior, and it is beneficial for the shuttle of sodium ions in the positive electrode. By controlling the content a% of the first additive and the content b% of the second additive, they can decompose together on the surface of the positive electrode during the battery formation process to form an interfacial film. This interfacial film can effectively maintain the crystal structure stability of the positive electrode active material. At the same time, during the subsequent charge and discharge cycles of the battery, the interfacial film on the positive electrode surface will be damaged. At this time, the first additive and the second additive in the non-aqueous electrolyte at the damaged position can play a role in continuously repairing the interfacial film. By correlating these three parameters, the first additive and the second additive can form a film sufficiently, have high thermal stability and low impedance, thereby effectively improving the initial efficiency and cycling performance of the sodium-ion battery and suppressing battery gas generation.

[0039] In a specific embodiment, (a + b) / c can be 0.19, 0.2, 0.3, 0.33, 0.37, 0.47, 0.5, 0.53, 0.67, 0.7, 0.79, 0.8, 0.83, 0.87, 0.90, 1.0, 1.2, 1.4, 1.5, 1.7, 2.0, 2.2, 2.5, 2.6, 2.67.

[0040] In a preferred embodiment, the sodium-ion battery satisfies the following condition: 0.3 ≤ (a + b) / c ≤ 2.0.

[0041] In a specific embodiment, the mass percentage content a% of the first additive in the non-aqueous electrolyte can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 2.0%, 2.5%, 2.7%, 2.9%, 3%.

[0042] In a preferred embodiment, the mass percentage content a% of the first additive in the non-aqueous electrolyte is 0.2 - 1.5%.

[0043] In the embodiments of the present invention, when the content of the first additive is too high or too low, it cannot effectively participate in film formation, resulting in poor film formation quality, which leads to poor stability of the positive and negative electrode interfaces during the cycling process, increased side reactions, serious gas generation during the battery cycling process, and accelerated capacity decay.

[0044] The first additive and the second additive have a synergistic effect in improving the quality of the formed interface film. When the mass content of the first additive in the non-aqueous electrolyte is too low, it is difficult to play a synergistic role with the second additive, affecting the film formation quality of the interface film on the positive electrode material layer; when the mass content of the first additive in the non-aqueous electrolyte is too high, the formed interface film is too thick, which easily leads to an increase in the impedance of the sodium-ion battery and is not conducive to the improvement of the cycling performance of the sodium-ion battery.

[0045] In a preferred embodiment, the first efficiency and cycling performance of the sodium-ion battery are further improved, and gas generation of the battery is further suppressed.

[0046] In a specific embodiment, the mass percentage content b% of the second additive in the non-aqueous electrolyte can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%.

[0047] In a preferred embodiment, the mass percentage content b% of the second additive in the non-aqueous electrolyte is 1% to 3%.

[0048] In the embodiments of the present invention, when the mass content of the second additive in the non-aqueous electrolyte is too low, it is difficult to play a synergistic role with the first additive, which will exacerbate the loss of irreversible capacity in the first cycle, deteriorate the first efficiency of the battery, and also have limited improvement in the high-temperature cycling performance of the sodium-ion battery; when the mass content of the second additive in the non-aqueous electrolyte is too high, it will lead to too high a thickness of the interface film on the positive electrode surface, thereby affecting the insertion and extraction of sodium ions in the positive electrode, affecting the ion conduction efficiency, and deteriorating the cycling performance and first efficiency.

[0049] In a preferred embodiment, the mass percentage content of the second additive in the non-aqueous electrolyte is greater than the mass percentage content of the first additive.

[0050] The second additive will preferentially participate in film formation before the first additive during the activation stage of the sodium-ion battery. Preferably, the addition amount of the second additive is greater than that of the first additive, which is beneficial to the effective film formation of the second additive and the synergistic effect with the first additive to form an excellent and stable electrode interface film, further reducing the consumption of the electrolyte and the loss of irreversible capacity in the first cycle, being beneficial to improving the reversibility of the battery during the cycling process, and further improving the cycling performance and first efficiency of the battery.

[0051] In a specific embodiment, the median particle size D of the positive electrode active material50 The value of c can be 2 μm, 2.5 μm, 3 μm, 4 μm, 5 μm, 5.2 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm.

[0052] In a preferred embodiment, the median particle size D of the positive electrode active material 50 The value of c is 3 - 7 μm.

[0053] The insertion and extraction reaction of sodium ions mainly occurs at the interface between the positive electrode and the non-aqueous electrolyte. If the median particle size of the positive electrode active material is too small, the specific surface area is large, which will excessively consume the electrolyte to form a film, resulting in a too low initial efficiency. And if the particle size is too small, the wettability of the electrode will deteriorate, degrading the rate performance; if the median particle size of the positive electrode active material is too large, the diffusion path of sodium ions in the material is prolonged, which will lead to a slow charge transfer rate and cause a decline in the rate performance.

[0054] In some embodiments, the positive electrode active material is selected from at least one of layered metal oxides, polyanion compounds, Prussian compounds, phosphate compounds, and sulfate compounds.

[0055] In a preferred embodiment, the chemical formula of the layered metal oxide is Na x M y O z , 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; preferably, the layered metal oxide is NaNi m Fe n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or NaNi m Co n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or at least one of them; specifically, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, NaFe 0.2 Mn 0.4 Ni 0.4 O2;

[0056] The chemical formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, where M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 ≤ z ≤ 20; preferably, the Prussian compound is Na x Mn[Fe(CN)6] y·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 ≤ z ≤ 20), at least one of them; specifically, Na2Fe2(CN)6;

[0057] The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x where 0 ≤ x ≤ 1, M is selected from at least one of Al, V, Ge, Fe, Ga. Preferably, the phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F; or the chemical formula of the phosphate compound is Na2MPO4F, M is selected from at least one of Fe, Mn. Preferably, the phosphate compound is at least one of Na2FePO4F or Na2MnPO4F; or the phosphate compound is Na3V2(PO4)2;

[0058] The chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

[0059] In the embodiments of the present invention, the positive electrode active material in the positive electrode is preferably selected, especially the layered metal oxide NaNi m Fe n Mn p O2, which can form a film synergistically with the additives used in the present invention, improve the film-forming quality, and is beneficial to further improving the performance of the battery.

[0060] In some embodiments, the solvent in the non-aqueous electrolyte includes at least one of C3 - C8 carbonates, C2 - C6 carboxylates, and C4 - C10 ethers.

[0061] In the preferred embodiments, the C3 - C8 carbonates include at least one of cyclic carbonates or chain carbonates with 3 - 8 carbon atoms. Further preferably, the cyclic carbonates with 3 - 8 carbon atoms include at least one of ethylene carbonate, vinylene carbonate, ethylene vinyl carbonate, propylene carbonate, γ-butyrolactone, and butylene carbonate; the chain carbonates with 3 - 8 carbon atoms include at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and dipropyl carbonate; more preferably, the C3 - C8 carbonates are selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC); the mass percentage content of the cyclic carbonate in the non-aqueous electrolyte is not less than 30%.

[0062] In a preferred embodiment, the C2-C6 carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and propyl propionate.

[0063] In a preferred embodiment, the C4-C10 ether includes at least one of cyclic ethers or chain ethers having 4 to 10 carbon atoms; further preferably, the cyclic ethers having 4 to 10 carbon atoms include at least one of 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, 2-methyltetrahydrofuran, and 2-trifluoromethyltetrahydrofuran; the chain ethers having 4 to 10 carbon atoms include at least one of dimethoxymethane, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether.

[0064] In some embodiments, the mass percentage of the solvent in the non-aqueous electrolyte is 70% to 92%.

[0065] In the embodiments of the present invention, there is no particular limitation on the solvent, and the solvents commonly used in sodium ion batteries can all be applicable to the present invention.

[0066] In some embodiments, the electrolyte salt in the non-aqueous electrolyte is selected from at least one of sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium hexafluorophosphate (NaPF6), sodium trifluoroacetate (CF3COONa), sodium tetraphenylborate (NaB(C6H5)4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]), or sodium bis(trifluoromethylsulfonyl)imide (Na[(CF3SO2)2N]). In the embodiments of the present invention, there is no particular limitation on the electrolyte salt. Preferably, it is sodium hexafluorophosphate (NaPF6), sodium trifluoromethanesulfonate (NaSO3CF3), or sodium bis(fluorosulfonyl)imide (Na[(FSO2)2N]).

[0067] In some embodiments, the additive further includes fluorinated carbonate. Preferably, the fluorinated carbonate includes at least one of fluorinated ethylene carbonate (FEC) or difluorinated ethylene carbonate (DFEC). In the embodiments of the present invention, the non-aqueous electrolyte further includes the additive fluorinated carbonate, which can further improve the film-forming quality and is beneficial to improving the battery performance.

[0068] In some embodiments, the mass percentage of the fluorinated carbonate in the non-aqueous electrolyte is 1% - 3%.

[0069] In a specific embodiment, the mass percentage of the fluorinated carbonate in the non-aqueous electrolyte can be 1%, 1.5%, 2%, 2.5%, or 3%.

[0070] In some embodiments, the negative electrode includes a negative electrode active material selected from at least one of hard carbon and soft carbon. In the embodiments of the present invention, there is no particular limitation on the negative electrode active material, and any negative electrode material that can be used in sodium ion batteries in the prior art can be applicable to the present invention.

[0071] In some embodiments, the method for preparing the positive electrode includes: mixing the positive electrode active material, binder, conductive agent, and solvent, coating the mixture on a substrate, and removing the solvent to obtain the positive electrode; the method for preparing the negative electrode includes: mixing the negative electrode active material, binder, conductive agent, and solvent, coating the mixture on a substrate, and removing the solvent to obtain the negative electrode. In the embodiments of the present invention, there is no particular limitation on the conductive agent, binder, and solvent, and common conductive agents, binders, and solvents in the art can be used.

[0072] The present invention will be described in detail below with reference to embodiments.

[0073] Example 1

[0074] The preparation of the sodium ion battery includes the following steps:

[0075] (1) Preparation of non-aqueous electrolyte: Mix 6.5 wt% electrolyte salt NaPF6, 90 wt% solvent (ethylene carbonate EC: propylene carbonate PC: ethyl methyl carbonate EMC = 1:1:1), 0.5 wt% first additive tris(trimethylsilyl) phosphate (TMSP), and 3 wt% second additive divinyl sulfone (DTD) uniformly to obtain the non-aqueous electrolyte.

[0076] (2) Preparation of positive electrode: Disperse the binder polyvinylidene fluoride, solvent N-methylpyrrolidone, conductive agent acetylene black, and positive electrode active material NaNi 50 with a median particle size D 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 uniformly to obtain a positive electrode slurry. Coat the positive electrode slurry on a current collector, and obtain a positive electrode sheet through coating, drying, and rolling processes.

[0077] (3) Preparation of negative electrode: Mix the negative electrode active material hard carbon, conductive agent carbon black, solvent water, and binder sodium carboxymethyl cellulose uniformly to obtain a negative electrode slurry. Coat the negative electrode slurry on a current collector, and obtain a negative electrode sheet through coating, drying, and rolling processes.

[0078] (4) Battery assembly

[0079] A separator is placed between the above-prepared positive electrode sheet and negative electrode sheet, and then the sandwich structure composed of the positive electrode sheet, negative electrode sheet and separator is wound. After that, the wound body is flattened and placed in an aluminum foil packaging bag, and vacuum baked at 75 °C for 48 h to obtain a battery cell to be injected with electrolyte. The above-prepared non-aqueous electrolyte is injected into the battery cell through the injection hole, and the amount of the electrolyte should ensure that the voids in the battery cell are filled.

[0080] Then, the film-forming process of constant-current charging formation is carried out according to the following steps: The sodium-ion battery is charged at a constant current of 0.05C for 180 min, then charged at a constant current of 0.3C until the charging is stopped when the voltage reaches 3.5V. Then, the sodium-ion battery is aged at room temperature for 30 min and sealed again under vacuum. The sodium-ion battery is continuously charged and formed at a rate of 0.3C. When the formation potential reaches 3.95V, the charging is stopped. Then, the sodium-ion battery is aged at room temperature for 24 h, and the sodium-ion battery is continuously charged and formed at a rate of 0.3C until 100% SOC is reached to obtain a sodium-ion battery.

[0081] A cyclic voltammetry (CV) test is carried out on the positive electrode of the sodium-ion battery by using an electrochemical workstation of model VSP-300. The test voltage range is 1.5 - 4.0V, the scanning rate is 0.1 mV / s, and the test results are shown in Table 1.

[0082] Example 2-28

[0083] Example 2-28 is used to illustrate the sodium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows:

[0084] The median particle size D of the positive electrode active material used in Example 2-28 50 And the types and mass contents of each additive in the non-aqueous electrolyte are shown in Table 1.

[0085] By using a positive electrode active material with a specific median particle size D 50 And adding the first additive and the second additive in a specified proportion to the non-aqueous electrolyte, and carrying out charging and forming treatment under specified film-forming conditions, a specific interfacial film is formed on the positive electrode surface, so that the current difference corresponding to the oxidation peak and reduction peak of the positive electrode is 0.002 - 0.008 A / g, as shown in Table 1.

[0086] Comparative Example 1-16

[0087] Comparative Example 1-16 is used to compare and illustrate the sodium-ion battery and its preparation method disclosed in the present invention, including most of the operation steps in Example 1. The differences are as follows:

[0088] The median particle size D of the positive electrode active material used in Comparative Example 1-16 50and the types and mass contents of various additives in the non-aqueous electrolyte are shown in Table 1.

[0089] Performance Test

[0090] The following performance tests were carried out on the sodium-ion batteries prepared above:

[0091] (1) First activation initial efficiency of the battery

[0092] Measure the total capacity C1 of the sodium-ion battery after the film-forming process is completed, and then measure the capacity C2 released when the sodium-ion battery is discharged from 3.95 V to 1.5 V at a rate of 0.2C.

[0093] First activation initial efficiency = C2 / C1 * 100%

[0094] (2) Cycle performance test

[0095] 25°C cycle performance test:

[0096] Place the sodium-ion battery in a constant-temperature environment at 25°C, charge it at a constant current of 0.5C to 3.95 V, then charge it at a constant voltage until the current drops to 0.03C, and then discharge it at a constant current of 1C to 1.5 V. Repeat this cycle, and record the discharge capacity of the first cycle and the last cycle.

[0097] Calculate the capacity retention rate of the 25°C cycle according to the following formula:

[0098] Capacity retention rate (%) = Discharge capacity of the last cycle / Discharge capacity of the first cycle × 100%.

[0099] 45°C cycle performance test:

[0100] Place the sodium-ion battery in a constant-temperature environment at 45°C, charge it at a constant current of 0.5C to 3.95 V, then charge it at a constant voltage until the current drops to 0.03C, and then discharge it at a constant current of 1C to 1.5 V. Repeat this cycle, and record the discharge capacity and battery volume of the first cycle, as well as the discharge capacity and battery volume of the last cycle.

[0101] Calculate the capacity retention rate and swelling rate of the 45°C cycle according to the following formula:

[0102] Capacity retention rate (%) = Discharge capacity of the last cycle / Discharge capacity of the first cycle × 100%;

[0103] Swelling rate (%) = Battery volume of the last cycle / Battery volume of the first cycle × 100%.

[0104] The battery parameters and electrical performance data of Examples 1 to 28 and Comparative Examples 1 to 16 are shown in Tables 1 and 2.

[0105] Table 1

[0106]

[0107]

[0108] Table 2

[0109]

[0110]

[0111] As can be seen from Table 1 and Table 2, for the sodium-ion batteries prepared in Examples 1-28, the electrolyte is composed of the first additives TMSP and / or TMSB and the second additives RPS and / or DTD in the designed dosages of the present invention, and the cathode active material with the selected particle size of the present invention is adopted. After formation, the current difference between the oxidation peak and the reduction peak of the CV curve corresponding to the cathode can meet the range requirement of 0.002-0.008 A / g, improving the cycle reversibility. At the same time, the second additive can preferentially participate in film formation during the battery activation stage, effectively reducing the consumption of the electrolyte and the irreversible capacity loss in the first cycle, and synergistically acting with the first additive to form a stable electrode interface film. The battery can maintain good reversibility during the cycle, achieving the purpose of improving the cycle and first efficiency of the full battery and suppressing battery gas generation.

[0112] When further satisfying the relational expression 0.19 ≤ (a + b) / c ≤ 2.67, by correlating the above three parameters, the first additive and the second additive can form a sufficient film, have high thermal stability and low impedance, thereby effectively improving the first efficiency and cycle performance of the sodium-ion battery and suppressing battery gas generation.

[0113] When further satisfying the preferred conditions 0.3 ≤ (a + b) / c ≤ 2.0 and / or further preferably the dosages of the first additive and the second additive and the median particle size D of the cathode active material 50 it is beneficial to further improve the first efficiency and cycle performance of the sodium-ion battery and reduce the gas expansion rate, and the sodium-ion performance is better.

[0114] From the test results of Examples 1 and 22-25, it can be seen that for different combinations of TMSP and / or TMSB as the first additive and RPS and / or DTD as the second additive, under similar conditions, their functions are similar, and they all have a good improvement effect on improving the first efficiency and cycle performance of the sodium-ion battery and reducing the gas expansion rate.

[0115] As can be seen from the test results of Example 1 and Examples 26 - 28, for different positive electrode active materials, under similar conditions, their effects are similar, and they all have a good improvement effect on improving the first efficiency and cycle performance of sodium - ion batteries and reducing the gas expansion rate.

[0116] As can be seen from the test results of Examples 6 - 8, the second additive participates in film - forming prior to the first additive during the activation stage of sodium - ion batteries. Preferably, the addition amount of the second additive is greater than that of the first additive, which is beneficial to the effective film - forming of the second additive and the formation of an excellent and stable electrode interface film in cooperation with the first additive, further reducing the consumption of the electrolyte and the irreversible capacity loss in the first cycle, being conducive to improving the reversibility of the battery during the cycle, and further enhancing the cycle performance and first efficiency of the battery.

[0117] In Comparative Example 1 and Comparative Example 2, only one additive was used, and the purpose of the synergistic effect of the two additives could not be achieved. The current differences between the oxidation peak and the reduction peak reached 0.0390 A / g and 0.0092 A / g, exceeding the requirement of not more than 0.008 A / g that the present invention hopes to control. The first efficiency and capacity retention rate of the battery decreased, and the gas expansion rate increased, indicating poor film - forming quality and poor stability of the formed interface film during the cycle. It was necessary to continuously consume the electrolyte to participate in repairing the interface film, resulting in extremely unstable interfaces at both electrodes and intense side reactions, thus deteriorating the battery performance.

[0118] In Comparative Example 4, too much of the first additive was added, and it participated in film - forming excessively, resulting in uneven film - forming of the interface film. The current difference between the oxidation peak and the reduction peak was 0.0010 A / g, deteriorating the battery cycle performance; in Comparative Example 6, too much of the second additive was added, and it could not effectively cooperate with the first additive, resulting in an overly thick interface film on the positive electrode surface, poor film - forming quality of the SEI film, affecting the insertion and extraction of sodium ions in the positive electrode, reducing the ion conduction efficiency, and thus deteriorating the cycle performance and first efficiency.

[0119] In Comparative Example 3, too little of the first additive was added, and it could not effectively participate in film - forming, resulting in poor cycle reversibility of the battery. After 400 cycles at 45 °C, the capacity retention rate was only 73.7%. At the same time, the formed film was uneven and had poor stability, deteriorating the battery performance. In Comparative Example 5, too little of the second additive was added, and it could not effectively participate in film - forming, resulting in poor film - forming quality and instability on the electrode, prone to side reactions. The current difference between the oxidation peak and the reduction peak reached 0.0089 A / g, resulting in a significant decrease in the first efficiency and cycle performance compared with the present invention.

[0120] In Comparative Example 9, (a + b) / c was too small, and the current difference corresponding to the oxidation peak and the reduction peak was as high as 0.0130 A / g, resulting in a significant decline in battery performance. The initial efficiency of the battery was only 75.4%. After 400 cycles at 25 °C, the capacity retention rate was only 75.6%. After 400 cycles at 45 °C, the capacity retention rate was only 73.8%, and the gas expansion rate during cycling at 45 °C was as high as 30.4%. In Comparative Examples 10 and 11, (a + b) / c was too large, and the current differences corresponding to the oxidation peak and the reduction peak were 0.0011 A / g and 0.0012 A / g, respectively. The film-forming quality was very poor, the thermal stability was low, and the impedance was high. The initial efficiency and cycling performance of the sodium-ion battery decreased, and the gas production of the battery increased, deteriorating the battery performance.

[0121] In Comparative Example 7, the particle size of the positive electrode active material used was too small, and the specific surface area of the active material was relatively large, which would excessively consume the electrolyte to participate in film formation, resulting in too low initial efficiency, only 73.9%. At the same time, the cycling performance was also reduced. After 400 cycles at 25 °C, the capacity retention rate was only 74.9%. After 400 cycles at 45 °C, the capacity retention rate was only 73.0%, and the gas expansion rate during cycling at 45 °C was as high as 31.0%. In Comparative Example 8, the particle size of the positive electrode active material used was too large, which prolonged the diffusion path of ions in the material, resulting in a decrease in the ion transport rate and a reduction in the cycling performance. After 400 cycles at 25 °C, the capacity retention rate was only 74.7%. After 400 cycles at 45 °C, the capacity retention rate was only 73.8%, and the gas expansion rate during cycling at 45 °C was as high as 30.7%.

[0122] In the present invention, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0123] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A sodium-ion battery, characterized in that, It includes a positive electrode, a negative electrode and a non-aqueous electrolyte. Among them, the non-aqueous electrolyte includes a solvent, an electrolyte salt and an additive. The additive consists of a first additive and a second additive. The first additive is at least one of tris(trimethylsilyl) phosphate or tris(trimethylsilyl) borate. The second additive is at least one of 1,3-propane sultone or vinylene sulfate. The mass percentage content a% of the first additive in the non-aqueous electrolyte is 0.1% - 3%. The mass percentage content b% of the second additive in the non-aqueous electrolyte is 1% - 5%. The positive electrode includes a positive electrode active material, and the median particle size D 50 of the positive electrode active material has a value c of 2 to 10 μm; Cyclic voltammetry test is carried out using an electrochemical workstation. The test voltage is 1.5 - 4.0V and the scanning rate is 0.1 - 1mV / s. The current difference corresponding to the oxidation peak and the reduction peak of the positive electrode is 0.002 - 0.008 A / g. The sodium-ion battery satisfies the following conditions: 0.3 ≤ (a + b) / c ≤ 2.0; where a% is the mass percentage content of the first additive in the non-aqueous electrolyte, in %. b% is the mass percentage content of the second additive in the non-aqueous electrolyte, in %. c is the median particle size D of the positive electrode active material 50 , with the unit of μm.

2. The sodium ion battery according to claim 1, wherein, The mass percentage content a% of the first additive in the non-aqueous electrolyte is 0.2 - 1.5%. The mass percentage content b% of the second additive in the non-aqueous electrolyte is 1% - 3%.

3. The sodium ion battery according to claim 1, characterized in that, The median particle size D of the positive electrode active material 50 has a value c of 3 to 7 μm.

4. The sodium ion battery according to claim 1, characterized in that, The positive electrode active material is selected from at least one of layered metal oxides, polyanion compounds, Prussian compounds, phosphate compounds, sulfate compounds.

5. The sodium ion battery according to claim 4, characterized in that, The chemical formula of the layered metal oxide is Na x M y O z , where 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V; The molecular formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, where M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, M is selected from at least one of Al, V, Ge, Fe, and Ga; alternatively, the chemical formula of the phosphate compound is Na2MPO4F, and M is selected from at least one of Fe and Mn; The chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, and M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V.

6. The sodium-ion battery according to claim 5, wherein The layered metal oxide is NaNi m Fe n Mn p O2 or NaNi m Co n Mn p O2 or at least one of them; wherein, in the NaNi m Fe n Mn p O2, m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1; in the NaNi m Co n Mn p O2, m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1; The Prussian compound is Na x Mn[Fe(CN)6] y ·zH2O or Na x Fe[Fe(CN)6] y ·zH2O, at least one of them; wherein, in the Na x Mn[Fe(CN)6] y ·zH2O, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; in the Na x Fe[Fe(CN)6] y ·zH2O, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; The phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F; or the phosphate compound is at least one of Na2FePO4F or Na2MnPO4F.

7. The sodium ion battery according to claim 1, wherein The solvent includes at least one of C3 - C8 carbonates, C2 - C6 carboxylates, C4 - C10 ethers.

8. The sodium ion battery according to claim 7, characterized in that, The C3 - C8 carbonate is selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and the mass percentage content of the cyclic carbonate in the non-aqueous electrolyte is not less than 30%.

9. The sodium-ion battery according to claim 1, characterized in that, The electrolyte salt is selected from at least one of sodium perchlorate, sodium tetrafluoroborate, sodium hexafluorophosphate, sodium trifluoroacetate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide.

10. The sodium-ion battery according to claim 1, wherein, The additive also includes fluorinated carbonate.

11. The sodium-ion battery according to claim 10, wherein, The fluorinated carbonate includes at least one of fluorinated ethylene carbonate or difluorinated ethylene carbonate.

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