Battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery. The battery comprises a positive plate and an electrolyte, in an XRD pattern of the positive plate, two diffraction peaks are contained at 15-20 degrees and 40-43 degrees, the peak intensity of the diffraction peak existing at 15-20 degrees is H1, the peak intensity of the diffraction peak existing at 40-43 degrees is H2, H1 / H2 is larger than or equal to 0.5, the electrolyte comprises propylene carbonate, and on the basis of the total weight of the electrolyte, the weight content A of the propylene carbonate is 15.4-40.6 wt%. The battery provided by the invention can reduce interface reaction and improve the cycling stability and storage performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a battery. Background Technology

[0002] Sodium-ion batteries have broad application prospects due to their combined advantages such as low cost, abundant resources, and environmental friendliness. Their working principle is similar to that of lithium-ion batteries, primarily utilizing the intercalation and deintercalation of sodium ions between the positive and negative electrodes to achieve energy storage and release. However, the electrolyte in sodium-ion batteries reacts on the surface of the positive electrode. This is because conventional electrolytes cannot effectively form a CEI film on the positive electrode, resulting in unstable cycle performance and poor storage performance in sodium-ion batteries. Summary of the Invention

[0003] The purpose of this invention is to overcome the aforementioned problems in the prior art and provide a battery. The battery of this invention can reduce interfacial reactions and improve the battery's cycle stability and storage performance.

[0004] This invention provides a battery comprising a positive electrode and an electrolyte. The XRD pattern of the positive electrode shows two diffraction peaks at 15°–20° and 40°–43°. The peak intensity of the diffraction peak at 15°–20° is H1, and the peak intensity of the diffraction peak at 40°–43° is H2, with H1 / H2 ≥ 0.5. The electrolyte comprises propylene carbonate, and based on the total weight of the electrolyte, the weight content of propylene carbonate, A, is 15.4 wt%–40.6 wt%.

[0005] In one example, the battery satisfies: H1 / H2+A≥0.6.

[0006] In one example, the battery satisfies: 0.6 ≤ H1 / H2 + A ≤ 1.4.

[0007] In one instance, the peak height H1 of the diffraction peak at 15°–20° and the peak height H2 of the diffraction peak at 40°–43° satisfy the condition: H1 / H2 ≥ 0.5.

[0008] In one example, the positive electrode comprises a composite oxide with the chemical formula Na. x Ni a Fe b Mn c A y O2, x satisfies 0.7≤x≤1, y satisfies 0≤y≤0.5, and A includes one or more of Li, Mg, Zn, Co, Ca, Ba, Sr, Al, B, Cr, V, Zr, Ti, Sn, Mo, Ru, Si, Sb, Nb and Te.

[0009] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0010] The battery of the present invention uses the positive electrode and the electrolyte to work together to enable the electrolyte to form a CEI film on the surface of the positive electrode, thereby reducing interfacial reactions and improving the cycle stability and storage performance of the battery. Attached Figure Description

[0011] Figure 1 The image shown is an XRD pattern of a positive electrode sheet provided in an embodiment of the present invention.

[0012] Figure 2 The image shown is the XRD pattern of a pair of positive electrode sheets provided in accordance with the present invention. Detailed Implementation

[0013] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0014] This invention provides a battery comprising a positive electrode and an electrolyte. The XRD pattern of the positive electrode shows two diffraction peaks at 15°–20° and 40°–43°. The peak intensity of the diffraction peak at 15°–20° is H1, and the peak intensity of the diffraction peak at 40°–43° is H2, with H1 / H2 ≥ 0.5. The electrolyte comprises propylene carbonate, and based on the total weight of the electrolyte, the weight content of propylene carbonate, A, is 15.4 wt%–40.6 wt%.

[0015] The XRD pattern of the positive electrode shows two diffraction peaks at 15°–20° and 40°–43°, respectively. The diffraction peak at 15°–20° is a diffraction peak of the (003) crystal plane, and the diffraction peak at 40°–43° is a diffraction peak of the (104) crystal plane. The presence of diffraction peaks of these two crystal planes in the XRD pattern of the positive electrode indicates that the positive electrode has high structural stability. This can reduce the risk of battery deactivation, expansion, rupture, and side reactions (such as gas generation) with the electrolyte caused by temperature changes during charging and discharging, thereby improving the cycle stability of the battery. Figure 1The XRD pattern of the positive electrode shows two diffraction peaks at 15°–20° and 40°–43°, respectively. The peak intensities H1 of the diffraction peak at 15°–20° and H2 of the diffraction peak at 40°–43° satisfy H1 / H2 ≥ 0.5. When H1 / H2 < 0.5, the structural stability of the positive electrode is poor, and the electrolyte cannot form a good CEI film on the surface of the positive electrode, resulting in poor cycle stability and poor storage performance of the battery. When H1 / H2 ≥ 0.5, the positive electrode can have good structural stability, which can promote the formation of a good CEI film on the surface of the positive electrode, reduce interfacial reactions, and thus improve the cycle stability and storage performance of the battery.

[0016] Based on the total weight of the electrolyte, the weight content of propylene carbonate can be from 15.4 wt% to 40.6 wt%. By further limiting the content range of propylene carbonate, the synergistic effect between propylene carbonate and the positive electrode can be further improved, resulting in higher stability of the CEI film formed on the surface of the positive electrode, thereby further improving the long-cycle performance and storage performance of the battery.

[0017] In this invention, through the synergistic effect of the positive electrode and the electrolyte, the battery achieves better cycle stability and storage performance than existing technologies. To further improve the performance, one or more of the technical features can be further optimized.

[0018] In one example, the battery can satisfy: H1 / H2+A≥0.6 (e.g., 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2). The inventors of this invention have discovered that when the positive electrode and electrolyte meet the above specific conditions, through the synergistic cooperation of the positive electrode and electrolyte, that is, the positive electrode of this invention can promote the formation of a passivation film of PC in the electrolyte on the surface of the positive electrode, reduce particle breakage and crystal orientation transformation of the positive electrode material during charging and discharging, and at the same time reduce interfacial reactions, thereby improving the cycle stability and storage performance of the battery.

[0019] In one example, the battery satisfies: 0.6 ≤ H1 / H2 + A ≤ 1.4.

[0020] In one example, H1 / H2 is 0.5–0.9 (e.g., 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9). By further limiting the value of H1 / H2, the cathode can have higher structural stability and lithium-ion intercalation / deintercalation, while improving the structural stability of the CEI film, reducing interfacial reactions between the cathode and the electrolyte, and improving the long-cycle performance and storage performance of the battery.

[0021] In one example, the weight content of propylene carbonate is 20 wt% to 35 wt% based on the total weight of the electrolyte. By further limiting the content range of propylene carbonate, the synergistic effect between propylene carbonate and the positive electrode can be further improved, resulting in higher stability of the CEI film formed on the surface of the positive electrode, thereby further improving the long-cycle performance and storage performance of the battery.

[0022] According to one specific embodiment, the positive electrode comprises a composite oxide, the chemical formula of which is Na. x Ni a Fe b Mn c A y O2, where x satisfies 0.7 ≤ x ≤ 1.05 (e.g., 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05), y satisfies 0 ≤ y ≤ 0.5 (e.g., 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5), and a satisfies 0.3 ≤ a ≤ 1 (e.g., 0.3, 0.4, 0.5, 0.6, 0.7). The positive electrode comprises 0.1 ≤ b ≤ 0.5 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5), and c satisfies 0.1 ≤ c ≤ 0.5 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5). A includes one or more of Li, Mg, Zn, Co, Ca, Ba, Sr, Al, B, Cr, V, Zr, Ti, Sn, Mo, Ru, Si, Sb, Nb, and Te. In this invention, the positive electrode comprising the composite oxide can satisfy H1 / H2 ≥ 0.5.

[0023] The chemical formula of the composite oxide is Na x Ni a Fe b Mn c A y In O2, the elements conform to the principle that the algebraic sum of the positive and negative valences of the elements in the compound is zero.

[0024] In one instance, x satisfies 0.9 ≤ x ≤ 1.03.

[0025] In one instance, y satisfies 0.01≤y≤0.1.

[0026] In one instance, when the composite oxide does not include dopant element A, i.e., when y = 0, the chemical formula of the composite oxide is Na. x Ni a Fe b Mn c O2. Chemical formula Na x Nia Fe b Mn c The elements in O2 conform to the principle that the algebraic sum of the positive and negative valences of the elements in a compound is zero.

[0027] In one example, the composite oxide includes dopant element A. The composite oxide including dopant element A exhibits higher positive electrode activity stability, prevents the dissolution of transition metal elements during charge and discharge, improves corrosion in the electrolyte, enhances the stability of the positive electrode material, and simultaneously makes the CEI film formed on the positive electrode surface more stable with fewer interfacial reactions, thereby improving the battery's long-cycle performance and storage performance.

[0028] In one example, the composite oxide includes NaNi 0.8 Fe 0.1 Mn 0.1 O2, NaNi 0.6 Fe 0.2 Mn 0.2 O2, NaNi 0.6 Fe 0.25 Mn 0.15 O2, NaNi 0.5 Fe 0.2 Mn 0.3 Al 0.01 O2, NaNi 0.5 Fe 0.2 Mn 0.3 O2 and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 One or more of O2.

[0029] In one example, the positive electrode sheet includes a positive current collector and a positive active material layer, the positive active material layer being located on one or both surfaces of the positive current collector, the positive active material layer including a positive electrode material, the positive electrode material including a composite oxide.

[0030] In one example, the positive current collector comprises aluminum foil or porous aluminum foil.

[0031] In one example, the positive electrode active material layer comprises a composite oxide.

[0032] According to one specific embodiment, based on the total weight of the positive electrode active material layer, the weight content of the composite oxide is 92wt% to 99wt% (e.g., 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt%, 99wt%).

[0033] In one example, the weight content of the composite oxide is 95 wt% to 98 wt%, based on the total weight of the positive electrode active material layer.

[0034] The composite oxide can be prepared by the following method:

[0035] (1) Mix soluble Ni salt, soluble Fe salt, soluble Mn salt and soluble salt containing Al element, add to solvent to obtain mixed solution; adjust the pH of the mixed solution to obtain coprecipitate containing Ni, Fe, Mn and Al, and obtain composite precursor by solid-liquid separation (e.g. filtration);

[0036] (2) The composite precursor is dried, and then mixed with sodium carbonate and sintered at high temperature.

[0037] In one example, the soluble Ni salt includes one or more of nickel sulfate and nickel nitrate.

[0038] In one example, the soluble Fe salt includes one or more of ferric sulfate and ferric nitrate.

[0039] In one example, the soluble Mn salt includes one or more of manganese sulfate and manganese nitrate.

[0040] In one instance, soluble salts containing Al include one or more of aluminum nitrate.

[0041] In one example, the molar ratio of the soluble Ni salt, soluble Fe salt, and soluble Mn salt is a:b:c.

[0042] In one example, the solvent includes one or more of water, ethanol, acetone, toluene, and diethyl ether.

[0043] In one example, the pH of the mixed solution is adjusted to be between 3 and 12.

[0044] In one example, the drying conditions are: a temperature of 100°C to 1000°C (e.g., 100°C, 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C) and a time of 1 hour to 20 hours (e.g., 1 hour, 3 hours, 5 hours, 8 hours, 10 hours, 13 hours, 15 hours, 18 hours, 20 hours).

[0045] In one example, the molar ratio of the sodium carbonate to the soluble Ni salt is x:a.

[0046] In one example, the conditions for high-temperature sintering are: a temperature of 770°C to 1000°C (e.g., 770°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C), a sintering time of 10h to 40h (e.g., 10h, 15h, 20h, 25h, 30h, 35h, 40h), and a sintering atmosphere of air, compressed air, N2 gas, or oxygen.

[0047] In one example, the conditions for high-temperature sintering are: temperature of 800℃~900℃, sintering time of 20h~38h, and sintering atmosphere of N2 gas.

[0048] According to one specific embodiment, the positive electrode active material layer includes a conductive agent and a binder.

[0049] In one example, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0050] In one example, the adhesive includes one or more of polyvinylidene fluoride, styrene-butadiene rubber, styrene-butadiene latex, polytetrafluoroethylene, and polyethylene oxide.

[0051] According to one specific embodiment, based on the total weight of the positive electrode active material layer, the weight content of the conductive agent is 0.01wt% to 7wt% (e.g., 0.01wt%, 0.05wt%, 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%), and the weight content of the binder is 0.1wt% to 8wt% (e.g., 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 8wt%).

[0052] In one example, based on the total weight of the positive electrode active material layer, the weight content of the conductive agent is 0.1 wt% to 2 wt%, and the weight content of the binder is 0.1 wt% to 5 wt%.

[0053] In one example, the electrolyte comprises sodium difluorosulfonate imide (NaFSi). The inventors of this invention have discovered that when the electrolyte includes NaFSi, the composite oxide in the positive electrode sheet satisfying H1 / H2≥0.5 can promote the formation of a CEI film by NaFSi anions on the surface of the positive electrode sheet, reducing interfacial reactions. Simultaneously, the PC in the electrolyte can also promote the dissociation of NaFSi, improving film formation efficiency, thereby further enhancing the cycle stability and storage performance of the battery.

[0054] According to one specific embodiment, the weight content of NaFSi is 0.1wt% to 10wt% (e.g., 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%), based on the total weight of the electrolyte.

[0055] In one example, the NaFSi content is 0.2 wt% to 6 wt% based on the total weight of the electrolyte.

[0056] In one example, the electrolyte also includes ethylene carbonate (EC).

[0057] According to one specific embodiment, the weight content of ethylene carbonate is less than 5 wt%, based on the total weight of the electrolyte. While ethylene carbonate can promote the dissociation of NaFSi, its participation in dissociation can cause it to react on the surface of the positive electrode sheet, affecting the composition of the CEI film and thus deteriorating battery performance. By limiting the content of ethylene carbonate in the electrolyte to the aforementioned specific range, the influence of ethylene carbonate on the CEI film composition can be reduced, thereby minimizing its impact on battery performance.

[0058] In a preferred embodiment, the electrolyte does not contain ethylene carbonate. When the electrolyte does not contain ethylene carbonate, the decomposition and volatilization of ethylene carbonate during battery charging and discharging can be avoided, reducing battery gas production and thus improving the battery's cycle performance and storage performance.

[0059] In one example, the electrolyte further includes pyridinium 1-hexyltetrafluoroborate (HTL), which has the structure shown in formula (I).

[0060]

[0061] As can be seen from the structure shown in formula (I), pyridinium 1-hexyltetrafluoroborate (HTL) includes cations and anions. These ions can move in the electrolyte, enabling current to be conducted in the sodium-ion battery, which can improve the stability of the electrolyte and form a dense protective film on the surface of the sodium-ion positive electrode.

[0062] According to one specific embodiment, the weight content of pyridinium 1-hexyltetrafluoroborate is 0.1wt% to 3wt% (e.g., 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%), based on the total weight of the electrolyte.

[0063] In one example, based on the total weight of the electrolyte, the weight content of 1-hexylpyridinium tetrafluoroborate is 0.5 wt% to 0.8 wt%.

[0064] When the HTL additive in the electrolyte satisfies the positive electrode sheet with H1 / H2≥0.5, a dense protective film can be formed on the surface of the positive electrode, significantly improving the cycle stability and storage performance of the sodium-ion battery.

[0065] In one example, the electrolyte includes an electrolyte and an additive.

[0066] In one example, the electrolyte includes one or more of sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSi).

[0067] In one example, the additive includes one or more of ethylene carbonate (VC), vinylene sulfate, and 1,3-propane sultone.

[0068] According to a specific embodiment, based on the total weight of the electrolyte, the weight content of the electrolyte is 6 wt% to 20 wt% (for example, 6 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%), and the weight content of the additive is 1 wt% to 15 wt% (for example, 1 wt%, 3 wt%, 5 wt%, 7 wt%, 10 wt%, 12 wt%, 15 wt%).

[0069] In one example, based on the total weight of the electrolyte, the weight content of the electrolyte is 9 wt% to 15 wt%, and the weight content of the additive is 2 wt% to 10 wt%.

[0070] In one example, the battery includes a negative electrode sheet and a separator.

[0071] The negative electrode sheet can be a conventional negative electrode sheet in the art. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both sides of the surface of the negative electrode current collector. The negative electrode active material layer includes a negative electrode material, a conductive agent, a binder, and a thickener.

[0072] In one example, the negative electrode current collector includes a copper foil or a porous copper foil.

[0073] In one example, the negative electrode material includes one or more of artificial graphite, natural graphite, mesocarbon microbeads, hard carbon, soft carbon, nanosilicon, silicon oxide material (SiO x (0 < x < 2)) and silicon-carbon materials.

[0074] In one example, the thickener includes one or more of sodium carboxymethyl cellulose and styrene-butadiene rubber.

[0075] According to one specific embodiment, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode material is 92wt% to 99wt% (e.g., 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, 98wt%, 99wt%), the weight content of the conductive agent is 0.1wt% to 7wt% (e.g., 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%), the weight content of the binder is 0.1wt% to 7wt% (e.g., 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%), and the weight content of the thickener is 0.1wt% to 7wt% (e.g., 0.1wt%, 0.5wt%, 1wt%, 3wt%, 5wt%, 7wt%).

[0076] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode material is 94wt% to 98wt%, the weight content of the conductive agent is 0.5wt% to 2wt%, the weight content of the binder is 0.5wt% to 2wt%, and the weight content of the thickener is 0.5wt% to 2wt%.

[0077] According to one specific embodiment, the battery is a sodium-ion battery.

[0078] The diaphragm can be a conventional diaphragm in the art. For example, the diaphragm includes one or more of polyethylene and polypropylene films.

[0079] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0080] The following examples illustrate the electrolyte and positive electrode of the present invention.

[0081] Example 1

[0082] (1) Preparation of ingredients

[0083] Positive electrode: Composite oxide (NaNi) 1 / 3 Fe 1 / 3 Mn 1 / 3 Al 0.04 O2) 95 parts by weight; conductive agent (carbon black) 2.5 parts by weight; binder (polyvinylidene fluoride) 2.5 parts by weight; positive electrode current collector: aluminum foil;

[0084] Electrolyte: 59.95 parts by weight of diethyl carbonate (DEC), 25.95 parts by weight of propylene carbonate (PC), 1 part by weight of NaFSi; 0.6 parts by weight of HTL; 12.5 parts by weight of electrolyte (sodium hexafluorophosphate (NaPF6)).

[0085] (2) Preparation of composite oxides

[0086] 1) Soluble Ni salt (nickel sulfate), soluble Fe salt (ferric sulfate), soluble Mn salt (manganese sulfate), and soluble aluminum nitrate containing Al are mixed in a stoichiometric ratio (Ni / Fe / Mn stoichiometric ratio of 1:1:1, and Al stoichiometry is 15% of iron stoichiometry) and added to solvent H2O to obtain a mixed solution; an appropriate amount of ammonia is slowly added to the mixed solution while stirring, and the pH of the mixed solution is adjusted to 11.5±0.2 to obtain a coprecipitate containing Ni, Fe, Mn, and M; the composite precursor is obtained by filtration.

[0087] 2) The composite precursor described in step [1] is washed with deionized water and dried. After drying, it is mixed with sodium carbonate in a stoichiometric ratio and subjected to high-temperature sintering at 900℃ for 20 hours in a N2 atmosphere. The sintered product is then ground to obtain NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Al 0.04 O2, denoted as complex oxide A.

[0088] (3) Preparation of positive electrode

[0089] Composite oxide A, conductive agent, and binder are dispersed in an appropriate amount of N-methylpyrrolidone and stirred thoroughly to form a uniform positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector, and then dried, rolled, and cut to obtain a positive electrode sheet. In the XRD pattern of the positive electrode sheet, there are two diffraction peaks at 16.7 and 41.7. The peak intensity H1 of the diffraction peak at 16.7 is 9458, and the peak intensity H2 of the diffraction peak at 41.7 is 12575. Therefore, H1 / H2 = 0.7521.

[0090] (4) Electrolyte preparation

[0091] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), PC / DEC are mixed evenly, and then fully dried electrolyte (sodium hexafluorophosphate (NaPF6)) is added. After dissolving, NaFSi and HTL are added and stirred evenly. After passing the tests for moisture and free acid, the desired electrolyte is obtained.

[0092] The battery obtained in Example 1: H1 / H2+A=0.7521+0.2595=1.0116≥0.6.

[0093] Example 1-1

[0094] The procedure was carried out in accordance with Example 1, except that EC was added to the electrolyte and HTL was not added, as detailed in Table 1.

[0095] Examples 1-2

[0096] The procedure was carried out in accordance with Example 1, except that the weight fraction of HTL in the electrolyte was changed, as detailed in Table 1.

[0097] Example 2

[0098] The procedure was carried out in accordance with Example 1, except that HTL was not added to the electrolyte and the weight fraction of NaFSi in the electrolyte was changed, as detailed in Table 1.

[0099] Example 2-1

[0100] The procedure was carried out in accordance with Example 2, except that EC was added to the electrolyte, as detailed in Table 1.

[0101] Example 2-2

[0102] The procedure was carried out in accordance with Example 2, except that HTL was added to the electrolyte, as detailed in Table 1.

[0103] Example 3

[0104] The procedure was carried out in accordance with Example 2, except that the weight proportions of PC and NaFSi in the electrolyte were changed, as detailed in Table 1.

[0105] Example 3-1

[0106] The procedure was carried out in accordance with Example 3, except that EC was added to the electrolyte, as detailed in Table 1.

[0107] Example 3-2

[0108] The procedure was carried out in accordance with Example 3, except that HTL was added to the electrolyte, as detailed in Table 1.

[0109] Example 4

[0110] The procedure was carried out in accordance with Example 2, except that the weight proportions of PC and NaFSi in the electrolyte were changed, as detailed in Table 1.

[0111] Example 4-1

[0112] The procedure was carried out in accordance with Example 4, except that EC was added to the electrolyte, as detailed in Table 1.

[0113] Example 4-2

[0114] The procedure was carried out in accordance with Example 4, except that HTL was added to the electrolyte, as detailed in Table 1.

[0115] Example 4-3

[0116] The procedure was carried out in accordance with Example 4-2, except that EC was added to the electrolyte, as detailed in Table 1.

[0117] Example 5

[0118] The procedure was carried out in accordance with Example 1, except that the specific selection of the composite oxide was changed by adjusting the element ratio and sintering temperature, and the content of PC in the electrolyte was also adjusted, as detailed in Table 1.

[0119] Example 5-1

[0120] The procedure was carried out according to Example 5, except that the specific selection of the composite oxide was changed by adjusting the element ratio and sintering temperature, as detailed in Table 1.

[0121] Example 5-2

[0122] The procedure was carried out according to Example 5, except that the specific selection of the composite oxide was changed by adjusting the element ratio and sintering temperature, as detailed in Table 1.

[0123] Example 6 group

[0124] Example 6-1

[0125] The procedure was carried out in accordance with Examples 1-2, except that the HTL content in the electrolyte was adjusted, as detailed in Table 1.

[0126] Example 6-2

[0127] The procedure was carried out according to Examples 1-2, except that the HTL content in the electrolyte was adjusted, as detailed in Table 1.

[0128] Example 7 group

[0129] Example 7-1

[0130] The procedure was carried out in accordance with Examples 1-2, except that the content of PC in the electrolyte was changed and HTL was not added. See Table 1 for details.

[0131] Example 7-2

[0132] The same procedure was performed as in Examples 1-2, except that the PC content in the electrolyte was changed, as detailed in Table 1.

[0133] Example 7-3

[0134] The procedure was carried out in accordance with Examples 1-2, except that the content of PC in the electrolyte was changed and HTL was not added. See Table 1 for details.

[0135] Example 7-4

[0136] The same procedure was performed as in Examples 1-2, except that the content of PC in the electrolyte was changed, as detailed in Table 1.

[0137] Example 8 group

[0138] Example 8-1

[0139] The procedure was carried out in accordance with Examples 1-2, except that the content of PC in the electrolyte was changed and HTL was not added. See Table 1 for details.

[0140] Example 8-2

[0141] The procedure was carried out in accordance with Examples 1-2, except that the content of PC in the electrolyte was changed, as detailed in Table 1.

[0142] Example 8-3

[0143] The procedure was carried out in accordance with Example 2, except that the NaFSi content in the electrolyte was changed, as detailed in Table 1.

[0144] Example 8-4

[0145] The procedure is carried out as described in Examples 8-3, except that HTL is added to the electrolyte, as detailed in Table 1.

[0146] Comparative Example 1

[0147] The process was carried out in accordance with Example 6, except that the high-temperature sintering temperature for preparing the composite oxide was adjusted to 650°C and the time was adjusted to 12h. The obtained composite oxide was denoted as composite oxide B. In the XRD pattern of the positive electrode of composite oxide B, the two diffraction peaks were located at 16.9° and 42.1°, respectively. The ratio of the peak height H1 of the diffraction peak at 16.9° to the peak height H2 of the diffraction peak at 42.1° was H1 / H2 = 0.3912.

[0148] Comparative Example 2

[0149] The procedure was carried out in accordance with Comparative Example 1, except that HTL was added to the electrolyte, as detailed in Table 1.

[0150] Table 1

[0151]

[0152] * indicates the same as in Example 1;

[0153] - indicates that it does not exist.

[0154] Preparation Example

[0155] The electrolytes and positive electrode sheets obtained in the examples and comparative examples were used to prepare batteries in the following manner.

[0156] (1) Preparation of positive electrode

[0157] The positive electrode sheets obtained from the above-described embodiments and comparative examples were used respectively.

[0158] (2) Preparation of negative electrode

[0159] Weigh out the negative electrode material (hard carbon), conductive agent (carbon black), binder (styrene-butadiene rubber), and thickener (sodium carboxymethyl cellulose) in a weight ratio of 90:2.5:5.0:2.5, disperse them in an appropriate amount of deionized water, and stir thoroughly to form a uniform negative electrode slurry. Coat the negative electrode slurry onto the negative electrode current collector copper foil, and then dry, roll, and cut to obtain the negative electrode sheet.

[0160] (3) Electrolyte

[0161] The electrolytes obtained in the above-described embodiments and comparative examples were used respectively.

[0162] (4) Preparation of sodium-ion batteries

[0163] The positive electrode sheet from step (1), the negative electrode sheet from step (2), and the separator are stacked in sequence, with the separator in the middle of the positive and negative electrode sheets. Then, the electrode tabs are welded and the core is wound. The core is then placed in an aluminum-plastic film packaging bag. Finally, the electrolyte is injected and the sodium-ion battery is prepared by vacuum sealing, settling, formation, and shaping.

[0164] Test case

[0165] 1. The positive electrode sheets prepared from the composite oxides obtained in the examples and comparative examples were subjected to XRD tests.

[0166] XRD analysis was performed on the positive electrode sheet prepared from the composite oxide of Example 1, and the XRD pattern of the positive electrode sheet of Example 1 was obtained, as shown below. Figure 1 As shown, it can be seen that there are two diffraction peaks in the XRD pattern at 16-17° and 41-42° respectively. The peak height H1 of the diffraction peak at 16-17° and the peak height H2 of the diffraction peak at 41-42° are given by H1 / H2 = 0.7521, which satisfies the condition that H1 / H2 ≥ 0.5.

[0167] XRD analysis was performed on the positive electrode sheet prepared from the composite oxide of Example 9 to obtain the XRD image of the positive electrode sheet of Comparative Example 1, as shown below. Figure 2As shown, it can be seen that there are two diffraction peaks in the XRD pattern at 16-17° and 41-42° respectively. The peak heights of the diffraction peak at 16-17° are H1 and H2 respectively, where H1 / H2 = 0.3912.

[0168] 2. The batteries obtained in the examples and comparative examples were subjected to the following tests respectively.

[0169] (1) Cyclic performance test

[0170] The sodium-ion battery was placed at 25°C and charged at a constant current of 0.5C to the upper limit voltage (4.0V), then charged at a constant voltage of 4.0V to 0.05C, and allowed to rest for 5 minutes; next, it was discharged at a constant current of 0.5C to 1.5V, and allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity of the first cycle was recorded as Q1, and the discharge capacity of the 200th cycle was recorded as Q. The cycle capacity retention rate was calculated as Q1 / Q*100%. See Table 2 for detailed results.

[0171] (2) Storage performance test

[0172] The sodium-ion battery was placed at 25°C and charged at a constant current of 0.5C to the upper limit voltage (4.0V), then charged at a constant voltage of 4.0V to 0.05C and allowed to stand for 5 minutes; subsequently, it was discharged at a constant current of 0.5C to 1.5V. The battery was then fully charged and stored at 60°C for 30 days. The battery was then subjected to one charge-discharge cycle at room temperature. The discharge capacity before storage was recorded as N1, and the discharge capacity after storage was recorded as N. The storage capacity retention rate was calculated as N1 / N*100%. See Table 2 for detailed results.

[0173] Record the results in Table 2.

[0174] Table 2

[0175]

[0176]

[0177] As can be seen from Table 2, and from the comparative examples and embodiments, the cycle capacity retention rate and storage capacity retention rate of the battery in the embodiments are significantly improved. This indicates that the battery of the present invention, through the synergistic cooperation of the positive electrode and the electrolyte, improves the cycle stability and storage performance of the battery.

[0178] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A battery, characterized in that, The battery includes a positive electrode and an electrolyte. The XRD pattern of the positive electrode contains two diffraction peaks at 15°–20° and 40°–43°. The peak intensity of the diffraction peak at 15°–20° is H1, and the peak intensity of the diffraction peak at 40°–43° is H2, with H1 / H2 ≥ 0.

5. The electrolyte includes propylene carbonate, and the weight content of propylene carbonate, A, is 15.4 wt%–40.6 wt% based on the total weight of the electrolyte.

2. The battery according to claim 1, wherein, The battery satisfies: H1 / H2+A≥0.6; Preferably, the battery satisfies: 0.6≤H1 / H2+A≤1.

4.

3. The battery according to claim 1, wherein, The peak intensity H1 of the diffraction peak existing at 15° to 20° and the peak intensity H2 of the diffraction peak existing at 40° to 43° satisfy: H1 / H2 is 0.5 to 0.9; And / or, based on the total weight of the electrolyte, the weight content of propylene carbonate is 20wt% to 35wt%.

4. The battery according to claim 1, wherein, The positive electrode includes a positive electrode active material, which includes Na. x Ni a Fe b Mn c A y O2, where x satisfies 0.7≤x≤1.05, y satisfies 0≤y≤0.5, A includes one or more of Li, Mg, Zn, Co, Ca, Ba, Sr, Al, B, Cr, V, Zr, Ti, Sn, Mo, Ru, Si, Sb, Nb, Zr and Te, a satisfies 0.3≤a≤1, b satisfies 0.1≤b≤0.5, and c satisfies 0.1≤c≤0.

5.

5. The battery according to any one of claims 1-4, wherein, The positive electrode sheet includes a positive electrode active material layer, which includes a composite oxide. Based on the total weight of the positive electrode active material layer, the weight content of the composite oxide is 92wt% to 99wt%.

6. The battery according to claim 5, wherein, Based on the total weight of the positive electrode active material layer, the weight content of the composite oxide is 95wt% to 98wt%.

7. The battery according to claim 1, wherein, The electrolyte includes sodium difluorosulfonate imide.

8. The battery according to claim 7, wherein, Based on the total weight of the electrolyte, the weight content of sodium difluorosulfonate is 0.1 wt% to 10 wt%.

9. The battery according to claim 1, wherein, The electrolyte also includes pyridinium 1-hexyltetrafluoroborate.

10. The battery according to claim 9, wherein, Based on the total weight of the electrolyte, the weight content of pyridinium 1-hexyltetrafluoroborate is 0.1wt% to 3wt%, preferably 0.5wt% to 0.8wt%.

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