Capacity compensating agent, battery positive electrode and application thereof

Abstract

The present invention provides a capacity compensator, a battery positive electrode and their applications. The capacity compensator of the present invention is applied to a sodium-ion battery and includes a sodium supplement agent and a lithium supplement agent. The sodium supplement agent and the lithium supplement agent both have the function of supplementing capacity. In the capacity compensator, the capacity Q Na that can be supplemented by the sodium supplement agent and the capacity Q Li that can be supplemented by the lithium supplement agent, that is, the capacity compensation ratio, satisfies 2 ≤ Q Na / Q Li ≤ 20; wherein, Q Na = m Na *C Na ; Q Li = m Li *C Li ; The dual-ion capacity compensator of the present invention can supplement more capacity compared with the sodium supplement agent in the prior art, and can also improve the capacity retention rate of the sodium-ion battery during long-term cycling.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries, and in particular relates to a capacity compensating agent, a battery positive electrode and applications thereof. Background Art

[0002] In recent years, energy storage technology has developed rapidly, among which lithium-ion batteries are the most representative. Lithium-ion batteries have the characteristics of long cycle life and high energy density, and are widely used in consumer electronics, new energy vehicles, aerospace and other fields. However, during the charging and discharging process, a SEI film will form at the negative electrode, resulting in the loss of active lithium, reducing the coulombic efficiency and energy density of the battery. To this end, researchers have invented lithium replenishment technology, including positive electrode lithium replenishment, negative electrode lithium replenishment, diaphragm lithium replenishment and electrolyte lithium replenishment. Among them, positive electrode lithium replenishment technology has developed the fastest, and some manufacturers have achieved industrialization. The method used in positive electrode lithium replenishment technology is to add a lithium replenisher to the positive electrode material. The charging capacity of the lithium replenisher is greater than the capacity of the positive electrode active material. Lithium ions will be released during the charging and discharging process of the battery to make up for the irreversible lithium ion loss caused by the growth of the negative electrode SEI film, thereby achieving the purpose of lithium replenishment.

[0003] The rapid development of the lithium battery industry has also led to a rapid rise in the price of lithium salts, resulting in a sharp increase in the cost of raw materials. However, the sodium resources on the earth are extremely abundant. In order to reduce costs, both the academic and industrial circles are developing sodium-ion batteries. Like lithium batteries, sodium batteries will form a SEI film at the negative electrode during the charging and discharging process, causing the loss of active sodium, resulting in a decrease in coulombic efficiency and energy density. Therefore, like the lithium battery lithium replenishment technology, the sodium battery sodium replenishment technology has been derived.

[0004] In the prior art, positive electrode sodium supplement materials can be divided into four types, including 1) sodium-rich ternary sodium salts, such as Na 2 NiO 2 、Na 5 FeO 4 、NaCrO 2 、Na 2 MnO 3 etc.; ② Sacrificial sodium salts (no inert residue after decomposition), such as NaN 3 、Na 2 C 4 O 4 、Na 2 C 3 O 5 、Na 2 C 4 O 6 etc.; ③ Nanocomposites based on conversion reactions, such as M / Na 2 O、M / Na x S, etc. (M=Mn, Ni, Co, etc.); ④ Over-intercalation sodium positive electrode salts: Na 4 V2 (PO 4 ) 3 、Na 4 V 2 (PO 4 ) 2 F, etc.; however, the sodium-rich ternary salts in the above-mentioned positive electrode sodium-supplementing materials have a medium sodium-supplementing performance, and the cost-effectiveness needs to be further improved; the sacrificial sodium salt has a high sodium-supplementing performance, but it will produce gas after decomposition, causing the battery to swell; the nanocomposite materials based on conversion reactions also have a high sodium-supplementing performance, but the preparation method is cumbersome and the cost is high; although the over-embedded sodium positive electrode salts have a lower cost, their sodium-supplementing performance is low.

[0005] Invention patent CN110783525A discloses a positive electrode additive for sodium ion batteries, wherein the positive electrode additive is a sacrificial salt with a chemical formula of Li x M y O z , wherein M is a combination of one or more elements in the third, fourth and fifth periods of the periodic table, x, y and z satisfy charge balance and satisfy x≥1, y≥1, z≥2; however, the lithium ions of the above-mentioned positive electrode additives will migrate into the electrolyte during charging, and the sodium ion battery electrolyte only contains sodium ions. Excessive lithium ions cause the sodium ion content in the electrolyte to decrease too much. During discharge, lithium ions will migrate into the lattice of the positive electrode active material. Since the ion migration channel of the positive electrode active material is specially designed for sodium ions and has the best matching, when the ion migration channel is occupied by too many lithium ions, the rate performance and cycle life of the positive electrode active material will be reduced. Summary of the invention

[0006] In view of the shortcomings and defects of the prior art, the present invention aims to provide a capacity compensator, a battery positive electrode and its application. The capacity compensator of the present invention is applied to a sodium ion battery, including a sodium supplement and a lithium supplement, the sodium supplement and the lithium supplement have the function of replenishing capacity at the same time, when charging, the sodium ions and the lithium ions will migrate into the electrolyte at the same time, and the sodium ions in the electrolyte will migrate to the negative electrode to complete the function of capacity replenishment; the dual-ion capacity compensator of the present invention can replenish more capacity than the sodium supplement in the prior art, and can also improve the capacity retention rate of the positive electrode active material during long-term cycling.

[0007] In order to achieve the above-mentioned object, the first aspect of the present invention provides a capacity compensating agent for a sodium ion battery, which adopts the following technical scheme:

[0008] A capacity compensator for a sodium ion battery, comprising: a sodium supplement and a lithium supplement; the sodium supplement and the lithium supplement have the function of replenishing capacity at the same time; in the capacity compensator, the replenishable capacity Q of the sodium supplement Na The replenishable capacity Q of the lithium supplement LiThe ratio, that is, the capacity compensation ratio, satisfies 2≤Q Na / Q Li ≤20 (for example, Q Na / Q Li =2.1, 2.2, 2.3, 2.5, 5, 10, 12, 15, 17, 19), where Q Na =m Na *C Na (m Na is the mass of sodium supplement, C Na is the gram volume of sodium supplement), Q Li =m Li *C Li (m Li is the mass of lithium supplement, C Li is the gram capacity of lithium supplement).

[0009] The capacity compensator in the present invention includes a sodium supplement and a lithium supplement, and is a dual-ion capacity compensator, which is applied to a sodium ion battery. During charging, sodium ions and lithium ions will migrate into the electrolyte at the same time, while the electrolyte of the sodium ion battery contains only sodium ions. If the capacity compensation ratio is less than 2, that is, the replenishable capacity of the lithium supplement in the capacity compensator is close to or greater than the replenishable capacity of the sodium supplement, it will cause excessive lithium ions to exist in the electrolyte, causing the sodium ion content in the electrolyte to decrease too much. During discharge, the lithium ions will migrate into the lattice of the positive active material, and the migration channel will be occupied by too many lithium ions, thereby reducing the rate performance and cycle life of the positive electrode material; if the capacity compensation ratio is greater than 20, the capacity replenishment effect of the capacity compensator is not obvious.

[0010] In the above-mentioned sodium ion battery capacity compensating agent, as a preferred embodiment, in the capacity compensating agent, the replenishable capacity Q of the sodium supplementing agent is Na The replenishable capacity Q of the lithium supplement Li The ratio of capacity compensation ratio is equal to 2.2.

[0011] In the above-mentioned sodium ion battery capacity compensating agent, as a preferred embodiment, the sodium supplement is selected from Na 2 NiO 2 、Na 5 FeO 4 、Na 2 MnO 3 、NaCrO 2 、Na 2 C 4 O 4 、Na 2 C 6 O 6 One or more of.

[0012] In the above-mentioned sodium ion battery capacity compensating agent, as a preferred embodiment, the lithium supplement agent is selected from Li 2 NiO 2 , Li 5 FeO 4 , Li 2 CuO 2 , Li 6 CoO 4 , Li 5 R 6 、LiN 3 , Li 2 C 4 O 4 , Li 2 C 3 O 5 , Li 2 C 4 O 6 、M1 / Li 2 O, M2 / LiF, M3 / Li x S. Li 1+y VPO 4 F, among which, in M1 / Li 2 O, M2 / LiF, M3 / Li x In S, M1, M2, and M3 are each independently selected from one of Mn, Ni, Co, and Ru, and the M3 / Li x S, 0<x≤6 (for example, x=1, 2, 3, 4, 5, 6); said Li 1+y VPO 4 F, 0<y≤1 (for example, y=0.1, 0.2, 0.5, 0.7, 0.8, 0.9).

[0013] The second aspect of the present invention provides a sodium ion battery positive electrode, comprising: a positive electrode current collector and a positive electrode active material layer adhered to at least one side of the positive electrode current collector; the raw materials of the positive electrode active material layer include: a positive electrode active material, the above-mentioned capacity compensating agent, a binder and a conductive agent; in terms of mass percentage, the positive electrode active material is 90%-98.5% (for example, 90.5%, 91%, 92%, 94%, 95%, 97%, 98%), the capacity compensating agent is 0.5%-5% (for example, 0.6%, 0.8%). %, 0.5%-5% (e.g. 0.6%, 0.8%, 1%, 2%, 3%, 4%, 4.5%) of the binder, and 0.5%-5% (e.g. 0.6%, 0.8%, 1%, 2%, 3%, 4%, 4.5%) of the conductive agent; a positive electrode slurry is obtained by dissolving the raw materials of the positive electrode active material layer in an organic solvent, and then coating, drying and rolling the positive electrode slurry on a current collector to obtain a sodium-lithium battery positive electrode.

[0014] In the above-mentioned sodium ion battery positive electrode, as a preferred embodiment, the positive electrode active material is selected from one or more of Prussian blue compounds, sodium vanadate, sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium cobalt phosphate, sodium iron phosphate, layered sodium manganate, sodium nickel manganate, sodium nickel cobalt manganate, sodium nickel cobalt aluminum, and sodium iron pyrophosphate; preferably, the chemical formula of the Prussian blue compound is Na z M[Fe(CN) 6 ]·mH 2 O, wherein 0<z<6 (for example, z=0.5, 1, 2, 3, 4, 5), 0<m<6 (for example, m=1, 2, 3, 4, 5), and M is selected from one or more of Fe, Co, Ni, and Cu.

[0015] In the above-mentioned sodium ion battery positive electrode, as a preferred embodiment, the binder is selected from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, and polyurethane resin.

[0016] In the above-mentioned sodium ion battery positive electrode, as a preferred embodiment, the conductive agent is selected from one or more of super P conductive carbon black, Ketjen black, lamellar graphite, graphene, carbon nanotubes, and carbon fibers.

[0017] In the above-mentioned sodium ion battery positive electrode, as a preferred embodiment, the organic solvent is selected from N-methyl-2-pyrrolidone, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), 1,2-difluoroethylene carbonate One or more of ethyl acetate, 1,1-difluoroethylene carbonate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran; preferably, the mass of the organic solvent is 25%-60% (such as 30%, 35%, 40%, 45%, 50%, 55%) of the mass of the raw material of the active material layer; more preferably, the mass of the organic solvent is 35% of the mass of the raw material of the positive electrode active material layer.

[0018] In the above-mentioned sodium ion battery positive electrode, as a preferred embodiment, the positive electrode current collector is an aluminum foil or a carbon-based current collector.

[0019] In the above-mentioned sodium ion battery positive electrode, as a preferred embodiment, the drying treatment temperature is 80°C-130°C (such as 90°C, 100°C, 110°C, 120°C, 125°C), and the drying time is 30-90min (such as 40min, 50min, 60min, 70min, 80min).

[0020] A third aspect of the present invention provides an application of the above-mentioned sodium ion battery positive electrode in a sodium ion battery.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The capacity compensator for sodium ion battery of the present invention comprises a sodium supplement and a lithium supplement, wherein the lithium supplement also has the function of supplementing capacity. During charging, sodium ions and lithium ions will migrate into the electrolyte at the same time, and the sodium ions in the electrolyte will migrate to the negative electrode to complete the function of capacity supplement. Compared with the sodium supplement in the prior art, the dual-ion capacity compensator of the present invention can supplement more capacity and can also improve the capacity retention rate of the positive electrode material during long-term circulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the structure of a sodium ion battery assembled with a capacity compensating agent for a sodium ion battery of the present invention;

[0024] Explanation of the reference numerals: 1. positive electrode plate; 11. positive electrode current collector; 12. positive electrode active material layer; 121. positive electrode active material; 122. lithium supplement; 123. sodium supplement; 2. negative electrode plate; 21. negative electrode current collector; 22. negative electrode active material layer; 221. negative electrode active material; 3. separator. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme in the embodiment of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present invention.

[0026] The embodiments of the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and processes are given, but the protection scope of the present invention is not limited to the following embodiments. The process parameters of the following embodiments that do not specify specific conditions are usually based on conventional conditions.

[0027] The endpoints and any values ​​of the ranges disclosed in the present invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in the present invention.

[0028] In the present invention, unless otherwise specified and / or described, all numerical values ​​involving the amount of components are "parts by weight" from beginning to end. The process parameters in the following examples that do not specify specific conditions are usually based on conventional conditions. The raw materials described in the following examples can all be obtained from public commercial channels. The structural schematic diagram of the sodium ion battery assembled with the sodium ion battery capacity compensator of the present invention can be found in Figure 1, including: a positive electrode sheet 1, a negative electrode sheet 2, a separator 3 and an electrolyte arranged therebetween; the positive electrode sheet 1 includes: a positive electrode collector 11 and a positive electrode active material layer 12 attached to at least one side of the positive electrode collector 11, the raw materials of the positive electrode active material layer 12 include: a positive electrode active material 121, a conductive agent, a binder and a capacity compensator, the capacity compensator includes: a lithium supplement 122 and a sodium supplement 123; the negative electrode sheet 2 includes: a negative electrode collector 21 and a negative electrode active material layer 22 attached to at least one side of the negative electrode collector 21; the raw materials of the negative electrode active material layer 22 include: a negative electrode active material 221, a conductive agent and a binder; the negative electrode sheet 2, the separator 3 and the electrolyte used in the sodium ion battery of the present invention are not particularly limited, and can be any type of material known in the existing sodium battery technology, as long as it can be used to manufacture a sodium ion battery with energy storage function. The sodium ion battery is charged to the de-lithium / de-sodium potential of the dual-ion capacity compensator during the formation process, so that the lithium / sodium ions therein can be released and migrate into the electrolyte. At the same time, the sodium ions in the electrolyte will be embedded in the negative electrode to achieve the purpose of compensating capacity.

[0029] The present invention will be further described in detail below with reference to specific embodiments.

[0030] Embodiment 1 A method for preparing a sodium ion battery comprises:

[0031] (1) Preparation of positive electrode sheet: The raw materials of the positive electrode active material layer are sodium iron phosphate, PVDF, super P conductive carbon black, carbon nanotubes, lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 , the mass percentages are: 94.6wt%, 1.5wt%, 0.7wt%, 0.7wt%, 0.67wt%, 1.83wt%;

[0032] First, PVDF was added to nitrogen methyl pyrrolidone (NMP) and stirred to dissolve, and then sodium iron phosphate, superP conductive carbon black, carbon nanotubes, and lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 Stir and disperse uniformly to obtain a positive electrode slurry, wherein the mass of the organic solvent accounts for 35wt% of the mass of the raw material of the positive electrode active material layer;

[0033] Then, 52 g of the positive electrode slurry was evenly coated on the surface of the aluminum foil, and then dried at 90 ° C for 1 h to obtain an active material layer with a mass of 33.8 g. The active material layer was then roller-pressed to obtain a compaction density of 2.5 g / cm 3After that, it is trimmed, cut into pieces, and slit. After slitting, it is dried at 105°C for 5 hours under vacuum conditions. Then the aluminum electrode is welded to the pole ears to make the positive electrode sheet.

[0034] (2) Preparation of negative electrode sheet: The raw materials of the negative electrode active material layer are hard carbon, styrene-butadiene rubber SBR, thickener sodium carboxymethyl cellulose CMC, and super P conductive carbon black, with the mass percentages being 95.5wt%, 1.7wt%, 1.8wt%, and 1wt%, respectively.

[0035] First, styrene-butadiene rubber (SBR) is added into deionized water and stirred to dissolve, then hard carbon and super P conductive carbon black are added and stirred to disperse evenly, then thickener sodium carboxymethyl cellulose (CMC) is added and stirred continuously to obtain negative electrode slurry;

[0036] Then, 22.7 g of the negative electrode slurry was coated on the surface of the copper foil, and then dried at 90 ° C for 1 h to obtain an active material layer with a mass of 13.6 g. The active material layer was then roller-pressed to obtain a compaction density of 1.5 g / cm 3 After that, it is trimmed, cut into pieces, and slit. After slitting, it is dried at 105°C for 5 hours under vacuum conditions. Then, the nickel electrode is welded to the ear to make the negative electrode sheet.

[0037] (3) Sodium ion battery: The separator is a purchased 16 μm thick porous PE (polyethylene) film; the electrolyte is sodium perchlorate (NaClO 4 ) was dissolved in a mixed solvent consisting of ethyl methyl carbonate (EMC), ethylene carbonate (EC), and dimethyl carbonate (DEC) (the mass ratio of the three being 1:1:1) to obtain an electrolyte with a concentration of 1 mol / L;

[0038] The positive electrode sheet, separator and negative electrode sheet are wound according to the N / P value of 1.15 to form a battery cell with a capacity of 4Ah, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, the positive electrode sheet is lead out with an aluminum tab by spot welding, and the negative electrode sheet is lead out with a nickel tab by spot welding; then the battery cell is placed in an aluminum-plastic packaging bag, injected with the above-mentioned electrolyte, and processed through packaging, formation, capacity division and other processes to form a sodium ion battery.

[0039] Example 2

[0040] The difference between Example 2 and Example 1 is that the sodium iron phosphate, the positive electrode active material in Example 1, is replaced with sodium vanadium phosphate, the mass of the negative electrode slurry is changed to 24.7 g, the mass of the negative electrode active material layer is changed to 14.8 g, the N / P ratio is 1.15, the cell capacity is changed to 4.4 Ah, and the preparation method is the same as Example 1.

[0041] Example 3

[0042] The difference between Example 3 and Example 1 is that the positive electrode active material sodium iron phosphate in Example 1 is replaced with Na 0.67 Ni 0.33 Mn 0.67 O 2 (abbreviated as NNMO), lithium supplement Li 2 NiO 2 Replaced with Li 5 FeO 4 , sodium supplement Na 2 NiO 2 Replaced with NaCrO 2 , lithium supplement Li 5 FeO 4 , sodium supplement NaCrO 2 The mass percentages are changed to 0.32wt%, 2.18wt% respectively, the mass of the negative electrode slurry is changed to 20.2g, the mass of the negative electrode active material layer is changed to 12.1g, the N / P ratio is 1.15, the capacity of the battery cell is changed to 3.1Ah, and the preparation method is the same as Example 1.

[0043] Example 4

[0044] The difference between Example 4 and Example 1 is that the lithium supplement Li in Example 1 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to 0.71wt% and 1.79wt% respectively.

[0045] Example 5

[0046] The difference between Example 5 and Example 2 is that the lithium supplement Li in Example 2 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to 0.71wt% and 1.79wt% respectively.

[0047] Example 6

[0048] The difference between Example 6 and Example 3 is that the lithium supplement Li in Example 3 5 FeO 4 , sodium supplement NaCrO 2 The mass percentages are changed to: 0.35wt% and 2.15wt% respectively.

[0049] Example 7

[0050] The difference between Example 7 and Example 1 is that the mass percentages of the lithium supplement Li2NiO2 and the sodium supplement Na2NiO2 in Example 1 are changed to 0.096wt% and 2.404wt% respectively.

[0051] Example 8

[0052] The difference between Example 8 and Example 2 is that the lithium supplement Li in Example 2 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to: 0.096wt% and 2.404wt% respectively.

[0053] Example 9

[0054] The difference between Example 9 and Example 3 is that the lithium supplement Li in Example 3 5 FeO 4 , sodium supplement NaCrO 2 The mass percentages were changed to 0.04wt% and 2.46wt% respectively.

[0055] Comparative Example 1

[0056] The difference between Comparative Example 1 and Example 1 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to 0.09wt% and 2.41wt% respectively.

[0057] Comparative Example 2

[0058] The difference between Comparative Example 2 and Example 2 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to 0.09wt% and 2.41wt% respectively.

[0059] Comparative Example 3

[0060] The difference between Comparative Example 3 and Example 3 is that the lithium supplement Li 5 FeO 4 , sodium supplement NaCrO 2 The mass percentages are changed to 0.038wt% and 2.462wt% respectively.

[0061] Comparative Example 4

[0062] The difference between Comparative Example 4 and Example 1 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages were changed to 1.1wt% and 1.4wt% respectively.

[0063] Comparative Example 5

[0064] The difference between Comparative Example 5 and Example 2 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages were changed to 1.1wt% and 1.4wt% respectively.

[0065] Comparative Example 6

[0066] The difference between Comparative Example 6 and Example 3 is that the lithium supplement Li 5 FeO 4 , sodium supplement NaCrO 2 The mass percentages are changed to: 0.61wt%, 1.89wt%

[0067] Comparative Example 7

[0068] The difference between Comparative Example 7 and Example 1 is that the positive electrode active material sodium iron phosphate and the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed successively to: 97.1wt%, 0wt%, and 0wt%.

[0069] Comparative Example 8

[0070] The difference between Comparative Example 8 and Example 2 is that the positive electrode active material sodium vanadium phosphate and the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed successively to: 97.1wt%, 0wt%, and 0wt%.

[0071] Comparative Example 9

[0072] The difference between Comparative Example 9 and Example 3 is that the positive electrode active material Na 0.67 Ni 0.33 Mn 0.67 O 2 , lithium supplement Li 5 FeO4 , sodium supplement NaCrO 2 The mass percentages are changed successively to: 97.1wt%, 0wt%, and 0wt%.

[0073] Comparative Example 10

[0074] The difference between Comparative Example 10 and Example 1 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to: 0wt% and 2.5wt% respectively.

[0075] Comparative Example 11

[0076] The difference between Comparative Example 11 and Example 2 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to: 0wt% and 2.5wt% respectively.

[0077] Comparative Example 12

[0078] The difference between Comparative Example 12 and Example 3 is that the lithium supplement Li 5 FeO 4 , sodium supplement NaCrO 2 The mass percentages are changed to: 0wt% and 2.5wt% respectively.

[0079] Comparative Example 13

[0080] The difference between Comparative Example 13 and Example 1 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to 2.5wt% and 0wt% respectively.

[0081] Comparative Example 14

[0082] The difference between Comparative Example 14 and Example 2 is that the lithium supplement Li 2 NiO 2 , sodium supplement Na 2 NiO 2 The mass percentages are changed to 2.5wt% and 0wt% respectively.

[0083] Comparative Example 15

[0084] The difference between Comparative Example 15 and Example 3 is that the lithium supplement Li5 FeO 4 , sodium supplement NaCrO 2 The mass percentages are changed to 2.5wt% and 0wt% respectively.

[0085] Performance Test:

[0086] The ambient temperature was maintained at 25±3°C. The sodium ion batteries prepared in the above embodiments and comparative examples were charged to a full charge state of 4V at 0.33C after formation; then discharged at 1C with a discharge cut-off voltage of 2.5V; the average discharge gram capacity of the positive electrode active material for the first five times was calculated; the cycle performance test was performed by charging at 0.5C to a cut-off voltage of 4V and then discharging at 1C. The specific test results are shown in Table 3.

[0087] Table 1 Composition of positive electrode active materials and capacity compensating agents in Examples 1-6 and Comparative Examples 1-15

[0088]

[0089]

[0090] Table 2 Gram capacity of each lithium supplement and sodium supplement in Examples 1-6 and Comparative Examples 1-15

[0091] name <![CDATA[Li 2 Nine 2 ]]> <![CDATA[Li 5 FeO 4 ]]> <![CDATA[Na 2 Nine 2 ]]> <![CDATA[NaCrO 2 ]]> <![CDATA[Capacity per gram / mAh g -1 > 413.5 710.6 330.6 230.5

[0092] Table 3 Performance of sodium ion batteries prepared using the positive electrodes in Examples 1-6 and Comparative Examples 1-15

[0093]

[0094] Analysis of Examples 1, 4, 7, Comparative Examples 1, 10 and Comparative Examples 4, 13 shows that the sodium iron phosphate with more lithium supplement added (lower capacity compensation ratio <2) has a higher discharge capacity per gram than the sodium iron phosphate with less lithium supplement added (higher capacity compensation ratio ≥2) during the first five charge and discharge cycles, but the latter has better cycle performance.

[0095] Analysis of Examples 1, 4, 7 and Comparative Examples 1, 10 and Comparative Example 7 shows that: when the capacity compensation ratio is ≥2, the sodium iron phosphate with the addition of a dual-ion capacity compensator has a higher discharge capacity per gram than the sodium iron phosphate without the addition of a capacity compensator, and the former has better cycle performance; however, when the capacity compensation ratio is too high (>20), the cycle performance of the positive electrode material will decrease.

[0096] Analysis of Examples 2, 5, 8, Comparative Examples 2, 11 and Comparative Examples 5, 14 shows that the sodium vanadium phosphate with more lithium supplement (lower capacity compensation ratio <2) has a higher discharge capacity per gram than the sodium vanadium phosphate with less lithium supplement (higher capacity compensation ratio ≥2) during the first five charge and discharge cycles, but the latter has better cycle performance.

[0097] Analysis of Examples 2, 5, 8 and Comparative Examples 2, 11 and Comparative Example 8 shows that: when the capacity compensation ratio is ≥ 2, the discharge gram capacity of sodium vanadium phosphate with the addition of a dual-ion capacity compensator is higher than that of sodium vanadium phosphate without the addition of a capacity compensator, and the former has better cycle performance; however, when the capacity compensation ratio is too high (> 20), the cycle performance of the positive electrode material will decrease.

[0098] The analysis of Examples 3, 6, 9, Comparative Examples 3, 12 and Comparative Examples 6, 15 shows that: Na 0.67 Ni 0.33 Mn 0.67 O 2 Its discharge capacity is higher than that of Na with less lithium supplement (capacity compensation ratio ≥ 2) in the first 5 charge and discharge cycles. 0.67 Ni 0.33 Mn 0.67 O 2 , but the latter has better cycle performance.

[0099] The analysis of Examples 3, 6, 9 and Comparative Examples 3, 12 and Comparative Example 9 shows that when the capacity compensation ratio is ≥ 2, the Na 0.67 Ni 0.33 Mn 0.67 O 2 , its discharge capacity is higher than that of Na 0.67 Ni 0.33 Mn 0.67 O 2 , and the former has better cycle performance; however, when the capacity compensation ratio is too high (>20), the cycle performance of the positive electrode material will decrease.

[0100] In summary, by setting an appropriate capacity compensation ratio, the dual-ion capacity compensator can replenish more capacity and improve the capacity retention rate during long-term cycling.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. A capacity compensator for sodium ion batteries, It is characterized in that include: Sodium supplement and lithium supplement; the sodium supplement and the lithium supplement have the function of replenishing capacity at the same time; in the capacity compensating agent, the replenishable capacity Q of the sodium supplement Na The replenishable capacity Q of the lithium supplement Li The ratio, that is, the capacity compensation ratio, satisfies 2≤Q Na / Q Li ≤20; Among them, Q Na =m Na *C Na ; Q Li =m Li *C Li ; m Na is the mass of sodium supplement, C Na is the gram volume of the sodium supplement; m Li is the mass of lithium supplement, C Li is the gram capacity of the lithium supplement.

2. The capacity compensating agent for sodium ion battery according to claim 1, It is characterized in that In the capacity compensator, the replenishable capacity Q of the sodium supplement is Na The replenishable capacity Q of the lithium supplement Li The ratio of capacity compensation ratio is equal to 2.

2.

3. The capacity compensating agent for sodium ion battery according to claim 1 or 2, It is characterized in that The sodium supplement is selected from Na 2 NiO 2 、Na 5 FeO 4 、Na 2 MnO 3 、NaCrO 2 、Na 2 C 4 O 4 、Na 2 C 6 O 6 One or more of.

4. The capacity compensating agent for sodium ion batteries according to any one of claims 1 to 3, It is characterized in that The lithium supplement agent is selected from Li 2 NiO 2 , Li 5 FeO 4 , Li 2 CuO 2 , Li 6 CoO 4 , Li 5 R 6 、LiN 3 , Li 2 C 4 O 4 , Li 2 C 3 O 5 , Li 2 C 4 O 6 、M1 / Li 2 O, M2 / LiF, M3 / Li x S. Li 1+y VPO 4 F, among which, in M1 / Li 2 O, M2 / LiF, M3 / Li x In S, M1, M2, and M3 are each independently selected from one of Mn, Ni, Co, and Ru, and the M3 / Li x S, 0<x≤6; said Li 1+y VPO 4 F, 0<y≤1.

5. A sodium ion battery positive electrode, It is characterized in that include: A positive electrode current collector and a positive electrode active material layer adhered to at least one side of the positive electrode current collector; The raw materials of the positive electrode active material layer include: a positive electrode active material, a capacity compensator for a sodium ion battery according to any one of claims 1 to 4, a binder and a conductive agent; In terms of mass percentage, the positive electrode active material comprises 90%-98.5%, the capacity compensator comprises 0.5%-5%, the binder comprises 0.5%-5%, and the conductive agent comprises 0.5%-5%. The positive electrode slurry is obtained by dissolving the raw material of the positive electrode active material layer in an organic solvent, and then the positive electrode slurry is coated on a current collector, dried, and rolled to obtain a positive electrode for a sodium-lithium battery.

6. The sodium ion battery positive electrode according to claim 5, It is characterized in that The positive electrode active material is selected from one or more of Prussian blue compounds, sodium vanadate, sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium cobalt phosphate, sodium iron phosphate, layered sodium manganate, sodium nickel manganate, sodium nickel cobalt manganate, sodium nickel cobalt aluminum, and sodium iron pyrophosphate; And / or, the chemical formula of the Prussian blue compound is Na z M[Fe(CN) 6 ·mH 2 O, where 0 < z < 6, 0 < m < 6, and M is selected from one or more of Fe, Co, Ni, and Cu.

7. The sodium ion battery positive electrode according to claim 5 or 6, It is characterized in that The binder is selected from one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, and polyurethane resin; And / or, the conductive agent is selected from one or more of super P conductive carbon black, Ketjen black, lamellar graphite, graphene, carbon nanotubes, and carbon fibers.

8. The sodium ion battery positive electrode according to any one of claims 5 to 7, It is characterized in that The organic solvent is selected from one or more of N-methyl-2-pyrrolidone, dibutyl ether, tetraglyme, diglyme, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl ethyl carbonate, ethylene carbonate, 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran; And / or, the mass of the organic solvent is 25%-60% of the mass of the raw material of the positive electrode active material layer.

9. The sodium ion battery positive electrode according to any one of claims 5 to 8, It is characterized in that The positive electrode current collector is an aluminum foil or a carbon-based current collector; And / or, the drying treatment temperature is 80° C.-130° C., and the drying time is 30-90 min.

10. Use of the sodium ion battery positive electrode according to any one of claims 5 to 9 in a sodium ion battery.

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