Positive sodium supplementing agent, positive slurry, preparation method of positive slurry, positive pole piece and electrode assembly

Abstract

The invention discloses a positive sodium supplementing agent, positive slurry, a preparation method of the positive slurry, a positive pole piece and an electrode assembly. The positive sodium supplementing agent comprises one or more of the following chemical formulas: NaxHMqOy, wherein the element M is any one of C, S, P, B and Si; z is the valence absolute value of the element M; x, y, z and q meet x + 1 + qz = 2y, z is a positive natural number, and the value of x is 1, 2 or 2.5. The positive electrode sodium supplementing agent not only contributes to stabilizing the positive electrode interface effect and improving the cycling stability, but also can prevent the viscosity of the slurry from rising too fast in the slurry preparation process, and plays roles in stabilizing the viscosity of the slurry and improving the stability of the positive electrode slurry.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a positive electrode sodium supplement, a positive electrode slurry and a preparation method, a positive electrode sheet and an electrode assembly. Background Art

[0002] At present, the first efficiency ICE of sodium-ion batteries is 85%~90% (depending on the voltage range and current size, for example, the first efficiency of the layered oxygen / hard carbon system 0.2C 0V-4V is close to 90%, the efficiency of 1.5V-4V is about 87%, and the first efficiency of 2-4V is about 85%). Compared with the first efficiency of 91%~93% of the lithium iron phosphate graphite system, there is still a big gap. In addition, under the same external dimensions of the packaging shell (soft pack, cylindrical or square battery cell), even the energy density of the layered oxygen / hard carbon system with the highest energy density at present is only 90% of the current lithium iron phosphate level. Furthermore, after comparing the energy efficiency of 0.5P at room temperature, it is found that the energy efficiency of lithium iron phosphate during the cycle process currently reaches 93%~95%, while the room temperature 0.5P energy efficiency of the layered oxygen / hard carbon system is 92%~93.5%, which is still different from that of lithium iron phosphate. Therefore, from the comparison of discharge capacity (energy density), first energy efficiency and energy efficiency during the cycle, sodium electricity is currently at a disadvantage and there is still a lot of room for development.

[0003] Compared with the negative electrode pre-sodium element, the negative electrode has a higher humidity environment requirement and the process involves the introduction of organisms, which can easily lead to the risk of fire and explosion, the increase in the difficulty of coating the diaphragm with sodium, and the need to consider the solubility of the electrolyte and the compatibility of the additive with the solvent and electrolyte. Therefore, adding pre-sodium materials to the positive electrode is a technical solution that is compatible with the existing process flow and easy to operate, while not increasing the difficulty of the environmental humidity requirements. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one purpose of the present invention is to provide a positive electrode sodium supplement, which not only helps to stabilize the positive electrode interface and improve the cycle stability, but also can prevent the slurry viscosity from rising too fast during the slurry making process, thereby stabilizing the slurry viscosity and improving the stability of the positive electrode slurry.

[0005] A positive electrode sodium supplement according to the first embodiment of the present invention comprises one or more of the following chemical formulas: Na x HM q O y ; Wherein, the element M is any one of C, S, P, B and Si; z is the absolute value of the valence state of the element M; x, y, z, q satisfy x+1+qz=2y, z is a positive natural number, and the value of x is 1, 2 or 2.5.

[0006] The positive electrode sodium supplement of the present invention not only helps to stabilize the positive electrode interface and improve the cycle stability, but also can prevent the slurry viscosity from rising too fast during the slurry making process, thereby stabilizing the slurry viscosity and improving the stability of the positive electrode slurry.

[0007] A positive electrode slurry according to an embodiment of the second aspect of the present invention includes: a positive electrode main material for a sodium ion battery; a conductive adhesive, wherein the conductive adhesive includes a conductive agent, a binder and a solvent; and a positive electrode sodium supplement, wherein the positive electrode sodium supplement is the positive electrode sodium supplement mentioned above.

[0008] Optionally, the total mass fraction of the positive electrode sodium supplement in the positive electrode slurry is 0.1%-10%, preferably 2%-5%.

[0009] Optionally, the positive electrode sodium supplement is selected from one or more of sodium hydrogen oxalate, sodium hydrogen thiosulfate, sodium metaborate, disodium bicarbonate, sodium hydrogen silicate, sodium hydrogen phosphite, sodium hydrogen rose bengalate, sodium hydrogen rose bengalate, and sodium hydrogen tetragonal.

[0010] Optionally, the main material of the sodium ion battery positive electrode is one or more of layered oxides, polyanions and Prussian blue (white).

[0011] According to a third aspect of the present invention, a method for preparing a positive electrode slurry comprises the following steps: mixing a conductive glue, a sodium ion battery positive electrode main material and a positive electrode sodium supplement to prepare a positive electrode slurry, wherein the conductive glue comprises a conductive agent, a binder and a solvent, and the positive electrode sodium supplement comprises one or more of the following chemical formulas: Na x HM q O y , where element M is any one of C, S, P, B and Si; z is the absolute value of the valence state of element M; x, y, z, q satisfy x+1+qz=2y, z is a positive natural number, and the value of x is 1, 2 or 2.5.

[0012] Optionally, when the conductive adhesive, the sodium ion battery positive electrode main material and the positive electrode sodium supplement agent are mixed, the sodium ion battery positive electrode main material and the positive electrode sodium supplement agent are added to the conductive adhesive at the same time.

[0013] A positive electrode plate according to an embodiment of the fourth aspect of the present invention comprises any of the positive electrode slurries described above.

[0014] According to an electrode assembly of a fifth aspect of an embodiment of the present invention, the electrode assembly is formed by winding or laminating a positive electrode sheet, a negative electrode sheet and a separator, and the positive electrode sheet is any one of the positive electrode sheets described above.

[0015] Optionally, the negative electrode plate is one or more of hard carbon, soft carbon, oxide, and alloy; and / or the electrolyte in the electrode assembly is one or more of liquid, semi-solid, and solid electrolytes; and / or the diaphragm is one or a combination of PP, PE, PET, PVDF, PI, PVC, and PPS.

[0016] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which: Figure 1 1 is a flow chart of preparing a positive electrode sheet according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following first describes the positive electrode sodium supplement according to an embodiment of the present invention.

[0019] The positive electrode sodium supplement according to an embodiment of the present invention includes one or more of the following chemical formula (1): Na x HM q O y (1); Wherein, in formula (1), the element M is any one of C, S, P, B and Si; z is the absolute value of the valence state of the element M; x, y, z, q satisfy x+1+qz=2y, z is a positive natural number; the value of x is one of 1, 2, and 2.5. For example, the positive electrode sodium supplement can be NaHC 2 O 4 (Sodium hydrogen oxalate), NaHS 2 O 3 (Sodium bithiosulfate), NaHB 4 O 7 (sodium hydrogen metaborate), Na 2 HCO 3 (sodium bicarbonate), NaHSiO 3 (Sodium hydrogen silicate) , Na 2 HPO 4 (Sodium hydrogen phosphite), NaHC 6 O 6 (Rose Bengal Sodium Hydrogenate a), Na 2.5 HC 6 O 6 (Rose Bengal Sodium Hydrogenate b), NaHC 4 O 4 (sodium hydrogen tetrahydrate).

[0020] It can be understood that when C is selected as the M element, in addition to providing an additional sodium source, it can provide an additional conductive carbon source for the positive electrode during oxidation and decomposition on the positive electrode side, reconstructing the conductive network to improve the electronic conductivity and improve the rate performance; When S is selected as the M element, in addition to providing an additional sodium source, it can seize the oxygen released by the positive electrode to generate sodium sulfate and sulfur dioxide gas during oxygen evolution at the high-potential positive electrode, thereby blocking the positive electrode oxygen release from crosstalking into the negative electrode side and causing adverse thermal reactions.

[0021] When P is selected as the M element, in addition to providing an additional sodium source, the phosphate group has certain flame retardant properties to ensure the safety of the battery cell.

[0022] When B is selected as the M element, in addition to providing an additional sodium source, it can balance the acidity and alkalinity of the slurry and provide support for the stability of the slurry.

[0023] When Si is selected as the M element, in addition to providing an additional sodium source, it can neutralize the HF acid in the electrolyte, reduce the etching of the positive electrode, and improve the stability of the positive electrode material.

[0024] Moreover, when x is one of 1, 2, and 2.5, it can ensure that the positive electrode sodium supplement agent has a sodium supplement effect, and at the same time ensure that the positive electrode sodium supplement agent provides at least one hydrogen radical to react with the alkaline positive electrode, reduce the alkalinity of the slurry, and ensure the stability of the slurry. At the same time, different values ​​of X can ensure that the M element plays a corresponding mechanism for protection.

[0025] And, due to Na x HM q O y There are hydrogen radicals in the electrolyte, which react in situ with the hydroxyl groups of the negative electrode, helping to stabilize the positive electrode interface and thus improve the cycle stability. Among them, the positive electrode interface is CEI (cathode electrolyte interpHase). The interface film is critical to maintaining the integrity of the electrode structure, ensuring the rapid migration of sodium ions and preventing the continuous decomposition of the electrolyte. Therefore, its stability is closely related to the cycle performance and service life of the battery.

[0026] Among them, when the main material of the positive electrode of the sodium ion battery is layered oxide, the layered oxide positive electrode is relatively alkaline, pH ≥ 9, and Na x HM q O y After anchoring, it will improve the interface stability and thus improve the cycle performance. For example, because the residual alkali of the layered oxygen cathode is too high and the pH is too large, when PVDF is used as a binder in an NMP oily solvent, the residual alkali OH radical will shear and capture the F in PVDF to form a carbon-carbon double bond, resulting in higher viscosity and worse slurry stability. Similarly, when the main material of the sodium ion battery cathode is polyanion, Prussian blue (white), etc., adding Na x HM q Oy It can also be anchored to improve interface stability and thus improve cycle performance.

[0027] The positive electrode sodium supplement in the embodiment of the present invention can prevent the slurry viscosity from rising too fast during the slurry making process, stabilize the slurry viscosity and improve the stability of the positive electrode slurry. The sodium supplement in the embodiment of the present invention can slowly release the main positive electrode material of the sodium ion battery.

[0028] The present invention also discloses a positive electrode slurry, comprising: a positive electrode main material of a sodium ion battery, a conductive glue and a positive electrode sodium supplement, wherein the conductive glue comprises a conductive agent, a binder and a solvent, for example, the conductive agent comprises SP, graphene and carbon nanotubes, the binder comprises PVDF, the solvent comprises NMP, etc., and furthermore, the positive electrode sodium supplement is mixed with the positive electrode active material, and the positive electrode sodium supplement is the positive electrode sodium supplement of any of the above embodiments. Since the positive electrode slurry according to an embodiment of the present invention comprises the positive electrode sodium supplement of any of the above embodiments, the sodium source content can be increased.

[0029] According to one embodiment of the present invention, the total mass fraction of the positive electrode sodium supplement agent in the positive electrode material is 0.1%-10%, that is, the positive electrode sodium supplement agent Na in the embodiment of the present invention is x HM (2y-x-1) / z O y The total mass fraction of the positive electrode material is 0.1% to 10%. For example, the positive electrode sodium supplement Na in the embodiment of the present invention x HM (2y-x-1) / z O y The total mass fraction of the positive electrode material is 0.1%, 0.5%, 0.8%, 1%, 3%, 5%, 6%, 8% or 10%, etc. In this embodiment, the content of the positive electrode sodium supplement is 0.1% to 10%, which can not only play a corresponding sodium supplement effect, but also help the slurry stability.

[0030] In some specific embodiments of the present invention, the positive electrode sodium supplement accounts for 2%-5% of the total mass fraction of the positive electrode material, for example, the positive electrode sodium supplement accounts for 2%, 2.1%, 2.2%, 2.5%, 3%, 3.5%, 4% or 5% of the total mass fraction of the positive electrode material. In this embodiment, the content of the positive electrode sodium supplement is preferably 2%-5%, which can achieve the best sodium supplement effect. If too much or too little sodium supplement is used, the sodium supplement effect of the positive electrode sodium supplement is limited.

[0031] According to one embodiment of the present invention, the positive electrode sodium supplement is selected from one or more of sodium hydrogen oxalate, sodium hydrogen thiosulfate, sodium metaborate, disodium bicarbonate, sodium hydrogen silicate, sodium hydrogen phosphite, sodium hydrogen rose bengalate, sodium hydrogen rose bengalate, and sodium hydrogen tetragonal. By adopting the above positive electrode sodium supplement, not only the stability of the positive electrode slurry can be improved, but also the sodium source content can be increased.

[0032] According to one embodiment of the present invention, the main material of the positive electrode of the sodium ion battery is one or more of layered oxides, polyanions, and Prussian blue, etc. That is, the positive electrode sodium supplement of the embodiment of the present invention can be used in a variety of positive electrode slurries and has wide applicability.

[0033] The present invention also provides a method for preparing a positive electrode slurry, which specifically comprises the following steps: The conductive glue, the main material of the positive electrode of the sodium ion battery and the positive electrode sodium supplement are mixed to prepare a positive electrode slurry. The conductive glue includes a conductive agent, a binder and a solvent. The positive electrode sodium supplement includes one or more of the following chemical formulas: Na x HM q O y , wherein the element M is any one of C, S, P, B and Si; z is the absolute value of the valence state of the element M; x, y, z, q satisfy x+1+qz=2y, z is a positive natural number, and the value of x is 1, 2 or 2.5. It can be seen that the preparation method of the positive electrode slurry of the embodiment of the present invention has the advantages of simple preparation method and the like.

[0034] In some specific embodiments of the present invention, when the conductive glue, the positive electrode material of the sodium ion battery and the positive electrode sodium supplement are mixed, the positive electrode material of the sodium ion battery and the positive electrode sodium supplement are added to the conductive glue at the same time, which can effectively ensure that the positive electrode sodium supplement is evenly mixed with the positive electrode material of the sodium ion battery. In addition to compensating for the additional sodium source, the positive electrode sodium supplement can neutralize the positive electrode residual alkali, thereby reducing the difficulty of slurry processing, and its M element can play a protective role in the corresponding mechanism. In this embodiment, by adding the positive electrode material of the sodium ion battery and the positive electrode sodium supplement to the conductive glue (for example, containing glue and conductive carbon), it can ensure that the positive electrode material of the sodium ion battery and the positive electrode sodium supplement are evenly mixed, and can also relatively independently ensure that their respective conductivity and bonding force are achieved, ensuring that the overall stability function of the positive electrode sodium supplement is exerted.

[0035] The present invention further provides a positive electrode plate, which includes the positive electrode slurry of any of the above embodiments, or the positive electrode slurry prepared by the method for preparing the positive electrode slurry of any of the above embodiments.

[0036] The present invention also provides an electrode assembly, which is formed by winding or laminating a positive electrode sheet, a negative electrode sheet and a separator, and the positive electrode sheet is any of the positive electrode sheets described above. The positive electrode slurry, positive electrode sheet and electrode assembly prepared by the positive electrode sodium supplement of any of the above embodiments can increase the additional sodium source, and can further increase the initial efficiency and energy density of the sodium ion battery by 1.5% to 5%.

[0037] Optionally, the negative electrode of the electrode assembly can be one or more of hard carbon, soft carbon, oxide, alloy, etc.; the electrolyte can be one or more of liquid, semi-solid, solid electrolyte; the diaphragm can be one or more of PP, PE, PET, PVDF, PI, PVC, PPS substrates. Optionally, the surface of the diaphragm can be coated with a functional coating, such as a coating of PVDF, ceramic Al 2 O 3 , coated with boron nitride AlOOH or sodium solid electrolyte, etc.

[0038] The present invention also provides a battery, which includes a shell, an electrode assembly, and an electrolyte. The electrode assembly includes a diaphragm, a negative electrode sheet, and a positive electrode sheet. The electrode assembly is the electrode assembly of any of the above embodiments.

[0039] The positive electrode sodium supplement, positive electrode slurry, positive electrode sheet and electrode assembly of the embodiments of the present invention are described in detail below in conjunction with specific embodiments.

[0040] Example 1 (1) Preparation of positive electrode By mass fraction, prepare PVDF with a mass fraction of 1.5%; a mixed liquid consisting of graphene (mass fraction of 0.3%) and carbon nanotubes CNT (mass fraction of 0.5%), which is an oil-based mixed liquid with a solid content of 2.7%; and a mixture of SP and NMP (mass fraction of 1.0%).

[0041] The mixed solution of the PVDF, graphene and carbon nanotubes, SP and NMP are prepared into a conductive adhesive.

[0042] Add 93.5% of NaNi, the main material of the positive electrode of sodium ion battery, into the conductive glue 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 And 3.2% of the mass fraction of the positive electrode sodium supplement Na 2.5 HC 6 O 6 , and obtain the positive electrode slurry.

[0043] The solid content of the positive electrode slurry is controlled to be 70%-75% according to the viscosity requirement, and the positive electrode is coated on the aluminum current collector to obtain a positive electrode sheet.

[0044] (2) Preparation of negative electrode sheet: By mass fraction, 94 parts of hard carbon, 1.5 parts of oxalic acid, 1.6 parts of sodium alginate and 0.4 parts of SP were added to 200 parts of deionized water. After stirring evenly, 2.4 parts of SBR were added and stirred at a low speed for 3 hours before coating on the aluminum current collector. (3) Preparation of diaphragm The diaphragm prepared by PP dry method is coated with sodium ion conductor electrolyte Na 1+x Zr 2 Si x P 3-x O 12 .

[0045] (4) Preparation of electrolyte 0.8 mol / L NaPF6+EC:DEC=1:1+5%FEC+1.5%VC+0.5%DDT+0.5%MSDS, injection coefficient is 4g / Ah. Among them, the sodium salt type is NaPF6, the concentration is 0.8 mol / L; the solvent type and proportion: EC:DEC=1:1; the types and proportions of the four additives are 5%FEC, 1.5%VC, 0.5%DDT, 0.5%MSDS; and the injection coefficient is 4g / Ah.

[0046] (5) Preparation of battery cells The core is formed by stacking or winding. When stacking, the single layer is stacked as diaphragm-negative electrode-diaphragm-positive electrode; when winding, it is wound as diaphragm-negative electrode-diaphragm-positive electrode. Then the core is welded, packaged, baked, and injected with electrolyte. After the initial negative pressure formation, static, secondary liquid injection and sealing, the electrode assembly is formed, and then it is screened by capacity and K value as a product battery cell.

[0047] Example 2 The difference between Example 2 and Example 1 is that: Positive electrode sodium supplement Na 2.5 HC 6 O 6 The mass fraction of the main material of the positive electrode of the sodium ion battery is 95.7%.

[0048] Example 3 The difference between Example 3 and Example 1 is that: Positive electrode sodium supplement Na 2.5 HC 6 O 6 The mass fraction of the main material of the positive electrode of the sodium ion battery is 94.7%.

[0049] Example 4 The difference between Example 4 and Example 1 is that: Positive electrode sodium supplement Na 2.5 HC 6 O 6 The mass fraction of the main material of the positive electrode of the sodium ion battery is 91.7%.

[0050] Example 5 The difference between Example 5 and Example 1 is that: Positive electrode sodium supplement Na 2.5 HC 6 O 6 The mass fraction of the main material of the positive electrode of the sodium ion battery is 88.7%.

[0051] Example 6 (1) Preparation of positive electrode By mass fraction, PVDF with a mass fraction of 1.3%; CNT with a mass fraction of 0.5%, oil-based, and a solid content of 4%; and a mixture of SP and NMP (mass fraction of 1.6%) were prepared.

[0052] The above-mentioned PVDF, CNT, SP and NMP are prepared into a conductive adhesive.

[0053] Add 96% of NaNi, the main material of the positive electrode of sodium ion battery, into the conductive glue 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 And the positive electrode sodium supplement NaHC with a mass fraction of 2.4% 2 O 4 , and obtain the positive electrode slurry.

[0054] The solid content of the positive electrode slurry is controlled to be 70%-75% according to the viscosity requirement, and the positive electrode is coated on the aluminum current collector to obtain a positive electrode sheet.

[0055] (2) Preparation of negative electrode sheet: By mass fraction, 94 parts of hard carbon, 0.5 parts of oxalic acid, 1.6 parts of CMC and 1.4 parts of SP were added to 200 parts of deionized water. After stirring evenly, 2.4 parts of SBR were added and stirred at a low speed for 3 hours before coating on the aluminum current collector.

[0056] (3) Preparation of diaphragm The diaphragm is prepared by a PP dry process and is coated with ceramic alumina.

[0057] (4) The same electrolyte as in Example 1 was used.

[0058] (5) Preparation of battery cells The negative electrode, diaphragm and positive electrode are wound or stacked to form a core, and then the core is welded, packaged, baked and injected with electrolyte. It is initially subjected to negative pressure formation, standing, secondary liquid injection and sealing to form an electrode assembly, and then subjected to capacity screening and K value screening to be used as a product battery cell.

[0059] Example 7 (1) Preparation of positive electrode By mass fraction, PVDF with a mass fraction of 1.5%; CNT with a mass fraction of 0.8%, oil-based, and a solid content of 4%; and a mixture of SP and NMP (mass fraction of 1.0%) were prepared.

[0060] The above-mentioned PVDF, CNT, SP and NMP are prepared into a conductive adhesive.

[0061] Add 96.5% of NaNi, the main material of the positive electrode of sodium ion battery, into the conductive glue 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 And 0.2% mass fraction of positive electrode sodium supplement NaHS 2 O 3 , and obtain the positive electrode slurry.

[0062] The solid content of the positive electrode slurry is controlled to be 70%-75% according to the viscosity requirement, and the positive electrode is coated on the aluminum current collector to obtain a positive electrode sheet.

[0063] (2) Preparation of negative electrode sheet: By mass fraction, 95 parts of hard carbon, 0.5 parts of oxalic acid, 1.6 parts of sodium alginate and 0.4 parts of SP were added to 200 parts of deionized water. After stirring evenly, 2.4 parts of SBR were added and stirred at a low speed for 3 hours before applying to the aluminum current collector.

[0064] (3) Preparation of diaphragm The diaphragm prepared by PP dry method is coated with Na 1+x Zr 2 Si x P 3-x O 12 .

[0065] (4) Preparation of electrolyte (5) Preparation of battery cells The negative electrode, diaphragm and positive electrode are wound or stacked to form a core, and then the core is welded, packaged, baked and injected with electrolyte. It is initially subjected to negative pressure formation, standing, secondary liquid injection and sealing to form an electrode assembly, and then subjected to capacity screening and K value screening to be used as a product battery cell.

[0066] Example 8 (1) Preparation of positive electrode By mass fraction, PVDF with a mass fraction of 1.5% is prepared; single-walled carbon nanotubes SWCNT with a mass fraction of 0.5%, oil-based, and a solid content of 2.5%; NMP purity is above 99.5%.

[0067] The above-mentioned PVDF, SWCNT and NMP are prepared into a conductive adhesive.

[0068] Add 97.5% of NaNi, the main material of the positive electrode of sodium ion battery, into the conductive glue 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 and 0.5% by mass of positive electrode sodium supplement (NaHSiO 3 With NaHC 6 O 6 , the mass ratio of the two is 1:1), to obtain the positive electrode slurry.

[0069] The solid content of the positive electrode slurry is controlled to be 70%-75% according to the viscosity requirement, and the positive electrode is coated on the aluminum current collector to obtain a positive electrode sheet.

[0070] (2) Preparation of negative electrode sheet: By mass fraction, 95 parts of hard carbon, 0.5 parts of oxalic acid, 1.6 parts of sodium alginate and 0.4 parts of SP were added to 200 parts of deionized water. After stirring evenly, 2.4 parts of SBR were added and stirred at a low speed for 3 hours before applying to the aluminum current collector.

[0071] (3) Preparation of diaphragm The diaphragm prepared by PP dry method is coated with Na 1+x Zr 2 Si x P 3-x O 12 .

[0072] (4) The same electrolyte as in Example 1 was used.

[0073] (5) Preparation of battery cells The negative electrode, diaphragm and positive electrode are wound or stacked to form a core, and then the core is welded, packaged, baked and injected with electrolyte. It is initially subjected to negative pressure formation, standing, secondary liquid injection and sealing to form an electrode assembly, and then subjected to capacity screening and K value screening to be used as a product battery cell.

[0074] Example 9 The difference between Example 9 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 2%; the mass fraction of the main material of the positive electrode of the sodium ion battery is 94.7%.

[0075] Example 10 The difference between Example 10 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 3%; the mass fraction of the main material of the positive electrode of the sodium ion battery is 93.7%.

[0076] Embodiment 11 The difference between Example 11 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 4%; the mass fraction of the main material of the positive electrode of the sodium ion battery is 92.7%.

[0077] Example 12 The difference between Example 12 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 5%; the mass fraction of the main material of the sodium ion battery positive electrode is 91.7%.

[0078] Example 13 The difference between Example 13 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 6%; the mass fraction of the main material of the positive electrode of the sodium ion battery is 90.7%.

[0079] Embodiment 14 The difference between Example 14 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 7%; the mass fraction of the main material of the positive electrode of the sodium ion battery is 89.7%.

[0080] Embodiment 15 The difference between Example 15 and Example 8 is that: The positive electrode sodium supplement is NaHSiO 3 , and the mass fraction is 8%; the mass fraction of the main material of the positive electrode of the sodium ion battery is 88.7%.

[0081] Example 16 The difference between Example 16 and Example 8 is that: The positive electrode sodium supplement is 2% by mass NaHSiO 3 and 2% NaHC 2 O 4 ; The mass fraction of the main material of the sodium ion battery positive electrode is 92.7%.

[0082] Comparative Example 1 (1) Preparation of positive electrode By mass fraction, PVDF with a mass fraction of 1.5%; CNT with a mass fraction of 0.5%, oil-based, and a solid content of 4%; and a mixture of SP and NMP (mass fraction of 1.5%) were prepared.

[0083] The above-mentioned PVDF, CNT, SP and NMP are prepared into a conductive adhesive.

[0084] Add 96.1% of NaNi, the main material of the positive electrode of sodium ion battery, into the conductive glue 1 / 3 Fe 1 / 3 Mn 1 / 3 O 2 and 0.4% by mass oxalic acid to obtain a positive electrode slurry.

[0085] According to the viscosity requirement, the solid content of the positive electrode slurry is controlled to be 70% to 75%, and the positive electrode is coated on the aluminum current collector to obtain a positive electrode sheet. It can be seen that in Comparative Example 1, no sodium supplement additive is added, and 0.4% oxalic acid is added.

[0086] (2) Preparation of negative electrode sheet: By mass fraction, 94 parts of hard carbon, 0.5 parts of oxalic acid, 1.6 parts of CMC and 1.4 parts of SP were added to 200 parts of deionized water. After stirring evenly, 2.4 parts of SBR were added and stirred at a low speed for 3 hours before coating on the aluminum current collector.

[0087] (3) Preparation of diaphragm The diaphragm is prepared by a PP dry process and is coated with ceramic alumina.

[0088] (4) The same electrolyte as in Example 1 was used.

[0089] (5) Preparation of battery cells The core is formed by stacking or winding. When stacking, the single layer is stacked as diaphragm-negative electrode-diaphragm-positive electrode; when winding, it is wound as diaphragm-negative electrode-diaphragm-positive electrode. Then the core is welded, packaged, baked, and injected with electrolyte. After the initial negative pressure formation, static, secondary liquid injection and sealing, the electrode assembly is formed, and then it is screened by capacity and K value as a product battery cell.

[0090] The phenomenon of the slurry chemical reaction in the positive electrode sheet preparation process of the above embodiment and the comparative example was observed, and the observed positive electrode slurry stability description was recorded in Table 1; and the following electrical performance tests were performed on the batteries prepared in the above embodiment and the comparative example, and the test results are shown in Table 1 below: (1) First efficiency test: The batteries prepared in the above-mentioned embodiments and comparative examples were first charged to 3.0V at a three-stage low current of 0.05C / 0.1C / 0.2C, then charged to 4.0V at 0.5C, and the first charging capacity was recorded; left to stand for 30 minutes; then discharged to 0V at a constant current of 0.5C, and the first discharge capacity of the battery was recorded. Among them, the first efficiency = first discharge capacity / first charging capacity×100%.

[0091] (2) Capacity retention rate test: The batteries prepared in the above-mentioned embodiments and comparative examples were kept at 25°C for 2h, then charged to 3.85V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage of 3.85V. After charging, the tested batteries were allowed to stand at 25°C for 2h, and then discharged to 2.0V at a DC rate of 0.5C, and the discharge capacity at room temperature was recorded as C0. The discharge and charge were repeated 200 times, and the discharge capacity of the 200th time was recorded as C1. Among them, the capacity retention rate (%) = (C1 / C0) × 100%.

[0092] Table 1 It can be seen from Table 1 that the slurry in Comparative Example 1 tends to be jelly-like, and the viscosity increases rapidly after 2 hours, which is unstable. The positive electrode sodium supplement in each embodiment of the present invention not only helps to stabilize the positive electrode interface and improve the cycle stability, but also can prevent the slurry viscosity from rising too fast during the pulping process, and plays a role in stabilizing the slurry viscosity and improving the stability of the positive electrode slurry. In addition, relative to the battery in Comparative Example 1, the first efficiency and energy density of the battery in each embodiment of the present invention are improved. In the embodiments of the present invention, the energy density is improved mainly by improving the first efficiency, that is, improving the discharge capacity. The first efficiency improvement range is 4%~9.2% as shown in Table 1. According to the proportion of the positive electrode sodium supplement, the energy density is improved in the range of 1.5%~5%.

[0093] In summary, the positive electrode sodium supplement agent of the present invention not only helps to stabilize the positive electrode interface and improve the cycle stability, but also can prevent the slurry viscosity from rising too quickly during the slurry making process, thereby stabilizing the slurry viscosity and improving the stability of the positive electrode slurry.

[0094] Other structures and operations of the battery according to the embodiment of the present invention are known to those skilled in the art and will not be described in detail here.

[0095] In the description of the present invention, it is necessary to understand that the terms "center", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "inside", "outside", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0096] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0097] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0098] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A positive electrode sodium supplement, characterized in that: Include one or more of the following chemical formulas: So x HM q O y ; Among them, the M element is any one of C, S, P, B and Si; z is the absolute value of the valence state of the element M; x, y, z, q satisfy x+1+qz=2y, z is a positive natural number, and x is 1, 2 or 2.

5.

2. A positive electrode slurry, characterized in that: include: Main material for positive electrode of sodium ion battery; Conductive adhesive, the conductive adhesive comprising a conductive agent, a binder and a solvent; A positive electrode sodium supplement, wherein the positive electrode sodium supplement is the positive electrode sodium supplement according to claim 1.

3. The positive electrode slurry according to claim 2, characterized in that The total mass fraction of the positive electrode sodium supplement in the positive electrode slurry is 0.1%-10%, preferably 2%-5%.

4. The positive electrode slurry according to claim 3, characterized in that: The positive electrode sodium supplement is selected from one or more of sodium hydrogen oxalate, sodium hydrogen thiosulfate, sodium metaborate, disodium bicarbonate, sodium hydrogen silicate, sodium hydrogen phosphite, sodium hydrogen rose bengalate, sodium hydrogen rose bengalate, and sodium hydrogen tetragonal.

5. The positive electrode slurry according to claim 2, characterized in that: The main material of the sodium ion battery positive electrode is one or more of layered oxides, polyanions and Prussian blue (white).

6. A method for preparing a positive electrode slurry, characterized in that: The steps include: The conductive glue, the main material of the positive electrode of the sodium ion battery and the positive electrode sodium supplement are mixed to prepare a positive electrode slurry, wherein the conductive glue comprises a conductive agent, a binder and a solvent, and the positive electrode sodium supplement comprises one or more of the following chemical formulas: Na x HM q O y , where element M is any one of C, S, P, B and Si; z is the absolute value of the valence state of element M; x, y, z, q satisfy x+1+qz=2y, z is a positive natural number, and the value of x is 1, 2 or 2.

5.

7. The method for preparing the positive electrode slurry according to claim 6, characterized in that: When the conductive glue, the positive electrode material of the sodium ion battery and the positive electrode sodium supplement are mixed, the positive electrode material of the sodium ion battery and the positive electrode sodium supplement are added to the conductive glue at the same time.

8. A positive electrode sheet, characterized in that: The positive electrode slurry comprises any one of claims 2-5.

9. An electrode assembly, characterized in that: The electrode assembly is formed by winding or laminating a positive electrode sheet, a negative electrode sheet and a separator, and the positive electrode sheet is the positive electrode sheet according to claim 8.

10. The electrode assembly according to claim 9, characterized in that: The negative electrode plate is one or more of hard carbon, soft carbon, oxide, and alloy; and / or the electrolyte in the electrode assembly is one or more of liquid, semi-solid, and solid electrolytes; and / or the diaphragm is one or a combination of PP, PE, PET, PVDF, PI, PVC, and PPS.

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