Electrolyte for quickly charging non-negative-electrode sodium ion battery and quickly-chargeable non-negative-electrode sodium ion battery

Abstract

The invention provides an electrolyte for quickly charging a sodium-ion battery without a negative electrode. The electrolyte comprises a sodium salt, a solvent and an additive. According to the electrolyte, metal oxide nanoparticles are introduced as a first additive, and a second additive is supplemented, so that rapid desolvation of sodium ions on an electrode interface and improvement of the ionic conductivity of an electrolyte body are realized at the same time, and compact and dendrite-free sodium deposition under high current density is realized. The negative-electrode-free sodium-ion battery prepared from the electrolyte can be quickly charged, and good cycling stability and high capacity retention ratio can be maintained, so that the use requirements of people can be met.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, specifically to an electrolyte that can be used for fast charging of a negative electrode-free sodium-ion battery and its preparation method, and also to a fast-charging negative electrode-free sodium-ion battery. Background Technology

[0002] Electrodeless sodium-ion batteries (AFSBs) have attracted widespread attention due to their unique structural design. Their actual negative electrode is the sodium ions (Na+) that are extracted and deintercalated from the positive electrode during charging. + AFSBs are formed in situ by direct deposition onto the current collector. This ease of preparation, requiring no excess sodium, gives AFSBs significant advantages in terms of high energy density and processability. However, the limited sodium source at the cathode necessitates highly reversible sodium deposition / stripping processes on the anode side. The high reactivity of sodium, the significant volume expansion during sodium plating / stripping, and the instability of the solid electrolyte interphase (SEI) all pose challenges to this requirement. These challenges are particularly pronounced under high-rate operating conditions: insufficient ion transport kinetics lead to uneven sodium ion flux and localized current concentration, increasing the risk of dendrite growth and premature battery failure.

[0003] Electrolyte engineering is considered a pragmatic and direct approach to achieving high-rate AFSBs, typically requiring the simultaneous promotion of rapid ion transport at both the electrolyte and electrode / electrolyte interfaces. On one hand, according to the Sand-time model, rapid ion transport within the electrolyte itself is crucial for preventing uneven sodium deposition. Increasing the effective ion concentration in the electrolyte through strong solvation can prolong ion depletion time, thereby achieving sustained sodium deposition at high rates. On the other hand, with the consensus that desolvation is the rate-determining step, optimizing ion desolvation behavior at the interface is considered significant. Weakly solvated electrolytes with abundant contact ion pairs (CIPs) and ion aggregates (AGGs) solvation structures can significantly reduce the desolvation barrier for cations while promoting the formation of anion-derived inorganic SEI-rich phases, effectively enhancing ion transport within the SEI and suppressing dendrite growth. However, focusing solely on bulk ion transport or interfacial desolvation leads to a fundamental imbalance: strongly solvated systems form solvent-derived interfaces, accompanied by a slow desolvation process; while weakly solvated designs suffer from insufficient ion replenishment, resulting in decreased electrolyte ionic conductivity. This limitation has so far hindered the development of AFSBs at high rates (>1 mA cm⁻¹). -2 Applications under these conditions. Therefore, an ideal electrolyte should maintain the high ion dissociation capacity of the bulk electrolyte while inducing anion aggregation at the interface, which is a better way to achieve high-rate AFSBs. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides an electrolyte for fast charging of a cathode-free sodium-ion battery. In addition to sodium salt and solvent, a first additive and a second additive are introduced. This enables rapid desolvation of sodium ions at the electrode interface, promotes the formation of anion-rich solid electrolyte interphase (SEI), inhibits sodium dendrite growth, and facilitates rapid ion dissociation in the peripheral region, thereby improving the bulk ionic conductivity of the electrolyte. This achieves dense and dendrite-free sodium deposition at high current densities, enabling fast charging of the cathode-free sodium-ion battery and meeting user needs.

[0005] The first aspect of the present invention aims to provide an electrolyte for fast charging of a negative electrode-free sodium-ion battery, which is prepared from raw materials including sodium salt, solvent and additives.

[0006] The sodium salt is selected from one or more fluorine-containing sodium salts, preferably one or more fluorine-containing sodium phosphate salts.

[0007] The solvent is selected from one or more ether solvents, preferably from one or more chain ether solvents.

[0008] The additive includes a first additive. Preferably, it also includes a second additive.

[0009] A second aspect of this invention aims to provide a method for preparing an electrolyte for fast charging of a cathode-free sodium-ion battery. The method involves adding a sodium salt to a solvent to dissolve it, obtaining a sodium salt solution. An additive is then added to the sodium salt solution, and the mixture is thoroughly mixed to obtain the electrolyte for fast charging of a cathode-free sodium-ion battery.

[0010] The third aspect of this invention aims to provide a fast-charging, electrodeless sodium-ion battery, wherein the electrolyte of the fast-charging, electrodeless sodium-ion battery is the electrolyte described in the first aspect for fast charging of electrodeless sodium-ion batteries.

[0011] The sodium metal battery without a negative electrode also includes a positive electrode, a separator, and a negative electrode current collector.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] (1) The electrolyte for fast charging of a negative electrode-free sodium-ion battery provided by the present invention improves the cation transport number and ion exchange current density of the electrolyte, and significantly improves the fast charging performance of the electrolyte.

[0014] (2) This invention utilizes a second additive to stably disperse metal oxide nanoparticles in the electrolyte. In the region adjacent to the metal oxide nanoparticles, a solvation structure dominated by anion-aggregated contact ion pairs (CIP) / aggregated ion pairs (AGG) promotes the desolvation of sodium ions at the electrode interface, forming an anion-rich solid electrolyte interphase (SEI), thereby inhibiting sodium dendrite growth. Simultaneously, the peripheral region of the metal oxide nanoparticles is dominated by a solvation structure of solvent-separated ion pairs (SSIP), achieving high bulk ionic conductivity. While maintaining the high ion dissociation capacity of the bulk electrolyte, it induces anion aggregation at the interface, providing a system basis for achieving high-rate AFSBs.

[0015] (3) The electrolyte of this invention is reasonably and ingeniously designed. The Al||NVP electrodeless coin cell, Al||NFM electrodeless coin cell, and Al||NFPP electrodeless coin cell obtained therefrom can maintain stable cycle performance under high current density, and the capacity retention rate is 70% or above. Attached Figure Description

[0016] Figure 1 a represents the charge-discharge curves of Al||NVP electrodeless coin cell I in Example 9 of this invention at different rates; Figure 1 b is the charge-discharge curve of Al||NVP electrodeless coin cell A in Comparative Example 5 of the present invention at different rates;

[0017] Figure 2 The graph shows the specific capacity variation of Al||NVP electrodeless coin cell I in Example 1 and Al||NVP electrodeless coin cell A in Comparative Example 5, and the coulombic efficiency variation of Al||NVP electrodeless coin cell I, at 5C rate from 1 to 1500 cycles.

[0018] Figure 3 a represents the charge-discharge curves of Al||NFM electrodeless button cell I in Example 10 of the present invention at different rates; Figure 3 b is the charge-discharge curve of Al||NFM electrodeless coin cell A in Comparative Example 6 at different rates;

[0019] Figure 4 The graph shows the specific capacity variation of Al||NFM electrodeless coin cell I in Example 10 and Al||NFM electrodeless coin cell A in Comparative Example 6 after 1 to 400 cycles at 1C rate, and the coulombic efficiency variation of Al||NFM electrodeless coin cell I in Example 10 after 1 to 400 cycles at 1C rate.

[0020] Figure 5The data are the rate charge-discharge curves of Al||NFPP electrodeless coin cell I assembled with the electrolyte in Example 1 in Example 9 of the present invention and the rate charge-discharge curves of Al||NFPP electrodeless coin cell A assembled with the electrolyte in Comparative Example 7 in Comparative Example 1.

[0021] Figure 6 This is a comparison chart of the specific capacity and coulombic efficiency of Al||NFPP electrodeless coin cell I and Al||NFPP electrodeless coin cell A at 1C rate for 1 to 500 cycles.

[0022] Figure 7 The graph shows the specific capacity variation of the Al||NFM electrodeless coin cell VI of the present invention from 1 to 480 cycles at a 1C rate;

[0023] Figure 8 The graph shows the specific capacity variation of the Al||NFM electrodeless coin cell VII of the present invention at 1C rate from 1 to 500 cycles.

[0024] Figure 9 The graph shows the specific capacity variation of the Al||NFM electrodeless coin cell VIII of the present invention during 1 to 80 cycles at a 1C rate.

[0025] Figure 10 a is the radial distribution function (RDF) curve of the bulk phase of the fast-charging electrolyte I prepared in Example 1; Figure 10 b is the radial distribution function (RDF) curve of the nano-alumina interface in the fast charging electrolyte I prepared in Example 1; Figure 10 c is the radial distribution function (RDF) curve of the basic electrolyte I prepared in Comparative Example 1;

[0026] Figure 11 a and 11c are graphs showing the relationship between current and time during constant voltage (ΔV = 10mV) polarization of Na||Na symmetric cells assembled using basic electrolyte I and fast-charging electrolyte I, respectively. Figure 11 b and 11d are the EIS test results of Na||Na symmetric cells assembled using basic electrolyte I and fast-charging electrolyte I before and after constant voltage (ΔV=10mV) polarization, respectively;

[0027] Figure 12 The infrared spectra of fast charging electrolyte I, fast charging electrolyte III, fast charging electrolyte IV in Examples 1, 3, and 4 of the present invention, and basic electrolyte I and G2 in Comparative Example 1 are shown.

[0028] Figure 13 The infrared spectra of solvent G2, first additive Al2O3 nanoparticles, second additive polydimethylsiloxane, and basic electrolyte V in Comparative Example 5 are shown.

[0029] Figure 14 This is a time-of-flight secondary ion mass spectrum of sodium metal deposited in Al||Na half-cell I of the present invention. Detailed Implementation

[0030] This invention introduces a fast-charging electrolyte by introducing silane coupling agents and nanoparticles into the electrolyte. By utilizing the synergistic effect of silane coupling agents and nanoparticles, the desolvation process is accelerated, and the ionic conductivity is improved, thereby increasing the cation transport number and ion exchange current density of the electrolyte and significantly improving the fast-charging performance of the negative electrode-free sodium-ion battery.

[0031] This invention provides an electrolyte for fast charging of a cathode-free sodium-ion battery, which is prepared from raw materials including sodium salt, solvent, and additives. The sodium salt is added to the solvent and dissolved to obtain a sodium salt solution. Additives are added to the sodium salt solution and mixed thoroughly to obtain the electrolyte for fast charging of the cathode-free sodium-ion battery. Preferably, after the sodium salt is dissolved in the solvent, it is dehydrated.

[0032] The sodium salt is selected from one or more fluorine-containing sodium salts, preferably one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium hexafluorophosphate, and sodium fluorosulfate, and more preferably sodium hexafluorophosphate. The molar volume ratio of the sodium salt to the solvent is 3 mmol:(1.5-30.0) mL, preferably 3 mmol:(2.0-6.0) mL, and more preferably 3 mmol:(2.5-3.8) mL. If the molar volume ratio of the sodium salt to the solvent is too low, below 3 mmol:30.0 mL, the conductivity of the electrolyte will be too low; if the molar volume ratio of the sodium salt to the solvent is too high, above 3 mmol:2 mL, the viscosity of the electrolyte will be too high, both of which will affect the performance of the electrolyte.

[0033] The solvent is selected from one or more ether solvents, preferably from one or more chain ethers, and more preferably from one or more of dimethoxymethane (DMM), 1,2-dimethoxyethylene (DME), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (G2), and tetraethylene glycol dimethyl ether (G4), such as diethylene glycol dimethyl ether (G2).

[0034] The type of solvent (molecular structure, chemical properties) directly determines the solubility, ionic conductivity, stability, interfacial compatibility, and safety performance of the electrolyte. By selecting linear ether solvents with high solubility for sodium salts, the Coulombic forces between cations and anions can be weakened, increasing the concentration of free ions in the electrolyte and thus improving its ionic conductivity. Simultaneously, these solvents have high oxidation decomposition potentials, making them compatible with high-voltage cathode materials and preventing premature oxidation and decomposition of the solvent on the cathode surface.

[0035] The additive includes a first additive. Preferably, it also includes a second additive.

[0036] The first additive is selected from one or more metal oxide nanoparticles, preferably from one or more of alumina, nickel oxide, magnesium oxide, copper oxide, zinc oxide, and α-iron oxide nanoparticles, and more preferably from one or more of alumina, zinc oxide, magnesium oxide, and nickel oxide nanoparticles, such as nano-alumina particles. In this invention, positively charged metal oxide nanoparticles act as anion aggregators, creating distinctly different solvation environments around and around the nanoparticles. In the region adjacent to the nanoparticles, solvation structures dominated by anion-aggregated contact ion pairs (CIPs) and aggregated ion pairs (AGGs) are predominant. This facilitates the desolvation of sodium ions at the electrode interface, accelerates sodium ion transport at the negative electrode-electrolyte interface, and promotes the formation of anion-rich solid electrolyte interphase (SEI), thereby inhibiting sodium dendrite growth. Conversely, the solvation structure in the peripheral region, dominated by solvent-separated ion pairs (SSIPs), achieves high bulk ionic conductivity through sufficient ion dissociation, increasing the migration rate of sodium ions within the electrolyte. These factors work together to enable dense, dendrite-free sodium deposition at high current densities, thus avoiding short circuits.

[0037] The average particle size of the metal oxide nanoparticles is 5-50 nm, preferably 5-35 nm, more preferably 5-20 nm, such as 10 nm. The particle size of the metal oxide nanoparticles affects conductivity in two ways: "dispersion state" and "ion channel construction". When the particle size is too small (<5 nm), the surface energy is extremely high, and agglomeration is easy to occur, forming "micron-sized aggregates", which hinders ion migration and leads to a decrease in conductivity. When the particle size is too large (>50 nm), it is easy to settle in the electrolyte or form "mechanical barriers", increasing the ion migration path length. Medium-sized particles (5-20 nm) form "ordered gaps" between them, which do not hinder ion migration and can guide ion directional transport through "interfacial polarization effect".

[0038] The mass ratio of the first additive to the solvent is 1:(1-160), preferably 1:(3-140), more preferably 1:(5-120), such as 1:(10-100). Insufficient metal oxide nanoparticles cannot form a continuous "protective layer" on the electrode surface; they can only locally participate in the modification of the negative electrode-electrolyte interface film, but cannot suppress interfacial side reactions. An appropriate amount of nanoparticles can be uniformly adsorbed on the electrode surface and participate in the in-situ formation of the negative electrode-electrolyte interface film.

[0039] The second additive is selected from one or more of titanate coupling agents, aluminum-titanium composite coupling agents, and organosilicon compounds, preferably from one or more of organosilicon compounds, more preferably from 3-isocyanopropyltriethoxysilane and / or polydimethylsiloxane, such as polydimethylsiloxane. The number-average molecular weight of the polydimethylsiloxane is 500-1200 g / mol, preferably 600-1000 g / mol, more preferably 700-850 g / mol. The second additive molecule has different reactive groups that can chemically combine with inorganic and organic materials, such as KH570. This enhances the compatibility of nanoparticles with other components in the electrolyte, ensuring their uniform dispersion in the electrolyte. The organosilicon compound, through the anchoring effect of silicon-oxygen bonds (Si-O-), acts as a bridge between the nanoparticles and the sodium metal surface, not only promoting the rapid diffusion of sodium ions but also achieving a uniform distribution of sodium ion flux. The volume ratio of the second additive to the solvent is 1:(60-240), preferably 1:(90-210), and more preferably 1:(120-180). When the amount of the second additive is below the critical threshold, sufficient "bridging" cannot be formed between the nanoparticles, and the particles cannot play their role. When the amount is in the optimal range, its molecules can uniformly cover the particle surface, fully exerting the coupling, dispersing, and stabilizing effects, and reducing the blockage of ion channels by particle agglomeration. Excessive use of the second additive will cause entanglement with solvent molecules and polymer chains, or aggregation due to intermolecular hydrogen bonds / van der Waals forces, leading to an increase in electrolyte viscosity.

[0040] The electrolyte used for fast charging of the negative electrode-free sodium-ion battery has a water content of <25ppm, preferably <18ppm, and more preferably <12ppm.

[0041] This invention also provides a method for preparing the electrolyte for fast charging of a cathode-free sodium-ion battery. The method involves adding a sodium salt to a solvent to dissolve it, obtaining a sodium salt solution. Additives are then added to the sodium salt solution, and the mixture is stirred until homogeneous to obtain the electrolyte for fast charging of a cathode-free sodium-ion battery.

[0042] The preparation method is carried out under a protective atmosphere. Preferably, the protective atmosphere is an atmosphere with a water content ≤0.01ppm and an oxygen content ≤0.01ppm, more preferably an argon atmosphere with a water content ≤0.01ppm and an oxygen content ≤0.01ppm.

[0043] In a preferred embodiment of the present invention, after the sodium salt is dissolved in a solvent, a solid dehydrating agent is added. After thorough dehydration, the dehydrating agent is separated to obtain a sodium salt solution. Preferably, the separation from the dehydrating agent is achieved by filtration or by taking the liquid portion after settling, such as taking the liquid portion after settling. The present invention does not specifically limit the dehydrating agent; any agent that can ensure the water content of the electrolyte meets the requirements can be used, such as a molecular sieve.

[0044] The present invention also provides a fast-charging, electrodeless sodium-ion battery, wherein the electrolyte of the fast-charging, electrodeless sodium-ion battery is the electrolyte used for fast charging of electrodeless sodium-ion batteries.

[0045] The electrodeless sodium-ion battery also includes a positive electrode, a separator, and a negative electrode current collector. The positive electrode includes a positive electrode current collector and a positive electrode active material layer on the positive electrode current collector. During charging, metallic sodium is gradually deposited on the negative electrode current collector of the electrodeless sodium-ion battery to form a negative electrode active material layer, i.e., a sodium metal layer.

[0046] In one embodiment of the present invention, the positive electrode active material of the negative electrode-free sodium-ion battery is selected from one or more of polyanionic positive electrode materials, Prussian blue compound positive electrode materials, polymer positive electrode materials, and transition metal oxides, preferably from one or more of phosphate positive electrode materials and transition metal oxides, more preferably from one or more of sodium vanadium phosphate Na3V2(PO4)3 (NVP), sodium iron phosphate, sodium iron pyrophosphate (NFPP), sodium manganese phosphate, sodium vanadium fluorophosphate, sodium iron fluorophosphate, sodium iron manganate, sodium nickel iron manganate, and sodium nickel iron manganese oxide (NFM), such as NVP, NFPP, and NFM. The transition metal oxide is Na x MeO2, where Me is selected from one or more of Fe, Co, Ni, Mn, Cr, and Ti, and x is a value that makes Na... x The algebraic sum of the positive and negative valences of the elements in MeO2 is zero.

[0047] This invention does not specifically limit the positive electrode current collector; any current collector that can be used for the above-mentioned positive electrode materials can be used, such as aluminum foil, carbon-coated aluminum foil, stainless steel current collector, etc.

[0048] This invention does not specifically limit the negative electrode current collector; any current collector suitable for use in a negative electrode-less sodium-ion battery is acceptable. In one embodiment of this invention, the negative electrode current collector is selected from one of copper foil, modified copper foil, carbon-coated copper foil, modified carbon-coated copper foil, aluminum foil, modified aluminum foil, carbon-coated aluminum foil (Al@C), and modified carbon-coated aluminum foil.

[0049] This invention does not specifically limit the separator; any separator suitable for use in negative electrode-less sodium-ion batteries is acceptable. In one embodiment of this invention, the separator is selected from polypropylene, polyethylene, glass fiber, ceramic-coated, functionalized polymer, metal-organic framework composite, and cellulose separators, preferably from polypropylene, polyethylene, glass fiber, and ceramic-coated separators, and more preferably from polypropylene (PP) separators.

[0050] Example

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1

[0053] In an argon-atmosphere glove box (water content ≤ 0.01 ppm, oxygen content ≤ 0.01 ppm), 0.003 mol of sodium hexafluorophosphate (NaPF6, purity 99.9 wt%) was added to 3 mL of diethylene glycol dimethyl ether (G2) (purity 99.5 wt%), mixed and dissolved. After adding an appropriate amount of molecular sieve to remove water and allowing it to stand (water content < 10 ppm after water removal), 2 mL of the dehydrated sodium hexafluorophosphate solution was pipetted onto a pipette, and 40 mg of nano-alumina (manufacturer: Suzhou Duoduo Chemical Technology Co., Ltd., average particle size 10 nm, purity 99.9 wt%) and 20 μL of polydimethylsiloxane (Aladdin Reagent (Shanghai) Co., Ltd., purity 99.5 wt%, number average molecular weight 770 g / mol) were added sequentially. The mixture was stirred until homogeneous to obtain fast-charging electrolyte I.

[0054] Example 2

[0055] Fast charging electrolyte II was prepared using the same method as in Example 1 for preparing fast charging electrolyte I, except that 20 mg of nano-alumina was added.

[0056] Example 3

[0057] Fast charging electrolyte III was prepared using the same method as in Example 1 for preparing fast charging electrolyte I, except that 100 mg of nano-alumina was added.

[0058] Example 4

[0059] Fast charging electrolyte IV was prepared using the same method as in Example 1 for preparing fast charging electrolyte I, except that 200 mg of nano-alumina was added.

[0060] Example 5

[0061] Fast charging electrolyte VI was prepared using the same method as in Example 1 for preparing fast charging electrolyte I, except that nano-alumina was replaced with an equal mass of nano-nickel oxide (manufacturer: Suzhou Duoduo Chemical Technology Co., Ltd., average particle size 15nm, purity 99.9wt%).

[0062] Example 6

[0063] Fast charging electrolyte VII was prepared using the same method as in Example 1 for preparing fast charging electrolyte I, except that nano-alumina was replaced with an equal mass of nano-zinc oxide (manufacturer: Suzhou Duoduo Chemical Technology Co., Ltd., average particle size: 15nm, purity: 99.9wt%).

[0064] Example 7

[0065] Fast charging electrolyte VIII was prepared using the same method as in Example 1 for preparing fast charging electrolyte I, except that nano-alumina was replaced with an equal mass of nano-copper oxide (manufacturer: Suzhou Duoduo Chemical Technology Co., Ltd., average particle size 15nm, purity 99.9wt%).

[0066] Example 8

[0067] Electrolyte V was prepared using the same method as in Example 1 for preparing fast-charging electrolyte I, except that polydimethylsiloxane was not added.

[0068] Example 9

[0069] In an argon-atmospheric glove box, the negative electrode shell, carbon spring sheet, gasket, negative electrode current collector aluminum foil (manufactured by Shenzhen Kejing Materials Technology Co., Ltd., battery grade), and polypropylene separator (manufactured by Celgard, 25μm thickness) are assembled in that order. 40μL of electrolyte is dropped onto the separator, followed by the sequential addition of sodium vanadium phosphate (Na3V2(PO4)3) (NVP) positive electrode sheet (custom-made by Beijing Xibei Power Technology Co., Ltd.). Specifically, sodium vanadium phosphate (manufactured by Beijing Xibei Power Technology Co., Ltd.), SP carbon black conductive agent (manufactured by Shenzhen Kejing), and polyvinylidene fluoride (PVDF) binder (manufactured by Shenzhen Kejing) are mixed in a mass ratio of 94:2:4, ground uniformly, and N-methyl-2-pyrrolidone is added as a solvent. The mixture is stirred thoroughly until there are no particles, resulting in a slurry. This slurry is coated onto carbon-coated aluminum foil, dried, and rolled to obtain the NVP positive electrode sheet. The areal density of NVP is 7.7 mg / cm³. 2 The positive electrode shell was pressed to obtain an Al||NVP electrodeless coin cell (CR2032 coin cell). The electrolyte used was electrolyte I to electrolyte VIII from Examples 1-8, respectively, to obtain Al||NVP electrodeless coin cell I to Al||NVP electrodeless coin cell VIII.

[0070] Example 10

[0071] Al||NFM electrodeless coin cell I was prepared according to the method of preparing Al||NVP electrodeless coin cell I in Example 9, the only difference being that sodium nickel iron manganese oxide NaNi was used. 1 / 3 Fe 1 / 3 Mn 1 / 3The O2 (NFM) positive electrode sheet (customized by Beijing Xibei Power Technology Co., Ltd.) is made by mixing sodium nickel iron manganese oxide (manufactured by Beijing Xibei Power Technology Co., Ltd.), SP carbon black conductive agent (manufactured by Shenzhen Kejing), and polyvinylidene fluoride (PVDF) binder (manufactured by Shenzhen Kejing) at a mass ratio of 94:2:4, grinding them evenly, adding N-methyl-2-pyrrolidone as a solvent to the mixture, and stirring thoroughly until there are no particles to obtain a mixed slurry. The mixed slurry is coated on carbon-coated aluminum foil, dried, and rolled to obtain the NFM positive electrode sheet. The areal density of NFM is 22 mg / cm³. 2 It can replace the NVP positive electrode.

[0072] Al||NFM electrodeless coin cell I was prepared using the same method as described above. The only difference was that equal volumes of fast-charging electrolyte II to VIII were used instead of fast-charging electrolyte I.

[0073] Example 11

[0074] Al||NFPP coin cell I without a negative electrode was prepared according to the method of preparing Al||NVP coin cell I in Example 9, with the only difference being: Sodium iron pyrophosphate NFPP positive electrode sheet (the positive electrode sheet was customized by Beijing Xibei Power Technology Co., Ltd.) was mixed at a mass ratio of 94:2:4, ground uniformly, and N-methyl-2-pyrrolidone was added as a solvent to the mixture. The mixture was stirred thoroughly until there were no particles, resulting in a slurry. The slurry was coated onto carbon-coated aluminum foil, dried, and rolled to obtain the NFPP positive electrode sheet. The areal density of the NFPP was 11.7 mg / cm³. 2 It can replace the NVP positive electrode.

[0075] Al||NFPP electrodeless coin cell I was prepared using the same method as described above. The only difference was that the fast-charging electrolyte I was replaced with an equal volume of fast-charging electrolyte II to VIII.

[0076] Example 12

[0077] Na||Na symmetric cell I was prepared according to the method of preparing Al||NVP electrodeless coin cell I in Example 9, with the only difference being that: sodium metal sheets with a diameter of 10 mm and a thickness of 400 μm (sodium metal from Aladdin Reagent (Shanghai) Co., Ltd., purity 99.9 wt%; the sodium oxide layer on the surface was removed in a glove box under argon atmosphere, the fresh sodium inside was taken, rolled into a sodium metal foil with a thickness of 400 μm, and punched into a metal sheet with a diameter of 10 mm) were used to replace Al and NVP respectively.

[0078] Using an electrochemical workstation (Solartron 1470E), constant voltage (ΔV = 10mV) polarization and electrochemical impedance (bias voltage 5mV, 10) were applied. 6 The test results (-0.01Hz) show that the initial impedance and steady-state impedance of fast charging electrolyte I are 0.48Ω and 0.52Ω, respectively. The Na content is calculated using the following formula (1). + Number of migrations (t) Na + The value is 0.65.

[0079]

[0080] Where ΔV is the applied bias voltage; I0 and I s Representing the initial and steady-state currents, R0 and R s These represent the interfacial impedance before and after polarization. Specific test results are as follows: Figure 11 c and Figure 11 As shown in d. Figure 11 c represents the change of current over time during the constant voltage polarization stage. Due to the limitation of the applied voltage, the current gradually changes from the initial migration of both anions and cations to the migration of only cations, and the current decreases until it stabilizes, thus obtaining the initial current and the steady-state current. Figure 11 d represents the EIS test results of Na||Na symmetric cell I before and after constant voltage polarization. In the fast-charging electrolyte I system, the cation transference number is larger, contributing more to the current and enabling rapid transport during charging and discharging, thus avoiding dendrite formation.

[0081] Example 13

[0082] Al||Na half-cell I was prepared according to the method of preparing Na||Na symmetric cell I in Example 12, with the only difference being that the Na metal sheet on the negative electrode side was replaced with an aluminum foil with a diameter of 19 mm (manufacturer: Shenzhen Kejing Materials Technology Co., Ltd., specification: battery grade).

[0083] Comparative Example

[0084] Comparative Example 1

[0085] In an argon-atmospheric glove box (water ≤ 0.01 ppm, oxygen ≤ 0.01 ppm), 0.003 mol of sodium hexafluorophosphate (purity 99.9 wt%) was added to 3 mL of diethylene glycol dimethyl ether (purity 99.5 wt%), and the mixture was allowed to dissolve. After adding an appropriate amount of molecular sieve to remove water completely, basic electrolyte I was obtained.

[0086] Comparative Example 2

[0087] Basic electrolyte II was prepared using the same method as that used to prepare basic electrolyte I in Comparative Example 1, except that the amount of sodium hexafluorophosphate added was 0.3 mmol.

[0088] Comparative Example 3

[0089] Basic electrolyte III was prepared using the same method as that used to prepare basic electrolyte I in Comparative Example 1, except that the amount of sodium hexafluorophosphate added was 1.5 mmol.

[0090] Comparative Example 4

[0091] Basic electrolyte IV was prepared using the same method as that used to prepare basic electrolyte I in Comparative Example 1, with the only difference being that the amount of sodium hexafluorophosphate added was 6 mmol.

[0092] Comparative Example 5

[0093] Basic electrolyte V was prepared using the same method as that used to prepare basic electrolyte I in Comparative Example 1, except that the amount of sodium hexafluorophosphate added was 0.

[0094] Comparative Example 6

[0095] Al||NVP electrodeless coin cell A was prepared according to the method of preparing Al||NVP electrodeless coin cell I in Example 9, the only difference being that an equal volume of basic electrolyte I was used instead of fast-charging electrolyte I.

[0096] Al||NVP electrodeless coin cell A was prepared using the same method as described above. Al||NVP electrodeless coin cell B to D were prepared, with the only difference being that equal volumes of basic electrolyte II to IV were used instead of basic electrolyte I.

[0097] Comparative Example 7

[0098] Al||NFM electrodeless coin cell A was prepared according to the method of preparing Al||NFM electrodeless coin cell I in Example 10, with the only difference being that an equal volume of basic electrolyte I was used instead of fast-charging electrolyte I.

[0099] Al||NFM electrodeless coin cell A was prepared using the same method as described above. Al||NFM electrodeless coin cell B to D were prepared, with the only difference being that equal volumes of basic electrolyte II to IV were used instead of basic electrolyte I.

[0100] Comparative Example 8

[0101] Al||NFPP electrodeless coin cell A was prepared according to the method of preparing Al||NFPP electrodeless coin cell I in Example 11, with the only difference being that an equal volume of basic electrolyte I was used instead of fast-charging electrolyte I.

[0102] Al||NFPP electrodeless coin cell A was prepared using the same method as described above. Electrodeless coin cells B to D were prepared, with the only difference being that equal volumes of basic electrolytes II to IV were used instead of basic electrolyte I.

[0103] Comparative Example 9

[0104] Na||Na symmetric cell A was prepared according to the method of preparing Na||Na symmetric cell I in Example 12, except that an equal volume of basic electrolyte I was used instead of fast-charging electrolyte I.

[0105] Using an electrochemical workstation (Solartron 1470E) with DC polarization (ΔV = 10mV) and electrochemical impedance (bias voltage 5mV, 10mV) 6 The test results (-0.01Hz) show that the initial impedance and steady-state impedance of the basic electrolyte I are 0.24Ω and 0.1Ω, respectively. The Na content was calculated using formula (1). + Number of migrations (t) Na + The value is 0.62. Specific test results are as follows: Figure 11 a and Figure 11 As shown in b. Figure 11 a represents the change of current over time during the constant voltage polarization stage. Due to the limitation of the applied voltage, the current gradually changes from the initial migration of both anions and cations to the migration of only cations, and the current decreases until it stabilizes, thus obtaining the initial current and the steady-state current. Figure 11 b shows the EIS test results of Na||Na symmetric cell I before and after constant voltage polarization. In the basic electrolyte I system, the cation transference number is lower than that of fast-charging electrolyte I. During charge and discharge, due to the slower cation migration rate, ions at the interface are rapidly consumed, resulting in dendrite formation and rapid degradation of battery performance.

[0106] Experimental Example

[0107] Experimental Example 1

[0108] At 25℃, variable rate charge-discharge tests were conducted on Al||NVP electrodeless coin cell I and Al||NVP electrodeless coin cell A. The test rates were 0.5C, 1C, 2C, 5C, 8C, and 10C (1C = 100mA / g), with a voltage range of 2.5-3.75V. The obtained charge-discharge curves (voltage (V) - specific capacity (mAh / g)) are shown below. Figure 1 a and Figure 1 As shown in b.

[0109] At 25℃, variable rate charge-discharge tests were conducted on Al||NFM electrodeless coin cell I and Al||NFM electrodeless coin cell A. The test rates were 0.5C, 1C, 2C, and 3C (1C = 100mA / g), and the voltage range was 2.0-4.1V. The obtained charge-discharge curves are shown below. Figure 3 a and Figure 3 As shown in b.

[0110] At 25℃, variable rate charge-discharge tests were conducted on Al||NFPP electrodeless coin cell I and Al||NFPP electrodeless coin cell A. The test rates were 0.5C, 1C, 2C, 3C, 4C, and 5C (1C = 100mA / g), and the voltage range was 2.0-3.8V. The obtained charge-discharge curves are shown below. Figure 5 a and Figure 5 As shown in b.

[0111] Experiment Example 2

[0112] Constant current charge-discharge tests were conducted on Al||NVP electrodeless coin cell I and Al||NVP electrodeless coin cell A at 25℃. The test rates were 5C (1C = 100mA / g), and the voltage range was 2.5-3.75V. The specific capacity and coulombic efficiency were obtained from 1 to 1500 cycles (the graphs showing the relationship between specific capacity and cycle number and coulombic efficiency and cycle number are shown below). Figure 2 As shown. After 1400 cycles, the Al||NVP electrodeless coin cell I retained 70% of its capacity and was able to continue to cycle stably for more than 1500 cycles, which is the longest cycle life achieved to date for an electrodeless battery at the highest current density.

[0113] At 25℃, variable rate charge-discharge tests were conducted on Al||NFM electrodeless coin cell I and Al||NFM electrodeless coin cell A. The test rates were 1C (1C = 100mA / g), and the voltage range was 2.0-4.1V. The specific capacity and coulombic efficiency were obtained after 1 to 400 cycles. Figure 4As shown, after 400 cycles, the capacity retention of Al||NFM electrodeless coin cell I was 70.2%. Because the nanoparticles accelerated sodium ion migration at the interface, sodium ions were rapidly replenished, and the deposited sodium metal exhibited high reversibility, maintaining a consistently high coulombic efficiency (>99%).

[0114] The specific capacity variation of Al||NFM electrodeless coin cell VI at 1C rate from 1 to 480 cycles is shown in the graph. Figure 7 As shown in the figure, the specific capacity change of Al||NFM electrodeless coin cell VII at 1C rate from 1 to 500 cycles is shown in the figure. Figure 8 As shown in the figure, the specific capacity change of Al||NFM electrodeless coin cell VIII at 1C rate from 1 to 80 cycles is shown in the figure. Figure 9 As shown, Al||NFM electrodeless coin cells using NiO, ZnO, CuO, and other nanoparticles as the first additive exhibit excellent cycle stability at 1C rate, demonstrating the universality of this invention.

[0115] At 25℃, variable rate charge-discharge tests were conducted on Al||NFPP electrodeless coin cell I and Al||NFPP electrodeless coin cell A. The test rates were 1C (1C = 100mA / g), and the voltage range was 2.0-3.8V. The specific capacity and coulombic efficiency were obtained after 1 to 500 cycles. Figure 6 As shown. After 528 cycles, the capacity retention of Al||NFPP electrodeless coin cell I was 70%.

[0116] Experimental Example 3

[0117] Based on production molecular dynamics simulation (MD simulation) of sodium ions (Na) + The solvation structure data of the electrolyte were analyzed using histograms with the MD Analysis Python package. VMD software was used to generate the bulk and interface (the interface between the solution and nano-alumina in fast-charging electrolyte I) and radial distribution function (RDF) curves of the basic electrolyte I, as shown below. Figure 10 As shown in a, 10b and 10c.

[0118] In the radial distribution function, g(r) describes the target particle, i.e., Na. + Centered on the solvent molecule G2, other particles (such as the anion PF6) - How likely is it that it will appear at different distances? Figure 10 a, 10b, and 10c are described by solid lines; N(r) is a "cumulative integral function" based on g(r), and its physical meaning is based on Na. +The average number of particles contained within a spherical region of radius r centered at a given point is often referred to as the "coordination number function"; Figure 10 a, 10b, and 10c are described by dashed lines. According to Figure 10 b can be deduced that in fast-charging electrolyte I, the Na near nano-alumina... + The solvated structure contains 1.31 G2 molecules and 0.74 PF6 molecules. - This region is more prone to forming contact ion pair (CIP) structures (accounting for 61.7%). In contrast, the solvation structures surrounding nano-alumina are predominantly solvent-separated ion pairs (SSIP) (accounting for 100%). Figure 10 a) Among them, the number of G2 molecules was significantly higher (2.28), while PF6... - The number was even lower (0.09), a characteristic similar to the solvation characteristics in basic electrolyte I. Figure 10 c).

[0119] Experiment Example 4

[0120] At 25°C, infrared spectroscopy was performed on the fast charging electrolyte I, fast charging electrolyte III, fast charging electrolyte IV prepared in Examples 1, 3, and 4, the basic electrolytes I to IV in Comparative Examples 1-4, and solvent G2. The test results are as follows: Figure 12 a and Figure 12 As shown in b. From Figure 12 It can be seen that as the amount of nanoparticles added increases, the concentration at ~704 cm⁻¹ increases. -1 A characteristic Al-O peak appears at ~1100 cm⁻¹. -1 The peak intensity of COC remains unchanged at ~1082 cm⁻¹. -1 The peak intensity of Na-OC gradually decreases. This phenomenon indicates that the introduced nano-alumina reacts with Na... + Competitive interactions occurred among the coordinated solvent molecules. Simultaneously, the incorporation of nano-alumina led to a ~557 cm⁻¹ -1 The antisymmetric stretching vibration of the PF bond undergoes a redshift, indicating that the anion activity is reduced due to the enhanced binding affinity between the anion and the cation.

[0121] Experimental Example 5

[0122] Infrared spectroscopy was performed on bulk sodium metal, Al2O3 nanoparticles (the first additive used in Example 1), polydimethylsiloxane (the second additive used in Example 1), and basic electrolyte V in Comparative Example 5 at 25°C. The test results are as follows: Figure 13 As shown, the trimethylsilyl (Si-(CH3)3) group of polydimethylsiloxane has a characteristic peak at 1013 cm⁻¹. -1 ) and sodium hydroxyl group (Na-OH, characteristic peak 3635cm)-1 A spontaneous hydrolysis reaction and subsequent dehydration condensation reaction occur between them, ultimately producing sodium silicate (Si-O-Na, characteristic peak at 980 cm⁻¹). -1 ).

[0123] Experimental Example 6

[0124] The Al||Na half-cell I prepared in Example 13 was subjected to constant current discharge testing at 25°C. The test current density was 1 mA / cm². 2 The discharge time was 3 hours. After discharge, the battery was disassembled in an argon-atmosphere glove box (water content ≤0.01ppm, oxygen content ≤0.01ppm), and the aluminum foil with deposited sodium metal was removed. Time-of-flight secondary ion mass spectrometry (PHI nano-TOF3 equipment, using 30 kEV Bi3+ as the primary ion beam and 1 kEV Cs) was then performed. + (as a sputtered ion beam) (sputtering area: 100μm×100μm).

[0125] Test results are as follows Figure 14 As shown, CH- (attributed to methyl) and Si(CH3)2OAl- fragments are mainly present in the surface layer, while Si(CH3)2ONa - They are concentrated in the bottom layer near the bulk sodium metal. This indicates that the polydimethylsiloxane molecules act as a bridge between the nano-alumina and the sodium metal surface through the anchoring effect of silicon-oxygen bonds (Si-O-).

[0126] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section. The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention.

[0127] Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An electrolyte for fast charging of a negative electrode-free sodium-ion battery, which is prepared from raw materials including sodium salt, solvent and additives.

2. The electrolyte according to claim 1, characterized in that, The sodium salt is selected from one or more fluorinated sodium salts, preferably one or more fluorinated sodium phosphates, and the molar volume ratio of the sodium salt to the solvent is 3 mmol:(1.5-30.0) mL, preferably 3 mmol:(2.0-6.0) mL.

3. The electrolyte according to claim 1, characterized in that, The solvent is selected from one or more ether solvents, preferably from one or more chain ethers, and more preferably from one or more of dimethoxymethane (DMM), 1,2-dimethoxyethylene (DME), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (G2), and tetraethylene glycol dimethyl ether (G4).

4. The electrolyte according to claim 1, characterized in that, The additive includes a first additive, which is selected from one or more metal oxide nanoparticles, preferably from one or more of aluminum oxide, nickel oxide, magnesium oxide, copper oxide, zinc oxide and α-iron oxide nanoparticles, and the mass ratio of the first additive to the solvent is 1:(1-160), preferably 1:(3-140).

5. The electrolyte according to claim 4, characterized in that, The particle size of the metal oxide nanoparticles is 5-50 nm, preferably 5-35 nm, and more preferably 5-20 nm.

6. The electrolyte according to claim 4, characterized in that, The additive further includes a second additive, which is selected from one or more of titanate coupling agents, aluminum-titanium composite coupling agents, and organosilicon compounds, preferably selected from one or more organosilicon compounds, more preferably 3-isocyanopropyltriethoxysilane and / or polydimethylsiloxane. The volume ratio of the second additive to the solvent is 1:(60-240), preferably 1:(90-210).

7. A method for preparing an electrolyte for fast charging of a negative electrode-free sodium-ion battery according to any one of claims 1 to 6, characterized in that, The method involves adding sodium salt to a solvent to dissolve it, obtaining a sodium salt solution, adding additives to the sodium salt solution, and mixing thoroughly to obtain an electrolyte for fast charging of a negative electrode-free sodium-ion battery.

8. A fast-charging, negative-electrode-free sodium-ion battery, characterized in that, The electrolyte of the fast-charging, electrodeless sodium-ion battery is the electrolyte for fast charging of electrodeless sodium-ion batteries according to any one of claims 1 to 6.

9. The fast-charging, negative-electrode-free sodium-ion battery according to claim 8, characterized in that, The sodium metal battery without a negative electrode also includes a positive electrode, a separator, and a negative electrode current collector.

10. The fast-charging, negative-electrode-free sodium-ion battery according to claim 9, characterized in that, The positive electrode active material of the negative electrode-free sodium-ion battery is selected from one or more of polyanionic positive electrode materials, Prussian blue compound positive electrode materials, polymer positive electrode materials and transition metal oxides, preferably selected from one or more of phosphate positive electrode materials and transition metal oxides.

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