Secondary battery, electrolyte and method for supplementing metal m

Abstract

The application belongs to the field of electrolyte, and particularly relates to a metal M supplementing secondary battery, an electrolyte and a method, wherein the metal M supplementing electrolyte is a solution of a metal M supplementing additive comprising a structure of formula 1, a metal M conductive salt and a solvent; and the metal M supplementing electrolyte is an electrolyte for a metal M secondary battery without a negative electrode. Researches show that the physicochemical characteristics of the compound of formula 1, particularly the anion of formula 1, can adapt to the charge-discharge characteristics of the metal M secondary battery without a negative electrode, can preferentially discharge to realize homogenization of the metal M supplementing, effectively reduce side reactions, optimize the interface structure of the pole piece of the metal M secondary battery without a negative electrode, and thus can significantly improve the initial efficiency, capacity and cycle stability of the metal M secondary battery without a negative electrode.

Description

Technical Field

[0001] This invention relates to the field of metal M (M is an alkali metal) secondary batteries, and more specifically to the field of metal M secondary batteries without a negative electrode. Background Technology

[0002] With the increasing global demand for clean energy and efficient energy storage, metal-based secondary batteries (where M is an alkali metal, such as Li, Na, or K) have become a research hotspot due to their high energy density and long cycle life. However, these batteries still face many challenges in practical applications, especially in electrodeless battery designs, where low initial coulombic efficiency and irreversible metal ion loss are particularly prominent. In traditional alkali metal batteries, during the first charge, the electrolyte decomposes on the negative electrode surface to form a solid electrolyte interphase (SEI) film. This process consumes a large amount of active metal ions (such as lithium and sodium) from the positive electrode, leading to irreversible capacity loss. Furthermore, side reactions (such as electrolyte decomposition and dendrite growth) further exacerbate the consumption of active metals, significantly reducing the battery's initial coulombic efficiency and cycle stability. For electrodeless batteries, since the negative electrode relies solely on the current collector to deposit metal during the first charge, the problem of irreversible loss of active metals is even more severe, seriously restricting their practical application.

[0003] In existing technologies, the main methods for addressing this problem include optimizing electrode materials, introducing pre-metallized additives, or improving electrolyte formulations. For example, adding metal-containing compounds (such as Li5FeO4, lithium oxalate, sodium oxalate, etc.) to the positive electrode or introducing sacrificial additives into the electrolyte attempts to compensate for the metal ions consumed by SEI film formation and side reactions. However, these methods often have limitations: incomplete decomposition of positive electrode additives can leave harmful residues, affecting battery performance; while the low solubility and high decomposition potential of inorganic additives may lead to increased electrolyte viscosity or gas generation inside the battery, thereby damaging the battery's structural integrity. In addition, traditional additives may generate gaseous or solid byproducts during the reaction process, which not only fails to achieve uniform metal replenishment but may also disrupt the stability of the electrode-electrolyte interface. Therefore, developing electrolyte metal replenishment additives that do not generate gas and can stabilize the positive and negative electrode interfaces is crucial for addressing the irreversible loss of active ions in alkali metal ion secondary batteries and improving the overall energy density and cycle stability of the battery. Summary of the Invention

[0004] To address the problems existing in the prior art, the primary objective of this invention is to provide a metal-replenishing electrolyte suitable for negative electrode-free metal M secondary batteries (also known as negative electrode-free alkali metal secondary batteries or negative electrode-free batteries), aiming to significantly improve the performance of negative electrode-free metal M secondary batteries based on the innovative use of metal-replenishing additives that can adapt to the characteristics of negative electrode-free batteries.

[0005] A second objective of the present invention is to provide a secondary battery comprising the aforementioned supplementary metal M electrolyte.

[0006] The third objective of this invention is to provide a method for replenishing metal M in a secondary battery with metal M.

[0007] For batteries, adding certain metal supplements (M) can help replace active materials for irreversible metal supplementation, thus improving the battery's initial efficiency. However, for electrodeless metal-based secondary batteries, the highly active metal is directly exposed to the electrolyte, leading to more intense side reactions. If the added metal supplement reacts severely with the metal, or if the gaseous products derived from the metal supplement diffuse to the negative electrode side, the active metal on the negative electrode side will be consumed, rendering the compensation effect ineffective. Compared to conventional ion battery systems, electrodeless batteries also exhibit more pronounced characteristics such as metal dissolution and uneven deposition, making the development of metal supplements compatible with electrodeless batteries more challenging and demanding. To address this issue, this invention provides the following improvement:

[0008] A metal M supplement electrolyte is a solution comprising a metal M supplement additive of formula 1, a metal M conductive salt, and a solvent; the metal M supplement electrolyte is an electrolyte used in a negative electrode-less metal M secondary battery.

[0009] Formula 1;

[0010] In Formula 1, R1 to R6 are individually C1 to C4 alkyl groups;

[0011] M and Y are each at least one of Li, Na, and K.

[0012] The present invention demonstrates that the physicochemical characteristics of the compound of Formula 1, especially the anion of Formula 1, are adapted to the charge and discharge characteristics of a secondary battery without a negative electrode metal M. It can preferentially discharge to achieve homogenization and replenishment of metal M, effectively reduce side reactions, optimize the interface structure of the electrode in the battery without a negative electrode, and thus significantly improve the initial efficiency, capacity and cycle stability of the secondary battery without a negative electrode metal M.

[0013] The present invention shows that the structural control of the anion in Formula 1 is the key to adapting to the characteristics and requirements of the metal supplementation M in a secondary battery without a negative electrode metal M. Based on this, the present invention also shows that further optimization and control of the anion in Formula 1 can help to further improve its adaptability to the requirements of the metal supplementation M in a secondary battery without a negative electrode metal M.

[0014] Preferably, the metal supplement M additive of Formula 1 is an asymmetric compound, wherein the asymmetric compound refers to a compound in which the substituents R4 to R5 are identical and different from at least one of the substituents R1 to R3. Research in this invention shows that using this preferred asymmetric structure of Formula 1 helps to further improve the metal supplement M effect in metal-free secondary batteries, and helps to further improve their capacity, rate capability, and cycle stability.

[0015] In a further preferred embodiment, in Formula 1, R1 is a C2-C4 alkyl group; the remaining substituents are all methyl groups.

[0016] Preferably, in the electrolyte containing the metal M, when M is Na, Y in the additive of Formula 1 is Li.

[0017] The present invention demonstrates that, in the presence of the anion of Formula 1, further controlling M to be Li helps to further optimize the interface structure of the negative electrode-free sodium metal secondary battery, and helps to further improve the capacity, rate capability and cycle stability of the negative electrode-free sodium metal secondary battery.

[0018] In this invention, the metal M conductive salt is a known conductive salt that contains metal M and meets the requirements of suitable battery applications, such as at least one of LiPF6, NaPF6, LiFSI, LiTFSI, LiBF4, LiClO4, LiBOB, LiDFOB, NaOTf, NaFSI, KPF6, KFSI, KBF4, KTFSI, and KClO4.

[0019] In this invention, the solvent includes at least one of ester solvents and ether solvents.

[0020] In this invention, the ester solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0021] In this invention, the ether solvent includes at least one of 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DEGDME), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), and 1,3-dioxolane (DOL).

[0022] In this invention, the concentration of the metal M additive is 0.05~3 M, further can be 0.1~0.5 M, and even further can be 0.1~0.2 M; the concentration of the metal M conductive salt is 0.5~2 M, further can be 1~1.5 M.

[0023] The present invention also provides a secondary battery with supplemented metal M, which is a secondary battery without a negative electrode and metal M. It includes a cell and an electrolyte soaking the cell. The cell includes a positive electrode, a separator and a metal-free negative electrode that are sequentially combined. The electrolyte is the metal-supplemented electrolyte of the present invention.

[0024] This invention provides a negative electrode-free metal M secondary battery with added metal M electrolyte. Based on the innovative use of metal M additives in the electrolyte, it can solve the problems faced by metal M supplementation in negative electrode-free metal M secondary batteries, and achieve metal M supplementation in negative electrode-free metal M secondary batteries, thereby solving their capacity, rate capability and cycle stability.

[0025] In this invention, the positive electrode can be any positive electrode well-known in the field of negative electrode-free metal M secondary batteries. For example, it includes a current collector and a positive electrode material composited on its surface. The positive electrode material includes a positive electrode active material, a conductive agent, and a binder. The composition and ratio of the positive electrode active material, conductive agent, and binder can be those known in the industry. For example, sodium battery positive electrode materials include at least one of sodium iron phosphate, layered oxide sodium salt, sodium vanadium phosphate, and Prussian blue. Lithium battery positive electrode active materials include at least one of lithium iron phosphate and NCM layered oxide lithium salt. Potassium battery positive electrode active materials include at least one of potassium ferrocyanide, transition metal potassium phosphate, and transition metal potassium pyrophosphate.

[0026] The diaphragm is at least one of polyethylene diaphragm, polypropylene diaphragm, or glass fiber.

[0027] The metal-free M negative electrode sheet is a conductive metal current collector or a carbon-coated current collector.

[0028] In this invention, the metal M secondary battery without a negative electrode is further described as a sodium secondary battery without a negative electrode.

[0029] The present invention also provides a method for replenishing metal M in a secondary battery without a negative electrode, using a compound with the structure of Formula 1 of the present invention as a metal M replenishing additive to prepare a secondary battery without a negative electrode that has the ability to replenish metal M.

[0030] The metal replenishment method M described in this invention can include the following two types:

[0031] Method 1: The negative electrode-free metal M secondary battery is a newly assembled battery, and its electrolyte is the metal M electrolyte with added components of Formula 1 as described in this invention.

[0032] Method 2: The negative electrode-free metal M secondary battery is an old battery that needs to be repaired after cycling. The metal M replenishing electrolyte of the present invention or the metal M replenishing additive of Formula 1 therein is added to the electrolyte of the old battery to obtain an old battery with metal M replenishing function.

[0033] Beneficial effects

[0034] (1) The present invention shows that the metal supplement M additive of Formula 1 has excellent solubility and stability, and can be used in a wide concentration range of 0.05~3 Mol / L, which is far superior to traditional metal supplement M additives. Thus, the amount of metal supplement M can be more flexibly controlled to meet the needs of different battery systems. Secondly, this additive can be adapted to the charging and discharging characteristics of sodium batteries without negative electrodes. It can release sodium ions through a highly selective and efficient self-sacrificing reaction during the first charge. Its decomposition potential matches the normal operating voltage of the battery. It can be completely converted into an active sodium source, and no gas is generated during the compensation process. It will not leave harmful substances or cause the battery to swell. It solves the problem that traditional additives affect battery performance due to incomplete decomposition or gas generation.

[0035] (2) The additive of Formula 1 can synergistically induce the formation of a thin and uniform solid electrolyte interphase (SEI) film at the positive and negative electrode interfaces during the metal M replenishment process, significantly improving the interfacial ion conductivity and mechanical stability, thereby reducing side reactions and metal M (such as sodium) loss during cycling, and enabling the battery to maintain a high capacity retention rate after 300 cycles. In contrast, existing technologies (such as NaSCN or NaNO2 additives) can improve the initial charge capacity, but they will deteriorate the electrode interface, leading to rapid degradation of cycle performance. The additive of this invention can also be added to the assembled battery by injection to achieve secondary activation of battery performance, providing an innovative solution for the long-term cycle stability of sodium-free batteries. In summary, this additive has the advantages of high metal M replenishment efficiency, interface optimization capability and process compatibility, and has significant advantages in improving the energy density and cycle life of alkali metal batteries. Attached Figure Description

[0036] Figure 1 These are electrochemical and electrode optical images of Example 1, wherein... Figure 1 The first charging curves of 0.2 M diethylene glycol dimethyl ether solution (Formula A) and 1 M NaPF6 diethylene glycol dimethyl ether solution (pristine) in Cu / / Al@C batteries are shown. Figure 1 Image b is an optical microscope image of the negative electrode side of the copper foil of a battery without type A electrode after charging. Figure 1 c is an optical image of the copper foil on the negative side of the battery of type A after charging.

[0037] Figure 2 The diagram shows the swelling of the pouch battery in Example 2 before and after charging. Figure 2 'a' represents the initial battery diagram; Figure 2 Figure b shows the battery diagram when the initial battery is charged to 3.9V.

[0038] Figure 3 Example 3 shows the first charge-discharge curves of sodium-ion batteries without negative electrodes using different additives. Figure 3 'a' represents the initial charge-discharge curve of electrolyte with additive formula A. Figure 3 b represents the initial charge-discharge curve of the electrolyte without the addition of formula A. Figure 3 c represents the initial charge-discharge curve of the electrolyte with 0.1 M NaSCN added. Figure 3 d represents the initial charge-discharge curve after the addition of NaNO2.

[0039] Figure 4 This is a long-cycle stability graph of the sodium-free battery without a negative electrode in Example 3.

[0040] Figure 5 The first charge-discharge curve of the negative electrode-free lithium battery in Example 5 is shown below. Figure 5 'a' represents the initial charge-discharge curve with 0.2 M E added; Figure 5 b represents the initial charge-discharge curve without the addition of E. Detailed Implementation

[0041] Example 1

[0042] A sodium-free battery was assembled using copper foil as the negative electrode, carbon-coated aluminum foil as the positive electrode, and polyethylene film as the separator. The electrolyte in the experimental group contained 0.2M additive (Formula A). ), 1M NaPF6 diethylene glycol dimethyl ether solution.

[0043] The electrolyte in the control group was a diethylene glycol dimethyl ether solution containing 1M NaPF6 without the addition of Formula A.

[0044] The assembled negative electrode-free battery was subjected to constant current and constant voltage charge and discharge, with a charging cutoff voltage of 4V, a cutoff current of 0.05mA, a current density of 100mA / g, and a test temperature of 30℃.

[0045] like Figure 1 As shown in Figure a, the battery using the electrolyte from the experimental group had a charging capacity of 0.39 mAh, while the battery from the control group had a charging capacity of only 0.03 mAh, indicating that the additive achieved self-sacrificing sodium replenishment.

[0046] The batteries in the experimental and control groups were disassembled, and the copper foil on the negative electrode side was characterized using optical microscopy. Figure 1 As shown in b, no sodium deposition was observed in the copper foil of the control group, while Figure 1 As shown in Figure c, sodium with a metallic luster was observed deposited on the copper foil surface of the experimental group. These results strongly demonstrate that formula A can perform self-sacrificial sodium replenishment.

[0047] Example 2

[0048] NFPP electrode (positive electrode): 92 wt.% NFPP (sodium iron pyrophosphate), 3 wt.% carbon black, 1 wt.% carbon nanotubes and 4 wt.% PVDF are mixed in NMP to form a slurry, which is then coated on a carbon-coated aluminum foil and dried under vacuum at 80°C to form single-sided (12.4 mg / cm²) or double-sided (30 mg / cm²) electrodes, which are used in button batteries and pouch batteries, respectively.

[0049] Using carbon-coated aluminum foil as the negative electrode, NFPP electrode as the cathode, and polyethylene film as the separator, and with the electrolyte from the experimental group in Example 1 as the electrolyte, a 1Ah sodium-filled pouch battery without a negative electrode was assembled. It was charged at a constant current rate of 0.5C to 3.9V, and the swelling of the pouch battery before and after the charging was observed. Figure 2 As shown, the battery cell using an electrolyte containing 0.2 M Formula A additive did not exhibit significant bulging after charging. This indicates that Formula A sodium replenisher does not generate gas during the sodium replenishment process, which is of great significance for the structural integrity of the battery, as gas generation would deteriorate the contact behavior between electrode materials.

[0050] Example 3

[0051] A 2032 button-type sodium metal battery without a negative electrode was assembled in a glove box with a high-purity argon atmosphere (O2 and H2O content both < 0.1 ppm). The negative electrode was a 14 mm diameter carbon-coated aluminum foil disc (carbon layer facing the positive electrode), the positive electrode was the NFPP electrode of Example 2, and the separator was a two-layer composite membrane consisting of a porous single-layer polypropylene membrane and glass fiber.

[0052] Electrolyte: (a) Group: Electrolyte of the experimental group in Example 1; (b) Group: Electrolyte of the control group in Example 1. (c) Group: Compared with (a), the only difference is that additive A is replaced with NaSCN. Due to solubility issues, the concentration of NaSCN in the electrolyte is controlled at 0.1M. (d) Group: Compared with (a), the only difference is that additive A is replaced with NaNO2. Due to solubility issues, the concentration of NaNO2 in the electrolyte is controlled at 10wt.%. Although the concentrations of additives in groups (a), (c), and (d) are different, the sodium supplementation capacity in each group is controlled to be the same, thus allowing for a single-factor comparison of the differences in performance caused by the additives.

[0053] The batteries in each group were subjected to constant current and constant voltage charge-discharge at a current density of 100 mA / g, with a cutoff current of 5 mA / g. The results are shown below. Figure 3While using NaSCN and NaNO2 can improve the charge specific capacity of a cathode-free sodium battery, its discharge specific capacity is lower than that of an unmodified cathode-free battery. This indicates that traditional NaSCN and NaNO2 additives cannot effectively replenish sodium in cathode-free sodium batteries; instead, they deteriorate the positive and negative electrode interface, leading to rapid capacity degradation (e.g., ...). Figure 4 (As shown).

[0054] Example 4

[0055] Compared with group (a) of Example 3, the only difference is that the type of additive in the electrolyte is changed. The experimental groups are as follows:

[0056] Group A: Additive is formula B ( ):

[0057] Group B: The additive is formula C ( ):

[0058] Group C: Additive is formula D ( ):

[0059] Group D: Additives are :

[0060] The addition weight of the additives in each group and other operations and parameters are the same as in Example 1;

[0061] The results are shown in Table 1.

[0062]

[0063] As shown in Table 1, groups A, B, and C are asymmetric additives. Compared to Example 3, they can further enhance the sodium replenishment capacity of the anode-free material at slightly lower effective Na levels, improving capacity and stability, and exhibiting superior performance. Furthermore, group D shows that adding Li-containing additives to the anode-free sodium battery can achieve better anode-free sodium metal compatibility, resulting in even better performance.

[0064] Example 5

[0065] Negative electrode-free lithium battery solution:

[0066] Negative electrode: Commercially available copper foil is used as the negative electrode;

[0067] Positive electrode: LFP electrode: consisting of aluminum foil and positive electrode material (including lithium iron phosphate, carbon black and PVDF in a weight ratio of 90:5:5).

[0068] Diaphragm: Polypropylene membrane;

[0069] Electrolyte: Control group: LiFSI solution with DME / DOL ratio of 1:1 was used as the base electrolyte; Experimental group electrolyte: 0.2M of E (…) was added to the base electrolyte. ).

[0070] Assemble a negative electrode-free lithium battery.

[0071] Test results are as follows Figure 5 As shown, constant current and constant voltage charge-discharge tests were conducted at a current density of 100 mA / g. The results showed that the negative electrode-free lithium battery with 0.2 M E electrolyte had a high discharge specific capacity of 169.5 mAh / g, while the negative electrode-free sodium battery assembled without E electrolyte had a discharge specific capacity of only 134.7 mAh / g. This indicates that E can effectively compensate for the problem of insufficient lithium source in the battery.

[0072] Example 6

[0073] Potassium battery solution without negative electrode:

[0074] In order to examine the formula F( To assess the potassium supplementation effect, a Prussian blue analogue (KFeHCF) was used as the positive electrode active material (mixed with Super P and PVDF at a mass ratio of 8:1:1 and coated onto aluminum foil). Carbon-coated copper foil was used as the negative electrode to assemble a negative electrode-free potassium battery. A Celgard 2325 three-layer composite separator (PP / PE / PP) was employed. The experimental group's electrolyte consisted of 0.8 M KPF6 / EC:DEC (1:1 v / v) with 0.1, 0.5, 1, 2, and 3 M F additives. The control group used the same basic electrolyte system. A 1 Ah soft-pack battery was assembled (electrolyte volume 3 mL / Ah), and electrochemical performance was tested after 48 hours of static aging. Table 2 shows the initial charge-discharge capacity and the charge-discharge capacity after 100 cycles of potassium-ion batteries using different concentrations of F additive. Constant current charge-discharge tests were conducted at a current density of 100 mA / g. The results show that increasing the concentration of F can improve the charge-discharge capacity of the battery (after 3 M, solute precipitates from F, and its solubility is about 3 mol / L). This indicates that F has a good effect on compensating for irreversible potassium ion loss.

[0075] Table 2. Initial charge-discharge capacity and discharge capacity after 100 cycles of batteries with different types of F added to the base electrolyte.

[0076]

[0077] Example 7

[0078] Compared to Example 4, the only difference is that the type of additive in the negative electrode-free sodium battery is changed. The experimental groups are as follows:

[0079] Group A: Electrolyte of formula A with a concentration of 0.1M;

[0080] Group B: Electrolyte of formula E with a concentration of 0.1M;

[0081] Group C: Electrolyte of formula F with a concentration of 0.1M;

[0082] The sodium electrodes without negative electrodes of each electrolyte group were tested at a rate of 2C, and the relevant performance is shown in Table 3.

[0083]

[0084] As shown in Table 3, when Formula E is used in sodium-ion batteries without a negative electrode, lithium-containing compensating additives can be added, resulting in better cycle stability.

Claims

1. A replenishing metal M electrolyte, characterized in that, A solution comprising a metal M supplementing additive of structure of formula 1, a metal M conductive salt and a solvent; the metal M supplementing electrolyte is an electrolyte for a metal M secondary battery without a negative electrode; Formula 1 In formula 1, R1-R6 are independently C1-C4 alkyl; M and Y are independently at least one of Li, Na and K; The metal M supplementing additive of structure of formula 1 is an asymmetric compound, which means that R4-R5 substituents are the same, and different from at least one of R1-R3 substituents.

2. The metal M supplement electrolyte according to claim 1, wherein M is Na and Y is Li.

3. The metal M supplement electrolyte according to claim 1, wherein The metal M conductive salt comprises at least one of LiPF6, NaPF6, LiFSI, LiTFSI, LiBF4, LiClO4, LiBOB, LiDFOB, NaOTf, NaFSI, KPF6, KFSI, KBF4, KTFSI, KClO4; The solvent comprises at least one of an ester solvent and an ether solvent.

4. The metal M supplement electrolyte according to any one of claims 1 to 3, wherein The concentration of the metal M supplementing additive is 0.05-3 M, and the concentration of the metal M conductive salt is 0.5-2 M.

5. A secondary battery which supplements a metal M, which is a negative-electrode-free metal M secondary battery, comprising a cell and an electrolyte solution which soaks the cell, wherein The battery cell comprises a positive electrode sheet, a separator and a metal M-free negative electrode sheet which are sequentially compounded, characterized in that the electrolyte is the metal M supplementing electrolyte according to any one of claims 1-4.

6. The secondary battery according to claim 5, wherein The positive electrode sheet comprises a current collector and a positive electrode material compounded on the surface of the current collector, and the positive electrode material comprises at least one of sodium iron phosphate, sodium salt of layered oxide, sodium vanadium phosphate, Prussian blue, lithium iron phosphate, NCM lithium salt of layered oxide, potassium ferrocyanide, potassium phosphate salt of transition metal, potassium pyrophosphate salt of transition metal; The separator is at least one of a polyethylene separator, a polypropylene separator or a glass fiber separator; The metal M-free negative electrode sheet is a conductive metal current collector or a carbon-coated current collector.

7. A method of supplementing a metal M in a metal M-free secondary battery, characterized by, The metal M supplementing additive of formula 1 in the metal M supplementing electrolyte according to any one of claims 1-4 is used to prepare a metal M secondary battery without a negative electrode with metal M supplementing capability.

8. The method of supplementing metal M according to claim 7, wherein The metal M secondary battery without a negative electrode is a newly assembled battery, and the electrolyte thereof is the metal M supplementing electrolyte according to any one of claims 1-4.

9. The method of supplementing metal M according to claim 7, wherein, The metal M secondary battery without a negative electrode is a used battery which needs to be repaired after cycling, and the metal M supplementing electrolyte according to any one of claims 1-4 or the metal M supplementing additive of formula 1 therein is added to the electrolyte of the used battery to obtain a used battery with metal M supplementing function.

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