Electrolyte for alkali metal batteries and alkali metal batteries thereof

Abstract

The present invention provides an electrolyte for an alkali metal battery and an alkali metal battery. The electrolyte includes a lithium salt, a non-aqueous organic solvent, and an additive. The additive includes a nitrogen-containing boron heterocyclic compound represented by Structural Formula I, where n is 2, 3, or 4, and R1 is a C1-C 10 hydrocarbon group or -OR3. The R1s in the nitrogen-containing boron heterocyclic compound are the same or not completely the same, and at least one R1 is -OR3. R3 is as shown in Structural Formula II, Structural Formula III, Structural Formula III, or Structural Formula V. R4 to R6 are each independently hydrogen, a C1-C5 hydrocarbon group, or R7, and R7 is as shown in Structural Formula VI. The R2s in the nitrogen-containing boron heterocyclic compound are the same or not completely the same, and R2 is hydrogen, an aryl group, or a C1-C 10 hydrocarbon. The alkali metal battery of the present invention has better cycling performance and can also exert the high energy density advantage of the alkali metal negative electrode.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and more particularly to an electrolyte, and even more particularly to an electrolyte for an alkali metal battery and an alkali metal battery using the same. Background Art

[0002] Currently, lithium-ion batteries have been widely used in technical products such as automobiles and mobile phones. Commercial lithium-ion batteries mainly use graphite as the negative electrode material, and their capacity utilization has approached the theoretical value of graphite (372 mAh / g). It is difficult to significantly improve the capacity of lithium-ion batteries by treating graphite. It is difficult to meet the requirements of rechargeable batteries with long-lasting and high energy density.

[0003] Lithium metal negative electrodes have extremely high theoretical capacities and the most negative equilibrium electrode potentials, and are known as the "holy grail" electrodes in rechargeable batteries. However, the reserves of lithium are very low, and the consumption in the lithium battery market is huge, resulting in its high price. In contrast, sodium and potassium metals have the advantages of rich reserves and low prices, and have also become a research hotspot for next-generation negative electrode materials. However, all three alkali metal negative electrodes have the common problem of dendritic growth, resulting in poor safety performance, low energy density, short cycle life, etc. of the battery, seriously hindering the application of alkali metal negative electrodes in actual batteries.

[0004] Therefore, how to effectively improve the surface properties of the lithium metal electrode and inhibit the formation of lithium dendrites is the key point to be solved for the further development of alkali metal batteries. Summary of the Invention

[0005] In order to solve the above problems, an object of the present invention is to provide an electrolyte for an alkali metal battery and an alkali metal battery using the same, wherein the additive can effectively inhibit the growth of dendrites and improve the cycle performance of the alkali metal battery.

[0006] To achieve the above object, in a first aspect of the present invention, there is provided an electrolyte for an alkali metal battery, comprising an alkali metal salt, a non-aqueous organic solvent, and an additive, wherein the additive comprises a nitrogen-containing boron heterocyclic compound represented by Structural Formula I,

[0007]

[0008] wherein n is 2, 3 or 4, R1 is a C1-C hydrocarbon group or -OR3, the R1s in the nitrogen-containing boron heterocyclic compound are the same or not completely the same, and at least one R1 is -OR3, R3 is as shown in Structural Formula II, Structural Formula III, Structural Formula III or Structural Formula V, R4 to R6 are each independently hydrogen, a C1-C5 hydrocarbon group or R7, R7 is as shown in Structural Formula VI, m is 1, 2 or 3, R8 and R 10 are each independently hydrogen, an aryl group or a C1-C hydrocarbon group, and R9 is a C1-C 10 are each independently hydrogen, an aryl group or a C1-C 10 hydrocarbon group, and R9 is a C1-C10 The hydrocarbon group, where R2 in the nitrogen-containing boron heterocyclic compound is the same or not completely the same, and R2 is hydrogen, an aromatic group or a C1-C 10 hydrocarbon,

[0009]

[0010] The additive in the electrolyte of the present invention includes a nitrogen-containing boron heterocyclic compound shown in Structural Formula I. This nitrogen-containing boron heterocyclic compound has an -OR3 group, where R3 is a benzo-oxygen heterocyclic compound. The double bond in the ring and the ester group on the ring can react at the electrode / electrolyte interface to form an organic SEI film with better stability. The N-B-N-B structure is deposited at the electrode / electrolyte interface to form a LiN x B y O Z inorganic SEI film. The double-layer SEI film formed by these two films has a synergistic effect. Therefore, it can effectively inhibit the growth of lithium dendrites, improve the cycling performance of the alkali metal battery, and also ensure the high energy density advantage of the alkali metal negative electrode.

[0011] The second aspect of the present invention provides an alkali metal battery, including a positive electrode material, a negative electrode material, and an electrolyte. The electrolyte is the aforementioned electrolyte applied to the alkali metal battery, and the negative electrode material is lithium metal, lithium alloy, sodium metal, sodium alloy, potassium metal, or potassium alloy.

[0012] The negative electrode material of the alkali metal battery of the present invention is lithium metal, lithium alloy, sodium metal, sodium alloy, potassium metal, or potassium alloy. Therefore, the battery has a high capacity, and the electrolyte includes a nitrogen-containing boron heterocyclic compound shown in Structural Formula I, which can inhibit dendrite growth and improve the cycling performance of the alkali metal battery. Detailed Embodiments

[0013] The alkali metal battery of the present invention includes a positive electrode material, a negative electrode material, and an electrolyte. The alkali metal battery of the present invention refers to a battery with an alkali metal substance as the negative electrode material. Specifically, the negative electrode material is lithium metal, lithium alloy, sodium metal, sodium alloy, potassium metal, or potassium alloy. Specifically, when the negative electrode material is lithium metal or lithium alloy, the positive electrode material is lithium cobaltate material, lithium iron phosphate material, nickel cobalt manganese oxide, or nickel cobalt aluminum oxide. The lithium cobaltate material is lithium cobaltate or lithium cobaltate doped and coated and modified. The lithium iron phosphate material is lithium iron phosphate or lithium iron phosphate doped and coated and modified. The chemical formula of nickel cobalt manganese oxide is LiNi x Co y Mn z M (1-x-y-z) O2, and the chemical formula of nickel cobalt aluminum oxide is LiNi x Co y Al z N (1-x-y-z)O2, where M is at least one of Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, and Ti, N is at least one of Mg, Cu, Zn, Sn, B, Ga, Cr, Sr, V, and Ti, 0 ≤ x < 1, 0 < y < 1, 0 < z < 1, and x + y + z ≤ 1. When the negative electrode material is sodium metal, sodium alloy, potassium metal, or potassium alloy, the positive electrode material is a composite metal oxide similar to the positive electrode of a lithium metal battery.

[0014] The electrolyte of the present invention includes an alkali metal salt, a non-aqueous organic solvent, and an additive. The additive includes a nitrogen-containing boron heterocyclic compound represented by Structural Formula I.

[0015]

[0016] Wherein, n is 2, 3, or 4, R1 is a C1-C 10 hydrocarbyl group or -OR3. The R1s in the nitrogen-containing boron heterocyclic compound are the same or not completely the same, and at least one R1 is -OR3. R3 is as shown in Structural Formula II, Structural Formula III, Structural Formula III, or Structural Formula V. R4-R6 are each independently hydrogen, a C1-C5 hydrocarbyl group, or R7. R7 is as shown in Structural Formula VI. m is 1, 2, or 3. R8 and R 10 are each independently hydrogen, an aryl group, or a C1-C 10 hydrocarbyl group. R9 is a C1-C 10 hydrocarbyl group. The R2s in the nitrogen-containing boron heterocyclic compound are the same or not completely the same, and R2 is hydrogen, an aryl group, or a C1-C 10 hydrocarbyl group.

[0017]

[0018] Further, n is 2 or 3, R1 is a C1-C3 hydrocarbyl group or -OR3, R4-R6 are hydrogen or R7, m is 1 or 2, R8 and R 10 are each independently hydrogen or a C1-C4 hydrocarbyl group, R9 is a C1-C3 hydrocarbyl group, and R2 is hydrogen or a C1-C4 hydrocarbyl group.

[0019] Further, the nitrogen-containing boron heterocyclic compound accounts for 0.01-5% of the sum of the masses of the alkali metal salt, the non-aqueous organic solvent, and the additive, preferably 0.05-1%, and specifically but not limited to 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%. When its content is less than 0.01%, an SEI film cannot be uniformly formed on the surface of the alkali metal negative electrode, so the desired effect cannot be obtained. On the contrary, when the content exceeds 5%, unnecessary reactions may occur during the driving of the alkali metal battery, thereby degrading the performance of the alkali metal battery.

[0020] Further, the nitrogen-containing boron heterocyclic compound is at least one of those shown in Compounds 1-6, preferably Compound 5.

[0021]

[0022]

[0023] The nitrogen-containing boron heterocyclic compound of the present invention can be obtained by a substitution reaction of coumarin compounds (such as Compounds 7-12) and nitrogen-containing boron heterocyclic chloride compounds (such as Compounds 13-18).

[0024]

[0025]

[0026] Further, the alkali metal salt is a lithium salt, a sodium salt or a potassium salt. Considering the ionic conductivity, solubility, etc. in the electrolyte, the alkali metal salt accounts for 6.5-15.5% of the total mass of the alkali metal salt, non-aqueous organic solvent and additive. The content of the alkali metal salt can specifically but not limited to be 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 11%, 12%, 13%, 14%, 15%, 15.5%.

[0027] The lithium salt is one or more of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiSbF6 (lithium hexafluoroantimonate), LiPF2O2 (lithium difluorophosphate), LiDTI (lithium 4,5-dicyano-2-trifluoromethylimidazole), LiBOB (lithium bis(oxalato)borate), LiDFOB (lithium difluoro(oxalato)borate), LiFSI (lithium bis(fluorosulfonyl)imide), LiN(SO2RF)2 and LiN(SO2F)(SO2RF), where RF = CnF 2n+1 and n is an integer from 1 to 10.

[0028] The sodium salt is one or more of NaPF6 (sodium hexafluorophosphate), NaBF4 (sodium tetrafluoroborate), NaClO4 (sodium perchlorate), NaAsF6 (sodium hexafluoroarsenate), NaSbF6 (sodium hexafluoroantimonate), NaPF2O2 (sodium difluorophosphate), NaDTI (sodium 4,5-dicyano-2-trifluoromethylimidazole), NaBOB (sodium bis(oxalato)borate), NaDFOB (sodium difluoro(oxalato)borate), NaFSI (sodium bis(fluorosulfonyl)imide), NaN(SO2RF)2 and NaN(SO2F)(SO2RF), where RF = CnF 2n+1 and n is an integer from 1 to 10.

[0029] The potassium salt is one or more of KPF6 (potassium hexafluorophosphate), KBF4 (potassium tetrafluoroborate), KClO4 (potassium perchlorate), KAsF6 (potassium hexafluoroarsenate), KSbF6 (potassium hexafluoroantimonate), KPF2O2 (potassium difluorophosphate), KDTI (potassium 4,5-dicyano-2-trifluoromethylimidazole), KBOB (potassium bis(oxalato)borate), KDFOB (potassium difluorooxalate borate), KFSI (potassium bis(fluorosulfonyl)imide), KN(SO2RF)2 and KN(SO2F)(SO2RF), where RF = CnF 2n+1 , and n is an integer from 1 to 10.

[0030] Further, the organic solvent is at least one of a chain carbonate, a cyclic carbonate, a carboxylic acid ester, and a lactone. The organic solvent is at least one of a chain carbonate, a cyclic carbonate, a carboxylic acid ester, and a lactone. Among them, the chain carbonate can be at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (PMC), and ethyl propyl carbonate (PEC). The cyclic carbonate can be at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), butylene carbonate, and pentylene carbonate. The carboxylic acid ester can be at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The lactone can be at least one of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0031] The following specific examples are used to further illustrate the purpose, technical solutions, and beneficial effects of the present invention, but do not constitute any limitation to the present invention. For those not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer can be followed. For the reagents or instruments not specified in the manufacturer, they are all conventional products that can be obtained through commercial channels.

[0032] Example 1

[0033] (1) Preparation of the electrolyte: In a vacuum glove box with an argon atmosphere and a water content < 1 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed according to a weight ratio of EC / EMC = 1:1. Then, each additive was added, dissolved, and stirred well, and then a lithium salt was added. After mixing evenly, the electrolyte was obtained.

[0034] (2) Preparation of the positive electrode: LiNi 0.6 Co 0.2 Mn 0.2 O2, the binder PVDF, and the conductive agent SuperP were mixed evenly according to a mass ratio of 95:2:3 to form a positive electrode slurry of an alkali metal battery with a certain viscosity. After the mixed slurry was coated on both sides of the aluminum foil, it was dried and roll-pressed to obtain the positive electrode sheet.

[0035] (3) Preparation of the separator: Polyethylene (PE) with a thickness of about 15 μm is used as the separator membrane.

[0036] (4) Preparation of the negative electrode: By means of physical roller pressing, metallic lithium is compounded onto a current collector copper foil with a thickness of about 10 μm. The pressure of the roller is adjusted to enable double-sided lithium coating on the copper current collector, and the thickness of the coated lithium is controlled to be about 35 μm, thus obtaining a lithium-copper composite tape negative electrode. Then, after cutting and slitting, it is placed in a dry argon atmosphere glove box for storage and standby.

[0037] (5) Preparation of the alkali metal battery: The positive electrode, the separator membrane, and the lithium-copper composite tape negative electrode are stacked in sequence, and then stacked as required. After the tabs are welded, they are placed in the aluminum-plastic film of the battery outer package. The prepared electrolyte is injected into the dried bare battery cell, and then vacuum packaging, standing, formation (constant current charging at 0.05C to 3.6V, and then constant current charging at 0.1C to 3.9V), shaping, capacity testing and other processes are carried out successively, and finally a 1 Ah soft-pack alkali metal battery is obtained.

[0038] The electrolyte formulations of Examples 2 to 9 and Comparative Examples 1 to 3 are shown in Table 1, and the steps for preparing the electrolyte and the battery are the same as those in Example 1.

[0039] Table 1 Electrolyte components of each example

[0040]

[0041]

[0042] The alkali metal batteries prepared in Examples 1 to 9 and Comparative Examples 1 to 2 are respectively subjected to a cycle test, and the specific test conditions are as follows. The performance test results are shown in Table 2.

[0043] (1) Cycle performance test

[0044] The alkali metal batteries of Examples 1 to 9 and Comparative Examples 1 to 2 are subjected to one 0.5C / 0.5C charge and discharge at 25 °C (the battery discharge capacity is C0), the upper limit voltage is 4.55V, and then 0.5C / 0.5C charge and discharge are carried out at room temperature for 300 cycles (the battery discharge capacity is C1), and the capacity retention rate = (C1 / C0) * 100%

[0045] Table 2 Performance test results of each example

[0046]

[0047]

[0048] As can be seen from the results in Table 2, the cycling performance of Examples 1-9 is better than that of Comparative Examples 1-2. This is because the additives in Examples 1-9 include a nitrogen-containing boron heterocyclic compound shown in Structural Formula I. This nitrogen-containing boron heterocyclic compound has an -OR3 group, where R3 is a benzo-oxygen-containing heterocyclic compound. The double bond in the ring and the ester group on the ring of this compound can react at the electrode / electrolyte interface to form an organic SEI film with better stability. The N-B-N-B structure is deposited at the electrode / electrolyte interface to form an inorganic SEI film of LiN x B y O Z The double-layer SEI film formed by these two films has a synergistic effect. Therefore, it can effectively inhibit the growth of lithium dendrites, improve the cycling performance of the alkali metal battery, and ensure the high energy density advantage of the alkali metal negative electrode. In Comparative Example 2, the additive is coumarin, which also has a double bond in the ring and an ester group on the ring, but it can only form a single organic SEI film, so the effect of inhibiting lithium dendrites is limited.

[0049] Comparing Examples 1-5 and Example 7, it can be seen that when the nitrogen-containing boron heterocyclic compound is Compound 5, its cycling performance is better. This may be because this compound not only has more N-B-N-B structures, but also the organic SEI film formed by the benzo-oxygen-containing heterocyclic compounds in the ortho position is more stable.

[0050] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An electrolyte for an alkali metal battery, comprising an alkali metal salt, a non-aqueous organic solvent, and an additive, characterized in that, The additive includes a nitrogen-containing boron heterocyclic compound, and the nitrogen-containing boron heterocyclic compound is at least one of those shown by Compounds 1-6. Compound 1 Compound 2 Compound 3 Compound 4 Compound 5 Compound 6.

2. The electrolyte for an alkali metal battery according to claim 1, characterized in that, The nitrogen-containing boron heterocyclic compound accounts for 0.01-5% of the sum of the masses of the alkali metal salt, the non-aqueous organic solvent, and the additive.

3. The electrolyte for an alkali metal battery according to claim 1, characterized in that, The alkali metal salt is a lithium salt, a sodium salt, or a potassium salt.

4. The electrolyte for an alkali metal battery according to claim 3, characterized in that, The alkali metal salt accounts for 6.5-15.5% of the sum of the masses of the alkali metal salt, the non-aqueous organic solvent, and the additive.

5. The electrolyte for an alkali metal battery according to claim 1, wherein The organic solvent is at least one of a chain carbonate, a cyclic carbonate, a carboxylic acid ester, and a lactone.

6. The electrolyte for an alkali metal battery according to claim 5, characterized in that, The organic solvent is at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, fluoroethylene carbonate, butylene carbonate, pentylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

7. An alkali metal battery, comprising a positive electrode material, a negative electrode material, and an electrolyte, characterized in that, The electrolyte is the electrolyte for an alkali metal battery according to any one of Claims 1-6, and the negative electrode material is lithium metal, a lithium alloy, sodium metal, a sodium alloy, potassium metal, or a potassium alloy.

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