Non-aqueous electrolyte and its alkali metal ion battery

Abstract

The present invention provides a non-aqueous electrolyte and an alkali metal ion battery thereof. The non-aqueous electrolyte includes an electrolyte salt, a non-aqueous organic solvent, and an additive, wherein the additive includes Compound A having the following structure. By using Compound A as an additive in the present invention, its structure contains a uracil structure and a pinacol borate structure. Through the synergistic effect of these two structures, the high-temperature cycle performance and high-temperature storage performance of the alkali metal ion battery at a high voltage of 4.5 V can be effectively improved, and at the same time, the impedance of the battery can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolytes, and in particular to a non-aqueous electrolyte and an alkali metal ion battery. Background Art

[0002] As a new battery technology, alkali metal ion batteries have received extensive attention and research in recent years. Alkali metal ion batteries, especially lithium ion batteries, are known for their high energy density and can provide long-term and high-intensity power support. At the same time, compared with traditional batteries, alkali metal ion batteries have a longer cycle life and can be charged and discharged multiple times without significantly reducing performance. With the rapid development of the electric vehicle industry, alkali metal ion batteries, as the core power source, have a continuous growing market demand. However, as people's understanding of battery usage conditions deepens, it is found that in a high-temperature environment, alkali metal ions may evaporate from the solid surface, resulting in a decrease in the metal content inside the battery, thereby affecting the battery performance. In addition, alkali metals are prone to react with carbon-containing fuels or other materials to form catalytically inactive compounds such as aluminosilicates, which will reduce the reactivity of the materials and the overall performance of the battery. At the same time, at high temperatures, alkali metals may corrode the metal components, electrolytes, and separators inside the battery, resulting in a decrease in battery performance or even failure. This corrosion effect may accelerate the battery aging process and shorten the battery life. This is because a series of changes will occur in the alkali metal ion battery system under high-temperature conditions. For example, when the negative electrode material is formed in the alkali metal ion battery, an SEI film will be formed on the surface. The SEI film will dissolve and be damaged under high-temperature conditions, thus affecting the battery cycle performance. At the same time, when the battery is stored in a high-temperature environment for a long time, the electrolyte will volatilize or undergo reduction decomposition, causing the "gas swelling" problem of the battery. Therefore, when facing high-temperature usage conditions, the design of the non-aqueous electrolyte of the alkali metal ion battery must consider the compatibility between the positive and negative electrode materials of the alkali metal ion battery and the electrolyte under high-temperature conditions, so as to reduce the probability of the electrolyte reacting with the positive and negative electrodes and improve the stability of the SEI film. At present, some researchers in the industry can solve the gas swelling problem of the battery to a certain extent by adding a certain amount of special additives, but it seriously affects the high-temperature cycle performance of the alkali metal ion battery. At the same time, some researchers can construct a firm SEI film on the cathode and anode by adding special additives, thereby significantly improving the high-temperature and high-pressure performance of the soft-pack full battery. However, due to its large interfacial impedance, it affects the battery cycle performance. Therefore, developing a new non-aqueous electrolyte to effectively balance the high-temperature cycle performance and high-temperature storage performance of alkali metal ion batteries is the key point to be solved for the further development of alkali metal ion batteries. Summary of the Invention

[0003] The object of the present invention is to provide a non-aqueous electrolyte and an alkali metal ion battery thereof. The non-aqueous electrolyte can effectively improve the high-temperature cycling performance and high-temperature storage performance of the alkali metal ion battery at a high voltage of 4.5 V, and can effectively reduce the impedance of the battery.

[0004] To achieve the above object, on the one hand, the present invention provides a non-aqueous electrolyte, comprising an electrolyte salt, a non-aqueous organic solvent and an additive. The additive comprises a compound A having the following structure:

[0005]

[0006] Compound A (CAS: 269410-01-7).

[0007] Compared with the prior art, the additive of the non-aqueous electrolyte of the present invention comprises compound A. Compound A contains a uracil structure and a boronic acid pinacol ester structure. The methyl group connected to the ring of compound A can provide protons at a high potential to protect the non-aqueous electrolyte to make it resistant to high voltage. The B-O bond in its boronic acid pinacol ester structure is easily broken during the formation process. After the B-O bond is broken, a protective layer can be preferentially formed on the surface of the positive electrode material. At the same time, it can also induce the formation of nanoscale MF (M refers to Li, Na or K), so that the battery has a higher capacity retention rate, and its film-forming property can also reduce the formation of the positive electrode salt rock phase, which has the effect of reducing impedance in the non-aqueous electrolyte system and improving the high-temperature cycling performance of the alkali metal ion battery. At the same time, the N-heterocyclic structure in the uracil structure can form a film on the surfaces of the positive and negative electrode plates during the formation process and construct a stable solid electrolyte interphase. This solid electrolyte interphase is not easily dissolved even under high-temperature conditions, thereby prolonging the battery cycle life. Therefore, the non-aqueous electrolyte of the present invention can improve the storage performance and cycling performance of the alkali metal ion battery under high-temperature use conditions and can effectively reduce its impedance.

[0008] As a preferred technical solution, the mass percentage of the additive in the non-aqueous electrolyte of the present invention is 0.5% to 1.0%. Specifically, the mass percentage of the additive in the non-aqueous electrolyte is 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%.

[0009] As a preferred technical solution, the electrolyte salt of the present invention is selected from lithium salts, sodium salts or potassium salts.

[0010] As a preferred technical solution, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium methylsulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium fluorosulfonate (LiSO2F), lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(bis(oxalato))phosphate (LiDFAP), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium lower aliphatic carboxylate.

[0011] The sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium tetrafluoroborate (NaBF4), sodium bis(oxalato)borate (NaBOB), sodium trifluoromethanesulfonate (NaCF3SO3), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI).

[0012] The potassium salt is selected from at least one of potassium hexafluorophosphate (KPF6), potassium tetrafluoroborate (KBF4), potassium perchlorate (KClO4), potassium hexafluoroarsenate (KAsF6), potassium hexafluoroantimonate (KSbF6), potassium difluorophosphate (KPF2O2), 4,5-dicyano-2-trifluoromethylimidazole potassium (KDTI), potassium bis(oxalato)borate (KBOB), potassium difluoro(oxalato)borate (KDFOB), potassium bis(fluorosulfonyl)imide (KFSI), KN(SO2RF)2, KN(SO2F)(SO2RF), potassium nitrate (KNO3), and potassium chloride (KCl), where RF = C n F 2n+1 , and n is an integer from 1 to 10.

[0013] As a preferred technical solution, the mass percentage of the electrolyte salt of the present invention in the non-aqueous electrolyte is 5% - 20%. Specifically, the mass percentage of the electrolyte salt of the present invention in the non-aqueous electrolyte is 5%, 6%, 7%, 8%, 9%, 10%, 12%, 14%, 16%, 18%, 20%.

[0014] As a preferred technical solution, the non-aqueous organic solvent of the present invention is selected from at least one of linear carbonates, cyclic carbonates, carboxylic acid esters, and lactones.

[0015] As a preferred technical solution, the chain carbonate may 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 may be at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and pentylene carbonate; the carboxylic acid ester may be at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate, methyl propionate, ethyl propionate (EP), and propyl propionate (PP); the lactone may be at least one of γ-butyrolactone (GBL), γ-valerolactone (GVL), γ-caprolactone, δ-valerolactone (DVL), and ε-caprolactone.

[0016] On the other hand, the present invention provides an alkali metal ion battery, which includes a positive electrode and a negative electrode, and also includes the aforementioned non-aqueous electrolyte, and the maximum charging voltage of the alkali metal ion battery is 4.5V.

[0017] As a preferred technical solution, the positive electrode of the present invention includes a positive electrode active material, and the positive electrode active material is selected from at least one of metal oxides and polyanion-type compounds.

[0018] Specifically, the metal oxide includes lithium cobaltate, lithium iron phosphate, nickel cobalt manganese oxide, sodium nickel iron manganese oxide, or nickel cobalt aluminum oxide. The lithium cobaltate may be lithium cobaltate or lithium cobaltate modified by doping and coating. The lithium iron phosphate may be lithium iron phosphate or lithium iron phosphate modified by doping and coating. The chemical formula of the nickel cobalt manganese oxide is LiNi x Co y Mn z M (1-x-y-z) O2, and the chemical formula of the 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 Mn, 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. The chemical formula of the polyanion-type compound is R x N y (XO z ) n , where R is independently selected from one of Li, Na, and K, N is independently selected from at least one of Fe, Mn, Ni, Cu, and V, X is independently selected from one of S, P, Si, Mo, and As, 1 ≤ x ≤ 4, 1 ≤ y ≤ 3, 1 ≤ n ≤ 3, and 1 ≤ z ≤ 4.

[0019] Further, the negative electrode of the present invention comprises a negative electrode active material selected from at least one of artificial graphite, hard carbon, natural graphite, and mesophase microspheres. Detailed Embodiments

[0020] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following described methods are further explanatory descriptions of the present invention and should not be construed as limitations on the present invention.

[0021] Example 1

[0022] (1) Preparation of non-aqueous electrolyte

[0023] In an argon atmosphere in a vacuum glove box with a water content < 1 ppm, ethylene carbonate (EC) and propyl propionate (PP) were mixed according to a weight ratio of EC:PP = 1:4 to obtain 87 g of a non-aqueous organic solvent. 0.5 g of compound A was added respectively, dissolved and stirred well, and then 12.5 g of LiPF6 was added. After mixing evenly, a non-aqueous electrolyte was obtained.

[0024] (2) Preparation of positive electrode

[0025] Lithium cobalt oxide LiCoO2, binder PVDF, and conductive agent SuperP were mixed evenly according to a mass ratio of 95:1:4 to form a positive electrode paste of an alkali metal ion battery with a certain viscosity. The mixed paste was coated on both sides of an aluminum foil, dried, and roll-pressed to obtain a positive electrode sheet.

[0026] (3) Preparation of separator

[0027] Polyethylene (PE) with a thickness of about 15 μm was used as the separator.

[0028] (4) Preparation of negative electrode

[0029] Negative electrode graphite material, binder PVDF, and conductive agent SuperP were mixed evenly according to a mass ratio of 90:2:8 to form a negative electrode paste of an alkali metal ion battery with a certain viscosity. The mixed paste was coated on both sides of a copper foil, dried, and roll-pressed to obtain a negative electrode sheet.

[0030] (5) Preparation of alkali metal ion battery

[0031] The positive electrode sheet, separator, and negative electrode sheet were stacked in sequence and then stacked as needed. After the tabs were welded, they were placed in an aluminum-plastic film for battery outer packaging. The prepared non-aqueous electrolyte was 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 were carried out. Finally, a 2 Ah soft-pack alkali metal ion battery was obtained.

[0032] Examples 2 - 5

[0033] The differences between the alkali metal ion batteries of Examples 2 - 5 and Example 1 are only in the non-aqueous electrolytes, and the rest are the same. The formulations of the non-aqueous electrolytes of Examples 2 - 5 are shown in Table 1.

[0034] Example 6

[0035] The differences between Example 6 and Example 1 are only in the preparation of the positive electrode sheet and the non-aqueous electrolyte, and the rest are the same. The preparation of the positive electrode sheet in Example 6 includes: mixing sodium nickel 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, binder PVDF, and conductive agent SuperP in a mass ratio of 95:1:4 to make a sodium ion battery positive electrode slurry with a certain viscosity. After coating the mixed slurry on both sides of the aluminum foil, it is dried and roll-pressed to obtain the positive electrode sheet. The formulation of the non-aqueous electrolyte of Example 6 is shown in Table 1.

[0036] Example 7

[0037] The differences between Example 7 and Example 1 are only in the preparation of the positive electrode sheet and the non-aqueous electrolyte, and the rest are the same. The preparation of the positive electrode sheet in Example 7 includes: mixing ball-milled K3V2(PO4)3, binder PVDF, and conductive agent SuperP in a mass ratio of 95:1:4 to make a sodium ion battery positive electrode slurry with a certain viscosity. After coating the mixed slurry on both sides of the aluminum foil, it is dried and roll-pressed to obtain the positive electrode sheet. The formulation of the non-aqueous electrolyte of Example 7 is shown in Table 1.

[0038] Comparative Examples 1 - 3

[0039] The differences between Comparative Examples 1 - 3 and Example 1 are in the non-aqueous electrolytes, and the rest are the same. The formulation of the non-aqueous electrolyte of Comparative Example 1 is shown in Table 1.

[0040] Comparative Example 4

[0041] The differences between Comparative Example 4 and Example 6 are in the non-aqueous electrolytes, and the rest are the same. The formulation of the non-aqueous electrolyte of Comparative Example 4 is shown in Table 1.

[0042] Comparative Example 5

[0043] The differences between Comparative Example 5 and Example 7 are in the non-aqueous electrolytes, and the rest are the same. The formulation of the non-aqueous electrolyte of Comparative Example 5 is shown in Table 1.

[0044] Table 1 Components of the non-aqueous electrolytes of each example and comparative example

[0045]

[0046]

[0047] In Table 1, the structures of Compound 1 and Compound 2 are shown as follows:

[0048]

[0049] Compound 1 (CAS: 66-22-8) Compound 2 (CAS: 193978-23-3)

[0050] The electrochemical performance of the alkali metal ion batteries prepared in Examples 1-7 and Comparative Examples 1-5 was tested. The specific test conditions are as follows, and the test results are shown in Table 2.

[0051] High-temperature cycling performance test

[0052] The alkali metal ion batteries of Examples 1-7 and Comparative Examples 1-5 were charged and discharged at 2.0C / 1.0C once at 45°C (the battery discharge capacity is C0), the upper limit voltage was 4.5V, and then charged and discharged at 2.0C / 1.0C for 300 cycles at 45°C (the battery discharge capacity is C1). The capacity retention rate was calculated according to the following formula:

[0053] Capacity retention rate = (C1 / C0) * 100%

[0054] High-temperature storage performance test

[0055] The alkali metal ion batteries of Examples 1-7 and Comparative Examples 1-5 were charged and discharged at 0.5C / 0.5C once at 25°C, the upper limit voltage was 4.5V, and then the battery was charged to full charge at 0.5C under normal temperature conditions, the upper limit voltage was 4.5V, and the battery thickness was recorded as V0. After storing the alkali metal ion battery in an 85°C environment for 24 hours, the battery thickness was measured as V1, and the thickness expansion rate was calculated according to the following formula:

[0056] Thickness expansion rate = (V1 - V0) / V0 * 100%

[0057] High-temperature storage internal resistance change rate test

[0058] The alkali metal ion batteries of Examples 1-7 and Comparative Examples 1-5 were subjected to 5 charge-discharge cycle tests at a charge-discharge rate of 0.5C / 0.5C at room temperature, the upper limit voltage was 4.5V, and finally charged to full charge state at a rate of 0.5C, the upper limit voltage was 4.5V. The internal resistance of the alkali metal ion battery was recorded as T0. The fully charged alkali metal ion battery was stored at 60°C for 15 days, and the internal resistance of the sodium ion battery was recorded as T. The internal resistance change rate was calculated according to the following formula:

[0059] Rate of internal resistance change = (T - T0) / T0 * 100%

[0060] Table 2 Performance test results of each example and comparative example

[0061]

[0062] Specifically, as shown in the test results in Table 2, the high-temperature cycling performance and high-temperature storage performance of Examples 1-7 and the alkali metal ion battery are superior to those of Comparative Examples 1-5. This may be because the non-aqueous electrolyte of the present invention includes Compound A, which contains a uracil-like structure and a pinacol borate-like structure. The methyl group connected to the ring of Compound A can provide protons at high potentials to protect the non-aqueous electrolyte and make it resistant to high voltages. The B-O bond in its pinacol borate-like structure is easily broken during the formation stage. After the B-O bond is broken, a protective layer can be preferentially formed on the surface of the positive electrode material. At the same time, it can also induce the formation of nanoscale MF (M refers to Li, Na, or K), making the battery have a higher capacity retention rate. Its film-forming property can also reduce the formation of the positive electrode salt rock phase and has the effect of reducing impedance in the non-aqueous electrolyte system, improving the high-temperature cycling performance of the alkali metal ion battery. At the same time, the N-heterocyclic structure in the uracil-like structure can form a film on the surfaces of the positive and negative electrode sheets during the formation stage and construct a stable solid electrolyte interphase layer. This solid electrolyte interphase layer is not easily dissolved even under high-temperature conditions, thus extending the battery cycle life. Therefore, the non-aqueous electrolyte of the present invention can improve the storage performance and cycling performance of the alkali metal ion battery under high-temperature usage conditions and can effectively reduce its impedance.

[0063] By comparing the performance data of Example 1 with those of Comparative Example 1 and Comparative Example 2, it can be seen that the high-temperature cycle performance, high-temperature storage performance, and its internal resistance growth rate of Comparative Example 2 are all worse than those of Example 1 but better than those of Comparative Example 1. This may be because Compound 1 in Comparative Example 2 can react on the cathode and anode prior to solvent molecules, and its inhibitory effect on the decomposition of the electrolyte solvent is the most obvious. However, since the molecular structure of uracil contains two carbonyl groups (C=O) and two nitrogen atoms, and the carbonyl group has a strong electron-withdrawing ability, this may lead to uneven distribution of the electron cloud around the molecule, affecting its interaction with ions in the electrolyte, being unfavorable for ion migration, and thus increasing the impedance. Although the nitrogen atoms in uracil can participate in a certain coordination effect, due to their chemical environment and position, they may not be able to effectively form a stable coordination structure with lithium ions that is beneficial for ion transport, resulting in blocked ion transport and increased impedance. At the same time, the conjugation degree of the uracil molecule is relatively low, and the delocalization degree of electrons within the molecule is limited, which may limit its ability to accept and transfer electrons in the electrolyte, and the promotion effect on ion conduction is not obvious, leading to an increase in impedance. In summary, the special structure of uracil makes it difficult to effectively promote ion transport in the electrolyte, thus showing a large impedance, and further resulting in relatively limited improvement in its high-temperature cycle performance and high-temperature storage performance. By comparing the performance data of Example 1 with those of Comparative Example 1 and Comparative Example 3, it can be seen that the high-temperature cycle performance and high-temperature storage performance of Comparative Example 3 are both worse than those of Example 1 but better than those of Comparative Example 1. This may be because Compound 2 containing a thiophene-2-pinacol borate structure is prone to undergo anodic oxidative polymerization reaction on the surface of the positive electrode to form a sulfur-containing interfacial film with low impedance, which can improve the cycle performance of the lithium-ion battery. However, due to the double bonds it contains being prone to ring-opening polymerization, the interfacial impedance is large at high temperatures, resulting in deterioration of the high-temperature cycle and storage performance. Therefore, its improvement of the high-temperature storage and high-temperature cycle of the alkali metal ion battery and its effect of reducing the impedance are also relatively limited.

[0064] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only those listed in the 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. A non-aqueous electrolyte solution, comprising an electrolyte salt, a non-aqueous organic solvent, and an additive, characterized in that, The additive includes compound A with the following structure:

2. The non-aqueous electrolyte according to claim 1, wherein The mass percentage of the additive in the non-aqueous electrolyte is 0.5% to 2.0%.

3. The non-aqueous electrolyte according to claim 1, wherein The electrolyte salt is selected from lithium salts, sodium salts or potassium salts.

4. The non-aqueous electrolyte according to claim 3, wherein The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium methanesulfonate, lithium trifluoromethanesulfonate, lithium fluorosulfonate, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium difluorophosphate, lithium difluoro(bis(oxalato)phosphate), lithium diphosphate and lithium lower aliphatic carboxylate; the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium bis(oxalato)borate, sodium trifluoromethylsulfonate and sodium bis(trifluoromethylsulfonyl)imide; the potassium salt is selected from at least one of potassium hexafluorophosphate, potassium tetrafluoroborate, potassium perchlorate, potassium hexafluoroarsenate, potassium hexafluoroantimonate, potassium difluorophosphate, 4,5-dicyano-2-trifluoromethylimidazole potassium, potassium bis(oxalato)borate, potassium difluoro(oxalato)borate, potassium bis(fluorosulfonyl)imide, KN(SO2RF)2, KN(SO2F)(SO2RF), potassium nitrate and potassium chloride.

5. The non-aqueous electrolyte according to claim 1, characterized in that, The mass percentage of the electrolyte salt in the non-aqueous electrolyte is 5% to 20%.

6. The non-aqueous electrolyte according to claim 1, characterized in that, The non-aqueous organic solvent is selected from at least one of chain carbonates, cyclic carbonates, carboxylic acid esters and lactones.

7. The non-aqueous electrolyte according to claim 6, wherein The chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate and ethyl propyl carbonate; the cyclic carbonate is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate and pentylene carbonate; the carboxylic acid ester is selected from at least one of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate; the lactone is selected from at least one of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone.

8. An alkali metal ion battery, comprising a positive electrode and a negative electrode, characterized in that, It further includes the non-aqueous electrolyte according to any one of claims 1 to 7, and the maximum charging voltage of the alkali metal ion battery is 4.5V.

9. The alkali metal ion battery according to claim 8, characterized in that, The positive electrode includes a positive electrode active material, and the positive electrode active material is selected from at least one of metal oxides and polyanion-type compounds.

10. The alkali metal ion battery according to claim 8, wherein The negative electrode includes a negative electrode active material, and the negative electrode active material is selected from at least one of artificial graphite, natural graphite, hard carbon and mesophase microspheres.

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