A nonaqueous electrolyte for lithium batteries and a lithium ion battery

Abstract

This invention discloses a non-aqueous electrolyte for lithium batteries and a lithium-ion battery. The non-aqueous electrolyte for lithium batteries of this invention comprises an electrolyte salt, a non-aqueous solvent, and additives, wherein the non-aqueous solvent is a morpholine compound. The non-aqueous electrolyte for lithium batteries of this invention, using a morpholine compound as a solvent, has a wider electrochemical window, resulting in stronger stability to high-nickel cathode materials and excellent resistance to reduction, significantly improving the storage performance and cycle life of batteries using high-silicon anodes.

Description

Technical Field

[0001] This invention relates to the field of electrolyte technology, and more particularly to a non-aqueous electrolyte for lithium batteries and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that primarily function by the movement of lithium ions between the positive and negative electrodes. Due to their significant advantages such as high voltage, high capacity, long cycle life, and good safety performance, lithium-ion batteries have broad application prospects in portable electronic devices, electric vehicles, space technology, and the defense industry. Lithium-ion batteries mainly consist of a positive electrode, a negative electrode, a separator, and an electrolyte.

[0003] Lithium-ion battery electrolytes mostly use organic solvent systems. Currently, widely used organic solvents include carbonates (such as ethylene carbonate), ethers (such as dimethoxyethane and tetrahydrofuran), lactones (such as γ-butyrolactone), amides (N,N-dimethylformamide), and nitriles (acetonitrile). Among them, ether solvents are commonly used in lithium-ion batteries because they have advantages such as stability to the negative electrode, strong resistance to reduction, and low viscosity.

[0004] However, ether solvents are unsuitable for use with mainstream high-nickel cathodes and cobalt-free high-voltage spinel-based materials due to their lack of antioxidant properties. Therefore, the current mainstream technology uses carbonate solvents. However, carbonate solvents have poor stability to the anode and rely heavily on electrochemical decomposition for film formation, resulting in a complex chemical system and ultimately high electrolyte costs. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a non-aqueous electrolyte for lithium batteries and a lithium-ion battery. The non-aqueous electrolyte for lithium batteries of the present invention uses morpholine compounds as solvents, which have a wider electrochemical window, resulting in stronger stability to high-nickel cathode materials and excellent resistance to reduction, thus significantly improving the storage performance and cycle life of batteries using high-silicon anodes.

[0006] One of the objectives of this invention is to provide a non-aqueous electrolyte for lithium batteries. To achieve this objective, the invention adopts the following technical solution:

[0007] A non-aqueous electrolyte for lithium batteries includes an electrolyte salt, a non-aqueous solvent, and additives, wherein the non-aqueous solvent is a morpholine compound represented by formula (I):

[0008] Formula (I),

[0009] In formula (I), R1 is a hydrocarbon group with 1 to 3 carbon atoms;

[0010] The degree of unsaturation of R2 to R5 is 0 to 2, and R2 to R5 are independently selected from hydrogen, a hydrocarbon group having 1 to 4 carbon atoms, fluorine, or lithium sulfonate.

[0011] The non-aqueous electrolyte for lithium batteries of the present invention uses morpholine compounds as solvents, which have a wider electrochemical window, making it more stable to high-nickel cathode materials and having excellent resistance to reduction, thus greatly improving the storage performance and cycle capacity of batteries using high-silicon anodes.

[0012] In this invention, the non-aqueous electrolyte for lithium batteries comprises the following components by weight percentage:

[0013] Lithium salts 0.01% to 20%

[0014] Lithium salt additive 0.01% to 10%

[0015] Non-aqueous solvents: 0.01% to 85%

[0016] Carbonate additives 0 to 40%

[0017] Sulfonate additives: 0.01% to 10%;

[0018] The non-aqueous solvent is a morpholine compound.

[0019] In this invention, the morpholine compound is , , , , , At least one of them.

[0020] Specifically, a non-aqueous electrolyte for lithium batteries comprises the following components by weight percentage:

[0021] The weight percentage of lithium salt is 0.01-20%, for example, 0.01%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19% or 20%, etc.

[0022] The weight percentage of lithium salt additives is 0.01-10%, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0023] The weight percentage of non-aqueous solvent is 0.01-85%, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%, etc.

[0024] The weight percentage of carbonate additives is 0-40%, for example, 0, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%, etc.

[0025] The weight percentage of sulfonate additives is 0.01-10%, for example, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0026] The non-aqueous solvent is a morpholine compound.

[0027] In this invention, the lithium salt is lithium hexafluorophosphate (LiPF6).

[0028] In this invention, the lithium salt additive is at least one of lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalate) phosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bis(oxalate) borate, lithium bis(trifluoromethanesulfonyl)imide, and lithium bis(fluorosulfonyl)imide (LiFSI).

[0029] In this invention, the carbonate additive is at least one of linear carbonate additives, cyclic carbonate additives, and fluorinated carbonate additives. "At least one" refers to any one of these additives or a combination of at least two of them. Typical, but not limited, combinations include: mixtures of linear carbonate additives and cyclic carbonate additives; mixtures of cyclic carbonate additives and fluorinated carbonate additives; mixtures of linear carbonate additives and fluorinated carbonate additives; and mixtures of linear carbonate additives, cyclic carbonate additives, and fluorinated carbonate additives.

[0030] The linear carbonate additive is at least one of methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate; at least one means any one or a combination of at least two of them, and the typical but not limited types of the combination are: a mixture of methyl ethyl carbonate and dimethyl carbonate, a mixture of dimethyl carbonate and diethyl carbonate, and a mixture of methyl ethyl carbonate, dimethyl carbonate, and diethyl carbonate.

[0031] The cyclic carbonate additive is at least one of ethylene carbonate (EC), propylene carbonate, vinylene carbonate (VC), and ethylene ethylene carbonate (VEC); at least one means any one or a combination of at least two of them, and the typical but not limited types of the combination are: mixtures of ethylene carbonate and propylene carbonate, mixtures of propylene carbonate and vinylene carbonate, mixtures of vinylene carbonate and ethylene ethylene carbonate, mixtures of ethylene carbonate, propylene carbonate, and vinylene carbonate, mixtures of propylene carbonate, vinylene carbonate, and ethylene ethylene carbonate, and mixtures of ethylene carbonate, propylene carbonate, vinylene carbonate, and ethylene ethylene carbonate.

[0032] The fluorinated carbonate additive is at least one of fluorinated ethylene carbonate (FEC), 1,2-difluoroethylene carbonate, methyltrifluoroethyl carbonate, and bis(trifluoroethyl) carbonate. "At least one" refers to any one or a combination of at least two of these, and typical but not limited types of such combinations include: mixtures of fluorinated ethylene carbonate and 1,2-difluoroethylene carbonate; mixtures of methyltrifluoroethyl carbonate and bis(trifluoroethyl) carbonate; mixtures of 1,2-difluoroethylene carbonate and methyltrifluoroethyl carbonate; mixtures of 1,2-difluoroethylene carbonate, methyltrifluoroethyl carbonate, and bis(trifluoroethyl) carbonate; and mixtures of fluorinated ethylene carbonate, 1,2-difluoroethylene carbonate, methyltrifluoroethyl carbonate, and bis(trifluoroethyl) carbonate, etc.

[0033] In this invention, the sulfonate additive is at least one of 1,3-propanesulfonyl lactone (PS), 1,3-propenesulfonyl lactone (PST), and vinyl sulfate (DTD). "At least one" refers to any one or a combination of at least two of these, and typical but not limited types of such combinations include: mixtures of 1,3-propanesulfonyl lactone and 1,3-propenesulfonyl lactone; mixtures of 1,3-propenesulfonyl lactone and vinyl sulfate; mixtures of 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, and vinyl sulfate.

[0034] A second objective of the present invention is to provide a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and a non-aqueous electrolyte for a lithium battery as described in one objective.

[0035] The positive electrode includes a positive electrode active material.

[0036] The positive electrode active material is selected from at least one of lithium iron phosphate (LFP), lithium nickel cobalt composite oxide, and lithium nickel manganese composite oxide with spinel structure.

[0037] The general formula of the lithium-nickel-cobalt composite oxide is Li x Ni y Co z Me (1-y-z )O a In the general formula, x satisfies the condition 1 ≤ x ≤ 1.2, y and z are positive numbers that satisfy the relationship y + z < 1, the value of y is less than 0.5, Me is any one or at least two metals selected from Al, Mn, Na, Fe, Cr, Cu, Zn, Ca, K, Mg and Pb, and a satisfies the condition 1.5 ≤ a ≤ 2.5.

[0038] The negative electrode comprises carbon materials with carbon as a constituent element, silicon materials with silicon as a constituent element, or carbon-silicon composite materials.

[0039] The carbon material is at least one of acetylene black, conductive carbon black, carbon fiber, carbon nanotubes, and Ketjen black.

[0040] The silicon material is at least one of silicon, silicon oxide, and silicon-based alloys.

[0041] The diaphragm is a commonly used diaphragm material in the art, for example, the diaphragm includes a base membrane and a nano-alumina coating coated on the base membrane.

[0042] The method for preparing the lithium-ion battery of the present invention includes the following steps:

[0043] A positive electrode is prepared using a positive current collector and a positive active material coated on the positive current collector as raw materials;

[0044] A negative electrode is prepared using a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector as raw materials;

[0045] A diaphragm is prepared by coating a base membrane with a nano-coating.

[0046] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The stacked wafers are then used to obtain a bare battery cell.

[0047] The bare cell is placed into an aluminum-plastic film, then baked to remove water, and then injected with the prepared non-aqueous electrolyte and sealed. After that, it goes through the processes of standing, hot and cold pressing, formation, clamping, and capacity testing to obtain a lithium-ion battery.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] The non-aqueous electrolyte for lithium batteries of the present invention has a wider electrochemical window, resulting in stronger stability to high-nickel cathode materials, excellent resistance to reduction, reduced impedance, and significantly improved storage performance and cycle life of batteries using high-silicon anodes. Specifically, the resulting lithium-ion batteries exhibit an initial DCR of 93 mOhm to 105 mOhm, a DCR growth rate of 10% to 34% after 60 days of storage at 60°C, a volume expansion rate of 22% to 30% after 60 days of storage at 60°C, and 803 to 1249 cycles at 45°C to 80% SOH. Detailed Implementation

[0050] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0051] The present invention provides a non-aqueous electrolyte for lithium batteries, comprising an electrolyte salt, a non-aqueous solvent, and additives, wherein the additives include olefin sulfonate additives.

[0052] In this invention, the lithium-ion battery is a primary lithium battery or a secondary lithium battery, comprising: a positive electrode, a negative electrode, a separator located between the positive electrode and the negative electrode, and an electrolyte.

[0053] The preparation method of the secondary lithium battery of the present invention is as follows:

[0054] (1) Preparation of non-aqueous electrolyte for lithium batteries

[0055] In a dry argon atmosphere, a non-aqueous solvent is prepared, and a fully dried electrolyte salt, lithium salt additive, non-aqueous solvent, and additive are added and mixed evenly to obtain a non-aqueous electrolyte for lithium batteries.

[0056] (2) Preparation of secondary lithium batteries

[0057] Using the electrolyte obtained in step 1) as a non-aqueous electrolyte for lithium batteries, a secondary lithium battery is prepared.

[0058] The cathode material is as follows:

[0059] 811 (abbreviated as 8-series) represents LiNi 0.8 Co 0.1 Mn 0.1 O2;

[0060] The negative electrode material is made of graphite or silicon carbide.

[0061] Example 1

[0062] The non-aqueous electrolyte for lithium batteries in this embodiment comprises the following components by weight percentage:

[0063] LiPF6 14%

[0064] LiPO2F2 0.8%

[0065] LiFSI 0.5%

[0066] Non-aqueous solvents: 83.7%

[0067] DTD 1%.

[0068] The non-aqueous solvent is N-ethylmorpholine.

[0069] The method for preparing the secondary lithium battery in this embodiment is as follows: using the electrolyte obtained above as a non-aqueous electrolyte for lithium batteries, a secondary lithium battery is prepared. The method for preparing a lithium-ion battery is as follows:

[0070] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder polyvinylidene fluoride are mixed thoroughly in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture is then coated onto aluminum foil, dried, and cold-pressed to obtain a positive electrode sheet with a compacted density of 3.5 g / cm³. 3 ;

[0071] The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber, and thickener sodium carboxymethyl cellulose were thoroughly mixed in a deionized water solvent system at a mass ratio of 96:2:1:1. The mixture was then coated onto copper foil, dried, and cold-pressed to obtain the negative electrode sheet with a compacted density of 1.65 g / cm³. 3 ;

[0072] A diaphragm was obtained by coating a 3 μm thick nano-alumina coating onto a 9 μm thick polyethylene base membrane.

[0073] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to act as an insulator, and the stacked electrodes are used to obtain a bare cell.

[0074] The bare battery cell is placed into an aluminum-plastic film, then baked at 80 ℃ to remove water, and then injected with the corresponding non-aqueous electrolyte and sealed. After that, it goes through processes such as standing, hot and cold pressing, formation, clamping, and capacity testing to obtain the finished soft-pack lithium-ion secondary battery.

[0075] Example 2

[0076] The non-aqueous electrolyte for lithium batteries in this embodiment comprises the following components by weight percentage:

[0077] LiPF6 14%

[0078] LiPO2F2 0.8%

[0079] LiFSI 0.5%

[0080] Non-aqueous solvents: 83.7%

[0081] DTD 1%.

[0082] The non-aqueous solvent is a mixture of N-ethylmorpholine and N-methyl-2-vinylmorpholine in a mass ratio of 9:1.

[0083] The method for preparing the lithium-ion battery in this embodiment is the same as in Embodiment 1.

[0084] Example 3

[0085] The difference between the non-aqueous electrolyte for lithium batteries in this embodiment and that in Example 1 is that the non-aqueous solvent is N-methyl-2-vinylmorpholine, while the others are the same as in Example 1.

[0086] The method for preparing the lithium-ion battery in this embodiment is the same as in Embodiment 1.

[0087] Example 4

[0088] The difference between the non-aqueous electrolyte for lithium batteries in this embodiment and that in Embodiment 1 is that the non-aqueous solvent is... (N-ethylmorpholine), A mixture of (N-methyl-3,5-dicarboxymethyl morpholine) in a mass ratio of 8:2, with all other parameters being the same as in Example 1.

[0089] The method for preparing the lithium-ion battery in this embodiment is the same as in Embodiment 1.

[0090] Example 5

[0091] The non-aqueous electrolyte used in the lithium battery of this embodiment is the same as that in Embodiment 1.

[0092] The difference between the preparation method of the lithium-ion battery in this embodiment and that in Example 1 is that the negative electrode material is replaced with silicon carbon, while the rest is the same as in Example 1.

[0093] Example 6

[0094] The non-aqueous electrolyte for lithium batteries in this embodiment comprises the following components by weight percentage:

[0095] LiPF6 14%

[0096] LiPO2F2 0.8%

[0097] LiFSI 0.5%

[0098] Non-aqueous solvents 71.1%

[0099] FEC 12.6%

[0100] DTD 1%.

[0101] The non-aqueous solvent is N-ethylmorpholine.

[0102] The difference between the lithium-ion battery preparation method in this embodiment and that in Example 1 is that the negative electrode material is replaced with silicon carbon, while everything else is the same as in Example 1.

[0103] Comparative Example 1

[0104] The difference between this comparative example and Example 1 is that the non-aqueous solvent is a mixture of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) in a mass ratio of 1:1. All other aspects are the same as in Example 1.

[0105] Comparative Example 2

[0106] The difference between this comparative example and Example 1 is that the non-aqueous solvent is a mixture of tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2-Me-THF) in a mass ratio of 1:1. All other aspects are the same as in Example 1.

[0107] Comparative Example 3

[0108] The difference between this comparative example and Example 1 is that the non-aqueous solvent is a mixture of ethylene carbonate EC and ethyl methyl carbonate EMC in a mass ratio of 3:7. Everything else is the same as in Example 1.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 1 is that the non-aqueous solvent is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7, and the negative electrode material is silicon carbide. Everything else is the same as in Example 1.

[0111] The lithium batteries prepared in Examples 1-6 and Comparative Examples 1-4 were subjected to performance tests, and the test results are shown in Table 1.

[0112] The secondary battery of the present invention is tested by the following method:

[0113] (1) Cyclic test of secondary battery

[0114] The battery is cyclically charged and discharged within a specified potential range at a current of 1 C, and the capacity of each cycle is recorded. The test ends when the battery capacity reaches 80% of the capacity of the first cycle.

[0115] (2) DC resistance (DCR) test of secondary battery

[0116] At a specified temperature, the battery is discharged to 50% SOC (State of Charge, reflecting the battery's remaining capacity) at a 1C current. The current is then increased to 4C and maintained for 30 seconds. The difference between the updated stable voltage and the original plateau voltage is measured, and the ratio of this difference to the 3C current value is the battery's DC resistance. The DCR at the end of the cycle is compared to the DCR at the beginning of the cycle to obtain the DCR growth rate.

[0117] (3) Test of gas volume change generated by secondary battery

[0118] After securing the secondary battery with a thin string, it was completely immersed in water at 60 ℃. The weight difference before and after immersion was recorded, and the volume difference was calculated based on the density of water at 60 ℃.

[0119] Table 1

[0120] Initial DCR (mOhm) Volume expansion rate (%) after 60 days of storage at 60℃ DCR growth rate (%) after 60 days of storage at 60℃ Cycle at 45℃ to 80% SOH (number of cycles) Example 1 93 30 10 803 Example 2 105 22 15 1249 Example 3 100 15 16 1322 Example 4 97 17 20 1540 Example 5 98 25 12 880 Example 6 100 30 34 1087 Comparative Example 1 120 129 94 546 Comparative Example 2 103 98 89 609 Comparative Example 3 118 86 106 751 Comparative Example 4 145 35 134 329

[0121] As can be seen from the data in Table 1, the lithium-ion battery prepared using the non-aqueous electrolyte of the present invention exhibits low battery impedance and superior cycle performance. Specifically, the initial DCR of the prepared lithium-ion battery is 93 mOhm to 105 mOhm, the DCR growth rate after 60 days of storage at 60°C is 10% to 34%, the volume expansion rate after 60 days of storage at 60°C is 22% to 30%, and the number of cycles to 80% SOH at 45°C is 803 to 1249.

[0122] Comparative Example 1 used a mixture of ethylene glycol dimethyl ether and 1,3-dioxolane as a solvent, which increased the battery impedance and worsened the cycle performance.

[0123] Comparative Example 2 used furan-based solvents, which increased battery impedance and deteriorated cycle performance.

[0124] Comparative Examples 3 and 4 used a mixture of ethylene carbonate and ethyl methyl carbonate as solvents and graphite and silicon carbide as negative electrode materials. The battery impedance increased and the cycle performance deteriorated in both cases.

[0125] This invention illustrates the detailed process equipment and process flow through the above embodiments. However, this invention is not limited to the detailed process equipment and process flow described above, meaning that this invention does not necessarily depend on the detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, additions of auxiliary components, and selection of specific methods, all fall within the protection scope and disclosure scope of this invention.

[0126] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0127] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0128] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A non-aqueous electrolyte for high-nickel lithium batteries, characterized in that, The non-aqueous electrolyte for lithium batteries comprises the following components in terms of weight percentage: Lithium salt 0.01 to 20% Lithium salt additive 0.01 to 10% Non-aqueous solvent 0.01 to 85% Carbonate-based additive 0 to 40% Sulfonate-based additive 0.01 to 10%; The non-aqueous solvent is a morpholine compound. The morpholine compound is and .

2. The nonaqueous electrolyte for a lithium battery according to claim 1, characterized by The lithium salt is lithium hexafluorophosphate.

3. The nonaqueous electrolyte for a lithium battery according to claim 1, characterized by The lithium salt additive is at least one of lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium bisoxalate borate, lithium bis(trifluoromethylsulfonyl)imide, and lithium bisfluorosulfonylimide.

4. The nonaqueous electrolyte for a lithium battery according to claim 1, characterized by The carbonate-based additive is at least one of a linear carbonate-based additive, a cyclic carbonate-based additive, and a fluorinated carbonate-based additive.

5. The nonaqueous electrolyte for a lithium battery according to claim 1, wherein The sulfonate-based additive is at least one of 1,3-propane sultone, 1,3-propene sultone, and ethylene sulfate.

6. A high nickel lithium ion battery, characterized in that, A lithium battery comprising a high-nickel positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and a non-aqueous electrolyte for lithium batteries according to any one of claims 1 to 5.

7. The lithium-ion battery of claim 6, wherein, The negative electrode comprises a carbon material containing carbon as a constituent element, a silicon material containing silicon as a constituent element, or a carbon-silicon composite material, The carbon material is at least one of acetylene black, conductive carbon black, carbon fiber, carbon nanotube, and Ketjen black. The silicon material is at least one of silicon, silicon oxide compound, and silicon-based alloy.

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