Electrolyte additive, carbonate electrolyte and lithium ion battery

Abstract

This invention discloses an electrolyte additive, a carbonate electrolyte, and a lithium-ion battery. The additive includes a single-ended UPy-terminated oligoethylene glycol, the general structural formula of which is: UPy-L-(CH2CH2O). n -R; where L is a carbamate group; n=4~12, and R is a methyl group. This invention reduces the initial irreversible lithium intercalation capacity (lithium consumption) without altering the basic electrolyte system; improves the first-cycle coulombic efficiency of graphite||lithium coin cells; and improves the consistency of electrolyte wetting and interface passivation within the dry electrode pore / fiber network.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to an electrolyte additive, a carbonate electrolyte, and a lithium-ion battery. Background Technology

[0002] Dry electrode technology eliminates the need for solvents and is suitable for applications such as thick electrodes. Dry graphite anodes typically utilize fluoropolymer binders such as PTFE to form a fiber network for film formation and strength. However, compared to conventional wet graphite electrodes, PTFE-containing dry graphite electrodes often exhibit higher irreversible capacity and lower first-cycle coulombic efficiency (ICE) during the initial lithium insertion process. In conventional coin cell half-cell evaluation systems, the initial efficiency of wet graphite electrodes is 90-92%, while that of dry graphite electrodes is 85-88%, indicating a significantly lower initial efficiency for dry electrodes, characterized by increased lithium consumption during the initial lithium insertion process.

[0003] The most prominent problem with dry-process graphite anodes is the significantly lower coulombic efficiency in the first cycle. The core reason is that the PTFE binder commonly used in dry processes undergoes reduction and decomposition at the low potential of the graphite anode, consuming a large amount of active lithium. This also results in a thick, uneven, and high-impedance SEI film. In addition, the dense electrode microstructure and poor electrolyte wetting under dry processing further exacerbate the irreversible capacity loss in the first cycle. Furthermore, dry-process electrodes generally suffer from low bonding strength, high brittleness, and susceptibility to powder shedding and cracking. The electrode interface contact and ion / electron conduction kinetics are also weaker than those of wet processes, further reducing the initial efficiency and cycle stability.

[0004] From the perspective of process and mass production, the dry process is extremely sensitive to raw materials, degree of fiberization, and rolling process. It has a narrow process window, is difficult to control consistency, requires high equipment investment, and has a low production line speed. The irreversible lithium loss caused by low initial efficiency needs to be compensated by pre-lithiation, special electrolytes, and additives, which increases the overall material and manufacturing costs and restricts the direct application of dry graphite anodes in high energy density systems.

[0005] In existing technologies, electrolyte additives are mostly applied to wet electrode systems, making it difficult to achieve directional enrichment and rapid passivation of the interface for the "PTFE fiber network-pore structure". As a result, it is difficult to simultaneously achieve wetting and suppression of low-potential side reactions in dry graphite / PTFE systems. Summary of the Invention

[0006] The technical problem to be solved by the embodiments of the present invention is to provide an electrolyte additive, a carbonate electrolyte, and a lithium-ion battery to reduce lithium consumption during the first lithium intercalation and improve the first-time efficiency.

[0007] To address the aforementioned technical problems, this invention provides an electrolyte additive comprising a single-ended UPy-terminated oligoethylene glycol. The general structural formula of the single-ended UPy-terminated oligoethylene glycol is as follows: UPy-L-(CH2CH2O) n -R; Where L is a carbamate group; n = 4 to 12; and R is a methyl group.

[0008] Accordingly, embodiments of the present invention also provide a carbonate electrolyte comprising the above-mentioned electrolyte additives.

[0009] Furthermore, the electrolyte additive accounts for 0.01% to 0.50% of the total mass of the carbonate electrolyte.

[0010] Furthermore, it also includes LiPO2F2 and / or LiDFOB.

[0011] Furthermore, the mass of LiPO2F2 and / or LiDFOB accounts for 0.05% to 1.00% of the total mass of the carbonate electrolyte.

[0012] Furthermore, it also includes lithium salt and solvent, wherein the solvent is a mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate.

[0013] Furthermore, the lithium salt is LiPF6 with a concentration of 1.0 M; the volume ratio of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate is 1:1:1.

[0014] Accordingly, embodiments of the present invention also provide a lithium-ion battery comprising the above-described carbonate electrolyte.

[0015] Furthermore, it also includes a dry graphite / PTFE electrode, wherein the carbonate electrolyte is vacuum-pulse pre-wetting to enrich the additives within the pore / fiber network of the electrode.

[0016] Furthermore, a coin cell system is constructed by using a dry graphite anode with PTFE binder and a lithium metal pair.

[0017] The beneficial effects of this invention are as follows: without changing the basic electrolyte system, this invention reduces the irreversible capacity (lithium consumption) of the first lithium insertion; improves the first-cycle coulombic efficiency of graphite||lithium coin half-cells; and improves the consistency of electrolyte wetting and interface passivation in the dry electrode pore / fiber network. Detailed Implementation

[0018] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be further described in detail below with reference to specific embodiments.

[0019] The electrolyte additive in this invention includes mono-UPy-terminated oligoethylene glycol. Based on a standard carbonate electrolyte system (1.0 M LiPF6, EC:EMC:DMC = 1:1:1, v / v), this invention introduces mono-UPy-terminated oligoethylene glycol (mono-UPy-OEG) as an interfacial self-assembly additive to suppress the irreversible reaction of dry graphite / PTFE during the initial lithium insertion process at low potential, reduce lithium consumption, and improve initial efficiency. Carbonates are common electrolyte solvents, mainly including EC, DMC, EMC, DEC, and PC. Currently, mixed solvents of EC, DMC, and EMC are commonly used. EC is ethylene carbonate, DMC is dimethyl carbonate, and EMC is ethyl methyl carbonate.

[0020] The “UPy-OEG” of this invention refers to an oligoethylene glycol derivative containing UPy end groups, preferably a UPy-terminated UPy-OEG (also known as “mono-UPy-OEG”), and the general structural formula of the UPy-terminated oligoethylene glycol is: UPy-L-(CH2CH2O) n -R; Wherein, L is a linking group, selected from urethane, ester, ether, amide, or urea / urethane groups containing alkylene linking arms; n=2~20, and R is H, C1–C6 alkyl, or other terminal groups. Preferably, n=4~12, R is methyl, and L is urethane. The molecule contains only one UPy group (single-terminated UPy) to avoid the adverse effects of bulk network formation / thickening caused by double-terminated UPy.

[0021] The mono-UPy-OEG of this invention has a "single UPy end group" structure, which combines interfacial self-assembly / enrichment with OEG solvation / ion channel capabilities, and maintains good compatibility in carbonate liquid systems.

[0022] In this invention, "UPy" is an abbreviation for 2-ureido-4-pyrimidinone, which can be referred to as a "ureidopyrimidinone" structural unit / group in Chinese; OEG is an abbreviation for oligoethylene glycol. The UPy structural unit contains both hydrogen bond donor and hydrogen bond acceptor sites, and can form stable associated structures (such as dimers or further self-assembled structures) through multiple intermolecular hydrogen bond interactions, thereby endowing the material with interface enrichment, self-assembly, or adhesion enhancement.

[0023] The preparation process of mono-UPy-OEG in this invention is as follows: Take monohydroxy oligoethylene glycol HO-(CH2CH2O). n-R (n=4–12, R is methyl), maintains low side reactions and low thickening in carbonate electrolytes, combines with UPy self-assembly to achieve low-dose lithium consumption reduction, dissolves in anhydrous tetrahydrofuran, and adds equimolar amounts of UPy, the structure is as follows: A catalyst (dibutyltin dilaurate) of 0.01-0.1 wt% was added. The reaction was carried out under nitrogen protection at room temperature to 50°C for 2–24 h with stirring. After the reaction, the solvent was removed under reduced pressure, and the crude product was purified by precipitation or column chromatography to obtain mono-UPy-OEG. The chemical reaction formula is: UPy-NCO + HO-(CH2CH2O) n -CH3 → UPy-NH-COO-(CH2CH2O) n -CH3.

[0024] In the formula, -NH-COO- belongs to the carbamate group.

[0025] The carbonate electrolyte of this invention includes a lithium salt, a solvent, and an electrolyte additive. The solvent is a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The lithium salt is LiPF6 with a concentration of 1.0 M; the volume ratio of ethylene carbonate:dimethyl carbonate:ethyl methyl carbonate is 1:1:1.

[0026] In one implementation, the carbonate electrolyte further includes LiPO2F2 and / or LiDFOB. Based on mono-UPy-OEG, this invention further adds LiPO2F2 and / or LiDFOB as synergistic additives to suppress side reactions, forming a synergistic mechanism of "interfacial self-assembly enrichment + inorganic enrichment of SEI / suppression of salt side reactions".

[0027] The synergistic system of this invention achieves faster passivation and fewer persistent side reactions in dry graphite / PTFE electrodes, thereby further reducing the irreversible capacity in the first cycle and significantly improving the first efficiency (with an unexpected improvement compared to a single additive).

[0028] In one embodiment, the electrolyte additive accounts for 0.01% to 0.50% of the total mass of the carbonate electrolyte. The electrolyte additive content is preferably 0.03-0.20 wt%, more preferably 0.05-0.10 wt%.

[0029] In one embodiment, the mass of LiPO2F2 and / or LiDFOB accounts for 0.05% to 1.00% of the total mass of the carbonate electrolyte. The synergistic inhibitor of side reactions is preferably 0.10-0.50 wt%.

[0030] The carbonate electrolyte of the present invention is applied to a coin cell system consisting of a dry graphite anode containing PTFE binder (1-3 wt%) and a lithium metal pair.

[0031] When the carbonate electrolyte of the present invention is used for dry graphite / PTFE electrodes, vacuum-pulse pre-wetting (vacuum → atmospheric pressure cycle, 2-8 times; 10-50 kPa; 1-10 min / stage; optional 30-60°C standing) is used to enrich the additives in the pore / fiber network, shorten the wetting completion time and accelerate the formation of the interface film, thereby further reducing lithium consumption.

[0032] The vacuum-pulse pre-wetting process of this invention is as follows: a) Contact the carbonate electrolyte with the dry graphite electrode; b) Apply a vacuum to 10-50 kPa and maintain it for 1-10 min; c) Return to normal pressure and maintain for 1-10 minutes; d) Repeat steps b)–c) 2–8 times; e) Optionally, allow to stand at 30-60°C for 0.5-12 h.

[0033] The PTFE content in the dry graphite electrode is 1-3 wt% of the electrode solid mass.

[0034] Compared to the baseline of 85-88% first-time efficiency of dry graphite electrodes using only a basic electrolyte (1.0 M LiPF6; EC:EMC:DMC=1:1:1), this invention can improve the first-time efficiency of dry graphite electrodes and reduce the irreversible capacity of initial lithium insertion. In some embodiments, this invention can bring the first-time efficiency of dry graphite electrodes closer to that of wet graphite electrodes (90-92%).

[0035] The lithium-ion battery of this invention includes a carbonate electrolyte. The lithium-ion battery also includes a dry-process graphite / PTFE electrode, wherein the carbonate electrolyte is pre-wetted using a vacuum-pulse method (vacuum → atmospheric pressure cycling, 2–8 times; 10–50 kPa; 1–10 min / stage; optional 30–60°C settling) to enrich additives within the pores / fiber network of the electrode.

[0036] The lithium-ion battery employs a coin cell half-cell system consisting of a dry-processed graphite anode with PTFE binder and a lithium metal pair, aiming to reduce lithium consumption and improve the first-cycle coulombic efficiency. Compared to the baseline difference between wet-processed graphite (90-92% first-cycle efficiency) and dry-processed graphite (85-88%), this system significantly improves the first-cycle efficiency of dry-processed graphite and reduces lithium consumption, narrowing the gap between dry and wet processes.

[0037] Example 1: Raw Materials and Equipment (General): 1. Electrolyte raw materials: LiPF6 (battery grade); EC, EMC, DMC (battery grade, moisture control); Synergistic additives: LiPO2F2 or LiDFOB (battery grade).

[0038] mono-UPy-OEG: Single-terminated UPy-capped oligoethylene glycol (OEG) with a structure satisfying the general formula UPy-(CH2CH2O)_n-R (n=2-20, preferably 4-12; R is a C1-C6 alkyl or carbonate end group), and containing only one UPy group in the molecule. mono-UPy-OEG can be commercially available or prepared by conventional methods in the art (e.g., by reacting the active UPy end group with a single-terminated hydroxyl OEG derivative).

[0039] 2. Electrode raw materials: Graphite anode material (battery grade); PTFE binder powder (battery grade, used as a dry fiber network binder); Current collector: copper foil (e.g., 6-12 μm).

[0040] 3. Equipment: Dry mixing equipment (such as high-speed shear mixers / planetary mixers / kneading mixers); Film forming / tableting equipment (hot or cold pressing is acceptable), calender; Vacuum chamber / vacuum liquid injection device; CR2032 button cell assembly tool; Electrochemical testing system.

[0041] II. Electrolyte Preparation Method (General): (1) In a dry environment, EC, EMC and DMC are mixed in a volume ratio of 1:1:1 to obtain a solvent system.

[0042] (2) Add LiPF6 to the above solvent system to make its concentration 1.0 M, stir until completely dissolved, and obtain the basic electrolyte.

[0043] (3) Add mono-UPy-OEG (0.01-0.50 wt%, preferably 0.03-0.20 wt%, more preferably 0.05-0.10 wt%) to the basic electrolyte and stir until uniform and clear.

[0044] (4) Optionally, add synergistic additives LiPO2F2 and / or LiDFOB (0.05-1.00 wt%, preferably 0.10-0.50 wt% based on the mass of the base electrolyte), and stir until uniform and clear to obtain the electrolyte of the example.

[0045] (5) Preferably, the water content of the electrolyte should be controlled to be ≤20 ppm (or the drying and dehydration should be controlled by conventional methods in the field) to avoid the amplification of side reactions and the resulting deviation.

[0046] III. Dry-process graphite / PTFE anode preparation method (general): (1) Weigh the graphite and PTFE according to the total mass of the electrode solids, so that the PTFE content is 1–3 wt% (corresponding to the 1%, 2%, and 3% example groups below, respectively).

[0047] (2) Add graphite and PTFE to a mixing device for dry mixing. It is preferable to use segmented mixing: first, premix the graphite evenly, and then add PTFE for fiber mixing; the total mixing time can be 10-60 min (which can be adjusted according to the shear strength of the equipment) to obtain a uniform PTFE fiber network wrapping and bridging structure.

[0048] (3) Place the mixed powder on the copper foil and form a self-supporting or semi-self-supporting film by pressing / hot pressing and then composite it with the copper foil; hot pressing (e.g., 40-120°C) can be performed to improve adhesion and interface bonding.

[0049] (4) The composite electrode is calendered to achieve a preset range in electrode thickness and compaction density. Preferably, the areal density (area loading corresponding to areal capacity) is controlled within the range of conventional graphite coin cells in the art (e.g., 3-10 mg·cm³). -2 And ensure that the surface density, thickness, and compaction density are consistent or the error is negligible between different comparative examples / implementations.

[0050] (5) The negative electrode sheet (Φ12-14 mm) is obtained by stamping and is ready for use.

[0051] IV. Assembly and Pre-wetting Methods for Button Half-Cells (General): (1) Assemble CR2032 button half-cells in a dry environment: dry graphite electrode is used as working electrode, lithium metal is used as counter electrode, and the separator is a commonly used separator in this field.

[0052] (2) Inject electrolyte (the amount of electrolyte should be in accordance with the requirements of conventional button cells) and let it stand to pre-wet.

[0053] (3) The vacuum-pulse pre-wetting / enrichment method can be used for the embodiments: Place the battery after liquid injection in a vacuum environment, evacuate to 10-50 kPa and maintain for 1-10 min; Return to normal pressure and maintain for 1-10 minutes; Repeat the above vacuum / atmospheric pressure cycle 2-8 times; Optionally, the sample can be left to stand at 30-60°C for 0.5-12 hours to promote impregnation and enrichment of additives within the pore / fiber network.

[0054] (4) The comparative example may not use the vacuum-pulse step, but simply stand at normal pressure for the same time to form a control.

[0055] V. Electrochemical Testing Methods (General): (1) The first charge and discharge cycle was carried out using a conventional graphite half-cell formation process, and the first lithium insertion capacity and the first lithium extraction capacity were recorded.

[0056] (2) The first-cycle coulombic efficiency (ICE) is calculated as follows: ICE = (first-cycle lithium insertion / extraction capacity / first-cycle lithium insertion capacity) × 100%.

[0057] (3) Test at least n≥3 batteries for each condition, and take the average value or statistical interval to reduce random errors.

[0058] The test results of this invention are shown in Table 1.

[0059] Table 1

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An electrolyte additive, characterized in that, This includes single-ended UPy-terminated oligoethylene glycol, the general structural formula of which is: UPy-L-(CH2CH2O) n -R; Where L is a carbamate group; n = 4 to 12; and R is a methyl group.

2. A carbonate electrolyte, characterized in that, Includes the electrolyte additive as described in claim 1.

3. The carbonate electrolyte as described in claim 2, characterized in that, The electrolyte additive accounts for 0.01% to 0.50% of the total mass of the carbonate electrolyte.

4. The carbonate electrolyte as described in claim 2, characterized in that, It also includes LiPO2F2 and / or LiDFOB.

5. The carbonate electrolyte as described in claim 4, characterized in that, The mass percentage of LiPO2F2 and / or LiDFOB is 0.05% to 1.00% of the total mass of the carbonate electrolyte.

6. The carbonate electrolyte as described in claim 2, characterized in that, It also includes lithium salts and solvents, with the solvent being a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

7. The carbonate electrolyte as described in claim 6, characterized in that, The lithium salt was LiPF6 with a concentration of 1.0 M; the volume ratio of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate was 1:1:

1.

8. A lithium-ion battery, characterized in that, Includes the carbonate electrolyte as described in any one of claims 2 to 7.

9. The lithium-ion battery as described in claim 8, characterized in that, It also includes dry graphite / PTFE electrodes, wherein the carbonate electrolyte is vacuum-pulse pre-wetting to enrich the additives within the pore / fiber network of the electrode.

10. The lithium-ion battery as described in claim 8, characterized in that, A coin cell system is constructed using a dry graphite anode with PTFE binder and a lithium metal pair.

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