Electrolyte and lithium ion battery
By using a combination of silane phosphates and fluorinated pyridine compounds with lithium salts in lithium-ion batteries, optimizing the electrolyte composition and constructing a dynamic stability layer at the electrode interface, the problem of high internal resistance of lithium-ion batteries was solved and battery performance was improved.
Patent Information
- Application Number
- CN202510730188.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-03
- Publication Date
- 2025-09-19
AI Technical Summary
The internal resistance of existing lithium-ion batteries is relatively high, which affects battery performance and safety. There are limited improvements to existing electrolytes, and single-component additives have limited effects.
Silane phosphate compounds and fluorine-containing pyridine compounds are used as additives, combined with lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide salts, to optimize the electrolyte composition through synergistic effects, construct a dynamic stability layer at the electrode interface, and reduce internal resistance.
Significantly reduce the internal resistance of lithium-ion batteries, improve the battery's power density, charge and discharge efficiency, and low-temperature performance, extend battery life, and improve safety.
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Figure CN120674590A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to an electrolyte and a lithium ion battery. Background Art
[0002] Compared to other types of secondary batteries, lithium-ion batteries offer advantages such as high energy density, long cycle life, fast charging capability, and non-toxicity. These advantages make lithium-ion batteries an ideal choice for modern consumer electronics, power tools, electric vehicles, and energy storage systems. The internal resistance of lithium-ion batteries significantly impacts battery performance, including energy density, power output, and cycle life. Lower internal resistance improves battery efficiency during charge and discharge, reducing heat generation and extending battery life and safety.
[0003] As a medium for ion transport, the electrolyte directly impacts the conductivity, cycle life, safety, and temperature adaptability of lithium-ion batteries. The internal resistance of a lithium-ion battery is closely related to the performance of its electrolyte. Optimizing the electrolyte can effectively reduce internal resistance, thereby improving the battery's power density, charge and discharge efficiency, and low-temperature performance.
[0004] Adjusting the electrolyte to reduce the internal resistance of lithium-ion batteries primarily involves four key approaches. First, improving the electrolyte's conductivity. Selecting a solvent with higher ionic conductivity or adding an appropriate amount of conductive additives can effectively reduce the battery's internal resistance. Generally, the lithium salt concentration in the electrolyte needs to be optimized, neither too low nor too high. Too low a concentration can lead to insufficient ionic conductivity, while too high a concentration can result in excessive viscosity, affecting the migration rate of lithium ions.
[0005] Secondly, use high-purity solvents and lithium salts. Impurities increase the internal resistance of the battery, so using high-purity solvents and lithium salts helps reduce unnecessary side reactions and impurities that hinder ion transport, thereby reducing internal resistance.
[0006] Secondly, optimize the solvent combination. By mixing different organic solvents, the physicochemical properties of the electrolyte (such as viscosity, boiling point, and melting point) can be adjusted to achieve optimal ion conductivity. For example, a mixture of commonly used carbonate solvents (such as EC / DMC) can provide good film-forming properties while ensuring high ionic conductivity, helping to form a stable SEI layer.
[0007] Finally, functional additives are added. Adding a small amount of functional additives to the electrolyte can improve the quality of the SEI layer. For example, adding additives such as fluoroethylene carbonate (FEC) can promote the formation of a more stable and thinner SEI layer, which not only reduces the interfacial resistance but also improves the safety and cycle life of the battery.
[0008] Considering the overall performance of lithium-ion batteries, the compatibility of the electrolyte with the positive and negative electrodes, there is limited room for improvement in lithium salts and solvents, but single-component functional additives have limited effect on improving the internal resistance of lithium-ion batteries. Summary of the Invention
[0009] In view of the problems existing in the prior art, the present invention aims to provide an electrolyte that can effectively reduce the internal resistance of a lithium-ion battery; another object of the present invention is to provide a lithium-ion battery with low internal resistance.
[0010] The present invention discloses an electrolyte comprising a lithium salt, an organic solvent, and an additive; the additive comprises a silane phosphate compound having a structure represented by formula (I) and a fluorine-containing pyridine compound having a structure represented by formula (II);
[0011] (I); (II);
[0012] Wherein, R1 to R9 are each independently selected from any one of hydrogen, substituted or unsubstituted alkyl, aryl, sulfonate, ether, and cyano; M1 to M4 are each independently selected from any one of hydrogen, fluorine, halogen, substituted or unsubstituted C1 to C20 alkyl, aryl, sulfonate, ether, and cyano.
[0013] The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorooxalatoborate, lithium bisoxalatoborate, lithium difluorophosphate, lithium tetrafluoroborate, lithium bisfluorosulfonyl imide, and lithium bistrifluorosulfonyl imide. It is understood that the lithium salt electrolyte that can be used in the present invention includes but is not limited to the above.
[0014] The additive further includes at least one of vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, fluoroethylene carbonate, propylene sulfite, vinyl ethylene sulfate and vinyl sulfate.
[0015] Furthermore, the silane phosphate compound has a structure shown in any one of the following (T1) to (T6):
[0016]
[0017] Furthermore, the fluorine-containing pyridine compound has a structure shown in any one of the following (S1) to (S8):
[0018]
[0019] Furthermore, the mass ratio of the silane phosphate compound to the fluorine-containing pyridine compound is (10-100):1.
[0020] Furthermore, the amount of the silane phosphate compound added is 0.1% to 1% of the total mass of the electrolyte; and the amount of the fluorine-containing pyridine compound added is 0.01% to 0.1% of the total mass of the electrolyte.
[0021] Furthermore, the additives also include conventional additives, and the addition amount of the conventional additives is 0.5% to 5% of the total mass of the electrolyte; the conventional additives include a combination of vinylene carbonate (VC), fluoroethylene carbonate (FEC), and diethylene sulfate (DTD).
[0022] Furthermore, the lithium source includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the amount of lithium hexafluorophosphate added is 6-10% of the total mass of the electrolyte; the amount of lithium bis(fluorosulfonyl)imide added is 3-6% of the total mass of the electrolyte.
[0023] The combined additives and the synergistic architecture of the dual salts of LiPF6 and LiFSI achieve a breakthrough in conductivity under conditions of similar total salt concentration through the dual mechanisms of enhanced liquid-phase ion mobility and optimized interface compatibility, overcoming the inherent contradiction between ion transport and interface impedance in a single lithium salt system.
[0024] Furthermore, the organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; the ratio of the mass of the ethylene carbonate to the mass of the dimethyl carbonate and the mass of the ethyl methyl carbonate is (2-4): (3-6):2.
[0025] The present invention also discloses a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte as described above.
[0026] The active material of the positive electrode sheet can be lithium cobalt oxide, ternary material, lithium iron phosphate, spinel nickel manganese oxide, etc.
[0027] The active material of the negative electrode sheet can be graphite, silicon-carbon composite material, silicon-oxygen composite material, lithium titanate, etc.
[0028] The diaphragm can use polyolefin-based film, ceramic coating diaphragm, dry / wet process diaphragm.
[0029] The present invention provides an electrolyte, in which a combination of silane phosphate compounds and fluorine-containing pyridine compound additives is added to the electrolyte, and synergistically constructing a dynamic stability layer at the electrode interface or regulating the charge transfer process to achieve efficiency enhancement, thereby realizing the construction of a dynamic stability layer at the electrode interface and effectively reducing the internal resistance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 2 is a graph showing the voltage and dQdV curves of Example 1, Comparative Example 1, and Comparative Example 2 of the present invention. DETAILED DESCRIPTION
[0031] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.
[0032] Example 1
[0033] Preparation of electrolyte:
[0034] In an argon atmosphere glove box (moisture <1 ppm, oxygen <1 ppm), ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly in a mass ratio of 30:50:20, and then two lithium salts, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), were slowly added in the mass ratio shown in Table 1, stirred until they were completely dissolved and mixed uniformly, and then an additive combination of tris(trimethylsilyl) phosphate (the compound structural formula is shown in T1) at 0.3% of the total mass of the electrolyte and 2-fluoropyridine (the compound structural formula is shown in S1) at 0.03% of the total mass of the electrolyte and conventional additives in the mass ratios shown in Table 1 were added to obtain an electrolyte.
[0035] Table 1 Electrolyte ratios of the examples and comparative examples
[0036] serial number Additive combination Conventional additives lithium salts Example 1 0.3% T1+0.03% S1 1.5%VC+1.5%FEC+1%DTD <![CDATA[8%LiPF6+4%LiFSI]]> Example 2 0.3% T1+0.05% S1 1.5%VC+1.5%FEC+1%DTD <![CDATA[8%LiPF6+4%LiFSI]]> Example 3 0.5% T1+0.05% S1 1.5%VC+1.5%FEC+1%DTD <![CDATA[8%LiPF6+4%LiFSI]]> Example 4 0.5% T1+0.05% S1 1.5%VC+1.5%FEC+1%DTD <![CDATA[11.25%LiPF6]]> Comparative Example 1 0.3%T1 1.5%VC+1.5%FEC+1%DTD <![CDATA[8%LiPF6+4%LiFSI]]> Comparative Example 2 0.03% S1 1.5%VC+1.5%FEC+1%DTD <![CDATA[8%LiPF6+4%LiFSI]]> Comparative Example 3 / 1.5%VC+1.5%FEC+1%DTD <![CDATA[8%LiPF6+4%LiFSI]]> Comparative Example 4 0.5% T1+0.05% S1 / <![CDATA[8%LiPF6+4%LiFSI]]>
[0037] The electrolytes of Examples 2 to 4 and Comparative Examples 1 to 4 were prepared in the same manner as in Example 1, with the only differences being the corresponding contents in Table 1, where “ / ” represents no addition, T1 represents tris(trimethylsilyl)phosphate having a structural formula such as T1, and S1 represents 2-fluoropyridine having a structural formula such as S1.
[0038] Assembling the battery:
[0039] Preparation of the positive electrode sheet: The positive electrode active material lithium iron phosphate, the binder polyvinylidene fluoride, the conductive agent carbon black and the carbon tube are mixed in a mass ratio of 97:1:0.5:0.5, N-methylpyrrolidone is added, and the mixture is stirred in a vacuum mixer until stable and uniform to obtain the positive electrode material. After the viscosity is tested and qualified, the obtained positive electrode slurry is coated on an aluminum foil with a thickness of 12µm. The coated aluminum foil is dried in an oven at 100°C, and then rolled and punched to obtain the positive electrode sheet.
[0040] Preparation of the negative electrode sheet: The negative electrode active material graphite, the binder styrene-butadiene rubber, the thickener sodium carboxymethyl cellulose, the conductive agent carbon black and the carbonic acid were mixed in a mass ratio of 98:0.5:0.5:0.5:0.5, deionized water was added, and the mixture was stirred in a vacuum mixer until stable and uniform to obtain a negative electrode slurry. After the viscosity was tested and found to be qualified, the obtained negative electrode slurry was coated on a copper foil with a thickness of 8µm. The copper foil after coating with the slurry was dried in an oven at 100°C, and then rolled and punched to obtain a negative electrode sheet.
[0041] The prepared positive electrode sheet, negative electrode sheet and separator (commercially available ordinary separator) were stacked, encapsulated with aluminum-plastic film to obtain a dry battery cell, and vacuum dried at 85°C.
[0042] Liquid injection and pre-charge formation: In a glove box, the prepared electrolyte is injected into the dry battery cell according to the designed liquid injection coefficient, sealed, placed at room temperature, formed, vented, and sealed again to obtain an activated lithium-ion battery.
[0043] Performance test method for lithium batteries:
[0044] The lithium-ion batteries prepared in the examples and comparative examples were tested, and the specific testing methods are as follows.
[0045] (1) dQdV test: Charge and discharge the battery at a constant current, record the corresponding data of voltage (V) and capacity (Q), perform differential calculation on the QV curve, and obtain the dQdV curve, as shown in the figure. Figure 1 shown.
[0046] (2) DCR test: Ensure the battery is in a stable state (no charge or discharge) and record the initial voltage. Apply a current pulse, applying a constant DC current I for a short period of time (e.g., 1C for a few seconds), and record the voltage change ΔV. Calculate the resistance: DCR = ΔV / applied current (I), i.e., R = ΔV / I. The test results are shown in Table 2.
[0047] Table 2 DCR test results
[0048] serial number DCR@50%SOC Example 1 0.51 Example 2 0.59 Example 3 0.56 Example 4 0.58 Comparative Example 1 0.63 Comparative Example 2 0.63 Comparative Example 3 0.72 Comparative Example 4 0.70
[0049] As shown in Table 2, the low concentration synergistic combination of tris(trimethylsilyl)phosphate (0.3%) and 2-fluoropyridine (0.03%) (as in Example 2) exhibited the lowest DC resistance (DCR=0.51). Figure 1 As shown, it is worth noting that the dQdV test further reveals a unique synergistic mechanism: when tris(trimethylsilyl) phosphate (such as Comparative Example 1) or 2-fluoropyridine (such as Comparative Example 2) is used alone, the dQdV curve does not show a characteristic response peak in the 1.47V potential range, while the additive combination (such as Example 1) shows a significant characteristic peak in this region. This phenomenon is highly correlated with the DCR reduction trend, confirming that the addition of tris(trimethylsilyl) phosphate and 2-fluoropyridine may achieve impedance optimization by inducing a specific interface reaction path.
[0050] The absence of the characteristic dQdV peak in Comparative Examples 1 and 2 indicates that the electrolyte system containing only tris(trimethylsilyl)phosphate or 2-fluoropyridine fails to activate the unique electrochemical response mechanism of the composite additive. It is speculated that tris(trimethylsilyl)phosphate and 2-fluoropyridine may achieve enhanced performance by synergistically constructing a dynamic stability layer at the electrode interface or regulating the charge transfer process. The combination of tris(trimethylsilyl)phosphate and 2-fluoropyridine, which induces a specific interfacial reaction pathway (activation of the 1.47V characteristic peak), achieves the construction of a dynamic stability layer at the electrode interface, overcoming the technical bottleneck of traditional single-component additives in effectively reducing DCR.
[0051] When the component concentrations were adjusted to higher levels (such as in Examples 2 and 3), the DCR values rebounded to varying degrees (0.59 and 0.56, respectively), but the composite system still maintained performance superior to that of the single-component system (DCR of 0.63).
[0052] As shown in Comparative Example 4, even with a high concentration of tris(trimethylsilyl)phosphate (0.5wt%) and 2-fluoropyridine (0.05wt%), the DCR remains as high as 0.70, far exceeding all other examples. This fully demonstrates the key role of conventional additives in regulating interfacial resistance. Furthermore, the combination of tris(trimethylsilyl)phosphate, 2-fluoropyridine, and conventional additives significantly reduces the internal resistance of lithium-ion batteries.
[0053] Further analysis of the synergistic effect of lithium salts shows that Example 3 uses a dual salt system of LiPF6 (8%) and LiFSI (4%) (DCR=0.56), which exhibits better conductivity than the single LiPF6 system of Example 4 (11.25%, DCR=0.58). Although the total lithium salt concentration of Example 4 is close to the total amount of the combination of Example 3, the lack of LiFSI still leads to a slight increase in resistance, revealing that LiFSI may enhance efficiency through a dual mechanism, namely, enhancing the mobility of ions in the electrolyte liquid phase and improving the compatibility of the electrode / electrolyte interface to reduce the interfacial impedance. The additive combination combines the synergistic architecture of the dual salts of LiPF6 and LiFSI, and achieves a breakthrough in conductivity under conditions of similar total lithium salt concentration through the dual mechanisms of enhanced liquid phase ion mobility and optimized interfacial compatibility, overcoming the inherent contradiction between ion transport and interfacial impedance of a single lithium salt system.
[0054] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.
Claims
1. An electrolyte, characterized in that: It includes lithium salt, organic solvent and additives; the additives include silane phosphate compounds with the structure shown in formula (I) and fluorine-containing pyridine compounds with the structure shown in formula (II); （Ⅰ）； （Ⅱ）； Wherein, R1 to R9 are each independently selected from any one of hydrogen, substituted or unsubstituted alkyl, aryl, sulfonate, ether, and cyano; M1 to M4 are each independently selected from any one of hydrogen, fluorine, halogen, substituted or unsubstituted C1 to C20 alkyl, aryl, sulfonate, ether, and cyano.
2. An electrolyte according to claim 1, characterized in that The silane phosphate compound has a structure shown in any one of (T1) to (T6):
3. The electrolyte according to claim 2, wherein The fluorine-containing pyridine compound has a structure shown in any one of (S1) to (S8):
4. An electrolyte according to claim 3, characterized in that The mass ratio of the silane phosphate compound to the fluorine-containing pyridine compound is 10-100:
1.
5. The electrolyte according to claim 1, characterized in that The amount of the silane phosphate compound added is 0.1% to 1% of the total mass of the electrolyte.
6. An electrolyte according to claim 5, characterized in that: The amount of the fluorine-containing pyridine compound added is 0.01% to 0.1% of the total mass of the electrolyte.
7. An electrolyte according to claim 1, characterized in that The additives also include conventional additives, and the addition amount of the conventional additives is 0.5% to 5% of the total mass of the electrolyte; the conventional additives include a combination of vinylene carbonate, fluoroethylene carbonate, and vinyl sulfate.
8. The electrolyte according to claim 1, characterized in that The lithium source includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide; the amount of lithium hexafluorophosphate added is 6-10% of the total mass of the electrolyte; the amount of lithium bis(fluorosulfonyl)imide added is 3-6% of the total mass of the electrolyte.
9. The electrolyte according to claim 1, characterized in that The organic solvent includes ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate; the mass ratio of the ethylene carbonate to the dimethyl carbonate and the ethyl methyl carbonate is 2-4:3-6:
2.
10. A lithium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte according to any one of claims 1 to 9.