KR20240047642A - Electrolyte for lithium ion battery containing n-(4-fluorophenyl)maleimide and lithium ion battery including the same - Google Patents

Abstract

The present invention provides N-(4-fluorophenyl)maleimide (FPMI), a functional additive for improving the interfacial stability of Ni-rich NCM anode materials. The present invention relates to an electrolyte solution for a lithium secondary battery containing N-(4-fluorophenyl)maleimide and a lithium secondary battery containing the same, specifically, N-(4-fluorophenyl)maleimide (N-( An electrolyte solution for a lithium secondary battery comprising an additive (4-fluorophenyl)maleimide (FPMI), a solvent, and a lithium salt, and a lithium secondary battery containing the same are provided. FPMI can form a cathode-electrolyte intermediate phase (CEI) layer and a solid electrolyte intermediate phase (SEI) layer through electrochemical oxidation and reduction reactions, which inhibits electrolyte decomposition in the cell.

Description

Electrolyte for lithium secondary battery containing N-(4-fluorophenyl)maleimide and lithium secondary battery containing same {ELECTROLYTE FOR LITHIUM ION BATTERY CONTAINING N-(4-FLUOROPHENYL)MALEIMIDE AND LITHIUM ION BATTERY INCLUDING THE SAME}

The present invention relates to an electrolyte solution for a lithium secondary battery containing N-(4-fluorophenyl)maleimide and a lithium secondary battery containing the same, specifically, N-(4-fluorophenyl)maleimide (N-( The invention relates to an electrolyte solution for a lithium secondary battery, characterized in that it contains a 4-fluorophenyl)maleimide (FPMI) additive, a solvent, and a lithium salt, and a lithium secondary battery containing the same.

A lithium-ion battery (LIB) is a device that can store and consume energy by repeatedly charging and discharging. LIB is receiving a lot of attention in the industry because it can serve as the main power source of EVs, enabling a global EV market to grow exponentially.

Therefore, since the overall energy density generally determines the driving mileage of an EV, numerous studies are being conducted to increase the overall energy density. In this regard, many advanced electrode materials that provide high specific capacity are being developed to replace existing electrode materials such as lithium cobalt oxide (anode) and graphite (cathode).

One prominent next _- generation anode material is Ni- _{rich layered} oxide ₍ LiNi Therefore, the specific capacity of NMC material can be increased by increasing Ni in the NMC structure.

However, Ni ⁴⁺ species, the charging product of Ni-rich NMC materials, are unstable and are easily reduced to Ni ²⁺ species within the cell. In this reduction step, Ni ⁴⁺ species receive electrons from the electrolyte at the electrode interface and continuously decompose the electrolyte within the cell.

When this decomposition reaction occurs, fluoride (F ^- , a decomposition adduct of the electrolyte) reacts with the metal component in the NMC structure, causing irreversible elution of the metal component into the electrolyte solution. As a result, the eluted MF _x complex is reduced on the interface of the cathode, greatly increasing the resistance of the cathode and ultimately causing a decrease in cycling performance.

These limitations of NMC have attracted considerable attention for advanced cathode materials such as SiO _x . _SiO Nevertheless, it still suffers from poor lifespan in the cell due to the occurrence of severe volume expansion and extraction accompanied by rapid deformation of the cathode along with fine differentiation _of the SiO These changes cause a rapid collapse in cycling conservation.

This parasitic reaction is also a response to exposure to new surfaces, which accelerates the ongoing electrolyte breakdown within the cell. In particular, all these advanced electrode materials generally suffer from low interfacial stability, which is a major bottleneck limiting their widespread use in high energy density-based LIBs.

Republic of Korea Patent Publication No. 10-2018-0098366

High-energy-density cells fabricated by _SiO

The present invention relates to an electrolyte solution for a lithium secondary battery containing N-(4-fluorophenyl)maleimide and a lithium secondary battery containing the same, specifically, N-(4-fluorophenyl)maleimide (N-( The invention relates to an electrolyte solution for a lithium secondary battery, characterized in that it contains a 4-fluorophenyl)maleimide (FPMI) additive, a solvent, and a lithium salt, and a lithium secondary battery containing the same.

In order to solve the above problems, the present invention proposes the incorporation of N-(4-fluorophenyl)maleimide (FPMI) as an electrolyte additive that can simultaneously improve the surface stability of the Ni-rich NMC anode and SiO _x cathode. .

Depending on its electrochemical reactivity, electrolyte additives can create a cathode-electrolyte interphase (CEI) layer on the anode or a solid electrolyte interphase (SEI) layer on the cathode.

These layers can be considered task-specific surface layers with electronic insulating and ion conducting properties. The intrinsic behavior of the electrolyte means that electrolyte decomposition at the interface can be efficiently managed.

The present invention proposes an FPMI additive (composed of maleimide and fluorinated functional groups) to promote the simultaneous formation of a maleimide-based CEI layer and a LiF-based SEI layer.

Specifically, FPMI oxidation in the charging step promotes the formation of maleimide-functionalized partial negative charges on the developing CEI layer on the Ni-rich NMC anode. It is advantageous not only for suppressing electrolyte decomposition but also for increasing Li ⁺ movement between electrodes.

Additionally, electrochemical reduction of the FPMI additive can improve the lifespan of the cell by forming a LiF-based SEI layer on the SiO _x cathode. LiF has high mechanical strength and can effectively prevent decomposition and micronization of SiO _x anode material caused by severe volume expansion and detachment within the cell.

Based on these considerations, the present invention evaluated the effect of the inclusion of FPMI additives on the Ni-rich NMC anode and SiO _x cathode, and explained the role of the FPMI additive using ex-situ analysis of recovered cells.

According to one embodiment of the present invention, an electrolyte solution for a lithium secondary battery containing an N-(4-fluorophenyl)maleimide (FPMI) additive, a solvent, and a lithium salt is provided.

The N-(4-fluorophenyl)maleimide (FPMI) additive is characterized in that it contains a fluoro functional group (F-) and a maleimide functional group.

The N-(4-fluorophenyl)maleimide (FPMI) additive forms LiF and N-C=O functional groups by electrochemical reduction, and forms N-C=O functional groups by electrochemical oxidation. It is characterized by forming a .

The additive is characterized in that it contains 0.5% by weight or more and 5.0% by weight or less based on the weight of the electrolyte.

The solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), vinyl It is characterized in that it includes one or more selected from the group consisting of lene carbonate (VC), vinyl ethylene carbonate (VEC), propylene carbonate (PC), and butylene carbonate (BC), but is not limited thereto.

The solvent preferably contains ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a ratio of 1:2 (v/v%).

The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI It may be at least one selected from the group consisting of, but is not limited thereto.

The lithium salt concentration is characterized as having a concentration of 0.01 to 2M.

According to another embodiment of the present invention, an anode; cathode; and an electrolyte layer disposed between the positive electrode and the negative electrode, wherein the electrolyte layer includes the electrolyte solution described above.

The anode is LNMC (LiNi _0.83 Co _0.10 Mn _0.07 O ₂ ) and the cathode is SiO _x (0 < x ≤ 1).

A solid electrolyte interphase (SEI) layer is formed between the cathode and the electrolyte layer, and the solid electrolyte interphase (SEI) layer includes an N-C=O functional group and a LiF functional group.

A cathode-electrolyte interphase (CEI) layer is formed between the anode and the electrolyte layer, and the cathode-electrolyte interphase (CEI) layer includes an N-C=O functional group.

In the present invention, N-(4-fluorophenyl)maleimide (N-( 4-fluorophenyl)maleimide (FPMI) was used.

Electrochemical reduction and oxidation of FPMI additives promote the formation of SEI layer and CEI layer on SiO _x cathode and Ni-rich NMC anode, respectively. The addition of FPMI also significantly increases the cycling retention rate because the FPMI-derived SEI and CEI layers effectively inhibit electrolyte decomposition during cycling, thereby improving the lifetime of the cell.

Additional spectroscopic analysis results show that the SEI layer and CEI layer developed on each electrode effectively prevent parasitic reactions such as electrolyte decomposition as well as transition metal elution within the cell, thereby improving the surface stability of the cell.

Electrochemical reduction of the FPMI additive forms LiF and NC=O functional groups, which are incorporated into the SEI layer of the SiO _x cathode.

Electrochemical oxidation of FPMI also produces N-C=O functional groups incorporated into the CEI layer of the LNMC anode.

Additional _in situ analysis by SEM and

These results support the conclusion that the FPMI additive significantly improves the lifetime of LNMC/SiO _x full cells by simultaneously creating a task-specific functionalized interfacial layer by a simple electrochemical reaction.

Specifically, the cell containing the standard electrolyte showed a continuous decrease in capacity as the cycle progressed, and only 69.4% of the capacity was maintained even after 100 cycles.

In contrast, cycling retention was higher _for LNMC/SiO increased to

Figure 1 is (a) a schematic diagram showing the role of N-(4-fluorophenyl)maleimide) (FPMI) additive on the surface of LNMC anode and SiO _x cathode, (b) molecular structure of FPMI additive and use of FPMI A diagram showing the strategy, and (c) the ionic conductivity of the standard electrolyte, 0.5 FPMI, and 5.0 FPMI added electrolytes.
Figure 2 shows (a) cycling retention and (b) rate capacity of SiO _x /LNMC811 full cells at 25 °C, _and (c) cycling retention and (d) rate capacity of SiO Electrode recovery and reassembly: Graph showing the potential profiles of (e) LNMC half-cell and (f) SiO _x half-cell at 0.1 C, second cycle.
Figure 3 shows cross-sectional SEM images of _SiO , XPS spectra for (e) standard electrolyte and (f) SiO _x cathode cycled with 5.0 FPMI; Represents C1s, F1s and N1s elements.
Figure 4 shows SEM images and EDS of LNMC anodes cycled with (a) standard electrolyte and (b) 5.0 FPMI after 100 cycles, and XPS spectra for LNMC anodes cycled with (c) standard electrolyte and (d) 5.0 FPMI. ; Represents C1s, F1s and N1s elements.

Hereinafter, the present invention will be described in more detail through examples. However, these examples are only intended to aid understanding of the present invention, and the scope of the present invention is not limited to these examples in any way.

Experiment

The LNMC (LiNi _0.83 Co _0.10 Mn _0.07 O ₂ , L&F material) anode was prepared as follows. 1.8 g of LNMC cathode material was stirred with 0.1 g of poly(vinylidene fluoride) (Kureha) and 0.1 g of carbon-conducting agent (Super-P) and then mixed with 1.8 mL of N-methylpyrrolidone (Pyrrolidone). Mixed and mechanically stirred for 1 hour. The obtained slurry was cast on an Al current collector. The LNMC anode was dried in a vacuum oven at 120°C for 12 hours before use. _{The SiO} The resulting slurry was coated on a Cu current collector. The SiO _x cathode was dried in a vacuum oven at 110°C for 11 hours before use.

The electrolyte was prepared as follows. The composition of the standard electrolyte is a mixture of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) in a 1:2 volume ratio and 1.0 M LiPF ₆ (donghwa electrolyte). The FPMI (Sigma-Aldrich) additive was added to the standard electrolyte solution in various amounts (0.5 wt%: 0.5 FPMI, 5.0 wt%: 5.0 FPMI). After preparing each electrolyte solution, the ionic conductivity at room temperature was measured using a conductivity meter (CM-41X, TOADKK).

The lifespan of the battery was evaluated by assembling a coin full cell with an LNMC anode, SiO _x cathode, separator, and each electrolyte. Afterwards, the battery was charged and discharged in the range of 3.0 to 4.2 V (vs Li/Li ⁺ ) at a rate of 0.1 C (formation step, 2 cycles) and 1.0 C (cycling step, 100 cycles).

When cycling was completed, the battery was disassembled and the LNMC anode and SiO _x cathode were recovered in an Ar-filled glove box. For the recovery test, a half cell was assembled for each electrode using pure Li metal, a separator, and a standard electrolyte solution, and the specific capacity of the recovered electrode was confirmed.

Cells assembled with the recovered LNMC anode were charged and discharged at 3.0 to 4.3 V (vs.Li/Li ⁺ ), and cells assembled with the recovered SiO _x cathode were charged and discharged at 1.5 to 0.005 V (vs.Li/Li ⁺ ). Charging and discharging were performed.

The surface behavior of each cycled electrode was analyzed by field emission scanning electron microscopy (FE-SEM, JSM-7001F, JEOL), and the chemical composition of each electrode was analyzed by X-ray photoelectron spectroscopy (XPS, PHI 5000 Versa Probe, ULVAC-PHI). was analyzed.

Results and Discussion

Figures 1A and 1B show the expected effects of FPMI additives on the cell and its molecular structure. Since the FPMI additive contains dual functionalized functional groups (F and maleimide moieties), the electrochemical reaction (reduction and oxidation) forms an F-based SEI layer and a maleimide-based CEI layer on the surfaces of the SiO _x cathode and LNMC anode, respectively. can do.

Since these SEI layers and CEI layers are essential for stable long-term preservation of the _SiOx cathode and LNMC anode, the use of FPMI additives was expected to help increase the cycling retention of the constructed cells.

The ionic conductivity measurements (FIG. 1c) were 8.12 mS cm ^-1 for the standard electrolyte solution, 7.65 mS cm ^-1 and 6.38 mS cm ^-1 for the electrolyte solution containing 0.5 FPMI and 5.0 FPMI, respectively.

It was found that the ionic conductivity decreased as the FPMI content increased, but the ionic conductivity was sufficient for use in LIB.

Figure 2a shows the cycling preservation state of LNMC/SiO _x full cells at room temperature with and without FPMI additive.

The cell containing the standard electrolyte showed a continuous decrease in capacity as the cycle progressed, and only 69.4% of the capacity was maintained even after 100 cycles.

In contrast, cycling retention was higher _for LNMC/SiO increased to

C-rate performance at room temperature (Figure 2b) was further improved when cycling with 0.5 FPMI electrolyte compared to the standard electrolyte. At slow speeds (less than 0.2 C), the retention rates of the standard FPMI electrolyte and the 5.0 FPMI electrolyte were similar, but above 0.5 C, significant differences appeared.

Cells cycled at 2.0 C with 5.0 FPMI electrolyte showed a 5.4% higher retention rate than cells without FPMI additive (standard electrolyte: 62.0%, 5.0 FPMI: 67.4%).

This indicates that the use of FPMI additive improves the cycling behavior of cells composed of LNMC/SiO _x electrode material.

Similar electrochemical behavior was observed even at high temperatures (Figures 2c and 2d). Cycling at high temperatures accelerated parasitic reactions such as electrolyte decomposition, resulting in a lower overall retention rate compared to cycling at room temperature.

In detail, the cell containing the standard electrolyte solution showed a retention rate of 65.8%, which was found to reflect the occurrence of undesirable interfacial reactions within the cell.

In contrast, cells cycled with 5.0 FPMI showed a clearly improved retention rate after 100 cycles, with a retention rate of 83.1% observed. This is almost 17.3% higher than when cells were cycled without FPMI additive.

Rate performance at high temperatures also confirmed that cells without FPMI additives continued to experience a sharp decrease in retention rate as C-rate increased due to acceleration of undesirable reactions, especially at high temperatures. In comparison, the cell containing 5.0 FPMI showed a 34.2% higher capacity retention rate than the cell without FPMI additive (standard electrolyte: 32.3%, 5.0 FPMI: 66.5%) at 10.0 C.

The specific role of the FPMI additive in cycling was confirmed by recovering _the cycled LNMC/SiO (Figures 2e and 2f).

In the case of the LNMC anode, the recovered LNMC anode controlled by the standard electrolyte provided only a specific capacity of 147.6 mAh g ^-1 and showed a large undifferentiation evident in the potential profile. The pure LNMC anode typically has a specific capacity of 202.0 mAh g ^-1 in the initial cycle, indicating that significant deformation of the LNMC anode cycled in the absence of FPMI additive occurred during cycling.

In comparison, the recovered LNMC anode using 5.0 FPMI additive showed a specific capacity of 181.0 mAh g ^-1 with less micronization behavior, resulting in less deformation of the LNMC anode.

For _the ^SiO _x cathode ^, the cell containing _the recovered SiO A specific capacity of ¹ was shown.

These results indicate that the FPMI additive suppressed large deformation of the LNMC/SiO _x electrode by suppressing undesirable reactions occurring at the interface of each electrode.

The structure of the recovered SiO _x cathode was analyzed by SEM to verify the effect of the FPMI additive (Figures 3a-3d).

Cross-sectional SEM images showed a significant increase in the thickness (25.0 μm) of the _SiO It _is believed _that the large expansion _of the SiO

The SEM image shown at the top also revealed the presence of many by-products due to the decomposition of the electrolyte accumulated on the SiO _x cathode surface, making it difficult to distinguish the boundaries of SiO _x particles in the cathode cycle without FPMI additive.

However, it was confirmed that there was little surface deformation and little electrolyte decomposition in the _SiO EDS analysis revealed interesting spectroscopic evidence supporting relatively higher amounts of Ni _and F species in the recovered _SiO It suggests that it was formed in

XPS results suggest the occurrence of an SEI layer on the SiO _x cathode (Figures 3e and 3f).

The C1s spectrum generally showed C-C (285.0 eV), C-O (286.7 eV), C=O (288.1 eV), and RCOOR (290.0 eV). In particular, C-O, C=O, and RCOOR are considered evidence of electrolyte decomposition.

As a result of the analysis, the decomposed C1s peak appeared larger in the cell cycle without using the FPMI additive, indicating that less electrolyte decomposition occurred in the presence of the FPMI additive.

_The recovered SiO It can be seen that the configured SEI layer can be formed.

The F1s spectrum showed resolved peaks related to Li _x PO _y F _z (686.5 eV) in the form of PF (687.5 eV) and Li _x PF _y (688.4 eV) for both _SiO The recovered SiO _x cathode that was cycled showed lower intensity peaks, which was consistent with the C1s XPS results.

In addition, the intensity of LiF (685.3 eV) was higher in the _SiO

Accordingly, electrochemical reduction of FPMI additives can promote the formation of LiF- and maleimide-functionalized SEI layers on the SiO _x cathode.

The recovered LNMC anode showed similar behavior in SEM analysis (Figures 4a and 4b).

The LNMC anode cycled without using FPMI additives had a large number of decomposed additives accumulated on the surface, making grain boundary discrimination of primary particles difficult. EDS analysis showed that the intensity of the F element in the LNMC anode without FPMI additive was higher than in the case with FPMI additive, which showed that more electrolyte decomposition occurred in the absence of FPMI additive.

On the other hand, the recovered LNMC anode with FPMI additive had a cleaner surface, showing that undesirable parasitic reactions within the cell were suppressed.

XPS analysis of the recovered LNMC anode also supported the inhibition of this undesirable reaction (Figures 4c and 4d).

The typical C1s peak associated with electrolyte decomposition was found for both electrodes, but the peak was much less intense for the recovered LNMC anode cycled using FPMI additive.

_The F1s _spectrum also showed peaks related to electrolyte decomposition _{, such} as _Li It showed lower intensity, which was consistent with the C1s XPS results. Interestingly, only the LNMC anode with FPMI additive showed NC=O peaks in the C1s and N1s spectra. These peaks originated from the molecular structure of the FPMI additive, and their presence was in good agreement with the EDS results for the LNMC anode using the FPMI additive.

Taken together, these strongly indicate that N-C=O chemical moieties (functional groups) are incorporated into the functionalized CEI layer of the LNMC anode due to electrochemical oxidation of the FPMI additive. This is expected to inhibit electrolyte decomposition.

These ex-situ analysis results show that the electrochemical reaction caused by the FPMI additive can simultaneously form an SEI layer containing LiF and NC=O functional groups on the surface of the SiO _x cathode and NC=O functional groups on the surface of the LNMC anode. This leads to the conclusion that a CEI layer can be formed.

conclusion

In the present invention, we propose a dual-functional FPMI additive as an electrolyte additive for LNMC/SiO _x full cells that simultaneously improves the interfacial stability of the cathode and anode. Electrochemical reduction of the FPMI additive forms LiF and NC=O functional groups, which are incorporated into the SEI layer of the SiO _x cathode. Electrochemical oxidation of FPMI also produces NC=O functional groups incorporated into the CEI layer of the LNMC anode. Additional _in situ analysis by SEM and

These results support the conclusion that the FPMI additive significantly improves the lifetime of LNMC/SiO _x full cells by simultaneously creating a task-specific functionalized interfacial layer by a simple electrochemical reaction.

The present invention described above is not limited to the above-described embodiments, as various substitutions and changes can be made by those skilled in the art without departing from the technical spirit of the present invention. .

Claims (12)

An electrolyte solution for a lithium secondary battery, comprising an N-(4-fluorophenyl)maleimide (FPMI) additive, a solvent, and a lithium salt.
According to paragraph 1,
The N-(4-fluorophenyl)maleimide (FPMI) additive is lithium, characterized in that it contains a fluoro functional group (F-) and a maleimide functional group. Electrolyte for secondary batteries.
According to paragraph 1,
The N-(4-fluorophenyl)maleimide (FPMI) additive forms LiF and NC=O functional groups by electrochemical reduction, and forms NC=O functional groups by electrochemical oxidation. An electrolyte for a lithium secondary battery, characterized in that it forms.
According to paragraph 1,
An electrolyte for a lithium secondary battery, characterized in that the additive contains 0.5% by weight or more and 5.0% by weight or less based on the weight of the electrolyte.
According to claim 1,
The solvent is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), ethylene carbonate (EC), vinyl An electrolyte solution for a lithium secondary battery, comprising at least one selected from the group consisting of lene carbonate (VC), vinyl ethylene carbonate (VEC), propylene carbonate (PC), and butylene carbonate (BC).
According to clause 5,
An electrolyte for a lithium secondary battery, characterized in that the solvent contains ethylene carbonate (EC):ethyl methyl carbonate (EMC) in a ratio of 1:2 (v/v%).
According to paragraph 1,
The lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiCl and LiI An electrolyte for a lithium secondary battery, characterized in that it is at least one selected from the group consisting of.
According to paragraph 1,
An electrolyte solution for a lithium secondary battery, characterized in that the lithium salt concentration is 0.01 to 2M.
anode; cathode; And an electrolyte layer disposed between the anode and the cathode,
The electrolyte layer is a lithium secondary battery, characterized in that it contains the electrolyte solution according to any one of claims 1 to 8.
According to clause 9,
A lithium secondary battery, characterized in that the positive electrode is LNMC (LiNi _0.83 Co _0.10 Mn _0.07 O ₂ ) and the negative electrode is SiO _x (0 < x ≤ 1).
According to clause 9,
A solid electrolyte interphase (SEI) layer is formed between the cathode and the electrolyte layer, and the solid electrolyte interphase (SEI) layer includes a NC=O functional group and a LiF functional group. Secondary battery.
According to clause 9,
A lithium secondary battery characterized in that a cathode-electrolyte interphase (CEI) layer is formed between the anode and the electrolyte layer, and the cathode-electrolyte interphase (CEI) layer includes an NC=O functional group.