KR102612069B1 - Separator for lithium ion battery containing tungsten oxide and trimesitylborane, manufacturing method thereof and lithium ion battery including the same - Google Patents

Abstract

In the present invention, the electrochemical performance of LIB is improved by developing a radical scavenging membrane functionalized with WO ₃ and TMB. TMB, a radical scavenging agent, is first inserted into the surface of WO ₃ through a simple condensation reaction. Then, a WO ₃ -TMB functionalized PE separator is formed through a dip coating process. An ex situ screening test using the chemical reaction between TMB, AIBN and a radical indicator (DPPH) confirmed that TMB effectively removes radical species by chemical reaction, confirming that the WO ₃ -TMB functionalized PE separator is electrochemical. This suggests that the chemical stability of the cell can be increased during the reaction.

Description

Separator for lithium secondary battery containing tungsten oxide and trimethylborane composite, manufacturing method thereof, and lithium secondary battery containing same

The present invention relates to a separator for a lithium secondary battery containing a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB), a method of manufacturing the same, and a lithium secondary battery containing the same.

Over the past few years, lithium-ion batteries (LIBs) have been considered the most convenient energy storage tool for small devices such as laptops and mobile phones. Currently, the application area of LIB is expanding exponentially to large-scale devices such as electric vehicles and energy storage systems. Therefore, increasing the energy density of LIBs has become an important technical issue because energy density has a significant impact on the overall specifications of the application. The energy density of a LIB cell is mainly influenced by the specific capacity of the cell voltage. Therefore, many attempts have been made to develop advanced electrode materials that can meet these requirements.

This is why Ni-rich layered ternary oxide (LiNi _x Co _y Mn _z O ₂ (NCM) or LiNi _x Co _y Al _z O ₂ (NCA) This is because the specific capacity of the oxide is large. Additionally, Si or Li metal has been considered as a promising advanced cathode material for advanced LIBs due to its specific capacity almost 10 times higher than that of conventional graphite cathodes.

Nevertheless, many technical challenges still remain in the fabrication of high energy density-based LIBs. One problem arises from undesirable surface reactions arising from the continued electrolyte decomposition of the electrode surface. Although the overall energy density of LIBs has increased by replacing older electrode materials with these advanced electrode materials, electrolyte decomposition is also much accelerated on the advanced material electrode surfaces due to the much higher surface reactivity.

In fact, the electrochemical oxidation reaction of the Ni-rich NCM anode material within the cell generates quite unstable Ni ⁴⁺ species on the surface of the Ni-rich NCM anode material, and these Ni ⁴⁺ species are converted to Ni ²⁺ through an electron transfer reaction with the nearby electrolyte. tends to decrease. This is a highly reactive radical species in the cell that can cause electrolyte breakdown and trigger uncontrollable cascade degradation of cell components. In particular, as the energy density of LIB increases, these undesired reactions become unavoidable. Therefore, it is necessary to reduce the radical concentration in the cell to increase the safety of LIB.

Republic of Korea Patent Publication No. 10-2020-0088657

In the present invention, when trimesitylborane (TMB) is fixed to tungsten oxide (WO ₃ ), the WO ₃ -TMB complex is easily coated on the PE separator by a simple dip coating process to quickly remove nearby radical species formed by electrolyte decomposition. I expected that I could easily erase it. The WO ₃ -TMB functionalized PE separator is effective in reducing the radical concentration of the cell and can improve the cycling performance of the cell. Based on these considerations, the WO ₃ -TMB functionalized PE separator is prepared in a two-step process, and its physicochemical and electrochemical properties are systematically explored using Ni-rich NCM anode material.

The present invention proposes a new strategy using a functional membrane composed of radical scavenging reagents for the removal of radical species from cells. In detail, trimethylborane (TMB), a radical scavenger, is embedded in the surface of nano-sized tungsten oxide (WO ₃ ) through a simple one-step process, and the resulting nanoparticles are produced by a dip coating process. It is coated on the existing separator. The screening test of the present invention conducted by chemical reaction of TMB, AIBN (Azobisobutyronitrile) and radical indicator substance (2,2-dipenyl-1-picrylhydrazyl, DPPH) confirmed that TMB effectively removes radical species through chemical reaction. This suggests that the use of a WO ₃ -TMB functionalized separator is effective in reducing radical concentration during the electrochemical process.

In electrochemical tests, cells cycled using the WO ₃ -TMB functionalized separator showed improved cycle retention and improved physical and mechanical properties compared to cells cycled without the separator.

In order to solve the above technical problem, the present invention provides a separator for a lithium secondary battery containing a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB).

In the present invention, a dual-functionalized radical scavenging reactive separator is proposed to improve the electrochemical performance of LIB (Figure 1a). The present approach is based on embedding effective radical scavengers into the separation membrane. However, because PE membranes are composed of highly stable aliphatic carbon-hydrogen components, commonly used poly(ethylene) (PE) membranes present serious limitations for the introduction of functional radical scavengers.

Therefore, since the hydroxyl group (OH) on the surface of WO ₃ can chemically bond with the radical scavenger trimethylborane (TMB), tungsten was used as an interlayer to embed the radical scavenging agent in the PE separator. Oxide (WO ₃ ) is used.

The separator for a lithium secondary battery is characterized in that the separator is coated with a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB).

The trimesitylborane (TMB) is characterized in that it is embedded in the surface of the tungsten oxide (WO ₃ ).

The surface of the separator for a lithium secondary battery is characterized in that a tungsten oxide (WO ₃ )-trimesitylborane (TMB) layer having an average thickness of 12 μm is disposed.

The separator for a lithium secondary battery containing a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB) is a separator for a lithium secondary battery that does not contain a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB). It is characterized by a reduced contact angle compared to a separator.

According to another embodiment of the present invention, trimesitylborane (TMB) is embedded in the surface of tungsten oxide (WO ₃ ) through a condensation reaction to form a complex of tungsten oxide (WO ₃ ) and trimesitylborane (TMB). steps to prepare; and coating the surface of the separator for a lithium secondary battery with the tungsten oxide (WO ₃ ) and trimesitylborane (TMB) composite.

The surface of the separator for a lithium secondary battery is characterized in that a tungsten oxide (WO ₃ )-trimesitylborane (TMB) layer having an average thickness of 12 μm is disposed.

The separator for lithium secondary batteries coated with the tungsten oxide (WO ₃ ) and trimesitylborane (TMB) composite is for lithium secondary batteries that does not contain the tungsten oxide (WO ₃ ) and trimesitylborane (TMB) composite. It is characterized by a reduced contact angle compared to a separator.

According to another embodiment of the present invention, an anode; cathode; and an electrolyte layer and a separator disposed between the anode and the cathode, wherein the separator is a separator according to an embodiment of the present invention.

The anode is characterized in that it contains LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811).

According to one embodiment of the present invention, the electrochemical performance of LIB is improved by developing a radical scavenging membrane functionalized with WO ₃ and TMB. TMB, a radical scavenging agent, is first inserted into the surface of WO ₃ through a simple condensation reaction. Then, a WO ₃ -TMB functionalized PE separator is formed through a dip coating process.

An ex situ screening test using the chemical reaction between TMB, AIBN and a radical indicator (DPPH) confirmed that TMB effectively removes radical species by chemical reaction, confirming that the WO ₃ -TMB functionalized PE separator is electrochemical. This suggests that the chemical stability of the cell can be increased during the reaction.

In fact, the cycling retention of cells cycled with WO ₃ -TMB functionalized membranes was improved compared to cells cycled with bare membranes because they suppressed continued electrolyte decomposition by terminating the reaction of reactive radical species during the electrochemical process.

This approach in the present invention will be an effective way to improve the cycle performance of LIB without serious trade-off effects in the cell.

Figure 1 shows (a) a schematic diagram of the manufacturing method and functionalization of WO ₃ -TMB-embedded PE, (b) SEM/EDS of the surface morphology of WO ₃ -TMB-embedded PE separator, (c) PE (black), WO ₃ - This is a diagram showing the Fourier transform infrared (FT-IR) spectrum of TMB-embedded PE (red).
Figure 2 shows (a) electrolyte absorption results and contact angle (inset), (b) ionic conductivity, (c) Gurley number, and (d) tension of PE (black) and WO ₃ -TMB-embedded PE (red) separators. This is a diagram showing strength.
Figure 3 is a diagram showing (a) images before and after the reaction of DPPH solution (left) and DPPH+TMB solution (right), and (b) UV-Vis spectroscopy results after reaction of DPPH (purple) and DPPH+TMB (green). .
Figure 4 shows linear sweep voltage measurement (LSV) results of (a) 3.0-4.5V (vs. Li/Li ⁺ ), (b) 3.0-0.0V (vs. Li/Li ⁺ ), (c) 1.0C 1 Cyclic potential profile, (d) diagram showing the NCM811/graphite full-cell electrochemical performance of PE (black) and WO ₃ -TMB-embedded PE (red).

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 example

WO ₃ -TMB functionalized PE membrane was prepared as follows. WO ₃ (Rovs) and TMB (Aldrich) were dispersed in acetone and mechanically stirred for 12 hours. After the condensation reaction was completed, TMB-immobilized WO ₃ was filtered and dried for 3 hours, and then dissolved in acetone of PVDF-HFP (Aldrich). Dispersed into solution and sonicated for 5 minutes. TMB-immobilized WO ₃ was coated on a poly(ethylene) (PE, Celgard) separator by a dip coating process.

The radical scavenging performance of TMB was screened by dissolving 0.02 g TMB and 0.05 mM DPPH (TCI) in 40.0 mL ethanol for 1 hour at room temperature. The resulting mixture was measured by UV-Vis spectroscopy (KLAB, OPTIZEN POP-V). The surface morphology of WO ₃ -TMB-functionalized PE separators was characterized by field emission scanning electron microscopy (FE-SEM/EDS-7001F, JEOL) and the chemical composition was determined by Fourier transform infrared (FT-IR) spectral analysis (Perkinelmer, Spectrum). 2) was analyzed. The Gurley number of the separator was measured with a Gurley-type density meter (Toyoshiki), and the mechanical properties were measured with a tensile strength machine (JSV H1000, USA) at a tensile speed of 30 mm min ^-1 . The membrane contact angle was measured with a contact goniometer (SEO Co. Ltd, Phoenix-MT), and the membrane ionic conductivity was measured with a Li symmetry cell. Electrochemical impedance spectroscopy was acquired using an electrostatic potentiometer (WonATech, Zive MP1) in the frequency range of 106-10-2 Hz and amplitude of 10 mV. Membrane electrochemical stability was measured with linear sweep voltage measurements (LSV) by electrostatic electrostatics (WonATech, Zive MP1).

Cycling performance was evaluated by preparing the anode and cathode as follows. The NCM811 anode was prepared by mixing 1.8 g NCM811 (L&F), 0.1 g carbon conductor (Super P), and 0.1 g poly(vinylidene fluoride) (PVdF, Kureha) in 1.5 mL N-methylpyrrolidone (Aldrich). did. This slurry was cast on Al foil and dried in a vacuum oven at 120°C for 12 hours. The graphite cathode is made from a slurry of 1.92g graphite (POSCO Chemtech), 0.02g carbon conductor (Super P), 0.02g carboxymethyl cellulose (CMC, Cellogen, DKS), and 0.04g styrenebutadiene rubber (SBR, Zeon, BM400B). manufactured. The slurry was coated on Cu foil and dried at 110°C for 11 hours in a vacuum oven. The battery cell was assembled with NCM811 anode, graphite cathode, separator, and electrolyte consisting of ethylene carbonate (EC):ethyl methyl carbonate (EMC) (1:2, vol%) + 1.0 M LiPF ₆ (assimilated electrolyte). . The cell was charged and discharged from 3.0 V to 4.2 V at a current rate of 0.1 C for 2 cycles and then from 1.0 C for 300 cycles at room temperature.

Results and Discussion

Figure 1a presents the molecular structure of a radical scavenging agent (TMB) and a simple method for embedding it into a PE separator by a dip coating process. However, the present invention also noted that it is quite difficult to embed TMB directly into the PE separator due to the extremely stable characteristics of the PE separator. For this reason, in the present invention, TMB was first inserted into WO ₃ by a condensation reaction, and then WO ₃ -TMB was dip-coated on the PE separator. Figure 1b shows the surface morphology of the WO ₃ -TMB-embedded PE separator. Compared to the PE separator without WO ₃ -TMB embedded, the surface of the dip coating separator appears to be well coated with the WO ₃ -TMB composite without severe pore clogging. The EDS results confirmed the presence of key elements W, B, and F, indicating effective coating with WO ₃ -TMB. Before the dip coating process, the thickness of the PE separator without WO ₃ -TMB was 14 μm, but the total thickness of the PE separator with WO ₃ -TMB increased to 26 μm. This means that a WO ₃ -TMB layer with an average thickness of 12 μm is formed on the bare PE separator surface by the process. Additional FT-IR analysis also confirmed that the WO ₃ -TMB layer was successfully formed on the PE separator surface (Figure 1c). Compared to the bare PE separator, the C=C transmission peak was found at 1606 cm ^-1 , meaning that the TMB material was well bound to the bare PE separator.

Figure 2 shows the physical properties of the WO ₃ -TMB-embedded PE separator. Contact angle analysis (inset of Figure 2a) showed a contact angle of 38.8° when the conventional electrolyte solution was dropped onto the PE separator, but a reduced contact angle of 11.7° for the WO ₃ -TMB functionalized PE separator, which is consistent with the hydrophobic PE separator. It shows that the wet stability of the WO ₃ -TMB-embedded PE separator was improved by coating the hydrophilic WO ₃ and TMB materials on it. This result is in good agreement with the electrolyte absorption results (Figure 2a), since the bare PE separator shows an electrolyte absorption performance of 201.1% after 1 hour. In contrast, the electrolyte absorption performance of the WO ₃ -TMB functionalized PE separator is significantly improved to 467.1%, indicating that the WO ₃ -TMB complex on the PE separator is conducive to physical interaction with the existing electrolyte.

Therefore, the ionic conductivity of the WO ₃ -TMB functionalized PE separator was clearly improved compared to the bare PE separator (0.57 mS cm ^-1 vs. 1.03 mS cm ^-1 ) (Figure 2b). The air permeability of the WO ₃ -TMB-embedded PE membrane was reduced compared to the bare PE membrane (224.5 s vs 365.1 s) with the new WO ₃ -TMB layer formed on the surface of the PE membrane, but this permeability was reduced by improved humidity. may still be permitted in LIB based on . By embedding nano-sized WO ₃ particles on the surface of the PE separator, the mechanical properties of the WO ₃ -TMB-embedded PE separator are also improved (Figure 2d). The final strength of the PE separator was 152.3 MPa, but the WO ₃ -TMB-embedded PE separator showed a final strength of 160.9 MPa, indicating that the mechanical properties of the separator were improved.

The central boron atom has an empty p-orbital, so it easily accepts nearby electrons to satisfy the octet rule. As a result, radical species remaining in the cell can be easily scavenged by chemical reaction with TMB. Therefore, the inclusion of TMB can rapidly form boron-radical bonds within the cell through a chemical scavenging reaction. In this regard, the present invention further clarified the radical scavenging performance of TMB through additional screening tests as shown in Figure 3. DPPH (2,2-diphenyl-1-picrylhydrazyl) is used as an indicator material because the DPPH radical reaction with TMB rapidly changes color (from purple to yellow) according to the change in the conjugated state of DPPH. This indicates that the color of the DPPH+TMB solution changed from purple to yellow, indicating that the radical species of DPPH are likely to be eliminated by chemical reaction with TMB. The UV-vis spectrum showed the maximum wavelength of DPPH at 517 nm, but shifted to 490 nm after the chemical reaction was completed, confirming that TMB can effectively scavenge radical species in the cell through chemical reaction.

Based on these results, the electrochemical performance of the WO ₃ -TMB functionalized PE separator was evaluated as shown in Figure 4.

LSV results (Figure 4a) showed that the WO ₃ -TMB functionalized PE separator had the same profile as that of the bare PE separator under cathodicization. This indicates that the oxidation stability does not change even when the WO ₃ -TMB complex is coated on the PE separator.

For anodization (Figure 4b), the electrochemical reduction of TMB can be measured at approximately 0.63 V (vs. Li/Li ⁺ ) to create a solid electrolyte interfacial (SEI) layer on the graphite cathode surface.

The voltage profile in full-cell cycling performance showed similar electrochemical behavior in graphite/NCM811 full cells (Figure 4c). Cells cycled with bare PE membrane and WO ₃ -TMB functionalized PE membrane showed identical voltage profiles without side reactions in the initial cycle.

According to cycling tests (Figure 4d), cells cycled with bare PE separators experienced sustained fading in cycling retention, with 77.9% of capacity loss observed at the end of cycling. In contrast, cell cycling using WO ₃ -TMB functionalized PE membrane showed improved cycling retention (84.5%) after 300 cycles. Continuous fading of cycling retention is commonly observed in cells with NCM811 anodes. This is because the relatively reactive Ni ⁴⁺ species (charged products) accelerate electrolyte decomposition during the electrochemical charging process. Electrolyte breakdown within the cell causes the formation of many different reactive radical species within the cell, and subsequent chemical/electrochemical reactions accelerate the decrease in cycling conservation within the cell. This means that the WO ₃ -TMB functionalized PE separator effectively scavenges radical species remaining in the cell through chemical reaction, significantly reducing the concentration of reactive radical species within the cell, leading to improved cycling preservation.

conclusion

The electrochemical performance of LIB is improved by developing a radical scavenging membrane functionalized with WO ₃ and TMB. TMB, a radical scavenging agent, is first inserted into the surface of WO ₃ through a simple condensation reaction. Then, a WO ₃ -TMB functionalized PE separator is formed through a dip coating process. An ex situ screening test using the chemical reaction between TMB, AIBN and a radical indicator (DPPH) confirmed that TMB effectively removes radical species by chemical reaction, confirming that the WO ₃ -TMB functionalized PE separator is electrochemical. This suggests that the chemical stability of the cell can be increased during the reaction.

In fact, the cycling retention of cells cycled with WO ₃ -TMB functionalized membranes was improved compared to cells cycled with bare membranes because they suppressed continued electrolyte decomposition by terminating the reaction of reactive radical species during the electrochemical process.

This approach in the present invention will be an effective way to improve the cycle performance of LIB without serious trade-off effects in the cell.

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 (10)

It includes a complex of tungsten oxide (WO ₃ ) and trimesitylborane (TMB) in which trimesitylborane (TMB) is embedded on the surface of tungsten oxide (WO ₃ ).
The trimesitylborane (TMB) embedded in the surface of the tungsten oxide (WO ₃ ) is a radical scavenger, and boron (B) and radicals of the trimesitylborane (TMB) A separator for lithium secondary batteries in which a bond is formed.
According to paragraph 1,
The separator for a lithium secondary battery is a separator for a lithium secondary battery, characterized in that the separator is coated with a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB).
delete According to paragraph 1,
A separator for a lithium secondary battery, characterized in that a tungsten oxide (WO ₃ )-trimesitylborane (TMB) layer having an average thickness of 12 μm is disposed on the surface of the separator for a lithium secondary battery.
According to claim 1,
The separator for a lithium secondary battery containing a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB) is a separator for a lithium secondary battery that does not contain a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB). A separator for lithium secondary batteries, characterized by a reduced contact angle compared to a separator.
Preparing a composite of tungsten oxide (WO ₃ ) and trimesitylborane (TMB) by embedding trimesitylborane (TMB) on the surface of tungsten oxide (WO ₃ ) through a condensation reaction; and
It includes the step of coating the tungsten oxide (WO ₃ ) and trimesitylborane (TMB) composite on the surface of a separator for a lithium secondary battery,
The trimesitylborane (TMB) embedded in the surface of the tungsten oxide (WO ₃ ) is a radical scavenger, and boron (B) and radicals of the trimesitylborane (TMB) A bond is formed of
Method for manufacturing separator for lithium secondary battery.
According to clause 6,
A method of manufacturing a separator for a lithium secondary battery, characterized in that a tungsten oxide (WO ₃ )-trimesitylborane (TMB) layer having an average thickness of 12 μm is disposed on the surface of the separator for a lithium secondary battery.
According to clause 6,
The separator for lithium secondary batteries coated with the tungsten oxide (WO ₃ ) and trimesitylborane (TMB) composite is for lithium secondary batteries that does not contain the tungsten oxide (WO ₃ ) and trimesitylborane (TMB) composite. A method of manufacturing a separator for a lithium secondary battery, characterized in that the contact angle is reduced compared to the separator.
anode; cathode;
It includes an electrolyte layer and a separator disposed between the anode and the cathode,
A lithium secondary battery, wherein the separator is a separator according to any one of claims 1 to 2 and claims 4 to 5.
According to clause 9,
The positive electrode is a lithium secondary battery comprising LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (NCM811).