따라서 급속 충전 시 발생하는 전극저항 문제를 해결하기 위해 커넥터 입장에서는 리튬이온의 전도성을 향상시켜 이를 최소화하는 것을 목표로 하고 있다. 전도성 고분자(바인더)의 성능을 확인하기 위해 이온전도도 분석, 리튬이온 전달수, 팽윤 시험, 접촉각 측정, 전극 접착력을 측정하였다. 특히, 전도성 고분자 바인더는 전극의 활물질, 도전재 및 집전체를 연결할 수 있는 전극 내부의 전기적 네트워크를 형성하는데 필수적인 소재이다.
Therefore, to solve the problem of electrode resistance that occurs during rapid charging, it is intended to improve the lithium ion conductivity by minimizing this from the binder's point of view. To check the performance of the conductive polymer (binder), ion conductivity analysis, lithium ion transfer number, swelling test, contact angle measurement and electrode adhesion were measured.
L ITHIUM ION BATTERY (LIB)
T HE CHARACTERISTICS OF ELECTRODE MATERIALS
Anode active materials
Cathode active materials
NCM and NCA due to high cost of cobalt and improved performance when mixing compared to other active cathode materials [11].
EXPERIMENTAL METHOD
- M ATERIALS
- S YNTHESIS OF NEW POLYMERIC BINDER
- P REPARATION OF THE SLURRY FILM FOR ANODE
- P REPARATION OF THE SLURRY FILM FOR CATHODE
- F ABRICATION OF 2032 COIN HALF CELLS
- P HYSICAL CHARACTERIZATION
- Zeta potential
- Particle Size Analysis
- Infrared spectra of the synthetic polymeric binder
- TEM of the synthetic polymeric binder
- Electrolyte uptake
- Contact angle measurement
- Adhesion strength
- Electrode resistance
- Ionic conductivity of the synthetic polymeric binder
- Lithium-ion transition number of the synthetic polymeric binder
- Morphology analysis as scanning electron microscopy
- E LECTROCHEMICAL PROPERTIES
- Galvanostatic charge-discharge test for anode
- Voltammetry and Impedance analysis
Schematic illustration of the fabrication of electrode using styrene-co-sytrenesulfonic acid sodium salt hydrate (St-NaSS) as binder. The particle size and size distribution of the emulsion were measured using a (Zetasizer Nano ZS, Malvern Panalytical) apparatus based on a laser distribution light scattering technique. The morphology of the PS and PS-co-NaSS particles was observed by field emission.
The electrolyte uptake of the binder films was also studied by means of an electrolyte absorption test. The contact angles of the polymer films are measured by an optical tensiometer (Theta life, Biolin Scientific) after 150 seconds of exposure to an electrolyte droplet. Using a texture analyzer (TA-PLUS, LLoyd Instruments Ltd.), the adhesion strength of graphite anode film was obtained by measuring the 180° peel strength of electrode strips with the peel rate of 100 mm min-1.
A wide part of the electrode is cast over a distance of 40 mm, and the thickness of the anode film is about 80-90 µm before pressing and about 60-70 µm after pressing and before peeling test. The electrical resistance of the thin films consisting of electrodes was measured using a 46 multi-point probe system (RM2610, HIOKI E.E. Co.). Then measure the volume of the composite layer, the surface area and the interfacial electrode resistance at regular intervals from the bottom to the top of the electrode.
Complex impedance measurements were performed in AC mode, in the frequency range of 100 kHz-10 Hz and 10 mV amplitude of the applied AC signal. Here is the frequency dependence of the cell impedance measured in the frequency range 100 kHz – 10 Hz at different degrees of polarization (OCV and 5-10 mV). The surface morphology of the graphite electrode was controlled by field emission line electron microscopy (FE-SEM, Jeol, JSM-6500F).
Cyclic voltammograms (CV) of the coin half-cell can be recorded at the different scan rates within a voltage range of 0.005 to 1.5 V as a BioLogic Science Instrument. In addition, the low-frequency Warburg region of the EIS allows the calculation of the diffusion coefficients of lithium ions.
RESULTS AND DISCUSSION
P HYSICAL CHARACTERISTICS OF BINDER
- B-TEM results
- FT-IR results
- Zeta potential results
- Particle size analyze results electric conductivity
- Ionic conductivity
- Lithium-ion transport number
- Dispersion stability results
- Electrolyte uptake results
- Contact angle results
The broad band near 3284 cm-1 is assigned to water absorbed in the sample due to As shown in Tables 3 and 4, core shell, the sample without a sulfone group was the lowest at -1.45mv, and. Tables 3, 4 and Figure 8 below show that when NaSS is emulsion polymerized with styrene as a core, the particle size decreases as the sulfone group increases.
I0, and Is are initial and steady state current values, respectively, and R0 and Rs are the initial and steady state measured resistances, respectively [23]. The result shows that the value of Li+ ion transport numbers increased as the NaSS content increases. As shown in the Figure 11 below, 0%, 2% and 7% samples showed overall stability, and the TSI result increased for the first 2 hours, and then showed a stable result.
Electrolyte uptake results are an experiment that shows how much electrolyte permeates itself into the bonding film [25]. The binary film was continuously immersed in the electrolyte for up to 6 hours, and the weights were measured for 30 minutes, 1 hour, 3 hours, and 6 hours. Shown in Figure 12, below after 3 hours, containing 7% NaSS monomer absorbs the electrolyte the most.
Basically, the contact angle is the angle between the gas or liquid drop and the solid surface when the droplet is in thermodynamic equilibrium with a solid surface. High contact angle means low wettability and hydrophobic property, on the other hand, low contact angle corresponds to high wettability and hydrophilic property [26], [27]. As shown in Figure 13 and Table 7, when the initial contact angle and the contact angle after 150 seconds were compared, the sample without NaSS showed the lowest change in contact angle and the 7% amount with NaSS content showed the largest change.
Photographs of the moment electrolyte was lost by bond film by bond film at 0s and 150s.
N ATURE GRAPHITE FOR ANODE
- Electrode resistivity & resistance and adhesive strength of anode results
- Cycle and rate capability results
- EIS and Cyclic voltammetry (CV) results for anode
- Thickness change after cycle test for anode
The EIS of the graphite electrode was measured at OCV and discharge/charge, 0.2V after two pre-cycles at 0.1C followed by two more cycles at 0.5C. Moreover, the size of the semicircle decreased with the increase of the amount of NaSS, indicating that the resistance size decreased. Due to the effect of NaSS, as shown in the graph and table, it can be expected that Rct is a value that is 7% easier for lithium-ion migration than 0% NaSS content.
Adhesion strength of natural graphite electrodes (a) and resistivity and resistivity of anode plate (b). a) Cyclic performance and Coulombic efficiency and (b) speed capability of the electrodes using each binder, current changes for every 0 cycles. a) EIS data expressed as Nyquist plot of meat anode with different binders (b) and cyclic voltammograms as scan rate 0.2 mV/s. EIS results of graphite electrodes. Measure the thickness of the electrode composite layer with a new electrode and disassemble the coin cell that has completed 100 cycles of charge and discharge test. As shown in Figure 18, the thickness change was largest in 0% without a sulfone group, and the thickness change gradually decreased as the sulfone group content increased.
It prevents volumetric expansion of the composite layer in graphite under the influence of sulfonic groups during the insertion and desorption of lithium ions. a) Graphite electrode with different binders before and after 100 cycles: (a) photo-image of the electrode, (b) upper FE-SEM image with ×2000 magnifications and (c) difference in
L ITHIUM IRON PHOSPHATE (LFP) FOR CATHODE
- Electrode adhesive strength for cathode
- Electrode resistivity & resistance and adhesive strength of cathode results
- Cycle and rate capability results
- EIS results for cathode
- Thickness change after cycle test and Cyclic voltammetry (CV) for cathode
In this experiment, the specific capacity (mAh/g) of the electrodes with each different binder ratio of styrene/NaSS and comparative experiments with commercially available PVdF binders are shown in Figure 20. As a result of the experiment, it was as stable as it was efficient as when 7% was applied to the anode electrode, but in the case of PVdF binder, the efficiency decreased rapidly under 20 cycles. At low scan speed up to 1C, the specific capacitance of 7% was higher than that of 0%, 2% and PVdF samples.
And after different scan rates for 2 cycles each, performance was evaluated for 2 cycles at 0.2C, and then 100 cycles at 1C. As a result of the experiment, 7% still showed superior performance compared to PVdF. The EIS of the LFP electrode was measured at OCV and discharge/charge, 0.2V after two pre-cycles at 0.2 C followed by two more cycles at 1C. EIS results are displayed in this Figure 21. The reason is that in the graph of the cycle test results, capacity value was less than 10 mAh/g in less than 10 cycles, so it can be predicted that electrochemical reaction did not occur. For the remaining samples, resistance occurred within the coin cell because the electrode surface was not clearly seen in Figure 21 below. a) Adhesion strength of the LFP electrodes containing different binders measured by 180° peel test (b) Sheet resistance of 65 µm thick LFP slurry films. a) Cyclic performance and Coulombic efficiency and (b) Rate capability of the LFP electrodes using each binder, current changes for every 10 cycles and (c) Rate capability of the. electrodes using each binder every 2 cycles thereafter revert to low current rate at 100 cycles. a) EIS curve of LFP electrode with different binders after pre-cycle at 0.2C and two cycles at 1.0 C and (b) Cyclic voltammograms as scan rate 0.2 mV/s.
As shown in Figure 22(a), measure the thickness of the electrode composite layer with a new electrode and disassemble the coin cell that has completed 100 cycles of charge and discharge test. In the case of PVdF binder, the electrochemical reaction did not take place because the cell capacity in the initial cycle was close to 0 mAh/g. Therefore, there was almost no change in the thickness of the composite layer before and after the cycle test.
For the remaining samples, the difference in thickness change gradually decreased as the sulfone group content increased, as in the anode. LFP electrode with different binders before and after 100 cycles: (a) photo image of the electrode, (b) top FE-SEM image with ×2000 magnifications, and (c) difference in composite.
CONCLUSION
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