An Effective Method to Reduce Residual Lithium on LiNi0.8Co0.1Mn0.1O2 Cathode Material Using a Reducing Agent.

Among the various cathode materials used in LIBs (Lithium ion batteries), nickel rich cathode materials have attracted an increasing amount of interest due to their high capacity, relatively low cost, and low toxicity when compared to LiCoO2. However, these materials always contain a large amount of residual lithium compounds such as LiOH and Li2CO3. The presence of lithium residues is undesirable because the oxidation of these compounds results in the formation of Li2O and CO2 gas at higher voltages, which lowers the coulombic efficiency between the charge and discharge capacities during cycling. In this study, using LiNi0.8Co0.1Mn0.1O2 as a starting material, a surface-modified cathode material was obtained by using reducing agent. The reducing agent not only plays the role of reducing the oxide conversion energy but also suppresses the side reaction with the electrolyte due to the surface modification. Residual lithium present on the cathode material surface was reduced from 11,702 ppm to 8,658 ppm, resulting in improved high temperature cycle performance and impedance characteristics.

Novel Composition of Co-Free LiNi0.875-xMn0.125AlxO2 Cathode Materials.

Ni-rich LiNi1-xMnxO2 cathode materials have attracted widespread interest as promising alternative cathode materials owing to their higher capacity, lower cost, and lower toxicity compared to those of LiCoO2. Therefore, we designed herein a LiNi0.875Mn0.125O2 positive electrode material. However, as the Ni content increases, the materials suffer from an extensive phase transition during the de-lithiation process owing to the low-bond strength of Ni (391.6 kJ mol-1) and Mn (402 kJ mol-1). In this study, Al-doped LiNi0.875-xMn0.125AlxO2 (x= 0, 0.05, 0.1) was synthesized using the coprecipitation method. Al had a higher bond strength (512 kJ mol-1) between oxygen and metal ions compared to that of Ni and Mn ions. Additionally, Al is usually stabilized in the form of Al3+. Therefore, the increased bond strength decreased the electrostatic repulsion with oxygen during the de-lithiation process and prevented cation mixing by stabilizing the Ni ion's valence, thereby resulting in increased structural stability. X-ray diffraction (XRD) was used to characterize their structures and calculate the cation mixing value. The electrochemical properties showed that LiNi0.775Mn0.125Al0.1O2 exhibited the high capacity retention of 97.1% after 30 cycles at 1 C at 55 °C.

Effect of PEDOT:PSS (Poly(3,4-ethylenedioxythiophene)-polystyrenesulfonate) Coating on Nanostructured Cobalt-Free LiNi0.9Mn0.1O2 Layered Oxide Cathode Materials for Lithium-Ion Battery.

Among cobalt-free layered oxides, Li(Ni1-xMnx)O2 (x ≤0.5) (LNMO) shows high reversible capacity, good cycling performance and thermal stability, and has relatively low cost and toxicity due to the absence of cobalt. In this study, we synthesized LNMO cathode materials having a porous fiber shape with primary particles that had an average diameter of about 328 nm. The prepared LNMO has an increased surface area, on which side reactions between the electrolyte and cathode material occur. Therefore, we coated the conductive polymer PEDOT:PSS to solve the problems that may arise. The coated LNMO exhibited a reversible capacity of 128.03 mAh g-1, and 87.1% capacity retention, at a current density of 0.1 C, for up to 30 cycles. It showed a better performance than uncoated LNMO. The process used in this study can be proposed as a new synthesis method for cobalt-free layered oxide materials.

Role of Hydrophilic APTES-PP Separator in Enhancing the Electrochemical Performance of Ni-Rich Cathode for Li-Ion Battery.

Polypropylene (PP) separators essentially have poor compatibility with normal liquid electrolytes, including EC/DEC, due to the low surface energies of their hydrophobic surfaces. Therefore, they have a poor ability to retain electrolyte solutions within the separators because of low absorption capacity for the liquid electrolytes, which could directly damage the AC impedance and C-rate performance of LIBs. This study aims to improve the hydrophilicity and adhesion properties using (3-aminopropyl)triethoxysilane (APTES) coating on hydrophobic PP separators. Their surfaces were treated with a thin and stable silane layer, using APTES with -NH2 of the hydrophilic group. Hydrophilic PP separator surfaces with pore structures were fabricated by a facile solution-immersion method. The contact angle of the APTES-PP separator decreased from 102±2.5° to 60±1.5°. The electrochemical measurement results indicate that the cell using the modified PP separator showed a better initial discharge capacity of 165.79 mAh g-1 during the first cycle, at a current density of 0.1 C, as compared with the initial discharge capacity (141.61 mAh g-1) of the cell with a bare PP separator. The performances of all cells with coated PP separators were improved with regard to interfacial resistance, discharge capacity and C-rate capacity, compared to the uncoated PP separator.

Novel Core-Shell-Type Design of Na0.5[Li0.5(Ni0.8Co0.1Mn0.1)1-x(Ni0.5 Co0.1Mn0.4)x]O2 Cathode Material for Sodium-Ion Batteries.

High-nickel cathode materials possess several disadvantages such as poor cycle performance and thermal instability resulting from the side reaction with the electrolyte that occurs during cycling. In order to improve the cycle performance and thermal stability of the Na0.5[Li0.5(Ni0.8Co0.1Mn0.1)]O2 (core), we synthesized the core-shell structure of Na0.5[Li0.5(Ni0.8Co0.1Mn0.1)1-x(Ni0.5Co0.1Mn0.4)x]O2. The results of energy-dispersive X-ray spectroscopy (EDS) line analysis showed that the core of the high-nickel NCM precursor and the shell of the low-nickel NCM precursor were successfully synthesized as two phases. The core-shell cathode material shows a small capacity loss after 30 cycles (capacity retention=60.78%) compared with the core cathode material (capacity retention = 48.57%). The results of differential scanning calorimetry (DSC) show that the 4.6 V charged core-shell cathode material has a large exothermic peak at 297.4 °C, and the low reaction releases 246.1 J·g-1 of heat. The core-shell cathode material shows improved electrochemical performance and is a thermally stable material for use as a cathode material for sodium-ion batteries.

New Observation Structural Change from O3 to P2 Type by Changing Sodium Contents for Na-Ion Batteries.

Stable Na+-ion-storage cathodes with adequate reversible capacities are increasingly needed for the application of Na-ion batteries in large-scale, low-cost electric storage systems. Ion-storage oxides have been classified into P2- and O3-type phases based on their sodium content. There have been few studies on the structural stability and electrochemical properties of such oxides. Here, we report the synthesis of a sodium-ion battery (SIB) cathode material Nax[Ni0.8Co0.1Mn0.1]O2 (x = 0.67, 1) using a hydroxide co-precipitation method. The effects of different sodium contents on the structural and electrochemical properties of this cathode material were studied. The results indicated better electrochemical performance of the P2-type materials compared to the O3-type in terms of high discharge capacity and good cycling performance. The P2-Na0.67[Ni0.8Co0.1Mn0.1]O2 cathode exhibited a good charge storage capacity of 108.74 mAhg-1, with a capacity retention of over 67% after 50 voltage cycles (between 2.0 and 4.5 V) at 0.1 C. The developed material may potentially be used as a cathode in sodium-ion batteries.

Mitigation of Volume Expansion of Silica Anodes by Porous Titanium Dioxide Coating for Lithium-Ion Batteries.

Silica (SiO2) is one of the most promising anode materials for LIBs due to its high theoretical capacity. However, the huge volume change of silica during the lithiation/delithiation processes is a disadvantage that results in poor electrochemical performance. In this study, the volume change of silica was effectively mitigated by coating the SiO2 anode with porous TiO2. The porous TiO2 has a large amount of internal space that can mitigate the volume expansion of SiO2. To verify the ratio of the volume change, the crosssection of the electrodes was analyzed by scanning electron microscopy (SEM). The ratio of the volume change decreased from 293.5% to 140.7% upon application of the TiO2 coating. Fourier transform infrared analysis suggested that the Ti-O-Si bond helped mitigate the volume expansion. Furthermore, the decrease in the volumetric expansion resulted in good electrochemical performance with increased charge capacity and stable cycle performance. The TiO2 coated SiO2 anode displayed a capacity of 72.33 mA h g-1 at a current density of 98 mA g-1 for up to 50 cycles, which was higher than that of the pristine SiO2 anode (42.29 mA h g-1). The TiO2 coated anode materials are applicable for rechargeable lithium-ion batteries.

Improvement of Electrochemical Properties of Ni-Rich Cathode Material by Polypyrrole Coating.

In this study, we attempted a nanosized coating layer of commercial polypyrrole (PPy) on LiNi0.6Co0.1Mn0.3O2 (HNCM) cathode material to overcome the side reactions with electrolyte and a decrease in the capacity of the inert coating layer. The coating method using commercial PPy is very simple. The energy dispersive X-ray spectroscopy (EDS) analysis and transmission electron microscopy (TEM) images confirmed that PPy coating layer was well dispersed and nanosized. The alternating current (AC) impedance studies revealed that the coating of PPy significantly decreased the charge-transfer resistance of HNCM electrodes. Moreover, the 1 wt% PPy-HNCM electrode exhibited good electrochemical performance with a specific discharge capacity of 177.52 mA h g(-1) at a rate of 0.1 C in the voltage range 3.0-4.3 V, whereas the capacity of the HNCM electrode was only 167.13 mA h g(-1).

Synthesis of Hollow Nanorods of SiO2 Anode Material by AAO Template Synthesis Method for Lithium Ion Battery.

Silicon oxide hollow nanorods (SiO2-HNs) were prepared via a two-step anodization of aluminum template. SiO2 was synthesized using tetraethyl orthosilicate (TEOS) as the Si source that has not been applied to the anodic aluminum oxide (AAO) template method. The SiO2-HNs obtained were characterized by X-ray diffraction, scanning electron microscopy and electrochemical test. The results show that SiO2 nanorods with hollow morphology were successfully formed by the AAO template. The SiO2-HNs were investigated as an anode material for lithium-ion batteries and delivered an initial reversible capacity of 1344.26 mA h g(-1) at a current density of 17 mAg(-1). To the best of our knowledge, this is the first report of the synthesis of SiO2-HN using TEOS as the Si source by a two-step anodization of AAO template.

Barium Doped Li2FeSiO4 Cathode Material for Li-Ion Secondary Batteries.

Barium-doped Li2Fe(1-x)Ba(x)SiO4 (x = 0, 0.01) cathode materials were synthesized by the sol-gel and electrospinning processes. The structures of the samples were confirmed by X-ray diffraction and Fourier transform infrared spectroscopy. The sizes and the morphologies of the particles and nanofibers were observed by field emission scanning electron microscopy and atomic force microscopy. The initial discharge capacity of Li2FeSiO4 particles was 28 mAh/g, Li2FeSiO4 nanofibers and barium (Ba)-doped Li2FeSiO4 nanofibers showed the discharge capacities of 78 and 85 mAh/g, respectively. The lithium-ion diffusion coefficients of Li2FeSiO4 particles, Li2FeSiO4 nanofibers and Ba-doped Li2FeSiO4 nanofibers were calculated 5.15 x 10-(16), 3.52 x 10(-16), and 2.27 x 10(-15) cm2/s, respectively. The Ba-doped Li2FeSiO4 cathode material showed the highest lithium-ion diffusion coefficient, and its electrochemical properties were better than that of the pristine material.