Research

Electrolyte Additive for Anode

Solid-electrolyte interface (SEI) on anode surface is the key, which is crucial to control the power and cycle performance of lithium ion battery. This SEI is fabricated by the electrochemical reduction and subsequent decompose of the carbonate based electrolytes. With the correct selection of electrolyte, a stable SEI is formed on electrode’s surface in which permits lithium ions transport. The SEI form from conventional electrolyte is unstable, which is composed by organic–inorganic mixed compounds after the first cycle, such as LiF, LiOH, Li2CO3, lithium alkyl carbonate and lithium allkyloxide. These products are probably responsible for various problems that can detrimentally affect the performance of batteries. Therefore, several functional additives have been developed in our research. Small amounts of additives are added to the electrolyte to modify the infrastructure of SEI and further improve the performance of battery.In our study, maleimide (MI) group-based compounds are synthesized as new anode additives that design for MCMB, Si and graphene materials. An attempt is made herein to increase capacity and cycle life by reducing the irreversible reaction during the charge and discharge process. A 3D nanostructure of SEI morphology is also being synthesized on MCMB, Si and graphene surfaces in which increase the electrochemical area and facilitate the ionic diffusion. MI anode additives.​​

Electrode Additive for Cathode

Since Sony commercialized its first lithium-ion batteries in 1991, their high energy density for power and energy sources has increased steadily over the last two decades. However, the marketing requirements of lithium batteries have increased due to advancements in electronics and green products, buildings, and devices. In addition, the performance of lithium ion batteries, such as their energy density and life cycle, cannot fully satisfy parts of the market demand, especially for the electric vehicles (EVs) of the near future. To guarantee that the operation of these next-generation lithium cells is safe, it is crucial to avoid batteries operating at high temperatures and overcharging under abnormal operations. This study reports the lab synthesis of a maleimide-based branched oligomer that functions as an internal short-protection additive. This additive can be synthesized and mixed in n-methyl-2-pyrrolidone (NMP) and can be dispersed as a membrane on the cathode surface well, and the membrane forms a nanofabrication self-polymerized solid electrolyte interface (SEI) after the battery is charged with electrochemical reaction. This SEI polymerizes further to an isolating organic layer on the cathode surface when the battery temperature rises to a specific condition, which depends on the molecular and structural design of the original additive. This study also investigates the performance of the membrane composite electrode and compares it to that of a bare electrode without a membrane. The full cell, electrode morphology, free volume, and internal short measurements reveal the self-polymerized membrane position, the occupied free volume of the membrane of the battery, and the protecting reaction mechanism of the battery.MI branched oligomer cathode additives.

Electrolyte Additive for Salt

In lithium ion battery, the formation of solid electrolyte interface (SEI) plays an important role for maintaining battery performance. Lithium salt arrangement is one of principal key to fabricate a good SEI composition. Excellent lithium salt requires wide temperature durability, facilitates good SEI composition, low cost, and easily production. Currently, the majority of Li-ion batteries perform poorly performance under high temperatures because of several problems, including the main drawback of the decomposition of Li salt. LiPF6, the most widely used salt in commercial batteries, provides excellent ionic conductivity and a wide electrochemical window. However, high-temperature applications accelerate the generation of HF and PF5 and destroy the battery infrastructure, including the SEI, electrode materials, and current collectors. Lithium-aromatic ring salt proposes a good ability toward high temperature application due to it’s phi electron. LIBOB is one of salt candidate to resolve high temperature application problem. Absence of PF5 and HF production lead a better battery performance especially at high temperature application. However, LIBOB show lower ionic conductivity against LiPF6 salt. In our study, we develop a new lithium benzimidazole salt and it’s derivative to improve battery performance at high temperature. Further research also focused on high voltage implementation to reinforce lithium salt application.

Charging Protocol

To alleviate the variability inherent in the battery-manufacturing process and to increase the utility of the solid electrolyte interface (SEI), a differential-pulse (DP) SEI-formation procedure was used and compared with the traditional method of constant-current (CC) charging. Previous results have indicated that DP charging affects the formation and the composition of the SEI layer in distinct and dynamic ways; however, the dynamic electrochemical equilibrium of both Li+ diffusion and the electron transfer must be re-examined because Li+ diffusion is extremely slow compared with electron conduction. We conducted this study to determine whether balanced SEI formation on the anode surface can be achieved by further refining the DP protocol.

In this study, we investigated the use of a new forward and reverse differential-pulse (FRDP) method developed for SEI formation. The following shows the SEI formation concepts of the charging protocols of CC and FRDP. Owing to Li+ diffusion in the bulk electrolyte being much slower than electron transfer in the current collector, we anticipate that the diffusivity of Li+ can be enhanced by the reverse pulse (RP) effect.

ALD Nanofabrication

Previous studies have investigated various methods to prevent SEI decomposition at high temperatures, such as graphite surface modification with metal/ metal oxide deposition or polymer coating, surface mild oxidation, and un-carbon-based anodes. However, some of the surface modifications, such as the sol-gel method, require high-temperature processes and large quantities of solvent. In addition, the electric conduction pathway between the active and the coating materials should be well established to reinforce the electron transfer during the redox reaction. However, electric conductivity is restricted by sophisticated coating methods because the thickness and uniformity of the coating materials cannot be precisely controlled. Atomic layer deposition (ALD) is an advanced technology for applying ultrathin and homogenous films on high-surface specimens using a self-limited reaction at below 100 °C. In this study, ALD coated metal oxide and graphite were used to comprehensively compare bare and ALD treated materials to discuss their effects on electric conductivity and the host performance. Furthermore, 55 °C was selected as the testing temperature of cycle-ability at which to appraise the vehicular application.

Plasma Nanofabrication

Governments and manufacturers in many countries have spent lots of effort developing E2W (Electrics Tow Wheel). Due to the driving force to the electric vehicle application, the high energy density of the technology of lithium ion battery is continuous developing. Because of the low price, long cycle life, environmental safety and high specific energy, the common cathode material of LiFePO4 is used in lithium-ion batteries. LiFePO4 is insulating in nature with a low electric conductivity at room temperature around 10-9 Scm-1 (compared with10-3 Scm-1 for LiCoO2 and 10-5 Scm-1 for LiMn2O4), including low rate capacity. Many efforts have been made to improve the electrochemical performance and electric conductivity of LiFePO4 at high temperature (55℃).This research demonstrates an in-operando surface modification of LiFePO4 by atmospheric pressure plasma jet (APPJ) treatment. TEM images show that the APPJ surface modification treated LiFePO4 particles was covered by a nano core-shell infrastructure, which is fabricated by an amorphous layer. The APPJ treatment provided plasma-induced grafting hydrophilic functional groups on LiFePO4 in which is used to synthesis a nano protecting layer. This nano layer was defined by contact angle, Raman and Optical Emission Spectroscopy analysis, respectively. After the high temperature electrochemical testing, the core-shell surface modification LiFePO4 enhances the cycle life due to the transition metal Fe ion will not be dissolved from the LiFePO4 structure.