2022 International Conference on Power Engineering and Energy Chemistry(PEEC 2022)

Oral presentation

李国华  Guohua Li

National Power Battery Innovation Center, GRINM Group Corporation Limited

Title: Highly Stable Surface and Structural Origin for Lithium-Rich Layered Oxide Cathode Materials

Abstract: Surface/interfacial engineering is critical for preventing particle degradation of Li-rich layered oxides (LLOs), particularly facet degradation, thereby optimizing their electrochemical performance. Thus, the current study details the investigative analysis of the surface structure of an LLO, followed by its surface engineering. The surface structure was analyzed using scanning transmission electron microscopy (STEM) and soft X-ray absorption spectroscopy (sXAS), and the electrochemical performance was evaluated. The results indicate that an integrated spinel/rock salt (ISR) surface structure formed on the surface in situ. More precisely, the spinel phase originated from the C2/m surface, whereas the rock salt phase originated from the R3m surface, which significantly increased the cycle stability and suppressed voltage decay. After 2,000 cycles, the surface-modified LLO cathode retained an extremely high capacity of 69.6% and a low discharge medium voltage with a decay rate of 0.44 mV cycle-1. Additionally, the structural and morphological changes observed after prolonged cycling confirmed the stability of the surface layer. The outstanding performance was attributed to the ultra-stable ISR surface layer, the presence of multiple ion conductivities (LiPO3 and Li2SO4), and the substantial prevention of electrochemical facet degradation. The findings, therefore, highly suggest that the ISR surface concept and the method for surface modification is highly likely to aid in the rapid commercialization of LLOs for battery applications.

夏一冕  Xia Yimian

National Power Battery Innovation Center, GRINM Group Corporation Limited

Title: Calendar aging mechanism of 3Ah NCM811/graphite-SiOx pouch cells at different temperature

Abstract: As a strong competitor of the next-generation lithium-ion battery anode materials, silicon-oxygen anode materials have the advantages of high specific capacity, good cycling performance and small volume effect. Nevertheless, the storage performance of batteries with silicon-oxygen anode been rarely studied. In this paper, the calendar aging experiment of graphite-SiOx/NCM811 pouch cells were carried out within the temperature range of 25~55℃. The differential curve analysis and post-mortem analysis were used to explore the aging mechanism. The results show that the calendar aging of pouch cells is mainly caused by the loss of lithium inventory and the loss of cathode active materials. When cells storage at higher temperature, the loss of lithium inventory and the loss of cathode active materials increase, while the loss of anode active materials remain remains relatively unchanged. Based on various test results, it can be inferred that the parasitic reactions on the surface of electrode lead to the loss of lithium inventory and the increase of SEI. With the increase of storage temperature, this side reaction continues and consumes more lithium inventory. It is worth mentioning that when storage at 55℃, the microcracking develops and even breaks some of the secondary particles of cathode materials. Therefore, the pouch cells suffer severe loss of cathode active materials, which makes it inappropriate to accelerate the aging of batteries at such high temperature.

卓浩翔  Zhuo Haoxiang

General Research Institute for Nonferrous Metals

Title: Impact of local structure on reaction mechanism for Li-rich and Mn-based oxide cathode materials

Abstract: Li-rich and Mn-based oxides (LRMO) have been an obvious choice of high specific energy batteries owing to their unique anion redox behavior based on the main component Li2MnO3. However, there are still electrochemical behaviors that cannot perfectly match the theoretical structure. So far, most theoretical research on LRMO has been carried out around the ideal Li2MnO3 structure. Nevertheless, there are a great number of non-ideal local configurations in the pristine materials under the case of practical situations. Herein, the ubiquitous complex local structures (defect-like) in the interior of Li2MnO3 particle, some of which have not been observed in the past, are directly presented through the atomic-level observation. We summarized these structures and proposed for the first time the great influence of these local structures on the electrochemical and the oxygen redox behavior of LRMO by combining observation, DFT calculation, XAS, XPS and electrochemical experiments. These micro-structures have been roughly divided into four categories by the advanced AC-STEM, including the so-called stacking faults caused by the slip of the adjacent TM layer, the local multi-Li or multi-Mn arrangement due to the combination of different stacking type along a-b plane, the expansion of the interlayer spacing, and even the distribution of polycrystalline domains, of which the second and third configurations were observed for the first time. These types of local structures dominate the electrochemical reaction of electrodes in some aspects by improving the activity of oxygen non-bonding 2p states, along with the improvement of (de)intercalation ability for Li ions in the bulk through reducing the energy barrier. This research has perfected a more comprehensive and practical understanding of LRMO under the case of practical situations, laying a key foundation for the further modification and application of LRMO cathode materials.

于成澳  Chengao Yu

Shandong University

Title: Fault Ranging Method Based on Multisynchrosqueezing Transform for Flexible DC Transmission Lines

Abstract:Due to the dispersion effect of the traveling wave, the wave speed has frequency variation characteristics, and the error of the fault ranging method using empirical wave speed is large. To address this problem, this paper proposes a fault ranging method based on Multisynchrosqueezing Transform (MSST) for flexible DC Transmission Lines, the MSST method is used to perform time-frequency analysis of the fault line mode voltage traveling wave, to obtain the precise time and frequency information of the traveling wave arriving at the measurement points on both sides of the line, and to calculate the distance of the fault point according to the double-end ranging principle by combining the frequency-variable characteristic curve of the wave speed. Since MSST squeezes the signal several times, it effectively improves the time-frequency aggregation of the signal, and the time-frequency feature extraction of the traveling wave and the identification of the wave head are more accurate. Finally, the effectiveness of the fault ranging algorithm was verified by the simulation of PSCAD and MATLAB.