Exploring the Limits of the Rapid-Charging Performance of Graphite as the Anode in Lithium-Ion Batteries

Graphite is, in principle, applicable as a high-power anode in lithium-ion batteries (LIBs) given its high intralayer lithium diffusivity at room temperature. However, such cells are known to exhibit poor capacity retention and/or undergo irreversible side reactions including lithium plating when charged at current rates above ~2C (~740 mA g-1). To explore the inherent materials properties that limit graphite anodes in rapid-charge applications, a series of full-cells consisting of graphite as the anode and a standard Li[Ni0.8Mn0.1Co0.1]O2 (NMC811) cathode was investigated. Instead of a conventional cathode-limited cell design, an anode-limited approach was used in this work to ensure that the overall cell capacity is only determined by the graphite electrode of interest. The optimized N:P capacity ratio was determined as N/P = 0.67, enabling stable cycling across a wide range of charging rates (4-20C) without inhibition by the NMC811 cathode. The results show that unmodified, highly crystalline graphite can be an excellent anode for rapid-charge applications at up to 8C, even with a standard electrolyte and NMC811 cathode and in cells with 1.0 mAh cm-2 loadings. As a rule, capacity and specific energy are inversely proportional to crystallite size at high rates; performance can likely be improved by electrolyte/cathode tuning.

How do Depth of Discharge, C-rate and Calendar Age Affect Capacity Retention, Impedance Growth, the Electrodes, and the Electrolyte in Li-Ion Cells?

Lithium-ion cells testing under different state of charge ranges, C-rates and cycling temperature have different degrees of lithium inventory loss, impedance growth and active mass loss. Here, a large matrix of polycrystalline NMC622/natural graphite Li-ion pouch cells were tested with seven different state of charge ranges (0-25, 0-50, 0-75, 0-100, 75-100, 50-100 and 25-100%), three different C-rates and at two temperatures. First, capacity fade was compared to a model developed by Deshpande and Bernardi. Second, after 2.5 years of cycling, detailed analysis by dV/dQ analysis, lithium-ion differential thermal analysis, volume expansion by Archimedes’ principle, electrode stack growth, ultrasonic transmissivity and x-ray computed tomography were undertaken. These measurements enabled us to develop a complete picture of cell aging for these cells. This then led to an empirical predictive model for cell capacity loss versus SOC range and calendar age. Although these particular cells exhibited substantial positive electrode active mass loss, this did not play a role in capacity retention because the cells were anode limited during full discharge under all the tests carried out here. However, the positive electrode mass loss was strongly coupled to positive electrode swelling and electrolyte “unwetting” that would eventually cause dramatic failure.

Review— A Review on the Anode and Cathode Materials for Lithium-Ion Batteries with Improved Subzero Temperature Performance

Lithium-ion batteries (LiBs) have been widely used in a variety of applications, however they still suffer from low capacity retention, large capacity fade ratio or inability to charge efficiently at low temperatures, especially below -20 oC. The reasons behind these drawbacks originate from the nature of active materials such as the anode and the cathode, along with the composition of electrolyte solutions. In particular, from the perspective of active materials, it has been reported that the most common problems arise from the dramatic increase in the resistances, especially charge transfer resistance, and the decrease of lithium-ion diffusivity, by more than one order of magnitude. In this report, we review the most recent strategies in the development of anode and cathode materials and composites, focusing on enhanced electronic and ionic conductivities for improved low-temperature electrochemical performance. Our overview aims to provide a comprehensive comparative study of the proposed methods to overcome the low-temperature challenges in order to develop high energy-density LiBs with enhanced capacity retention, cycling stability and high-rate capability under extreme conditions.

Reactivating Dead Li by Shuttle Effect for High-Performance Anode-Free Li Metal Batteries

Anode-free Li metal batteries are considered the ultimate configuration for next-generation Li-based batteries due to the nonuse of excess Li metal and high energy density. However, the limited Li source worsens the issues in anode caused by Li dendrites and dead Li. Any Li loss in the formation of SEI and dead Li has a great influence on the full cell. Here, we introduce LiI with shuttle effect to suppress the Li dendrites and reactivate the dead Li in the anode-free LiFePO4 (LFP) |Cu full cells. During cycling, the iodine will transform between I and I3, and a chemical reaction will occur spontaneously between I3 and Li dendrites or dead Li. The generated Li in the electrolyte will be active in the following cycling. The anode-free LFP|Cu cells deliver an initial discharge capacity of 139 mAh g-1 and maintain capacities of 100 mAh g-1 with a capacity retention of 72% after 100 cycles. Both the anode-free LFP|Cu coin cells and pouch cells with LiI additive show much-improved performances. This work provides a new strategy for high-performance anode-free Li metal batteries.

A Study on the Self-Discharge Behavior of Zinc-Air Batteries with CuO Additives

Zn-air batteries have promise as the next generation of batteries. However, their self-discharge behavior due to the hydrogen evolution reaction (HER) and corrosion of the Zn anode reduce their electrochemical performance. Copper (II) oxide (CuO) effectively suppresses the corrosion and HER. In addition, different electrochemical behavior can be obtained with different shape of nano CuO. To improve the performance of Zn-air batteries, in this study we synthesized nano CuO by the hydrothermal synthesis method with different volumes of NaOH solutions. Materials were characterized by XRD, FE-SEM, and EDX analysis. The sphere-like nano CuO (S-CuO) showed a specific discharge capacity of 428.8 mAh/g and 359.42 mAh/g after 1 h and 12 h storage, respectively. It also showed a capacity retention rate of 83.8%. In contrast, the other nano CuO additives showed a lower performance than pure Zn. The corrosion behavior of nano CuO additives was analyzed through Tafel extrapolation. S-CuO showed an Icorr of 0.053 A/cm2, the lowest value among the compared nano CuO materials. The results of our comparative study suggest that the sphere-like nano CuO additive is the most effective for suppressing the self-discharge of Zn-air batteries.

Nitrogen-Doped Carbon Boosting Fe2O3 Anode Performance for Long-Life Supercapacitors

Here, we report Fe2O3/N-doped carbon (Fe2O3/CN) composites via one-step facile calcination process by using FeOOH and PANI as precursor. The results show that N-doped carbon is helpful to enhance the electrochemical properties of Fe2O3. N-doped carbon not only enhances the conductivity of Fe2O3 electrode, but also alleviates the volume expansion of Fe2O3 in the process of repeated charge and discharge. In addition, the synergistic effect of Fe2O3 and N-doped porous carbon makes the composites show higher capacitive properties (538.7 mF/cm2 at 5 mA/cm2) and cycle life (100% retention after 2000 cycles). In addition, its superior electrochemical performance is also proved in symmetrical supercapacitor. After 4900 cycles with current density of 10 mA/cm2, its capacity retention rate is 100%. So Fe2O3/N-doped carbon as electrode materials for long-life symmetrical supercapacitors has broad application prospects.

Li2ZrO3-Coated Monocrystalline LiAl0.06Mn1.94O4 Particles as Cathode Materials for Lithium-Ion Batteries

Li2ZrO3-coated and Al-doped micro-sized monocrystalline LiMn2O4 powder is synthesized through solid-state reaction, and the electrochemical performance is investigated as cathode materials for lithium-ion batteries. It is found that Li2ZrO3-coated LiAl0.06Mn1.94O4 delivers a discharge capacity of 110.90 mAhg−1 with 94% capacity retention after 200 cycles at room temperature and a discharge capacity of 104.4 mAhg−1 with a capacity retention of 87.8% after 100 cycles at 55 °C. Moreover, Li2ZrO3-coated LiAl0.06Mn1.94O4 could retain 87.5% of its initial capacity at 5C rate. This superior cycling and rate performance can be greatly contributed to the synergistic effect of Al-doping and Li2ZrO3-coating.