Review of energy storage technology development in the first half of 2015

Since 2015, the research and development of various energy storage technologies have made continuous breakthroughs. Summarizing the research and development trends of energy storage technologies since 2015, lithium-ion batteries are still the most active type of energy storage technology.

The research and development of lithium-ion batteries is mainly divided into two directions. One direction is based on the conventional positive and negative electrode material system, and improves the cycle life of materials and optimizes the electrochemical performance of the battery system by designing and preparing new materials, developing new synthesis and preparation processes, controlling and optimizing the morphology and structure of materials. The other direction starts from the lithium-ion battery system and explores new battery systems such as aluminum-ion batteries, sodium-ion batteries, lithium-sulfur batteries, and lithium-air batteries that are similar to it.

The Zhongguancun Energy Storage Industry Technology Alliance has been paying long-term attention to and tracking the development of energy storage technology. This article will briefly introduce the representative research results of energy storage technology in the first half of 2015.

Combine solar cells with secondary batteries to achieve energy conversion and storage at the same time

Ohio University scientists have developed the concept of lithium-iodine solar flow battery (Li-I SFB) by integrating the TiO2 photoelectrode of dye-sensitized solar cells with lithium-iodine flow batteries, which can realize the simultaneous conversion and storage of solar energy.

The Li-I SFB system is a three-electrode structure, with metallic lithium as the negative electrode, Pt as the counter electrode, and dye-sensitized TiO2 as the photoelectrode; the Pt counter electrode and the dye-sensitized TiO2 photoelectrode are stored in the positive electrode chamber at the same time, opposite to the metallic lithium negative electrode, and an iodine solution is used as the electrolyte. In the light-supported charging process, I- is photoelectrochemically oxidized to I3-, thereby capturing and storing solar energy. Due to the support of photovoltage, the charging voltage of the system can be reduced to 2.9V, which is lower than the discharge voltage of 3.3.V. The reduction in charging voltage also means that 20% of energy can be saved compared to traditional lithium-ion batteries. This concept can also be extended to other metal flow battery systems.

Previously, the research group had also used a similar concept to develop a new type of solar lithium-air battery. This battery combines a dye-sensitized photoelectrode with the oxygen electrode of a lithium-air battery to achieve photo-assisted ging of the lithium-air battery, greatly reducing the overpotential caused by the difficulty of Li2O2 decomposition during the charging process, improving the cycle efficiency and avoiding the performance degradation of the oxygen electrode.

New high-capacity anode materials continue to emerge, improving the energy density and power performance of lithium-ion batteries

Researchers from Tsinghua University and MIT have jointly developed a high-capacity, long-life, and high-rate negative electrode material for lithium-ion batteries. This material consists of a core-shell structure composed of nano-aluminum and TiO2, can be cycled 500 times at a 10C rate, and has a discharge capacity of more than 650mAh/g, which is of great significance for improving the power performance and energy density of lithium-ion batteries. Although aluminum has a high theoretical capacity as a negative electrode for lithium-ion batteries, it will experience problems such as volume expansion and structural collapse during the cycle process, so the cycle life is short and cannot be used in practice. The research results can greatly promote the application of aluminum in negative electrode materials for lithium-ion batteries.

Silicon anode materials have always been the focus of research on lithium-ion battery anode materials. In recent years, the performance of silicon anode materials has been continuously improved, and lithium-ion batteries with silicon as anode materials have begun quasi-commercial applications. ASA's Game Changing Development (GCD) project has entered its second phase, with the goal of developing advanced, large-capacity, and long-life battery systems for future U.S. outer space exploration. Among the two selected energy storage technologies, one is the high-energy lithium-ion battery system based on silicon anode materials from California's Amprius.

In 2015, Samsung Advanced Institute of Technology developed a high-capacity composite silicon negative electrode material with the help of graphene, which effectively solved the volume expansion problem of silicon negative electrode materials and greatly improved the volume capacity of lithium-ion batteries. When combined with LiCoO2 to form a battery, the volume energy density of the system was 972 and 700Wh/L in the first week and 200 weeks, respectively, which is 1.8 and 1.5 times higher than the current commercial cobalt oxide lithium battery products.

Develop solid electrolyte systems to improve battery safety performance

Unlike traditional liquid electrolyte systems such as LiPF6, solid electrolytes have excellent safety performance, which can greatly reduce the thermal expansion of the battery system, avoid electrolyte recovery leakage problems and short circuit problems caused by dendrite growth.

Researchers from MIT, Samsung Advanced Institute of Technology, University of California, San Diego, University of Maryland and other institutions jointly published their research results, developed a solid lithium-ion electrolyte composed of lithium, germanium, phosphorus and sulfur elements, and studied the structure and path that are conducive to the rapid migration of ions, laying the foundation for the development of solid-state electrolyte systems.

In 2015, PATHION obtained a patent license from Los Alamos National Laboratories. It recently developed and launched two new superionic solid electrolyte materials and received support from the ARPA-E project. The first is LiRAP material (Lithium-Rich Anti-Perovskite, lithium-rich anti-spinel material), which can be used in lithium-ion batteries and lithium-sulfur batteries. In addition to having good conductivity for Li+, LiRAP solid electrolyte materials can also directly use metallic lithium as the negative electrode and achieve high voltage and high current, thereby greatly improving the energy and power density of the solid electrolyte system. The second is LiGlass material, which can be used in sodium-ion batteries. LiGlass can achieve ultra-fast sodium ion conduction in the range of room temperature to 200 degrees, and the energy density reaches 1000Wh/kg.

Develop a fast and reversible aluminum-ion battery system to achieve a major breakthrough in aluminum batteries

Dai Hongjie's research group at Stanford University published their research results in Nature, developing an aluminum-ion battery system with ultrafast reversible charge and discharge capabilities. This battery solves the problems that traditional aluminum-ion batteries have always faced during development, such as poor positive electrode embedding, low discharge voltage, no discharge voltage platform, short cycle life (less than 100 cycles), and fast capacity decay (capacity is only 26-85% after 100 cycles). The battery has a discharge voltage platform at around 2V, a discharge capacity of nearly 70mAhg-1, an energy density of ~40Whkg-1 (close to lead-acid batteries), and a power density of 3000Wkg-1 (close to supercapacitors).

The battery uses aluminum foil as the negative electrode, AlCl4- as the conductive ion, and ionic liquid AlCl3/[EMIm]Cl as the electrolyte, and compares two positive electrode material systems: foamed graphite and pyrolytic graphite. The system with foamed graphite as the positive electrode can achieve a fast charge and discharge of 5000mAg-1 (75C), and the capacity retention rate is close to 100% after 7500 cycles.