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Japan's next generation of high energy density battery research tracking

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1 Japan's next generation battery technology research and development project

(1) ALCA-SPRING and GST projects

Japan's lithium battery technology research and development rely on the ALCA-SPRING and GST projects, which are two national projects launched by the Japan Science and Technology Commission. The aim of the project is to promote a new generation of innovative battery materials research, and then promote the development of high-capacity batteries, research and development of secondary batteries, and breakthroughs in next-generation lithium battery technology to explore innovative applications of secondary batteries.

ALCA-SPRING is an advanced low-carbon technology research and development project, which was launched by the Japan Science and Technology Agency (JST)'s "New Generation Next Generation Battery Special Promotion Research (SPRING) Project". It was launched in 2013 and is a special priority for ALCA. . The project aims to accelerate the development of high-capacity secondary batteries and next-generation batteries for existing lithium-ion batteries, as well as to develop innovative secondary battery technologies. This battery technology will far exceed the performance of current secondary batteries and accelerate its technical research for practical applications.

In promoting the research, ALCA-SPRING not only develops unique materials such as active materials, electrolytes and separators, component technology and understands the reaction mechanism of various types of batteries, but also obtains secondary batteries by optimizing the entire battery system. The best performance, ALCA-SPRING research organization structure is shown in Figure 1. The R&D team can continue to be subdivided into oxide groups, sulfide groups, and all-solid battery groups. There are also many sub-studies in the university to promote the development of AL-CA-SPRING.

Figure 1 ALCA- SPRING Research Organization Structure

(2) RISING2 project

RISING2 is a new generation of battery technology innovation research and development national project, derived from Japan's new energy industry technology development organization (NEDO). The project is dedicated to the development of long-life range electric vehicles, mainly to develop innovative batteries such as zinc-air batteries, nano-interface control batteries (halides and their conversion products), and lithium-sulfur batteries. The project aims to achieve an energy density of 500 Wh/kg for electric vehicles in 2030.

The project builds a battery technology research and development platform. The platform is divided into three technical research and development groups: anion working technology group, cationic working technology group and advanced battery testing and analysis technology group. The research direction of the anion working technology group includes nano interface control (halide and its transformant) material technology, water metal air battery technology and basic theory of metal oxide cation (fluoride) deintercalation and adsorption mechanism; cation working technology group The research direction includes lithium sulfide battery technology, nano interface control material technology and basic theory of cation deintercalation and adsorption mechanism.

The research direction of the advanced battery test and analysis technology group includes synchronous accelerator, nuclear magnetic resonance (NMR), neutron diffraction, micro-electron microscopy, computational science, electrochemical precision measurement and other analytical testing techniques. RISING2 is a project that promotes battery development and is driven by Japan's new energy and industrial technology development agencies.

This project aims to promote the battery to increase the specific energy and extend the mileage of new energy vehicles. The RISING2 project includes technical studies on zinc-air batteries and nano-interface cells (including halides and their conversions). Kyoto University researchers promoted the RISING project from 2009 to 2016, leading four of the six innovative batteries. Figure 2 is a diagram of the cooperation division of cooperation around the project. Figure 3 is a schematic diagram of the participating project partners and their geographical distribution.

图2 项目分工合作框架

Figure 3 Schematic diagram of the participating project partners and their geographical distribution

2 Research on all solid state battery technology

The National Lithium Battery Technology and Evaluation Center Committee hopes to advance the development of all-solid-state batteries. This evaluation center committee is composed of a number of research team members, and will also support relevant technology development, safety assessment, etc., to better help manufacturers to innovate. .

The all-solid-state battery national project is based on the development of the all-solid-state battery technology for lithium-ion battery technology and evaluation center alliance (LIBTEC) for electric vehicles. It is expected that by 2025, the battery technology of high power and long cruising range (550km) will be realized through the project; by 2030, the cruising range will be upgraded from the current 400km to 800km, and the design flexibility and flame retardant performance are excellent, and the applicable temperature range wide. Figure 4 is a schematic diagram of the principle of an all-solid battery.

Figure 4 principle of all solid state battery

Toyota recently released an all-solid-state battery. All solid-state batteries can be loaded on physical vehicles in 2020, and the experimental prototypes are shown in Figure 5. For all-solid-state batteries, Japanese technology is constantly being developed. The material safety of all all-solid-state batteries will be further improved, the electrolyte stability is higher, and the conductivity is high. The mainstream electrode material system, as well as some materials of Panasonic Corporation, including some phosphate materials, these materials are very sensitive to water, and research and development in this area is progressing. There may be more material breakthroughs in technology in the future. Figure 6 is a diagram of a new material system for an all-solid battery.

Figure 5 all solid-state battery car carrying experiment

The solid-state battery technology project is mainly carried out around the research and development of material systems. Because the most important energy carriers in electrochemical systems are the active materials of the positive and negative electrodes. Whether the material system has excellent electrochemical properties (specific energy, chemical stability, reversibility, etc.) will directly determine the performance of the battery cell. Of course, other separators, electrolytes, etc., which constitute the electrochemical system, also have an effect on the performance of the battery, but the influence weight is slightly smaller. Therefore, the leap in battery technology is often brought about by breakthroughs in materials technology.

Figure 6 new solid battery system

Japan's recent research on the positive and negative materials of batteries has become more and more important. Tables 1 and 2 are the summaries of the trends in the development of the two materials.

Table 1 Development trend of cathode materials for lithium ion batteries

Table 2 Development trend of cathode materials for lithium ion batteries

(1) New alloy anode (negative electrode)

All-solid-state battery technology is carried out around the main line of research and development of positive and negative materials. First, the anode material, which is the anode material of the battery, is mainly researched and developed on the alloy anode Si-C-O material. As early as seven years ago, there was preparation for the study of electrodeposition of such negative electrode materials. At that time, the focus of the research was on the deposition of this silicide and the deposition of silicon. The silicon, oxygen and carbon in the sediment were evenly distributed, but the durability was poor. At present, carbon, silicon, and oxygen ion architecture models have been established, and on this basis, more in-depth research has been conducted to improve the performance of silicon oxide carbon anodes. The electrodepositor is used to prepare the negative electrode, which is formed by direct, simple and mature industrial preparation process, directly formed on the current collector, with less binder and simple slurry coating process.

A schematic diagram of the preparation of the negative electrode by electrodeposition in an organic electrolyte is shown in FIG. Using propylene carbonate and silicon tetrachloride as solvents, silicon deposition and solvolysis occur simultaneously, microcomposite of silicon and organic/inorganic compounds, and the plan and cross section of the deposited silicon compound are shown in Fig. 8. Si, O, and Si are found in the figure. C is evenly distributed in the sedimentary layer.

Fig. 7 shows the structure of electrodeposited C, O and Si on a metal Cu foil in an organic electrolyte

Figure 8 C, O, Si plan and section

The experimentally prepared Si-O-C negative electrode was subjected to charge and discharge experiments. The charge-discharge efficiency reached 98%-99%, and the discharge specific capacity was 830 mAh/g, which could achieve more than 7 000 cycles. The charge and discharge curve is shown in Figure 9.

Current density: 250 μA/cm2 (1.0 C), relative potential 0.01 - 1.2 V (vs .Li/Li+)
Figure 9 Si- O- C negative charge and discharge test

(2) High-capacity sulfide cathode (positive electrode)

The method for realizing a high-capacity lithium-sulfur battery is to prepare a high-capacity positive electrode. For the study of the sulfide material of the positive electrode material, the focus is on how to apply sulfur and increase the density of sulfur composite. By using a nickel or aluminum foam material as a 3D current collector, it is desirable to increase its load and increase the active material loading surface density and specific energy. In order to achieve a high loading of sulfide positive electrode, it is necessary to increase the surface area density of sulfur. Increasing the sulfur loading surface density is limited by conventional metal foil current collectors. Therefore, the preparation of the 3D structure current collector can effectively increase the surface density of the load.

In general, the 3D structure current collector has the following advantages: it can increase the surface area density of sulfur because the 3D structure current collector has a high specific surface area; even a thick electrode can ensure the ion conduction path, which is due to the 3D structure. Enriched with electrolyte. The 3D structure current collector is shown in Figure 10.

Figure 10 is a picture of the 3D structure current collector and a current collector of the active material sulfur

Increasing the sulfur loading can increase the area specific capacity, increase the surface area density of sulfur, and obtain a high area specific capacity. Since the electrolyte remains stable, sulfur has a high mass ratio energy. Optimizing the components of the lithium-sulfur battery can achieve a specific energy of 200Wh/kg. Figure 11 - 13 is the relationship between sulfur positive load, voltage, gram capacity, and areal density.

Figure 11 Sulfur loading and area specific capacity of the positive electrode

Figure 12 area specific capacity, gram capacity and voltage curve of the positive electrode

Figure 13 Charge and discharge curves of sulfur positive electrode under different magnification conditions

(3) 1Ah Li-S battery

Figure 14 Laboratory made 1Ah flexible packaging Li-S battery

Figure 15 Charge and discharge curves of 1Ah flexible packaging Li-S battery made in the laboratory

Figure 14 is a laboratory-made 1 Ah flexible packaging Li-S battery with a sulfur loading of 17.5 mg/cm2. The lithium-sulfur battery consists of a 1 mm thick sulfur positive electrode and a 0.2 mm thick lithium negative electrode. The 5 Ah lithium sulfur battery can be obtained by stacking several such single cells. Figure 15 is the charge and discharge curve of the battery.

Figure 16 Lithium-sulfur battery positive charge and discharge curve

Fig. 16(a) is a discharge curve of the S/KBPVdF foamed aluminum sulfur positive electrode, and Fig. 16b) is a discharge curve of the S/KB-CMC+SBR foamed aluminum sulfur positive electrode, and the solid line and the broken line are the area specific capacity and the gram capacity, respectively. In the charge and discharge test, the cut-off voltage is 1.0-3.3 V, and the charge/discharge rates of the S/KBPVdF foamed aluminum-sulfide positive electrode are 0.03 C and 0.01 C, respectively. The charge/discharge rates of the S/KB-CMC+SBR foamed aluminum-sulfur positive electrode are both 0.01 C.

The current density of the electrode can be increased by improving the Si-O-C negative electrode. By combining the Si-O-C negative electrode and the Li2S positive electrode, the energy density of the battery can be increased to a high degree, and it is expected to eventually reach the target of 500 Wh/kg.

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