The market always has many expectations for solid-state batteries. In the early days, the focus was on breakthroughs and selection of technological routes. Now, as sulfide solid electrolytes gradually become a consensus in the industry and anchor 2027 as the time point for the initial mass production of all solid state batteries, the market is once again pursuing solid-state batteries to become "hexagonal warriors". As an urgent need for power batteries to be used in vehicles, coupled with the promotion of emerging markets such as eVTOL, solid-state batteries are expected to achieve balanced development in terms of safety, energy density, cycle life, charge discharge rate, and cost.

Among them, rate performance is increasingly becoming one of the key indicators for "examining" solid-state batteries. Despite the breakthrough in energy density bottleneck and the ability to reduce charging frequency, solid-state batteries are still expected to achieve fast charging capabilities above 4C in order to compete with liquid batteries.

Meanwhile, eVTOL、 Applications such as humanoid robots are based on more diverse scenarios, and also require higher demands for instantaneous charging and discharging of batteries and high rate continuous discharging. Starting from the second half of 2024, the market has begun to speculate on the expected and logical growth in demand for new conductive agents (such as single-walled carbon nanotubes) driven by solid-state batteries.

However, despite high expectations from the market for fast charging solid-state batteries, actual progress has been relatively slow.

According to the review of recently released solid-state battery products by Gaogong Lithium Battery, the vast majority of products claiming to achieve fast charging performance of 4C or above are still semi-solid state batteries. There is currently no mature fast charging all solid state battery product on the market, and the technological breakthroughs of the released all solid state batteries rarely focus on rate performance.

Taking eVTOL enterprise Yihang Intelligence as an example, in order to match different operational scenarios, it chooses to cooperate with battery companies and promote the research and development of high-energy density and high rate solid-state batteries in parallel. This indirectly confirms that fast charging performance remains a key bottleneck that all solid state batteries urgently need to overcome.

Recently, solid-state battery company Zhongke Shenlan Huize pointed out at an industry conference that the core of fast charging solid-state batteries is to achieve rapid coordinated transport of ions and electrons. All solid state batteries have inherent advantages in achieving fast charging, as solid electrolytes typically have higher ionic conductivity than liquid electrolytes, and the lithium ion transport process does not require solvation/desolvation steps. But its bottleneck is also very obvious, reflected in the fact that lithium ions need to be transported through the solid solid interface.

Therefore, solving the problem of solid solid interface is the primary issue for achieving fast charging all solid state batteries.

Taking sulfide solid electrolytes as an example, although the ion conductivity is high, in order to avoid the formation of lithium dendrites in lithium metal or carbon based negative electrodes and cause short circuits, batteries usually need to operate at lower current densities. In addition, to maintain contact at the electrolyte active material interface, external pressure of 5 MPa or more may be required.

At present, the strategies summarized by academia to improve the fast charging performance of solid-state batteries include: increasing electrolyte conductivity, constructing ion/electron mixed transport channels in positive and negative electrode materials, and improving solid solid interface problems. These strategies mainly involve the development and design of new materials, such as high entropy solid electrolytes, composite electrolytes, alloyed lithium metal negative electrodes, and homogenized positive electrodes.

It is worth noting that the design of homogenized positive electrodes can endow the positive electrode material system with excellent electron and ion transport capabilities, thereby reducing the demand for ion transport materials, conductive additives, etc. in traditional positive electrodes (by nearly 20% of the amount added). As a result, the previously occupied space can be released and used entirely to increase the proportion of active positive electrode materials, ultimately achieving simultaneous improvement in energy density and rate performance.

Based on the above strategies, some research teams have made significant progress. For example, a team based on sulfide halide composite solid electrolytes achieved ultra-high rate charging and discharging at 49C and maintained a long cycle life when the positive electrode active material ratio reached 95%.

In addition, artificial intelligence has also played an important role in accelerating the development of new materials. For example, Zhang Qiang's team at Tsinghua University has developed a high-throughput electrolyte calculation software that can screen electrolyte materials suitable for fast charging systems from a large number of molecules, and verify their performance through experiments, providing a new breakthrough point for the development of fast charging all solid state batteries.

However, although fast charging all solid state batteries have made some progress in the laboratory stage, they still face many challenges on the road to industrialization. For example, during the production process of solid electrolytes, their transformation from powder to thin film form may lead to a decrease in ionic conductivity and may require the introduction of additional conductive materials for improvement.

Another industry insider pointed out that according to patent searches, Japan's layout in the field of high-power solid-state batteries is relatively leading, which puts significant competitive pressure on domestic solid-state battery teams in terms of technology layout and industrialization promotion of all solid state fast charging batteries. Therefore, promoting collaborative innovation in the industrial chain and breaking through the bottleneck of fast charging technology will become one of the key directions for realizing the commercial application of all solid state batteries in the future.