High Throughput Experimental Methodologies for Accelerating Solid State Lithium-Ion Battery Development
Authors: Huang Andy 
Published: February 2020

Breakthrough in lithium-ion battery technology is crucial for modern sustainable energy applications, especially the electric vehicles. Compared to conventional lithium-ion battery with liquid electrolyte, solid state battery with solid inorganic electrolyte or flexible composite electrolyte possesses the advantages of higher energy density, higher working voltage, non-flammability, and lithium dendrite prevention [1, 2]. One of the main challenges of developing this next generation of batteries is to find the optimized structure and composition of solid electrolyte material, which usually has a ternary, quaternary, or even more complex composition. High throughput experimental methodologies, in which dozens of parallel experiments are carried out with small sample quantities per experiment, can greatly accelerate new material discovery and process optimization for solid electrolyte and solid state lithium ion battery development.

To support this high-throughput experimental demand, the experimental instrument must meet requirements such as maximizing productivity through parallel experiments and automation, working with small amount of sample per experiment, and compatibility with Ar gas glove box operation. MTI Corporation (Richmond CA, USA) strive to provide highly efficient and economical experimental equipment and solutions for high throughput battery development. In this work, MTI Corporation¡¯s efforts on developing high throughput experimental solutions for solid state lithium-ion battery are discussed.

The first step is solid inorganic electrolyte powder synthesis and pellet fabrication. For solid dispensing, four or more dispensing heads and balances, with one dispensing head for each solid electrolyte component, are integrated with a carousel type sample changer for automatic powder dispensing of 32 electrolyte powder samples. Next, the powder samples are ball milled in a planetary ball mill with 4 sets of 4 cavities milling jars for totally 16 parallel experiments. Then, the electrolyte powders are pressed into pellets for coin cell assembly using a hydraulic press with carousel type 16-sample changer. The powders and pellets are sintered, annealed, or quenched in a compact, 16-channel tube furnace up to 1700 ¡ãC with quenching option.

Novel sintering techniques, such as spark plasma sintering (SPS) [3] and hydrothermal-assisted cold sintering process (CSP) [4], are employed for solid inorganic electrolyte sintering. These techniques, whether for the fast processing time of spark plasma sintering, or the low temperature processing capability of cold sintering process, open up possibilities of low cost, rapid fabrication of solid electrolytes, cathode pellets, or even the whole solid electrode-electrolyte stack [3].

Solid inorganic electrolyte is usually too brittle for practical use. Composite electrolyte, which is made by embedding solid inorganic electrolyte powder in flexible polymer electrolyte, is a promising solution. By varying the ratio between inorganic and polymer components, a balance between electrical and mechanical properties can be achieved [4, 5]. The process of composite electrolyte fabrication starts with powder and liquid dispensing. For liquid dispensing, an automatic pipette robot with integrated XYZ stage is used for dispensing organic solvents and liquid electrolytes. The as-prepared high viscosity samples are mixed in a planetary centrifuge mixer for mixing 6 samples of 5 ml in one run. With addition of a 4-channel film applicator, existing doctor blade coater can be modified into high throughput equipment. The as-prepared sample with four strips of different composite electrolytes can be passed onto hot calendar machine or hot press for solvent evaporation and thickness reduction, and coin cell die cutter for high throughput preparation of composite electrolyte discs.

Finally, the solid electrolyte powder and discs are analyzed by a compact X-ray fluorescence (XRF) spectrometer integrated with a XY sample stage for high throughput composition characterization. 32 samples can be qualitatively and quantitatively analyzed in one auto run. For high throughput assembling of coin cells, one route is to use an automatic coin cell crimper machine to facilitate coin cell assembling process. The other route is to use multiple split cells with quick, easy, repeatable assembling for parallel comparison of different solid electrolyte materials. This further saves time and labor by eliminating the coin cell crimping step.

In conclusion, high throughput experimental solutions accelerate new material discovery and process optimization for solid state lithium ion battery research. Existing experimental techniques are modified for high throughput application by smart design of sample fixture, by integration, and by automation. Novel processing methods, such as spark plasma sintering and cold sintering, enable reduced processing time and low production cost.