(306c) Gas-Assisted Electrospray for Ultrauniform, Ultrafast, Instantly-Dry, and Binder-Free Electrode Preparation

Lithium-ion batteries has been a hot research focus in recent years due to their high energy density, flexible and lightweight design, long lifespan, and wide application in portable electronic devices and electric vehicles. Among all the battery-related researches, most focus on electrode materials, a small portion focus on binder, separator, electrolyte, and almost none focus on the preparation of electrode. For the tons of researches, materials preparation could vary a lot, but almost all used either drop cast or slurry coating for final electrode preparation. However, both drop cast and slurry coating methods involve toxic organic solvents and consist of multi steps including mixing, sonication, blading, calendaring, and long-time vacuum drying. Even after all these tedious steps, the as-prepared electrodes still suffer from exfoliation of the active material from current collector, leading to poor cycling stability. Though there are also some free-standing electrodes skipping the traditional electrode preparation procedure, they are not versatile and are often limited to certain kinds of materials.

 To simplify the preparation process, and more importantly get better adhesion and high uniformity, we have developed a facile electrospray process from the already industrialized electrospining process. It can be applied to spray slurry (binder, additive carbon, active materials) from both organic and water system. The as-sprayed electrodes not only show no exfoliation upon bending, but also have lower resistance demonstrated by smaller impedance circle in comparison with conventionally made electrodes.  The flow rate is 10 or 20 times fast of electrospinning, thus desired mass loading of electrodes can be achieved with only a few minutes of spraying. Excitingly, the electrodes made can be directly used for battery assembly, no extra drying step required. We further advanced the technique to a general binder-free electrode preparation approach where only graphene oxide is added. The graphene oxide sheets not only act as binder and conductive agents, but also act as “pocket” to hold active materials and help resist mechanic stress during charge and discharge, giving outstanding battery stability. In addition to battery electrodes, this approach can be also applied for many other electrode preparations such as supercapacitors, fuel cell, and solar cell etc.