Boron in Batteries and Capacitors

Batteries: Improving safety and efficiency

Lithium-ion batteries used in portable electronics use graphite as an anode material. However, graphite anodes are susceptible to lithium deposition and dendrite formation at high charge rates. These issues can short out the battery cell and cause safety issues. Borate surface coating may protect against lithium deposition, leading to better safety characteristics and potentially improving the stability of the SEI, which forms a boundary between electrode and electrolyte. (Several studies have shown that borates are beneficial to the formation of the SEI.)

But borates can help save energy even earlier in the process. High-temperature heat treatment of the graphite used in batteries contributes to a highly ordered crystalline graphite structure. But high-temperature graphitization is an expensive and energy-intensive process that requires temperatures in the 3000°C range. Adding borate before graphitization improves electrochemical properties and lowers the temperatures required for graphitization. In addition to increasing crystallinity, boron is thought to incorporate into the lattice structure of graphite at higher temperatures, initiating greater alignment and changing the electronic structure. In the graphite lattice, boron can act as an electron acceptor, leading to a specific capacity of 437 mAh/g—higher than the theoretical maximum for pure graphite (372 mAh/g).

Borates, supercapacitors, and electric vehicles

Supercapacitors (also known as ultracapacitors, electric double-layer capacitors, power capacitors, and electrochemical capacitors) are electrochemical energy storage devices. These devices offer the charge and discharge rates of conventional capacitors at an energy density near that of batteries.

When a DC voltage is applied, supercapacitors electrostatically store the charge at the interface between a polarizable electrode and an electrolyte solution. The charge separation that results form the reversible adsorption of electrolyte ions into the electrode creates energy storage. Borates are used in the electrolyte solution.

Supercapacitors offer charge and discharge times of 30 seconds or less, compared with hours for a conventional lithium-ion battery. They also have a much higher cycle life and power density. They cannot be overcharged, contain no heavy metals, and have higher energy and power densities than conventional capacitors do. Though these devices have existed for decades, they are increasing in popularity as a component of portable consumer electronic goods, backup power supplies, and electric or hybrid vehicles.