Boron Salts for Batteries

Oct 19, 2021 | RESEARCH, ADVANCED ENERGY, Batteries and Capacitors

Research on Boron Salts for batteries

Research on Boron salts for batteries continues to be of significant interest in universities and commercial partners globally. Boron is a chemical element that has been used for some time to improve the performance of lithium-ion batteries. Boron salts and boron nanotubes are two new materials being developed for use in Li-ion and Li-S batteries. 

The goals behind using these materials are to increase battery capacity, decrease cost, and reduce environmental impact. Let’s explore some of the basic chemistry behind boron’s role as a cathode material, talk about what makes them so special, and discuss some of the challenges that researchers face when developing new technologies for future energy storage devices. 

We will also examine how borate salts can be synthesized from solar power or hydroelectricity with little pollution involved in their production.

Boron Salts for Batteries

Boron-based salts for lithium-ion batteries

A new anion design concept, based on combining a boron atom as the central atom and conjugated systems as ligands, is presented as a route for finding alternative Li-salts for lithium-ion batteries.

The properties of a wide range of novel anions designed in this way have been evaluated by DFT calculations focusing on three different fundamental success factors/measures: the strength of the cation-anion interaction, ultimately determining both the solubility and the ionic conductivity, the oxidation limit, determining their possible use vs. high voltage cathodes, and the reduction stability, revealing a possible role of the anion in the SEI-formation at the anode. 

For a few anions, superior properties vs. today’s existing or suggested anions are predicted, especially the very low cation-anion interaction strengths are promising features. The design route itself is shown to be versatile in determining the correlation between different choices of ligands and the resulting overall properties – where the most striking feature is the decreased lithium cation interaction energy upon using the (1Z,3Z)-buta-1,3-diene-1,2,3,4-tetracarbonitrile ligands. This also opens avenues for the further design of novel anions beyond those with a boron central atom. (

Electrolytes at extra-high temperatures

Broadening the temperature range of lithium-ion batteries can be achieved by optimizing the composition of lithium salts in the electrolyte, which is currently one of the most popular methods.

This study reports research into examining an extra-high temperature electrolyte by optimizing the proportion of mixed lithium salts (LiBOB and LiBF ) with ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl (EMC) as an equal volume mixture. An extra-high temperature of 75 °C is applied in a half cell with lithium iron phosphate (LFP) as the cathode and a lithium foil as the anode. 

The cycle stability and rate performance of the cell with various electrolytes based on mixed lithium salts are systematically investigated and a comparison of the polarization and impedance characteristics is conducted as well. The most outstanding electrolyte composition is electrolyte B (0.6 M LiBOB + 0.1 M LiBF -EC/DEC/EMC). 

The optimized electrolyte not only maintains good cycle stability (the capacity retention rate is 98% after 80 cycles) and excellent rate performance at the extra-high temperature but also minimizes the polarization during cycling, which is mainly due to the formation of a dense and smooth cathode electrolyte interface (CEI) film, as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 

The CEI film that contains B–O bonds and organic components are systematically analyzed by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS), which shows that the aid of the component the extra-high temperature cycling stability of the cell. Our data indicate that the composition of lithium salts in the electrolyte is pivotal to the properties of the CEI film, which largely determines the performance of the cell at extra-high temperatures. The conclusions of this work can contribute significantly to the application of extra-high temperature electrolytes for better battery power for instance. (

Boron and oxygen dual-doped, multi-walled carbon nanotubes

Lithium-sulfur (Li–S) batteries have been the apple of people’s eyes with their high energy density and high theoretical capacity. However, challenges arising from the nature of materials have plagued the commercialization of this technology, among which the notorious shuttle effect, serious volume expansion and insulating nature of sulfur and its low order reduced products are key problems. 

Constructing nanocomposites of sulfur with heteroatom-doped carbon nanostructures is an efficient and promising approach. However, there are limited reports on boron and oxygen dual doping treatment used in lithium-sulfur batteries, let alone explaining an in-depth mechanism. 

A study prepared boron and oxygen dually doped multi-walled carbon nanotubes (BO-MWNTs) as the host material for sulfur. With the successful introduction of boron and oxygen, the electrical conductivity of the carbon material is increased. 

Furthermore, the effect of doped heteroatoms on the carbon/sulfur (C/S) composites and their mechanistic understanding were explored and confirmed via both experiments and Density Functional Theory (DFT) calculations. It was found that B and O dual dopants can offer abundant adsorptive sites and lead to strong chemisorption between the carbon and the sulfides.

This dual doping treatment leads to improved cycling stability and rate capability performance of the C/S cathode. Hence, the proposed innovative mechanistic understanding of boron and oxygen doping on carbon materials may shed light on the designing principle for advanced C/S composites.

Boron-doped porous carbon-graphene hybrid

A hybrid structure consisting of boron-doped porous carbon spheres and graphene (BPCS-G) has been designed and synthesized toward solving the polysulfide-shuttle problem, which is the most critical issue of current Li-S batteries. The proposed hybrid structure showing the high surface area (870 m2·g−1) and high B-dopant content (6.51 wt.%) simultaneously offers both physical confinement and chemical absorption of polysulfides.

On one hand, the abundant-pore structure ensures high sulfur loading, facilitates fast charge transfer, and restrains polysulfide migration during cycling. On the other hand, density functional theory calculations demonstrate that the B dopant is capable of chemically-binding polysulfides.

As a consequence of such dual polysulfide confinement, the BPCS-G/S cathode prepared with 70 wt.% sulfur loading presents a high reversible capacity of 1,174 mAh·g−1 at 0.02 C, a high rate capacity of 396 mAh·g−1 at 5 C, and good cyclability over 500 cycles with only 0.05% capacity decay per cycle. The present work provides an efficient and cost-effective platform for the scalable synthesis of high-performance carbon-based materials for advanced Li-S batteries. (