Lithium-ion batteries are an advanced battery technology that uses lithium ions as a key component of its electrochemistry. During a discharge cycle, lithium atoms in the anode are ionised and separated from their electrons. The lithium ions move from the anode and pass through the electrolyte until they reach the cathode, where they recombine with their electrons and electrically neutralise. The lithium ions are small enough to be able to move through a micro-permeable separator between the anode and cathode. This is in part responsible for the fact that Li-ion batteries can have a very high voltage and charge storage per unit mass and unit volume.
Now (2021), scientists at Argonne National Laboratory have discovered a means to drastically improve the efficiency of lithium-ion batteries. They have created a new electrode design for the lithium-ion battery using low-cost materials such as lead, as well as carbon, with the aim of investigating lead as an alternative to graphite for the anode material. The anode consisted of innumerable microscopic particles with an intricate structure: lead nanoparticles embedded in a carbon matrix and enclosed by a thin lead oxide shell. Tests in the laboratory over 100 charge-discharge cycles showed that the new lead-based nanocomposite anode had twice the energy storage capacity of current graphite anodes. Stable performance during cycling was possible because the small particle size reduced stresses while the carbon matrix provided the needed electrical conductivity and acted as a buffer against damaging volume expansion during cycling. The team also discovered that adding fluoroethylene carbonate to the standard electrolyte significantly improved performance. With the help of synchrotron X-ray diffraction, they were able to analyse the changes in phases of the anode material while it was being charged and discharged. These characterization results revealed a previously unknown electrochemical reaction between lead and lithium ions that occurred upon charge and discharge.
Scientists have long been searching for cheaper anode materials able to improve the efficiency of batteries. In 2012, a self-assembly method to synthesize graphene oxide nanosheets (GON) with tunable thickness ranging from ∼1 nm (monolayer) to ∼1500 nm was developed. The lateral sizes of the monolayer and few-layer (<5) GONs were about 20 μm and 100 μm, respectively. The GONs were prepared by a hydrothermal method using glucose as a sole reagent. The method was environmentally friendly, easy, low-cost as well as adaptable to mass production. The electrical resistivity of the GONs could be tuned by annealing for 8 orders of magnitude ranging from 106 Ω cm to 10−2 Ω cm. A GO-based photodetector was designed, demonstrating the optoelectronic properties of the GONs.
In 2015, scientists created nanostructured composites of lead oxide/copper–carbon (PbO/Cu–C) by means of in situ solvothermal synthesis and heat treatment of PbO/Cu with polyvinyl pyrrolidone (PVP) and used them as lithium-ion battery anodes. A PbO active particle was embedded in the Cu and PVP–C matrix, accommodating volume changes and maintaining the electronic conductivity of PbO. The composite exhibited a superior electrochemical performance, with a capacity of 420 mA h g−1 at a current density of 165 mA g−1, compared with previously reported Pb and PbO composite anodes. The anode showed>90% capacity retention after 9500 cycles, beginning from the second cycle, at a current density of 5.5 A g−1.
There are several advantages to using lead as an anode in lithium-ion batteries: the material is especially suitable because it is abundant and inexpensive. In addition, it has a well-established supply chain owing to the long history of lead-acid batteries providing ancillary power for automobiles and is one of the most recycled materials in the world. The new anode could offer an additional revenue stream for the large industry currently active in lead-acid battery manufacturing and recycling. Also, the fundamental insights the scientists have gained into electrode material may also prove important in understanding the reaction mechanism of silicon anodes, as the silicon anode is another low-cost, high-performance candidate for next-generation lithium-ion batteries.
This discovery challenges the current understanding of electrode materials. It also provides exciting implications for designing low-cost, high-performance anode materials for transportation and stationary energy storage, such as backup power for the electric grid.