Due to its extremely high specific capacity and excellent electrical conductivity, lithium metal is an extremely promising anode material for future high-energy-density, high-rate batteries. However, the development of metal lithium batteries is severely restricted by the generation of lithium dendrites. Not only will dendrites break and cause battery capacity degradation, but they may also pierce the separator and short-circuit the battery, causing serious safety problems. With the rapid development of portable electronic equipment and electric vehicles, people are more concerned about the safety of lithium batteries in addition to the large capacity and charging and discharging speed of lithium batteries.
Recently, Liang Kaijie's group from Nankai University, Professor Chen Yongsheng's group, and Lai Chao's group from Jiangsu Normal University have proposed an optimization strategy to solve this problem. Based on this strategy, they successfully prepared silver nanowires with multi-level structure-graphene three-dimensional A porous carrier and supported metal lithium as a metal lithium composite anode material. Related results were published in Advanced Materials.
"Metal lithium is considered to be the most ideal anode material for lithium secondary batteries due to its high theoretical capacity and low electrochemical potential, and it has a wide range of industrial applications. However, lithium dendrites during the charge and discharge process And the formation of dead lithium, the extremely shrinkage and expansion of the electrode volume, and the instability of the solid electrolyte phase interface film are the main reasons for the problems of short cycle life and poor safety of lithium metal anode materials. "Liang Jiajie introduced.
In recent years, many related studies have made important breakthroughs in the design and synthesis of lithium anode materials, but still cannot suppress the problems of dendrite growth and electrode volume expansion of lithium metal under high current density charge and discharge, so it is still difficult to achieve long lithium battery growth. Long-life, high-capacity "quick charge and quick release". "Depositing metal lithium into a porous current collector with a three-dimensional network structure to build a metal lithium composite anode material is one of the effective ways to solve the above difficulties." Liang Jiajie said.
Based on this understanding, the three research groups first proposed five basic requirements for material selection and optimization of the ideal lithium lithium three-dimensional carrier for achieving ultra-high current density and long cycle life, including: Crystal overpotential; continuous ultra-high electrical conductivity; large specific surface area and uniformly distributed conductive structure; porous structure with excellent mechanical strength and electrochemical stability; excellent mechanical toughness. On this basis, they used a three-dimensional network of graphene macrostructures as a mechanical skeleton and a two-dimensional network of silver nanowires as a conductive structure. The coating-cold-drying method compatible with industrial production at low cost was used to prepare multi-level structures. A silver nanowire-graphene three-dimensional porous support, and supported metal lithium as a metal lithium composite anode material.
After testing, the specific capacity of the metal lithium composite anode material can reach 2573 mAh / g; in the symmetrical battery test, it was repeatedly charged and discharged for more than 1,000 weeks at an extremely high current density of 40 mAh / cm2, and the overpotential was less than 120. mV. It can be seen through electron microscopy that the multi-level three-dimensional structure carrier can successfully suppress the growth of lithium dendrites and the change of the electrode volume in the metal lithium negative electrode even under the cycling condition of the maximum current charge and discharge. The team further assembled a full battery with excellent rate performance and high rate cycle stability with NCM523 cathode material.
"In the future, we will continue to optimize the mechanical properties of the lithium negative electrode carrier with a multi-dimensional three-dimensional structure, further increase the electrode material's charge capacity in the fast charge state, and strive to achieve early metal lithium with ultra-high energy density and power density. Anode material. "Liang Jiajie said.