Superlattice-structured films by magnetron sputtering as new era electrodes for advanced lithium-ion batteries

Sustaining a sound structure in Si-based anodes is extremely challenging because of the high volumetric expansion that occurs upon cycling. To maintain capacity retention during the cycling, there is a need for new designs that rely on engineering-specific hierarchical geometries and/or optimized composite compositions such that at least one of the multiple elements serves as buffer and/or electron conductive pathway in the electrodes. Here, we report an innovative design in which alternate layers of atomic structures involving multiple elements form a new anode material for lithium-ion batteries. In this work, a superlattice-structured film containing Si, Mo, and Cu is fabricated by a simple and scalable magnetron sputtering process for the first time. With the help of the formation of a continuous and repetitive superlattice along the film thickness, a homogeneous stress-strain distribution is attained. In our superlattice thin film, the Si atoms are distributed along the film thickness within the alternate Mo–Cu layers, which act as inactive-conductive layers and as a backbone web to handle the volume expansion of active Si while restricting electrochemical agglomeration. This nano-functional superlattice approach enables harnessing the high energy density of Si while maintaining its structural stability. As a result, the electrode exhibits high energy density and capacity retention even at high cycling rates. The possible use of the film in a full cell is also evaluated using LiMn_1.5Ni_0.5O₄ cathodes. The full cell maintained a stable capacity of about 900 mAh g_anode⁻¹ (~93 mA g_cathode⁻¹) over 150 cycles at the ~600 mA g⁻¹ rate. The remarkable performance of this nanostructured, multifunctional superlattice film is found to be promising for applications that require high energy, long calendar life, and excellent abuse tolerance, such as electric vehicle batteries.