High-capacity and long-lasting lithium-ion batteries with novel germanium composite anodes

Lithium-ion batteries (LIBs) are widely used due to their high energy densities and high operating voltages, powering various technologies like portable electronics and electric vehicles while also serving as the key energy storage solution for renewable energy from solar and wind energy. LIBs consist of a positive electrode, called cathode, made of lithium (Li)-based materials, a negative electrode, the anode, typically made using graphite, and an electrolyte between them. While graphite offers cost advantages and stable charging and discharging performance, its limited storage capacity falls short of meeting the current global push towards renewable energy. Consequently, developing high-capacity anode materials has become a key focus in LIB research.

Semiconductors such as Silicon (Si) and Germanium (Ge) have emerged as promising anode materials due to their extremely high theoretical Li-ion storage capacities. However, they undergo large volume changes during charge-discharge cycles, resulting in rapid degradation and considerable reduction in storage capacity. Additionally, the solid-electrolyte interface (SEI) layer, which forms on the anode during charging to maintain stability, repeatedly breaks and reforms with these materials. This process further reduces capacity and causes issues like electrolyte breakdown, Li-ion loss, and increases internal resistance.

To address these challenges, a research team led by Professor Giichiro Uchida from the Faculty of Science and Technology at Meijo University, Japan, developed a novel anode material: a composite of amorphous Ge (a-Ge) with amorphous LiAlGePO (a-LiAlGePO), a Li solid electrolyte containing Ge atoms and exhibiting a high Li-ion conductivity. “Using composites is an effective approach to overcome the shortcomings of pure Ge anodes. Composites of Li oxides and anode materials can help stabilize the reaction interface between the anode and the electrolyte, preventing degradation and capacity reduction,” explains Prof. Uchida. “In this study, we developed a novel Ge/LiAlGePO composite material for LIB anodes.” Their findings were published in the journal Advanced Materials Technologies on February 15, 2025.

The researchers fabricated three types of a-Ge/a-LiAlGePO composite anodes using a special plasma co-sputtering process: a multilayer anode with LiAlGePO on top and Ge at the bottom, a single Ge-LiAlGePO mixed layer anode, and a multilayer anode with LiAlGePO on top and mixed Ge-LiAlGePO layer below it. All three anodes showed significantly improved capacity retention: the LiAlGePO/Ge multilayer anode retained 97.3% of its capacity after 300 charge-discharge cycles, the Ge-LiAlGePO mixed layer anode retained 87.3%, and the LiAlGePO/Ge-LiAlGePO multilayer anode retained 100%, with discharge capacities of 799, 1074, and 810 mAhg^-1, respectively. For comparison, the pure Ge anode retained only 43.8% of its capacity after 200 cycles.

As for how this new composite improves capacity retention, the researchers found that for the multilayer anodes, the LiAlGePO layer behaves as a stable artificial SEI that does not undergo volume changes and prevents direct contact of Ge with the electrolyte. This also helps avoid electrolyte breakdown, Li-ion loss and large internal resistances, while allowing only Li ions to pass through. In the mixed anode, a rigid and inorganic-rich SEI layer forms on the anode surface which improves capacity retention.

However, under practical high charge-discharge conditions, the capacity retention of these anodes is reduced drastically. To address this, the researchers doped the LiAlGePO layer with nitrogen atoms, improving its ionic conductivity by 1.6 times. The anodes with this modified LiAlGePON layer demonstrated excellent capacity retention, with the LiAlGePON (top)/Ge(bottom) multilayer anode showing the highest capacity retention of 95.2% after 120 cycles at high current densities. Furthermore, this enhanced conductivity achieved through nitrogen doping is crucial for developing all-solid-state LIB batteries.

“These findings suggest that the LiAlGePO/Ge composite is a promising anode structure for developing high-capacity LIBs with a long cycle life,” notes Prof. Uchida. “Next-generation LIBs using this novel structure could enable electric vehicles to travel longer distances between charges and significantly extend the lifespan of portable devices.”

This innovative anode material could enable high-capacity LIBs that can meet the growing demand for renewable energy, paving the way towards a carbon-neutral society.