A solid-state lithium battery including a lithium-containing anode and a phosphorus-containing cathode is disclosed. The cathode may include any of a number of electronically conductive allotropes of phosphorus, referred to as a group as black phosphorus. A solid discharge product of the cell acts as an electrolyte for the cell. The cathode may include an auxiliary electronic conductor phase to improve the conductivity of the cathode, improve the cathode utilization during discharge and reduce the overall cell impedance.