Negative electrode active material, negative electrode, and power storage device

摘要

An object is to improve characteristics of a power storage device and achieve a long lifetime. In the case where a lithium nitride is used for a negative electrode active material of a power storage device, a plurality of lithium nitride layers with different lithium concentrations are stacked. For example, in the case where a first lithium nitride layer and a second lithium nitride layer are stacked over a current collector, lithium is contained in the first lithium nitride layer at a lower concentration than lithium contained in the second lithium nitride layer. In this case, a concentration of a transition metal of the first lithium nitride layer is higher than a concentration of the transition metal of the second lithium nitride layer. Note that another alkali metal may be used instead of lithium.