A high-temperature electrochemical energy storage device , comprising: a. a container comprising a reactive metal ; b. a current collector ; and c. a seal that seals said container from an environment external to said container, said seal comprising: i. a ceramic material selected from the group consisting of aluminium nitride and silicon nitride, wherein said ceramic material is exposed to said reactive metal, wherein the ceramic material is chemically resistant to the reactive metal at a temperature of at least 100°C, wherein the ceramic material is electrically isolating, wherein the ceramic material comprises a common element capable of forming a first compound with the reactive metal, and wherein the ceramic material has a normalized Gibbs free energy of formation (ΔG r,n ) that is more negative than a ΔG r,n of the first compound of the reactive metal; ii. a first metal collar and a second metal collar adjacent to said ceramic material; and iii. a first metal braze disposed between the ceramic material and at least one of the first metal collar and the container and a second metal braze disposed between the ceramic material and at least one of the second metal collar and the current collector, wherein the first metal braze comprises at least one metal that chemically reduces the ceramic material, wherein the reactive metal comprises calcium. a. a container comprising a reactive metal ; b. a current collector ; and c. a seal that seals said container from an environment external to said container, said seal comprising: i. a ceramic material selected from the group consisting of aluminium nitride and silicon nitride, wherein said ceramic material is exposed to said reactive metal, wherein the ceramic material is chemically resistant to the reactive metal at a temperature of at least 100°C, wherein the ceramic material is electrically isolating, wherein the ceramic material comprises a common element capable of forming a first compound with the reactive metal, and wherein the ceramic material has a normalized Gibbs free energy of formation (ΔG r,n ) that is more negative than a ΔG r,n of the first compound of the reactive metal; ii. a first metal collar and a second metal collar adjacent to said ceramic material; and iii. a first metal braze disposed between the ceramic material and at least one of the first metal collar and the container and a second metal braze disposed between the ceramic material and at least one of the second metal collar and the current collector, wherein the first metal braze comprises at least one metal that chemically reduces the ceramic material, i. a ceramic material selected from the group consisting of aluminium nitride and silicon nitride, wherein said ceramic material is exposed to said reactive metal, wherein the ceramic material is chemically resistant to the reactive metal at a temperature of at least 100°C, wherein the ceramic material is electrically isolating, wherein the ceramic material comprises a common element capable of forming a first compound with the reactive metal, and wherein the ceramic material has a normalized Gibbs free energy of formation (ΔG r,n ) that is more negative than a ΔG r,n of the first compound of the reactive metal; ii. a first metal collar and a second metal collar adjacent to said ceramic material; and iii. a first metal braze disposed between the ceramic material and at least one of the first metal collar and the container and a second metal braze disposed between the ceramic material and at least one of the second metal collar and the current collector, wherein the first metal braze comprises at least one metal that chemically reduces the ceramic material, <EOS>