An electrochromic multi-layer stack comprising: a first substrate; a first electrically conductive layer on the first substrate; a first electrode layer on the first electrically conductive layer, wherein the first electrode layer comprises a cathodic tungsten oxide electrochromic material; a second substrate; a second electrically conductive layer on the second substrate; a second electrode layer on the second electrically conductive layer; an ion conductor layer between the first electrode layer and the second electrode layer; and a redox element (120, 121), wherein: the redox element is electrically isolated from the first and second electrically conductive layers (106, 109) and the first and second electrode layer (105, 108) and is laterally adjacent to either the first electrically conductive layer and the first electrode layer, or the second electrically conductive layer and the second electrode layer; the redox element comprises an auxiliary electrode and a sequestration material in contact with the auxiliary electrode, wherein the sequestration material can be electrochemically oxidized or reduced in a redox reaction by applying a potential between the auxiliary electrode and either the first or the second electrically conductive layer (106, 109); characterised in that the second electrode layer comprises an anodic nickel oxide electrochromic material; the sequestration material comprises LiFePO 4; and the sequestration material is electrochemically reducible in the redox reaction in an electrical potential range versus lithium/lithium-ion that is greater than or equal to 2 Volts and less than or equal to 4.2 Volts. a first substrate; a first electrically conductive layer on the first substrate; a first electrode layer on the first electrically conductive layer, wherein the first electrode layer comprises a cathodic tungsten oxide electrochromic material; a second substrate; a second electrically conductive layer on the second substrate; a second electrode layer on the second electrically conductive layer; an ion conductor layer between the first electrode layer and the second electrode layer; and a redox element (120, 121), wherein: the redox element is electrically isolated from the first and second electrically conductive layers (106, 109) and the first and second electrode layer (105, 108) and is laterally adjacent to either the first electrically conductive layer and the first electrode layer, or the second electrically conductive layer and the second electrode layer; the redox element comprises an auxiliary electrode and a sequestration material in contact with the auxiliary electrode, wherein the sequestration material can be electrochemically oxidized or reduced in a redox reaction by applying a potential between the auxiliary electrode and either the first or the second electrically conductive layer (106, 109); characterised in that the second electrode layer comprises an anodic nickel oxide electrochromic material; the sequestration material comprises LiFePO 4; and the sequestration material is electrochemically reducible in the redox reaction in an electrical potential range versus lithium/lithium-ion that is greater than or equal to 2 Volts and less than or equal to 4.2 Volts. the redox element is electrically isolated from the first and second electrically conductive layers (106, 109) and the first and second electrode layer (105, 108) and is laterally adjacent to either the first electrically conductive layer and the first electrode layer, or the second electrically conductive layer and the second electrode layer; the redox element comprises an auxiliary electrode and a sequestration material in contact with the auxiliary electrode, wherein the sequestration material can be electrochemically oxidized or reduced in a redox reaction by applying a potential between the auxiliary electrode and either the first or the second electrically conductive layer (106, 109); characterised in that the second electrode layer comprises an anodic nickel oxide electrochromic material; the sequestration material comprises LiFePO 4; and the sequestration material is electrochemically reducible in the redox reaction in an electrical potential range versus lithium/lithium-ion that is greater than or equal to 2 Volts and less than or equal to 4.2 Volts.