Electrochemical element, method for manufacturing same, and electrochemical device

An electrochemical element comprising a current collector, an active material layer, and an interfacial surface between the current collector and the active material layer, wherein

• the active material layer includes active material particles,
• the active material particles each include lithium silicate composite particles each including a lithium silicate phase and silicon particles dispersed in the lithium silicate phase, and a first coating that covers at least a portion of respective surfaces of the lithium silicate composite particles,
• the first coating includes an oxide of a first element other than a non-metal element,
• the active material layer has a thickness TA, in μm, in a thickness direction,
• the lithium silicate composite particles include:
• first lithium silicate composite particles located at a distance of 0.25TA, in the thickness direction, from the interfacial surface of the active material layer, and
• second lithium silicate composite particles located at a distance of 0.75TA, in the thickness direction, from the interfacial surface of the active material layer, and T1b>T1t is satisfied,
• where
• T1b is an average thickness, in nm, of the first coating of the first lithium silicate composite particles, and
• T1t is an average thickness, in nm, of the first coating of the second lithium silicate composite particles.