Significant Accounting Policies - Mezzanine Equity (Details) - Legacy Solid Power
12 Months Ended
Dec. 31, 2021
shares
Temporary Equity [Line Items]  
Conversion ratio 1
Series A1 Preferred Stock  
Temporary Equity [Line Items]  
Number of shares converted into common stock 14,069,187
Series B Preferred Stock  
Temporary Equity [Line Items]  
Number of shares converted into common stock 8,777,812