Note 2 - Summary of Significant Accounting Policies (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	September 30,
Excluded potentially dilutive securities (1):	2020		2019
Options to purchase common stock		1,390,340		3,623,138
Unvested restricted stock units		3,947,819		403,154
Financing warrants to purchase common stock		103,500		4,839,197
Total potential dilutive securities		5,441,659		8,865,489

Schedules of Concentration of Risk, by Risk Factor [Table Text Block]

	Revenue						Revenue						Trade Accounts Receivable
	Three Months Ended September 30,						Nine Months Ended September 30,						September 30, 2020			December 31, 2019
	2020			2019			2020			2019
Clarios (successor of Johnson Controls Battery Group, Inc.)		—	%		80	%		16	%		71	%		—	%		100	%
P. Kay Metals		100	%		17	%		84	%		26	%		—	%		—	%