Investors are still waiting for a breakthrough.Shares of QuantumScape (QS -9.58%) were sliding today after the solid-state battery company posted another loss in its second quarter and demonstrated relatively modest progress in its goal of becoming a viable company and scaling production of quantum batteries, which are more efficient than lithium-ion electric batteries.QuantumScape has no revenue as the company is a development-stage technology company that's still building its product, but investors want t ...