What is the correct way to block current going into a solar panel from battery
Your proposed standard diode is rated for 1000V .You do not need more than 10V for your 2 series Li cells. The power wasted is very significant in % terms due to your low voltages. 1 volt drop is 16% of 6V so efficiency could never top 90% .Si      Schottky diodes come in lower reverse voltage ratings and have about half of the voltage drop .The 20V types drop less than the 200V types in the same series. This is simple and easy to understand .Mosfets can do even better but are slightly more complicated.