For this, manufacturers include a material called a “separator” between the electrodes in each cell; batteries that satisfy UL standards have separators that meet certain thickness, stability, and performance requirements.

Source: https://slate.com/business/2023/02/e-bike-fires-batteries-lithium-ion-explode-new-york-city-delivery-workers.html?via=rss

In fact it has erroneously been referred to a refinery over the years when it is essentially a separator of finished fuel products.

Source: https://www.lusakatimes.com/2023/03/12/tazama-pipeline-conversion-process-nears-completion-offers-hope-for-cheaper-diesel-prices-in-zambia/

Since zirconium oxide-based material that is routinely used is expensive, they came up with a cellulose-based separator which allows the hydroxide ions to pass through from the cathode to the anode.

Source: https://www.thehindu.com/sci-tech/science/iit-madras-generates-hydrogen-from-seawater-using-solar-energy/article66951534.ece