Large excess reserves, central bank digital currency, and monetary policy

In this paper I examine the effect of introducing an account-based central bank digital currency (CBDC) on liquidity insurance and monetary policy implementation. An asset-exchange model is constructed with idiosyncratic liquidity risk, in which one type of agents require currency and/or CBDC to consume while the other type of agents can use any assets to trade. There arises a liquidity insurance to distribute assets efficiently by type. Since central bank reserve accounts are accessible by the public directly, the large excess reserves (LER) in a floor system can make it difficult to separate the types under private information. Therefore, raising the interest on reserves in the floor system can reduce the aggregate liquidity excessively, and the equilibrium allocation with the LER can be suboptimal.