The concept of vehicle-to-grid (V2G) is that electric vehicles (EVs) communicate with the smart grid to sell demand response services by delivering electricity into the grid. Due to the scale of the network, the speed of the vehicles, their geographic positions, and the very sporadic connectivity between them, V2G communications have the crucial requirements of fast session key establishment. In this paper, we propose a threshold-based privacy-preserving key management scheme for V2G networks, which utilizes the threshold-based secret sharing and symmetric key technique to protect the identities of the EV owners and to establish the shared session key between the aggregator and the vehicle. The proposed scheme can achieve the property of identity privacy, confidentiality of the communications, and known-key security.