The us aircraft giant Boeing has joined the global battle for efficient batteries. Boeing, , announced on January 29th that its venture-capital firm Boeing HorizonX Ventures had bought a small stake in battery start-up called Cuberg. Boeing did not disclose more details about the price of the deal. According to Megan Hilfer, a spokeswoman for Boeing, a single investment of Boeing HorizonX Ventures ranges from tens of billions of dollars to $15 million. Previously, the Boeing venture had invested in Zunum Aero, an electronics and hybrid aircraft start-up. Zunum Aero is trying to start selling hybrid aircraft by 2022. Why does Boeing invest in new energy aircraft start-ups? Richard Wang, Cuberg's co-founder and chief executive, said: "at present, the size of the battery is quite huge, so it can't apply to existing commercial aircraft models. It has to be radically improved to develop a new generation of batteries." In California, Cuberg, born at the UC Berkeley, is developing a lighter, less flammable aircraft battery that they hope will be tested later this year. The carbon pollution produced by fuel aircraft is attracting more and more attention from the international community. The international civil aviation organization estimates that the amount of carbon emitted by aircraft will triple by 2050. At the end of November last year, the European industrial giant, Rolls Royce, Airbus and Germany's Siemens electric aircraft department signed a cooperation agreement, they will collaborate to develop a hybrid testing machine. After a comprehensive ground test, the E-Fan X hybrid electric technology verifier is expected to debut in 2020. This will be an important step to promote the development of civil aircraft hybrid electric propulsion technology.