In the summer of 1968, during the Cultural Revolution, Mao's wife, Jiang Qing, placed Li's life in danger by accusing him of trying to poison her. Li managed to hide, living incognito with the workers of the Beijing Textile Factory. These workers were among the 30,000 Mao dispatched to Qinghua University to quell the warfare there between two factions of the Red Guards.
On 13 February 1995, Li died following a heart attack at his son's house in Carol Stream, Illinois, where he had been living since emigrating.
Li was interested in psychiatry. In October 1986, Li wrote the preface for the first Chinese textbook on psychopharmacology, Psychopharmacological Treatment for Psychiatric Disorders edited by Tsai Neng (蔡能) and Shi Hong-zhang (史鸿璋), and published by Shanghai Scientific Technology Publisher in May 1987.