Does a divorce occur if a husband says to his undivorced wife, "You are divorced," while claiming to be angry and wishing to keep her as his wife? And would they be required to renew the marriage contract?

If the husband utters a clear statement of divorce, being aware and choosing to do so, his divorce takes effect even if he is angry, unless his mind is completely lost. If the husband secludes himself with his wife in a valid seclusion (khalwa sahihah), this divorce is considered revocable according to the Hanbalis. It is sufficient for the husband to take her back during her 'iddah by saying: "I take you back," without the need for a new marriage contract.