A patient experiencing a manic or hypomanic phase of Bipolar illness has no insight regarding his or her illness and therefore does not realize that he or she is ill.
At least he is taking Lithium
which is a good thing because Lithium is a very effective Mood stabilizer
which can not only control his depressive or manic phase but can also prevent the future manic / depressive phase of Bipolar illness. Most patients are willing to take medicines once their symptoms are under control and they realize that they need help to control these symptoms.
You can discuss with his doctor about the option of increasing the dose of Lithium if you think that his symptoms are not under control.
Once he started responding to medicine his doctor can explain to him the sign and symptoms of Bipolar illness.
Please feel free to discuss further if you have any other doubt.