There is a conversation on this site, under Aging Well, discussing the use of Lithium Oranate by individuals themselves.

My significant other, 82 yo female was diagnosed with Alz last Nov. She's been on memantine since then and donepezil since May. She has the Apoe4 gene which indicates the highest probability of Alz. We just received results of her amyloid PETscan. Her score was 146 which is exceedingly high. Her short term memory is very poor but aside from that she's pretty normal. Yesterday her neurologist said because of that result she should start Leqembi infusions. The local clinic that does them is booked until next March. It's an epidemic! We're concerned about the limited benefit and side effects of Leqembi, particularly brain bleeds, so we will probably decline the infusions.

I decided to start her on 10 mg lithium orotate capsules on Aug 23. We don't have time to wait for Big Pharma to invent the next wonder drug that actually treats Alz. There is no evidence that Leqembi infusions improve memory by removing amyloid deposits.

Recent lab studies with lithium orotate at Harvard look promising and data from areas where lithium content in water is high have lower levels of Alz. Li compounds at very high levels have been used to treat bipolar disorders in the past. The compound/supplement lithium orotate is available otc at levels much lower than the near-toxic levels of lithium carbonate used to treat bipolar. There is no way to determine if it is going to help but we have no other choice.

The website drugs dot com has a lot of useful information. You need to do your own internet search to find the specific webpage since it appears my first reply containing hyperlinks was rejected.

Of particular interest is

consumption of higher dosages (up to 240 mg of lithium orotate per day), with no apparent signs of toxicity
However I believe the 5mg dossage may be too low. Yes, extrapolation from the dosage given to the mice suggests that a dose of anywhere between 1 to 10 mg may be effective. Do an internet search on raffaelemedical and lithium-orotate-and-alzheimer-s-harvard-study-reveals-a-breakthrough-in-brain-aging. Not that it matters much, but my own extrapolation reached the same conclusion – actually as little as 2 mg may be effective). HOWEVER, you need to keep in mind that the mice were fed the Lo in their water and they were actually young rats which developed the condition because they were totally deprived of lithium.
This is important as the it relates to how the humans developed the disease at an OLDER age. A rational supposition is that it was due to age related degradation of the digestive system leading to a reduced absorption of Li from food. Thus the dosage in pill form needed to deliver the same amount of Li to the human brain may be MUCH higher.
You may consider say a 20mg dose – especially since that is the highest dosage in one pill I could find on Amazon. You could look at the reviews to see if you find anything that might be important in your husband's case.