How to make γ-MnO2 in a lab?

Question

I am working on Li-ion batteries, and I need to use γ-$\ce{MnO2}$ (electrolytic manganese dioxide). I have googled and read quite a few papers, but I am not very sure of those methods. I'd love to know if you are aware of some! The ones which I encountered, again and again, was the one involving precipitation of $\ce{MnO2}$. But is it possible to precipitate the γ form? Also, I think the commercially available $\ce{MnO2}$ is the α form. Is there any way to convert it to γ form? I am particularly looking for a way to synthesize $\ce{MnO2}$ using electrolysis.

I know that I can also break a few batteries to get my $\ce{MnO2}$, but it would be heavily contaminated by carbon. Commercially available $\ce{MnO2}$ is very expensive.

Answer 1

A quick search yields this.

[Electrolytic manganese dioxide] is produced in a similar fashion as electrolytic tough pitch (ETP) copper: The manganese dioxide is dissolved in sulfuric acid (sometimes mixed with manganese sulfate) and subjected to a current between two electrodes. The $\ce{MnO2}$ dissolves, enters solution as the sulfate, and is deposited on the anode.

Unfortunately, there is no source for the information.

Some further searching yields this article, with the following information:

EMD ($\gamma$-$\ce{MnO2}$) can be prepared from the direct electrolysis of an aqueous bath of manganese sulfate and sulphuric acid. The electrochemical deposition of $\ce{MnO2}$ on an inert electrode from an electrolyte containing $\ce{Mn^2+}$ occurs as per the reaction noted below:

$\begin{alignat*}{3}&\textrm{anode: }\quad&&\ce{Mn^2+ + 2H2O} &&\ce{-> MnO2 + 4H+ + 2e-} \\ &\textrm{cathode: } \quad&&\ce{2H+ + 2e-} &&\ce{->H2} \end{alignat*}$

Note that the linked article is a review, with a lot of information, both about the actual structure of $\gamma$-$\ce{MnO2}$ as well as the reactions that lead to the production of the correct crystalline structure in the presence of acid. There are a number of references that you may find useful as well.