Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Revisiting the storage capacity limit of graphite battery anodes:
  spontaneous lithium overintercalation at ambient pressure   The market quest for fast-charging, safe, long-lasting and performant
batteries drives the exploration of new energy storage materials, but also
promotes fundamental investigations of materials already widely used.
Presently, revamped interest in anode materials is observed -- primarily
graphite electrodes for lithium-ion batteries. Here, we focus on the upper
limit of lithium intercalation in the morphologically quasi-ideal highly
oriented pyrolytic graphite (HOPG), with a LiC$_6$ stoichiometry corresponding
to 100\% state of charge (SOC). We prepared a sample by immersion in liquid
lithium at ambient pressure and investigated it by static $^7$Li nuclear
magnetic resonance (NMR). We resolved unexpected signatures of superdense
intercalation compounds, LiC$_{6-x}$. These have been ruled out for decades,
since the highest geometrically accessible composition, LiC$_2$, can only be
prepared under high pressure. We thus challenge the widespread notion that any
additional intercalation beyond LiC$_6$ is not possible under ambient
conditions. We monitored the sample upon calendaric aging and employed ab
initio calculations to rationalise the NMR results. The computed relative
stabilities of different superdense configurations reveal that non-negligible
overintercalation does proceed spontaneously beyond the currently accepted
capacity limit.

3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
20
The categories of this paper are: acc-phys
17
The categories of this paper are: q-fin
5
The categories of this paper are: gr-qc
21
The categories of this paper are: adap-org
30
The categories of this paper are: q-alg
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The categories of this paper are: astro-ph
37
The categories of this paper are: supr-con
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex