150
6 Nanomaterials for Batteries
II. Non-graphite carbon-based anode materials
The non-graphitic carbon-based negative electrode material has a large interlayer
spacing and disordered structure, which is advantageous for the insertion/absorption
of Na
+ , and is currently the most studied type of sodium-ion battery carbon-based
negative electrode material. According to the degree of difficulty in graphitization
and the arrangement of graphite crystallites, non-graphitic carbon-based negative
electrode materials are mainly classified into soft carbon (graphitized mesocarbon
microbeads, coke, etc.) and hard carbon (carbon black, resin carbon, etc.). Two major
categories. Both soft carbon and hard carbon are amorphous carbons and are mainly
composed of graphite-like microcrystals having a small width and thickness, but
the arrangement is more disordered than graphite and has a relatively large distance
between carbon layers.
In general, carbon materials that can be graphitized above 2800 °C are called soft
carbons, and the internal arrangement of graphite crystallites is relatively orderly,
and the width and thickness of the microwafer layer are large, and the sodium storage
mechanism is mainly expressed as carbon. Adsorption of Na
+ is on the edge of the
layer, the surface of the carbon layer, and the microcrystalline gap. The experimental
results show that the random layer microcrystals of the soft carbon anode material
will expand with the change of the pyrolysis temperature, and the interlayer spacing
increases from about 0.36 nm to about 0.42 nm, thereby improving the electrochemical performance. The soft carbon negative electrode material obtained by pyrolysis at
900 °C showed a reversible capacity of 114 mAh/g at a current density of 1000 mA/g
with excellent rate performance and cycle performance.
Hard carbon is a carbon material that is difficult to graphitize at temperatures
above 2800 °C. Its internal graphite crystallite arrangement is more disorderly than
soft carbon, and it contains a part of micro-nanopore regions, which has a high sodium
storage capacity. It is the ideal sodium storage carbon-based anode material.
6.3.2.2 Titanium-Based Anode Material
Titanium-based materials are based on Ti
3+ /Ti
4+ valences, but also have a class of
deintercalation materials in LIBs. Li 4 Ti 5 O 12 and TiO 12 materials are the most studied
titanium-based materials in sodium-ion batteries. Due to the greater variety of sodium
compounds, there are more options for active sodium-ion titanium-based materials.
Among many titanium-based materials, Na 2 Ti 3 O 7 has the lowest embedded
sodium potential and has a specific capacity of 178 mAh/g at 0.3 V (vs. Na
+ /Na)
voltage platform. It also has good cycling and rate performance. Na 2 Ti 3 O 7 is a
layered structure composed of TiO 6 octahedra, and the two Ti–O bonds shared by
the three TiO 6 octahedra slowly move to form a parallel axis. This will form a zigzag
(Ti 3 O 7 )
2− transition metal layer. The sodium ions can be reversibly deintercalated
in the middle Na layer, and since the transition metal layer is zigzag, sodium ions
can occupy two positions in the Na layer. The transition metal layer can form stable
covalent bonds, and sodium ions can form strong ionic bonds with TiO 6 octahedra.
6 Nanomaterials for Batteries
II. Non-graphite carbon-based anode materials
The non-graphitic carbon-based negative electrode material has a large interlayer
spacing and disordered structure, which is advantageous for the insertion/absorption
of Na
+ , and is currently the most studied type of sodium-ion battery carbon-based
negative electrode material. According to the degree of difficulty in graphitization
and the arrangement of graphite crystallites, non-graphitic carbon-based negative
electrode materials are mainly classified into soft carbon (graphitized mesocarbon
microbeads, coke, etc.) and hard carbon (carbon black, resin carbon, etc.). Two major
categories. Both soft carbon and hard carbon are amorphous carbons and are mainly
composed of graphite-like microcrystals having a small width and thickness, but
the arrangement is more disordered than graphite and has a relatively large distance
between carbon layers.
In general, carbon materials that can be graphitized above 2800 °C are called soft
carbons, and the internal arrangement of graphite crystallites is relatively orderly,
and the width and thickness of the microwafer layer are large, and the sodium storage
mechanism is mainly expressed as carbon. Adsorption of Na
+ is on the edge of the
layer, the surface of the carbon layer, and the microcrystalline gap. The experimental
results show that the random layer microcrystals of the soft carbon anode material
will expand with the change of the pyrolysis temperature, and the interlayer spacing
increases from about 0.36 nm to about 0.42 nm, thereby improving the electrochemical performance. The soft carbon negative electrode material obtained by pyrolysis at
900 °C showed a reversible capacity of 114 mAh/g at a current density of 1000 mA/g
with excellent rate performance and cycle performance.
Hard carbon is a carbon material that is difficult to graphitize at temperatures
above 2800 °C. Its internal graphite crystallite arrangement is more disorderly than
soft carbon, and it contains a part of micro-nanopore regions, which has a high sodium
storage capacity. It is the ideal sodium storage carbon-based anode material.
6.3.2.2 Titanium-Based Anode Material
Titanium-based materials are based on Ti
3+ /Ti
4+ valences, but also have a class of
deintercalation materials in LIBs. Li 4 Ti 5 O 12 and TiO 12 materials are the most studied
titanium-based materials in sodium-ion batteries. Due to the greater variety of sodium
compounds, there are more options for active sodium-ion titanium-based materials.
Among many titanium-based materials, Na 2 Ti 3 O 7 has the lowest embedded
sodium potential and has a specific capacity of 178 mAh/g at 0.3 V (vs. Na
+ /Na)
voltage platform. It also has good cycling and rate performance. Na 2 Ti 3 O 7 is a
layered structure composed of TiO 6 octahedra, and the two Ti–O bonds shared by
the three TiO 6 octahedra slowly move to form a parallel axis. This will form a zigzag
(Ti 3 O 7 )
2− transition metal layer. The sodium ions can be reversibly deintercalated
in the middle Na layer, and since the transition metal layer is zigzag, sodium ions
can occupy two positions in the Na layer. The transition metal layer can form stable
covalent bonds, and sodium ions can form strong ionic bonds with TiO 6 octahedra.