6.2 Lithium Batteries and Lithium-Ion Batteries
131
The main problem of tin oxide anode materials is that for the first time the irreversible capacity is large. The result is mainly due to the generation of Li 2 O during
the first charge and discharge and the formation of SEI film; another problem is
the volume change of the material itself (the density of SnO 2 , Sn, Li is 6.99, 7.29,
2.56 g/cm
3 , causes the volume of material before and after the reaction to change
greatly) to cause the electrode to “powder” or “reunite”. Consequently, the specific
capacity of the material decreases and the cycle performance decreases. To reduce the
“volume effect” of tin oxide electrode materials, the following measures are usually
taken:
1. Preparation of tin oxides with special morphology (such as thin films, nanoparticles or amorphous form), so that the volume expansion rate is minimized.
2. Select a suitable battery operating voltage window to reduce the occurrence of
the side reactions.
3. Doping the electrode, for example, the incorporation of Mo, P, and B elements,
to prevent the formation of tin clusters in charge and discharge reactions.
Tin-Based Composite Oxide
The study of tin-based composite oxide (TCO) began at Japan’s Coats. The
researchers found that amorphous tin-based composite oxides have better cycle life
and higher reversible specific capacity which result in great attention. Subsequently,
there are many studies on this area in succession. Tin-based composite oxides can
solve the problem of large volume change of Sn oxide anode materials, high irreversible capacity for first charge and discharge, and unsatisfactory cycling performance to some extent by adding some metal or non-metal oxides to Sn oxides.
Oxides of elements such as B, Al, Si, Ge, P, Ti, Mn, Fe, etc. are then obtained by
heat treatment.
Tin-based composite oxides have an amorphous structure, and other oxides added
to make the mixture form an amorphous glass body, and so it can be the general
formula SnM x O y (x = 1), in which M represents a group of metal or non-metal
elements. Structurally, the tin-based compound oxide consists of an active-site Sn–O
bond and a surrounding random network structure. The random network consists of
added metal or non-metal oxides, which separate the active centers from each other.
Therefore, Li can be effectively stored, and the capacity is related to the active center.
The reversible specific capacity of tin-based composite oxides can reach 600 mAh/g,
and the volume specific capacity is greater than 2200 mAh/cm
3 , which is around
two times the charge/discharge capacity of the highest carbon negative electrode
material (amorphous carbon and graphitized carbon, respectively, less than 1200 and
500 mAh/cm
3 ).
There are two types of lithium storage mechanism for tin-based compound oxides:
one is ion type and the other is alloy type. The ionic mechanism suggests that the Li
is embedded with the TCO electrode, and Li exists in the ion form in the product.
Taking SnB 0.5 P 0.5 O 3 as an example, the mechanism can be expressed as
xLi + SnB 0.5 P 0.5 O 3 LixSnB 0.5 P 0.5 O 3
131
The main problem of tin oxide anode materials is that for the first time the irreversible capacity is large. The result is mainly due to the generation of Li 2 O during
the first charge and discharge and the formation of SEI film; another problem is
the volume change of the material itself (the density of SnO 2 , Sn, Li is 6.99, 7.29,
2.56 g/cm
3 , causes the volume of material before and after the reaction to change
greatly) to cause the electrode to “powder” or “reunite”. Consequently, the specific
capacity of the material decreases and the cycle performance decreases. To reduce the
“volume effect” of tin oxide electrode materials, the following measures are usually
taken:
1. Preparation of tin oxides with special morphology (such as thin films, nanoparticles or amorphous form), so that the volume expansion rate is minimized.
2. Select a suitable battery operating voltage window to reduce the occurrence of
the side reactions.
3. Doping the electrode, for example, the incorporation of Mo, P, and B elements,
to prevent the formation of tin clusters in charge and discharge reactions.
Tin-Based Composite Oxide
The study of tin-based composite oxide (TCO) began at Japan’s Coats. The
researchers found that amorphous tin-based composite oxides have better cycle life
and higher reversible specific capacity which result in great attention. Subsequently,
there are many studies on this area in succession. Tin-based composite oxides can
solve the problem of large volume change of Sn oxide anode materials, high irreversible capacity for first charge and discharge, and unsatisfactory cycling performance to some extent by adding some metal or non-metal oxides to Sn oxides.
Oxides of elements such as B, Al, Si, Ge, P, Ti, Mn, Fe, etc. are then obtained by
heat treatment.
Tin-based composite oxides have an amorphous structure, and other oxides added
to make the mixture form an amorphous glass body, and so it can be the general
formula SnM x O y (x = 1), in which M represents a group of metal or non-metal
elements. Structurally, the tin-based compound oxide consists of an active-site Sn–O
bond and a surrounding random network structure. The random network consists of
added metal or non-metal oxides, which separate the active centers from each other.
Therefore, Li can be effectively stored, and the capacity is related to the active center.
The reversible specific capacity of tin-based composite oxides can reach 600 mAh/g,
and the volume specific capacity is greater than 2200 mAh/cm
3 , which is around
two times the charge/discharge capacity of the highest carbon negative electrode
material (amorphous carbon and graphitized carbon, respectively, less than 1200 and
500 mAh/cm
3 ).
There are two types of lithium storage mechanism for tin-based compound oxides:
one is ion type and the other is alloy type. The ionic mechanism suggests that the Li
is embedded with the TCO electrode, and Li exists in the ion form in the product.
Taking SnB 0.5 P 0.5 O 3 as an example, the mechanism can be expressed as
xLi + SnB 0.5 P 0.5 O 3 LixSnB 0.5 P 0.5 O 3