Secondary battery and electronic device
A secondary battery includes a positive electrode plate. The positive electrode plate includes a current collector and a positive active material layer. The positive active material layer includes a positive active material and a carbon material. The carbon material includes carbon nanotube bundles with a ratio of an average length of the carbon nanotube bundles to an average diameter of the carbon nanotube bundles being in a range of 2.5 to 100. The carbon nanotube bundle includes a plurality of first carbon nanotubes. The carbon nanotube bundles reduce an initial direct-current resistance of the battery, ensure integrity of a conductive network during cycling, effectively reduce the growth of the direct current resistance, and increase the charging speed.
1 . A secondary battery, comprising: a positive electrode plate, wherein the positive electrode plate comprises a current collector and a positive active material layer; and
the positive active material layer comprises a positive active material and a carbon material, wherein the carbon material comprises carbon nanotube bundles, a ratio of an average length of the carbon nanotube bundles to an average diameter of the carbon nanotube bundles is in a range of 2.5 to 100, wherein each carbon nanotube bundle comprises a plurality of first carbon nanotubes;
wherein a diameter of each first carbon nanotube is 15 nm to 40 nm;
a fully-charged-state film resistance of the positive electrode plate is R Ω, and a number of carbon nanotube bundles within an area of 20 μm×20 μm of an SEM image is m;
R
×
m
≤
5
;
and
0
Ω
<
R
≤
0.5
Ω
.
2 . The secondary battery according to claim 1 , wherein the carbon nanotube bundles satisfy at least one of the following conditions:
(i) an average length of the carbon nanotube bundles is 2 μm to 10 μm; and
(ii) an average bundle diameter of the carbon nanotube bundles is 0.01 μm to 2 μm.
3 . The secondary battery according to claim 1 , wherein a number of carbon nanotube bundles within an area of 20 μm×20 μm of an SEM image is m, and 2≤m≤30.
4 . The secondary battery according to claim 1 , wherein an average number of first carbon nanotubes in each carbon nanotube bundle is n, and 50≤n≤10000.
5 . The secondary battery according to claim 1 , wherein based on a total mass of the positive active material layer, a mass percent of the carbon material is 0.1% to 1%.
6 . The secondary battery according to claim 1 , wherein the carbon material further comprises second carbon nanotubes, and the second carbon nanotubes are provided on a surface of a particle of the positive active material and a surface of the carbon nanotube bundles.
7 . The secondary battery according to claim 6 , wherein the second carbon nanotubes satisfy at least one of the following conditions:
(a) an average length of the second carbon nanotubes is 0.1 μm to 2 μm; and
(b) an average diameter of the second carbon nanotubes is 3 nm to 40 nm.
8 . The secondary battery according to claim 6 , wherein based on a total mass of the positive active material layer, a mass percent of the carbon nanotube bundles is 0.1% to 1%; and/or
a mass percent of the second carbon nanotubes is 0.1% to 1%.
9 . The secondary battery according to claim 6 , wherein based on a total mass of the positive active material layer, a mass percent of the carbon nanotube bundles is less than a mass percent of the second carbon nanotubes.
10 . An electronic device, comprising: a secondary battery, the secondary battery comprising a positive electrode plate, wherein the positive electrode plate comprises a current collector and a positive active material layer; and
the positive active material layer comprises a positive active material and a carbon material, wherein the carbon material comprises carbon nanotube bundles, a ratio of an average length of the carbon nanotube bundles to an average diameter of the carbon nanotube bundles is in a range of 2.5 to 100, wherein a carbon nanotube bundle comprises a plurality of first carbon nanotubes;
wherein a diameter of each first carbon nanotube is 15 nm to 40 nm;
a fully-charged-state film resistance of the positive electrode plate is R Ω, and a number of carbon nanotube bundles within an area of 20 μm×20 μm of an SEM image is m;
R
×
m
≤
5
;
and
0
Ω
<
R
≤
0.5
Ω
.
11 . The electronic device according to claim 10 , wherein the carbon nanotube bundles satisfy at least one of the following conditions:
(i) an average length of the carbon nanotube bundles is 2 μm to 10 μm; and
(ii) an average bundle diameter of the carbon nanotube bundles is 0.01 μm to 2 μm.
12 . The electronic device according to claim 10 , wherein a number of carbon nanotube bundles within an area of 20 μm×20 μm of an SEM image is m, and 2≤m≤30.
13 . The electronic device according to claim 10 , wherein an average number of the first carbon nanotubes in each carbon nanotube bundle is n, and 50≤n≤10000.
14 . The electronic device according to claim 10 , wherein
based on a total mass of the positive active material layer, a mass percent of the carbon material is 0.1% to 1%.
15 . The electronic device according to claim 10 , wherein the carbon material further comprises second carbon nanotubes, and the second carbon nanotubes exist on a surface of a particle of the positive active material and a surface of the carbon nanotube bundles.
16 . The electronic device according to claim 15 , wherein the second carbon nanotubes satisfy at least one of the following conditions:
(a) an average length of the second carbon nanotubes is 0.1 μm to 2 μm; and
(b) an average diameter of the second carbon nanotubes is 3 nm to 40 nm.
17 . The electronic device according to claim 15 , wherein a mass percent of the carbon nanotube bundles is 0.1% to 1%; and/or
a mass percent of the second carbon nanotubes is 0.1% to 1% based on a total mass of the positive active material layer.
18 . The electronic device according to claim 15 , wherein a mass percent of the carbon nanotube bundles is less than a mass percent of the second carbon nanotubes based on a total mass of the positive active material layer.