Is ceramic coating geometric for improved li-ion battery diaphragm performance?

The diaphragm (Separateor) is one of the important components of lithium batteries, in the lithium battery to isolate the positive and negative poles, prevent short circuits, provide li-migration micro-porous channel function, and can be out of control conditions, closed pores to prevent the migration of Li-plus, to ensure the safety of the battery. The diaphragm is not directly involved in the electrode reaction, but it has an important effect on the comprehensive performance of lithium batteries.
01
traditional diaphragm vs coating diaphragm
traditional polyethylene (
PE) and polypropylene (PP) organic diaphragm, in the actual use of the process, there will be low melting point, mechanical strength is not enough problems, and in extreme conditions easily lead to battery short circuit . Inorganic ceramic materials due to high melting point, good chemical stability, good affinity with electrolytes and other advantages, so that the ceramic coating improved composite diaphragm (organic material as a base film, ceramic particles as a coating material) has received attention. At present, including Shanghai Enjie, Xingyuan material and Zhangzhou Pearl and other mainstream battery diaphragm manufacturers have launched their own coating diaphragm. Figure 1 shows the back-and-forth comparison of ceramic particles coated on the substyl film.
figure
1 before and after the coating of ceramic particles on the substation (Photo: Shanghai Enjie)
So, how much does the ceramic coating diaphragm improve the performance of the battery diaphragm? Can there be specific quantitative experiments to illustrate it? The answer is yes. In order to facilitate the reader to read, according to two different units for the composite diaphragm and traditional diaphragm comparison experiments, combed out the advantages of ceramic coating diaphragm.
02
ceramic coating on the performance of the diaphragm itself improved
the first set of comparative experimental results from Dongguan Zhige Battery Technology Co., Ltd., which focuses on the modified diaphragm itself performance research and comparison. Table
1 is the conditions involved in the experimental comparison.
table
1 to grid battery experimental conditions
Dongguan Zhige Battery Technology Co., Ltd.
base film
16um thick PE diaphragm (Suzhou production)
refile powder
25g nanoAl
2
O
3
particles (Made in Japan,
AKP-3000 type)
important equipment
P-5 ball mill (Made in Germany): for powder, binder mixed ball grinding
electrolyte
1.2mol/L lithium hexafluorophosphate and EC-DEC-EMC (Zhuhai production)
to compare the physical and chemical properties of the base film and coated film itself. The results of the experiment are shown in Table 2.
2 modified front and rear diaphragm performance comparison
Dongguan Zhige Battery Technology Co., Ltd.
PE diaphragm
Al
2
O
3
coated diaphragm
breathability
287s/100ml
303s/100ml
porosity
38.82%
40.82%

9. 3g/m
2
15.90g/m
2
physical performance, small changes in breathability and porosity, indicating that ceramic particles did not block the
PE diaphragm gap
microscopic
the PE diaphragm has a consistent pore structure that allows the ions to move quickly, and the
coated diaphragm can see evenly distributed ceramic particles, with no obvious hole-blocking phenomenon
thermal shrinkage (
130 degrees C)
longitudinal.
landscape
longitudinal
landscape
18.0
17.8
1.1
1.1
under the support of the skeleton,
130 degrees C, pe diaphragm longitudinal and transverse thermal shrinkage rate of about 18%, the edge of severe contraction, may make the battery positive and negative direct contact, there is a thermal risk;
coating diaphragm high temperature resistance is more obvious, because ceramic particles resistant to high temperature and insulation, the formation of a rigid support skeleton, can significantly improve the heat contraction of the diaphragm
septicity
experiment
diffusion phenomenon
uneven diffusion, elliptical diffusion
uniform diffusion, circular diffusion
diffusion diameter
31.4mm
29.0mm
diffusion time
26.0s
24.4s
disappear time
53.6s
43.4s.
the electrolyte droplets on the diaphragm, the modified diaphragm can significantly shorten the electrolyte diffusion time, because
. Al
2
O
3
ceramic particles have higher polarity and better affinity with electrolytes
03
ceramic coating improves battery performance
It uses homemade, highly dispersed polymethyl acrylates (
PMMA) clad with Al
2
O
3
nanomeheric materials (short for
Al
2
O
3
@PMMA nano-hybrid materials). On the basis of the homemade cladding material, the PP/Al
2
O
3
@PMMA/PVDF-HFP composite diaphragm is prepared, and the important basic materials used are shown in Table 3.
Table
3 Important materials involved in Tsinghua University's experiments
Tsinghua University Institute of Nuclear Energy and New Energy Technology
-based film
25um thick PP-based Celgard 2325 membrane (U.S.-made)
al-modified powder
1g homemade Al
2
O
3
@PMMA nano-hybrid material
other substrates
N, N-dimethyl methamide (DMF, China Pharmaceutical Group), PVDF-HFP (Aldrich Corporation, battery grade)
Table
4 for Tsinghua University on polymer diaphragm, composite diaphragm performance comparison.
Table
4 Composite Diaphragm vs. Traditional Diaphragm Performance
Tsinghua University Institute of Nuclear Energy and New Energy Technology
PP/PVDF-HFP Diaphragm
Composite Diaphragm
Microscopic
PP/PVDF-HFP
Diaphragm Surface Pores Are Smaller and Smaller;
addition of
Al
2
O
3
@PMMA hybrid material, the formation of mesh micropores, a large aperture
product rate
composite diaphragm preservation capacity than
PP diaphragm and PP/PVDF-HFP diaphragm,
this is because
al
2
O
3
@PMMA nm hybrid material has a stronger affinity
cycle performance
when
100 cycles, composite diaphragm, PP diaphragm and PP/ PVDF-HFP diaphragm-assembled batteries with capacity hold rates of 89.8%, 86.6% and 78.4%, respectively, indicate that Al
2
O
3
nanoparticles can improve electricity The ion conductivity of the electrolyte and the interface compatible with the electrode are good for the transmission
-fold performance of
Li plus
PP/PVDF-HFP diaphragm-assembled batteries reduced to 4 after 8C discharge 0mAh/g, while the composite diaphragm and PP diaphragm remain high, indicating that the addition of Al
2
O
3
particles improves battery multiplle performance
04
Summary and Outlook
Taken together, ceramic particles (currently dominated by Al
2
O
3
) can be applied to the coating of traditional diaphragms, and their advantages are reflected in the improved physical and chemical properties of the diaphragm itself: heat-resistant shrinkage, Immersion (experimental results of the gridded battery) can improve the cycle performance and multiply performance of the battery after it is assembled into the battery (the experimental results of Tsinghua University).
In the past 2019, the li-ion battery diaphragm industry reshuffle accelerated, the biggest winner should belong to Shanghai Enjie, whose 19-year net profit is expected to reach more than 770 million yuan, an increase of more than 50% year-on-year, with a market value of 40 billion yuan. Among them, the wet diaphragm production and sales of two million. It is worth noting that Shanghai Enjie in 2010 in the early days of the establishment of the main funds and technology concentrated in the wet diaphragm enterprises, and in 2014 successfully applied the wet method and single-sided /double-sided ceramic coating diaphragm to lithium batteries.
, as the energy density of lithium batteries increases, so does the demand for diaphragms. Until solid-state electrolytes are fully arrived, wet
plus coating is the best solution for the lithium battery diaphragm that can be seen today.
reference
. Al
2
O
3
ceramic modified diaphragm safety performance, Dongguan Zhige Battery Technology Co., Ltd., Yang heshan;
highly dispersed nano
. Al
2
O
3
modified composite electrolyte diaphragm performance, Tsinghua University Institute of Nuclear Energy and New Energy Technology, Zhou Ranran, He Zhiming, Shang Yuming; Yanshan University, Li Jianjun.
.