In the past 20 years, China's lithium-ion battery technology and industry
have made great progress. The lithium-ion battery material system has developed
from lithium cobalt oxide to lithium iron phosphate, ternary materials, and then
to high-nickel and manganese-rich systems. The negative electrode has evolved
from graphite to polycarbonate. materials, and then developed to
lithium-containing alloys and even lithium metal. At the same time,
manufacturing technology has developed from workshop-style production to
automation and today's intelligence, and the scale of the industry continues to
expand. China has become the world's largest producer and consumer of
lithium-ion batteries. Looking to the future, the technology development trend
is high specific energy, high specific power, high safety, long life, and low
cost. All-solid-state batteries, new principle light metal batteries, and
customized products will achieve technological breakthroughs. The industry will
be intelligent and unmanned, scaled and alliance-based, and segmented and
specialized.
Source of this article: Power Technology Magazine WeChat ID: dianyuanjishu
Author: Liu Xingjiang
1. The origin of lithium-ion batteries and the industrialization of lithium
batteries in China
Lithium-ion batteries work by inserting/extracting lithium ions into and
out of the positive and negative electrodes and moving between the positive and
negative electrodes to achieve the charge and discharge process. The principle
is simple and there is no electrolyte consumption. Therefore, lithium-ion
batteries are ideal high specific energy battery systems. The world's first
industrialized lithium-ion battery was a lithium cobalt oxide positive electrode
invented by Goodenough, a coke negative electrode combination proposed by A.
Yoshino, and a mixed solvent electrolyte of propylene carbonate and diethyl
carbonate of LiPF6. SONY introduced it in 1992 Achieve mass production, battery
specific energy is 80Wh/kg.
2. Development of lithium-ion battery technology in China
2.1 Research on cathode materials
The earliest practical cathode material is layered lithium cobalt oxide
(LCO) material, with a charging cut-off voltage of 4.2V and an operating voltage
of 3.7V. It is mainly used in consumer electronics. After surface coating and
doping, high-voltage lithium cobalt oxide materials can now be charged to 4.45V
and operate stably, with a specific capacity of more than 180mAh/g. A common way
to increase the charging voltage of LCO is to coat the surface of LCO particles
with a layer of Al2O3, TiO2, ZrO2, etc. to prevent LCO from direct contact with
the electrolyte. Later, in order to reduce costs and improve safety, the layered
ternary materials Li(NiCoMn)O2 (NCM) and spinel lithium manganate LiMn2O4
attracted widespread attention and began to be mixed with lithium cobalt oxide
for consumer electronics or used alone. On motivation. Nowadays, ternary
materials are developing from Ni:Co:Mn ratio 1:1:1 to high nickel 532, 622, and
811. With the increase of nickel content, the specific capacity increases from
150mAh/g to 200mAh/g, but the production process environment The requirements
are getting higher and higher, and battery safety is getting lower and lower. At
the same time, domestic manufacturers using NCM materials patented by 3M are
likely to face similar risks of patent disputes during the export process. In
recent years, anionic active materials such as layered lithium-rich
manganese-based materials have also achieved tremendous theoretical
breakthroughs and technological progress, with specific capacities even reaching
400mAh/g. Spinel materials are developing towards Fd3m and P4332 space group
miscible 5V spinel LiNi0.5Mn1.5O4. This type of material has a three-dimensional
tunnel structure, lithium ions can be completely extracted, has a high diffusion
coefficient and is safe. In addition, polyanionic phosphate materials, such as
LiFePO4, LiMnPO4, LiCoPO4, LiNiPO4, etc., have an olivine structure and are very
stable because the oxygen in the phosphate materials is fixed in the form of
strong phosphate groups. The volume changes during charging and discharging are
small and safe. Good sex. Particularly worth mentioning is lithium iron
phosphate (LiFePO4), which supports half of China's lithium-ion battery
materials industry. This material has the advantages of good safety, long cycle
life, and low cost. It is the main cathode material for power and energy storage
batteries. Through nanonization and surface carbon coating, lithium iron
phosphate has achieved the performance of larger power discharge, and the
well-carbon-coated samples do not contain γ-Fe2O3 and Fe3+ impurities. This
material has achieved the world's largest application in China. Large-scale
production. Lithium iron phosphate is facing complex patent disputes, including
Goodenough of the University of Texas, Nippon Telegraph & Telephone, and
A123, all claiming patent rights to LFP. However, in 2015, with the efforts of
industry experts, China claimed the patent rights of Canada's Hydro-Québec. It
achieved “invalidation” and protected the domestic lithium iron phosphate
material and battery industry. Lithium manganese iron phosphate materials have
attracted the attention of the industry due to their high voltage and high
specific capacity. Some manufacturers have added this type of material to
ternary materials to improve the safety of lithium-ion batteries. Figure 1 shows
the specific energy potential of other materials compared to traditional lithium
cobalt oxide.
Figure 1 Comparison of relative energy densities of various cathode
materials
2.2. Research on negative electrode materials
The rapid rise of graphite materials benefits from technological
innovations in electrolytes and graphite materials. Graphite materials can be
mainly divided into artificial graphite and natural graphite. China's industrial
research on lithium-ion battery anode materials started with artificial
graphite. Among them, mesocarbon microsphere (MCMB) material has the advantages
of high tap density and low specific surface area, which reduces the formation
of SEI film during the first charging process and reduces the irreversible
capacity. Therefore, MCMB is widely used. However, its production temperature is
as high as 2800°C, so the cost has remained high. Natural graphite is very low
in cost, but the co-embedding problem of PC affects the application of natural
graphite. Therefore, natural graphite requires an electrolyte with a high EC
content or modification of the surface of natural graphite, and surface-modified
natural graphite It is the mainstream of the current market. In addition, soft
carbon and hard carbon materials have high lithium ion insertion potential,
especially hard carbon materials with a layer spacing of 0.372nm, which is
easier for lithium ion diffusion. Therefore, soft carbon and hard carbon
materials have been used as part of composite anodes for power battery anodes to
meet the requirements of fast charging and low-temperature charging. During this
period, alloy anode materials also received widespread attention, such as Si and
Sn materials, but the huge volume expansion of these materials during the
lithium insertion process limited their applications. Now, in pursuit of higher
energy density, significant progress has been made in the development of Si-C
materials and SiO materials.
2.3. Electrolyte research
LiPF6's carbonate mixed solvent electrolyte was first used in commercial
lithium-ion batteries. With the technological advancement of electrode
materials, matching electrolytes are also constantly developing. During the
initial charging process, the electrolyte will form a layer of SEI film on the
surface of the graphite negative electrode. If the SEI film is not completely
inert, the electrolyte will decompose on the surface of the negative electrode
in each subsequent cycle, increasing the resistance of the negative electrode
and causing consumption. electrolyte, so if the SEI membrane cannot be
controlled well, good cycle performance cannot be obtained. In the early days,
efforts to improve the performance of the electrolyte were mainly focused on the
purification of the solvent (removal of water). Later, the concept of functional
electrolyte additives was proposed. Common additives mainly include SEI
film-forming additives EC, FEC, etc., as well as resistors. Combustion
additives, anti-overcharge additives, wetting additives, etc. Functional
additives also drive technological advancements in high-capacity graphite
materials. Polyoxyethylene and other polymer electrolytes can only be used above
60°C. In order to solve this problem, a part of the liquid electrolyte can be
added to polymers such as PEO, PAN, PMMA, PVdF-HFP, etc. to form a so-called gel
electrolyte. Bell The laboratory once launched a battery using PVdF-HFP gel
electrolyte. This technology has also attracted widespread attention from the
Chinese industry. With the help of this gel electrolyte, we do not need to use a
hard shell structure to exert a certain squeezing force on the battery, so we
can use a lighter plastic shell (such as aluminum plastic film) to increase the
mass specific energy of the lithium-ion battery. .
In recent years, in order to further improve the specific energy and safety
of lithium batteries, there has been an upsurge in solid-state lithium battery
research in China. Its core technologies are highly stable and high conductivity
solid electrolyte materials and interface control technology between solid
electrolytes and electrode materials. Solid-state lithium batteries work on the
same principle as traditional lithium batteries. However, because the key
components are all solid, the interface is more complex, and interface
compatibility directly affects the performance of solid-state batteries. Solid
electrolytes mainly include polymers, oxides and sulfides. The performance
comparison of various solid electrolytes is shown in Table 2. At present, Japan,
represented by Toyota, uses sulfide solid electrolyte as the main system. The
bipolar solid-state battery developed at the same time has an average voltage of
14.4V. It is expected to launch the first electric vehicle equipped with a
solid-state battery in 2022. The technical level is internationally Leading;
South Korea mainly uses sulfide and inorganic/organic composites. Samsung
Yokohama Research Institute has developed a 2Ah sulfide solid-state battery,
which can obtain specific energy of 200Wh/kg and 500Wh/L. It is in the
small-scale trial stage; France and Canada use PEO Mainly based on polymers, it
has small-scale production capabilities; the research focus of Sakti3 (Dyson)
and others in the United States is LiPON-based ultra-thin oxide solid-state
batteries, but it is currently in the laboratory stage; a hundred flowers are
blooming in China, and organic/inorganic composite solid electrolytes are
practical It is advancing rapidly, especially Ganfeng Lithium Industry, which is
the first in China to prepare soft-package all-solid-state lithium batteries
with a capacity of 4~10Ah, with a specific energy of up to 286Wh/kg (628Wh/L),
and a thousand-cycle capacity retention rate of 87.6%. Investment 240 million to
build the first-generation solid-state lithium battery research and development
pilot production line.
3. Development and current situation of China’s lithium battery
industry
China's lithium-ion battery industry technology has gradually moved from
tracking research and imitation to independent innovation, and product
applications have gradually moved from the initial mobile phones and laptops to
power and energy storage applications. After 20 years of development, China has
become a major manufacturer and consumer of lithium-ion batteries. It has grown
from a few companies to hundreds, with the most complete industrial chain, and
its global market share has reached 52%. Figure 2 shows the statistical chart of
China's lithium-ion battery production in recent years. In 2017, total
production reached 100.9 billion watt-hours, and sales revenue reached 158.9
billion yuan. Figure 3 is a list of China’s top 20 power batteries. Among them,
CATL has developed into the world’s largest lithium-ion battery manufacturer.
Driven by the electric vehicle subsidy policy, lithium-ion batteries for power
have developed rapidly. Cylindrical, square, and polymer battery types coexist,
but square accounts for up to 54%, cylindrical accounts for 26%, and polymer
accounts for 20%. The material system has developed from 70% lithium iron
phosphate system in 2016 to the coexistence of lithium iron phosphate and
ternary systems in 2017 (accounting for 49% and 45% respectively). The
electrical performance of batteries has also been continuously improved. The
specific energy of large-capacity square lithium iron phosphate single cells has
exceeded 170Wh/kg, and the specific energy of high-nickel material 21700
batteries has reached 240~280Wh/kg. But in 2018, people have realized the
importance of safety from the frequent fire accidents of electric vehicles. The
phosphate system has certain advantages in terms of energy and safety, which may
affect the layout of phosphate and high-nickel systems in power batteries.
And upstream material production is also expanding rapidly. Among them, the
ranking of ternary cathode materials is Hunan Shanshan, Xiamen Tungsten
Industry, Ningbo Jinhe, Shenzhen Zhenhua, Xinxiang Tianli, Beijing Dangsheng,
etc., with a single monthly output of more than 10,000 tons; the ranking of
anode materials is Beterui , Shanshan, Jiangxi Zichen, Kaijin, etc. The domestic
matching rate of electrolytes and separators has increased rapidly, and there
has been a trend of overcapacity.
Regarding lithium primary batteries, due to its small overall market size,
it is only a market of more than 3 billion yuan, with an annual growth rate of
about 15%. At the same time, its chemical system is shown in Table 3 with less
changes. There are only a few R&D and production units in China such as
Yiwei Lithium Energy, the state-owned 752 Factory, and Wuhan Lixing. The 18th
Institute of China Electronics Technology took the lead in developing new system
primary batteries such as lithium fluorocarbon with the highest specific energy,
with a specific energy of 700Wh/kg, filling a domestic gap.
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