Lithium-ion batteries are composed of positive electrode, negative
electrode, electrolyte, separator, current collector, casing and other parts.
Mix the positive electrode material, conductive agent and organic binder of the
battery evenly and apply it on both sides of the aluminum foil current
collector. Mix the negative electrode material, conductive agent and organic
binder evenly and apply it on both sides of the copper foil current collector.
Use a medium between the positive and negative electrodes. Separated by
diaphragms, both are immersed in organic electrolyte, and finally wrapped in a
shell. Before recycling, waste lithium-ion batteries must be completely
discharged to ensure no harm to the human body before being dismantled, removing
the casing, and separating the positive and negative electrode materials,
current collectors, electrolytes, etc., before proceeding to the next step of
recycling.
I. Overview
Lithium-ion batteries are deeply loved by various electronic product
manufacturers because of their excellent performance, such as high voltage,
large specific capacity, and no memory effect, and their output is increasing
year by year. Lithium-ion batteries have penetrated into every corner of our
work and life. They can be seen everywhere. Mobile phones, computers, cameras,
power banks, electric bicycles, new energy vehicles, etc. all use lithium-ion
batteries as ideal power sources. At present, the total consumption of
lithium-ion batteries in the country is about 7.8 billion.
At present, the total production of mobile phones in our country has
exceeded 2 billion. If a mobile phone is equipped with a lithium-ion battery,
and the average life of these batteries is 3 years, then in 3 years, the number
of used lithium-ion batteries around us may reach tens of billions. piece. This
does not include lithium-ion batteries used in commonly used devices such as
laptops, cameras, and power banks. With the increasing popularity of new energy
vehicles, the application of lithium-ion batteries in new energy vehicles will
drive the production of lithium-ion batteries. From mobile phones to electric
bicycles to electric cars, there are more and more used lithium-ion batteries in
our lives, but resources are getting tighter and environmental protection
requirements are becoming increasingly stringent. If tens of thousands of used
lithium-ion batteries are not handled properly, people will Your physical health
will be harmed directly or indirectly.
Mobile phone lithium-ion batteries will bulge after being used for a long
time, and may be damaged after being exposed to external force. The battery
contains unstable electrolyte solution, and leakage will pollute the
environment. Its electrolyte lithium hexafluorophosphate (LiPF6) will decompose
in humid air to produce harmful substances, while carbonate organic solvents
will cause serious pollution to water, atmosphere and soil, seriously harming
the ecosystem. Even if the waste lithium battery is not damaged, if it is
landfilled with domestic waste, the heavy metals such as cobalt and copper that
leak out will cause potential pollution to the environment over time. Data shows
that a 20g used mobile phone lithium battery can pollute 6,000m3 of water
resources and 1km2 of land for about 50 years. It can be seen that if tens of
billions of waste mobile phone batteries are disposed of together with the
garbage, the pollution caused to the human environment can be imagined.
In fact, used lithium batteries can be recycled and reused, and some
valuable heavy metals are of great recycling value. Usually, the proportions of
cobalt, lithium, and nickel in used lithium-ion batteries are 5% to 15%, 2% to
7%, and 0.5% to 2% respectively. These metals are primary resources. In
particular, metallic cobalt has no separate ore deposits and is mostly
associated with copper and nickel ores, and is of low grade, so it is very rare
and expensive. If it is effectively recycled, it can alleviate the shortage of
cobalt resources in our country. In addition, used lithium batteries also
contain copper, aluminum, iron and other metal elements, which can be recycled
and reused to make the best use of materials and turn waste into treasure. This
not only has significant environmental benefits, but also has objective economic
benefits.
The recycling and processing of used lithium batteries helps to form a
cyclic chain of "production-recycling-reproduction", solves the problems of used
lithium battery pollution and waste utilization, realizes the sustainable
development of new energy vehicles, and alleviates the shortage of strategic
metal resources in my country.
2. Lithium-ion battery recycling and processing technology
Lithium-ion batteries are composed of positive electrode, negative
electrode, electrolyte, separator, current collector, casing and other parts.
Mix the positive electrode material, conductive agent and organic binder of the
battery evenly and apply it on both sides of the aluminum foil current
collector. Mix the negative electrode material, conductive agent and organic
binder evenly and apply it on both sides of the copper foil current collector.
Use a medium between the positive and negative electrodes. Separated by
diaphragms, both are immersed in organic electrolyte, and finally wrapped in a
shell. Before recycling, waste lithium-ion batteries must be completely
discharged to ensure no harm to the human body before being dismantled, removing
the casing, and separating the positive and negative electrode materials,
current collectors, electrolytes, etc., before proceeding to the next step of
recycling.
1. Recycling of lithium-ion battery casings
Lithium battery shells include steel shells (square type is rarely used),
aluminum shells, nickel-plated iron shells (used for cylindrical batteries),
aluminum-plastic films (soft packaging), etc., as well as battery caps, which
are the terminals of the positive and negative electrodes of the battery. Before
recycling the casing, the used lithium battery needs to be discharged and
pre-processed before it can be disassembled. The disassembled plastic and iron
casing can be recycled. Usually there are: mechanical crushing and screening
method, that is, mechanical crushing, sieving, and sorting out the shell
materials; manual disassembly, and try not to use this method considering the
harm to the human body; dismantling after low-temperature freezing, this process
The technology is very environmentally friendly, but it can only recycle some
metal materials and lithium salts. The recycling efficiency is low and it is
impossible to effectively recycle plastics.
2. Recycling of cathode materials
Lithium-ion batteries use lithium-containing compounds as the positive
electrode, with only lithium ions and no metallic lithium. Usually they are
lithium manganate, lithium cobalt oxide, lithium iron phosphate, lithium nickel
cobalt manganate and other materials. At present, most of the active materials
of the positive electrode of lithium-ion batteries still use lithium cobalt
oxide, because lithium nickel cobalt manganate is combined with lithium
manganate. The advantages of both materials and lithium cobalt oxide have
attracted the interest of many researchers. They have great potential as power
batteries for electric bicycles and electric vehicles.
With the depletion of this non-renewable mineral resource, and cathode
materials accounting for 40% of the total battery cost, if heavy metals such as
cobalt, nickel, and lithium in cathode materials are effectively recovered,
waste can be turned into treasure, and materials can be recycled. It can not
only alleviate the mineral resource crisis and achieve sustainable development,
but also bring huge economic benefits.
(1) Separation of active material and current collector
First, the cathode active material must be effectively separated from the
conductive current collector aluminum foil in order to realize the recovery of
the cathode material. Currently, the commonly used methods are:
①Scraper. If the positive electrode material is directly scraped off the
aluminum foil, this method will scratch the aluminum foil current collector and
produce current collector debris, making it difficult to separate the positive
electrode active material and the aluminum foil.
② High temperature incineration. The organic binder is removed through
high-temperature decomposition, and the materials constituting the lithium
battery are separated, so that the metals and their compounds in the battery are
oxidized, reduced and decomposed, volatilized in the form of vapor, and then
condensed and collected.
③ Organic solvent dissolves. Based on the principle of organic matter
dissolving organic matter, a suitable organic solvent is used to dissolve the
organic binder polyvinylidene fluoride (PVDF) in the cathode material, thereby
peeling off the active material from the aluminum foil. The organic solvent that
is currently being studied more is N-methylpyrrolidone (NMP). Experiments have
shown that NMP can completely peel off the active material when soaking the
positive electrode cobalt-lithium film at 70°C, and the metal form of the
aluminum foil does not change in any way and can be directly recycled. , the
used organic solvent can be recycled by removing the binder through
distillation. The only disadvantage is that NMP is too expensive, about 30,000
yuan/t, and the high cost limits its application.
④Electrolytic peeling. An electrolysis process is used to separate the
battery cathode material and the aluminum foil current collector. Use the spent
lithium battery cathode as the cathode, lead as the anode, and dilute sulfuric
acid solution dissolved in citric acid as the electrolyte. Electrolysis occurs
at a certain current density for 15 to 30 minutes. The active material falls off
the aluminum foil and falls into the solution. It is filtered to obtain
electrolysis. fluid and battery residue. The leaching rate of cobalt reaches 50%
under low acidity conditions, and the current efficiency reaches more than
70%.
(2) Recovery of active substances
① Acid leaching: The separated cathode active material is leached in a
system of sulfuric acid and hydrogen peroxide to obtain Co2+ and Li +, and then
the leach solution containing Co2+ and Li + is first leached with
bis(2-ethylhexyl) phosphate (P2O4 ) extraction agent to remove impurity ions,
and then use ethylhexyl mono-2-ethylhexyl phosphate (P5O7) extraction agent to
extract and separate the cobalt ions in the water phase to obtain a cobalt-rich
organic phase.
②Alkali leaching: When the positive active material is electrolytically
stripped, the aluminum on the surface will be oxidized to form a dense oxide
film, which reacts with acid to generate aluminum ions and enters the solution.
The aluminum ions are toxic to the extraction agent, so the aluminum removal
effect is If it is not ideal, it will directly affect the separation effect.
Therefore, alkali leaching is first used to recover aluminum, and then acid
leaching is used to recover cobalt and lithium. The best conditions for aluminum
recovery by alkali leaching are: 90°C temperature, 10% sodium hydroxide (NaOH)
solution, the aluminum recovery rate reaches 96%; the best conditions for acid
solution recovery of cobalt and lithium are: 90°C temperature, 4 mol /L sulfuric
acid solution, solid-liquid ratio 1:8, reaction time 100 min, the leaching rate
of cobalt and lithium reached 92%. This method can recover valuable metals in
waste lithium-ion batteries, has a simple process flow, does not cause secondary
pollution to the environment, and has certain practical value.
③ Using biomass straw sulfuric acid system to leach battery residue, the
cobalt leaching rate reaches more than 99%. And through the 2-stage and 3-stage
leaching process, the acid and organic pollutants (COD) in the leachate are
fully utilized. The leached cobalt is precipitated with oxalic acid, and the
battery material prepared has better discharge performance [7].
④ Directly generate cathode materials through chemical reactions. The above
methods all separate aluminum and cobalt first. To obtain the cathode material,
further synthesis is required. The process is complicated and the cost is high.
If the cathode material is directly synthesized during the separation process,
the production process can be greatly simplified and the economic benefits can
be improved. The positive electrode material in the scrap electrode sheet has
only deteriorated in structure during use, and can be reused as long as it is
adjusted after effective separation. Direct and comprehensive utilization of
lithium, nickel, cobalt, manganese and other valuable metals in waste
lithium-ion batteries does not require the separation of nickel, cobalt,
manganese, lithium and other elements. The element utilization rate is high and
raw material costs are saved.
3. Recycling of negative electrode materials
There are many types of negative electrode materials for lithium batteries:
① Metal materials, such as lithium metal. ② Inorganic non-metallic materials,
mainly carbon materials, silicon materials and other non-metallic composite
materials. ③Transition metal oxides. Currently, carbon, graphite and
non-graphite carbon materials are widely used. Lithium titanate can also be used
as anode material in electric vehicles due to its excellent cycle life, safety
and rate performance. The main disadvantage is that it reduces the energy
density of the battery. There are also some companies developing tin alloys as
negative electrode materials, but they are still in the research stage and have
few applications. The conductive current collector uses electrolytic copper foil
with a thickness of 7 to 15 μm, so the copper in it can be recycled (the content
is about 35%), and the carbon powder adhered to it can also be recycled and used
as an additive for plastics, rubber, etc. Therefore, we must first effectively
separate the negative electrode materials of waste lithium batteries to maximize
the resource utilization of waste lithium batteries.
Through hammer vibration crushing, the carbon powder and copper foil are
effectively separated from each other, and then the copper foil and carbon
powder are preliminarily separated based on the size difference and shape
difference between the particles. Copper foil is enriched in the particle size
range greater than 0.250 mm, while carbon powder is enriched in the particle
size range less than 0.125 mm. Depending on the particle size, it can be
directly recycled.
For broken particles with a particle size of 0.125 ~ 0.250 mm, the air flow
separation method is used to achieve effective separation between copper and
carbon powder. Through the combined process of hammer crushing, vibration
screening and air flow sorting, the resource utilization of metal copper and
carbon powder in the negative electrode materials of waste lithium batteries can
be realized.
4. Recycling of organic electrolytes and separators
Most of the electrolytes of digital waste lithium-ion batteries are not
recycled and are usually burned by fire. As a power source, the electrolyte of
lithium-ion batteries accounts for about 15% of the battery cost and contains
rich contents.
Rich lithium ions have higher recycling value. Moreover, currently commonly
used electrolytes generally use carbonate organic solutions of LiPF6. In humid
air, LiPF6 reacts with water to generate harmful gas hydrogen fluoride. It can
be seen that effective recycling of electrolytes can not only reduce harmful gas
emissions, but also has certain economic benefits. benefit. The separator of the
lithium battery has a microporous structure, which can prevent electrons from
passing through and allow lithium ions to pass freely. Part of the electrolyte
is dispersed in the gaps between the electrode and the separator, so the
separator is recycled together.
After the electrodes and separators are soaked in a suitable solvent for a
certain period of time, the electrolyte will completely escape into the solvent.
Polycarbonate (PC) has a relatively large relative dielectric constant, which is
beneficial to the dissolution of lithium salts. After Tong Dongge, Lai Qiongyu,
Ji Xiaoyang and others soaked the electrolyte and separator in PC solvent for a
period of time, the recovered electrolyte LiPF6 can be reused in batteries.
A Canadian company used low-temperature technology to reduce the relative
activity of each component in the electrolyte, and then used NaOH solution to
neutralize the electrolyte to realize the recycling of lithium battery
electrolyte.
3. Difficulties faced by lithium battery recycling
1. People’s awareness of waste lithium battery recycling is weak
Most people don’t know how to dispose of used lithium batteries after use,
and the government has not set up a special recycling agency, resulting in a
large number of lithium batteries being buried with the garbage; on the other
hand, the recycling of used lithium batteries requires sufficient recycling
volume. Regarding the value of reuse, government agencies need to vigorously
promote the significance of lithium battery recycling to awaken the public's
awareness of recycling, lay out a recycling network, and form a recycling system
for used lithium batteries.
2. Recycling and processing of used lithium batteries is complex and
costly
After the waste lithium batteries are separated into materials, they need
to be recycled through multiple processes. The process is relatively
complicated. Therefore, this is a time-consuming and labor-intensive business
with low economic benefits. No company is willing to do it. There are currently
no relevant policies to support the recycling of lithium batteries, and the
environment has not been greatly affected for the time being.
3. Insufficient government support
The supporting policies and regulations are not yet complete enough. At
present, the recycling of lithium-ion batteries is basically done by small
companies and has not yet become a phenomenon. The industrial standards for
recycling and dismantling of power lithium batteries, as well as the
standardization and scale of recycling channels, need to be further improved as
the scale of the industry expands.
4. Outlook
With the development of science and technology, the safety and service life
of lithium batteries have been greatly improved, but the recycling of lithium
batteries has not kept pace. As the demand for new energy vehicles increases
across the board, lithium-ion batteries will be in short supply. If there are
only battery manufacturing companies and no battery recycling agencies, and
waste batteries have nowhere to dispose, the development of new energy will lose
its original significance. Some experts predict that the recycling market for
used power lithium batteries will explode from 2018, and the recycling market
size will further grow in 3 to 5 years. Therefore, it is urgent to establish a
specialized recycling organization to recycle and reuse power lithium-ion
batteries. In short, achieving sustainable development of lithium batteries is
closely related to alleviating the energy crisis, ecological environment, energy
conservation and emission reduction, etc. It benefits the country and the people
and has a huge role in promoting industrial development.
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