The huge market demand for lithium-ion batteries will, on the one hand,
lead to the emergence of a large number of used batteries in the future. How to
deal with these used lithium-ion batteries to reduce their impact on the
environment is an urgent problem; on the other hand, in order to cope with the
huge market Demand requires manufacturers to produce large quantities of
lithium-ion batteries to supply the market. At present, the cathode materials
used in the production of lithium-ion batteries mainly include lithium cobalt
oxide, lithium manganate, lithium nickel cobalt manganate ternary materials and
lithium iron phosphate, etc. Therefore, used lithium-ion batteries contain more
cobalt (Co), lithium (Li), nickel (Ni), manganese (Mn), copper (Cu), iron (Fe)
and other metal resources, including a variety of rare metal resources. Cobalt
is a scarce strategic metal in my country and is mainly imported. meet growing
demand. Some metal contents in used lithium-ion batteries are higher than those
in natural ores, so recycling and processing used batteries has certain economic
value amid the increasing shortage of production resources.
2. Lithium-ion battery recycling and processing technology
The recycling process of used lithium-ion batteries mainly includes
pre-treatment, secondary treatment and advanced treatment. Since there is still
some power left in used batteries, the pretreatment process includes deep
discharge process, crushing, and physical sorting; the purpose of secondary
treatment is to achieve complete separation of positive and negative active
materials from the substrate. Commonly used heat treatment methods and organic
solvent dissolution methods , alkali solution dissolution method and
electrolysis method to achieve complete separation of the two; advanced
treatment mainly includes two processes of leaching and separation and
purification to extract valuable metal materials. According to the
classification of extraction process, battery recycling methods can be mainly
divided into three major categories: dry recycling, wet recycling and biological
recycling.
1. Dry recycling
Dry recycling refers to the direct recovery of materials or valuable metals
without using media such as solutions. Among them, the main methods used are
physical separation method and high temperature pyrolysis method.
(1)Physical sorting method
The physical sorting method refers to dismantling and separating the
battery, crushing, screening, magnetic separation, fine crushing and
classification of battery components such as electrode active materials, current
collectors and battery casings, thereby obtaining valuable high-content
substances . A method proposed by Shin et al. to recover Li and Co from
lithium-ion battery waste liquid using sulfuric acid and hydrogen peroxide
includes two processes: physical separation of metal-containing particles and
chemical leaching. Among them, the physical separation process includes
crushing, screening, magnetic separation, fine crushing and classification. The
experiment uses a set of rotating and fixed blade crushers for crushing, uses
sieves with different apertures to classify the crushed materials, and uses
magnetic separation for further processing to prepare for the subsequent
chemical leaching process.
Based on the grinding technology and water leaching process developed by
Zhang et al., Lee et al., and Saeki et al., Shu et al. developed a new method
for recovering cobalt and lithium from lithium-sulfur battery waste using
mechanochemical methods. This method uses a planetary ball mill to jointly grind
lithium cobalt oxide (LiCoO2) and polyvinyl chloride (PVC) in the air to form Co
and lithium chloride (LiCl) in a mechanochemical manner. Subsequently, the
ground product is dispersed in water to extract the chloride. Grinding promotes
mechanochemical reactions. As grinding proceeds, the extraction yields of both
Co and Li increase. 30 minutes of grinding resulted in the recovery of more than
90% of Co and nearly 100% of lithium. At the same time, about 90% of the
chlorine in the PVC sample has been converted into inorganic chlorides.
The operation of physical sorting method is relatively simple, but it is
not easy to completely separate lithium-ion batteries, and mechanical
entrainment losses are prone to occur during screening and magnetic separation,
making it difficult to achieve complete separation and recovery of metals.
(2) High temperature pyrolysis method
The high-temperature pyrolysis method refers to decomposing lithium battery
materials that have undergone preliminary separation treatment such as physical
crushing and decomposing them at high temperature to remove the organic binder
and thereby separate the constituent materials of the lithium battery. At the
same time, it can also oxidize, reduce and decompose metals and their compounds
in lithium batteries, volatilize them in the form of steam, and then collect
them by condensation and other methods.
When Lee et al. used waste lithium-ion batteries to prepare LiCoO2, they
used a high-temperature pyrolysis method. Lee et al. first heat-treated the LIB
sample in a muffle furnace at 100-150°C for 1 hour. Second, the heat-treated
cells are shredded to release the electrode material. The samples were
disassembled using a high-speed crusher designed specifically for this study and
classified according to size, ranging from 1 to 50 mm. Then, two steps of heat
treatment are performed in the furnace. The first heat treatment is at 100-500°C
for 30 minutes, and the second time is at 300-500°C for 1 hour. The electrode
material is released from the current collector through vibration screening.
Next, the carbon and binder are burned off by burning at a temperature of 500 to
900°C for 0.5 to 2 hours to obtain the cathode active material LiCoO2.
Experimental data shows that carbon and binder are burned off at 800°C.
High-temperature pyrolysis treatment technology is simple in process, easy
to operate, has fast reaction speed and high efficiency in high-temperature
environments, and can effectively remove adhesives; and this method does not
have high requirements on the composition of raw materials, and is more suitable
for processing large amounts or more complex materials. Battery. However, this
method has high equipment requirements; during the treatment process, the
decomposition of organic matter in the battery will produce harmful gases, which
is not friendly to the environment. Purification and recycling equipment needs
to be added to absorb and purify harmful gases to prevent secondary pollution.
Therefore, the processing cost of this method is higher.
2. Wet recycling
The wet recycling process is to crush and dissolve the waste batteries, and
then use appropriate chemical reagents to selectively separate the metal
elements in the leaching solution to produce high-grade cobalt metal or lithium
carbonate, etc., for direct recycling. Wet recycling is more suitable for
recycling waste lithium batteries with a relatively single chemical composition.
Its equipment investment cost is low, and it is suitable for the recycling of
small and medium-sized waste lithium batteries. Therefore, this method is
currently widely used.
(1)Alkali-acid leaching method
Since the cathode material of lithium-ion batteries will not dissolve in
alkaline solution, but the base aluminum foil will dissolve in alkaline
solution, this method is often used to separate aluminum foil. When Zhang Yang
et al. recycle Co and Li in batteries, they leached the aluminum with alkali in
advance, and then soaked it with dilute acid to destroy the adhesion between the
organic matter and the copper foil. However, the alkali leaching method cannot
completely remove PVDF, which has a negative impact on subsequent leaching.
Most of the positive active materials in lithium-ion batteries are soluble
in acid, so the pre-treated electrode materials can be leached with acid
solution to separate the active materials from the current collector, and then
combine the principles of neutralization reaction to target the metal. Perform
precipitation and purification to achieve the purpose of recovering high-purity
components.
The acid solutions utilized by the acid leaching method include traditional
inorganic acids, including hydrochloric acid, sulfuric acid, and nitric acid.
However, since harmful gases such as chlorine (Cl2) and sulfur trioxide (SO3)
that have an impact on the environment are often produced during the leaching
process using inorganic strong acids, researchers have tried to use organic
acids, such as citric acid, to treat waste lithium batteries. , oxalic acid,
malic acid, ascorbic acid, glycine, etc. Li et al. used hydrochloric acid to
dissolve the recovered electrodes. Since the efficiency of the acid leaching
process may be affected by hydrogen ion (H+) concentration, temperature,
reaction time and solid-liquid ratio (S/L), in order to optimize the operating
conditions of the acid leaching process, experiments were designed to explore
the reaction time, H+ concentration and temperature effects. Experimental data
show that when the temperature is 80°C, the H+ concentration is 4mol/L, and the
reaction time is 2h, the leaching efficiency is the highest, in which 97% of Li
and 99% of Co in the electrode material are dissolved. Zhou Tao et al. used
malic acid as the leaching agent and hydrogen peroxide as the reducing agent to
perform reduction leaching of the pretreated cathode active material, and
studied the effects of different reaction conditions on the leaching rates of
Li, Co, Ni, and Mn in the malic acid leaching solution, thereby finding out find
the best reaction conditions. Research data shows that when the temperature is
80°C, the malic acid concentration is 1.2mol/L, the liquid-liquid volume ratio
is 1.5%, the solid-liquid ratio is 40g/L, and the reaction time is 30 minutes,
the efficiency of malic acid leaching is the highest, among which Li, The
leaching rates of Co, Ni and Mn reached 98.9%, 94.3%, 95.1% and 96.4%
respectively. However, compared with inorganic acids, the cost of leaching with
organic acids is higher.
(2) Organic solvent extraction method
The organic solvent extraction method uses the principle of "similar
compatibility" and uses a suitable organic solvent to physically dissolve the
organic binder, thereby weakening the adhesion between the material and the foil
and separating the two.
Contestabile et al. used N-methylpyrrolidone (NMP) to selectively separate
components in order to better recover the active materials of the electrode when
recycling lithium cobalt oxide batteries. NMP is a good solvent for PVDF
(solubility is about 200g/kg), and its boiling point is relatively high, about
200°C. The study utilized NMP to treat the active material at approximately
100°C for 1 h, effectively achieving the separation of the film from its support
and thus recovering the metallic form of Cu by simply filtering it out of the
NMP (N-methylpyrrolidone) solution. and Al. Another benefit of this method is
that the recovered Cu and Al metals can be directly reused after sufficient
cleaning. In addition, recovered NMP can be recycled. Because of its high
solubility in PVDF, it can be reused many times. Zhang et al. used
trifluoroacetic acid (TFA) to separate the cathode material from the aluminum
foil when recycling cathode waste for lithium-ion batteries. The waste
lithium-ion batteries used in the experiment used polytetrafluoroethylene (PTFE)
as an organic binder. The effects of TFA concentration, liquid-to-solid ratio
(L/S), reaction temperature and time on the separation efficiency of cathode
materials and aluminum foil were systematically studied. . Experimental results
show that in a TFA solution with a mass fraction of 15, a liquid-to-solid ratio
of 8.0 mL/g, a reaction temperature of 40°C, and a reaction of 180 minutes with
appropriate stirring, the cathode material can be completely separated.
The experimental conditions for using organic solvent extraction to
separate materials and foils are relatively mild, but organic solvents have
certain toxicity and may be harmful to the health of operators. At the same
time, because different manufacturers have different processes for making
lithium-ion batteries, they choose different binders. Therefore, manufacturers
need to choose different organic solvents when recycling used lithium batteries
for different manufacturing processes. In addition, for large-scale recycling
processing operations at an industrial level, cost is also an important
consideration. Therefore, it is very important to choose a solvent with wide
sources, affordable price, low toxicity and harmlessness, and wide
applicability.
(3) Ion exchange method
The ion exchange method refers to the use of different adsorption
coefficients of ion exchange resins for the metal ion complexes to be collected
to achieve metal separation and extraction. After Wang Xiaofeng et al. acid
leached the electrode material, they added an appropriate amount of ammonia to
the solution to adjust the pH value of the solution and react with the metal
ions in the solution to generate [Co(NH3)6]2+, [Ni(NH3) 6]2+ and other complex
ions, and continuously pass pure oxygen into the solution for oxidation. Then,
ammonium sulfate solutions of different concentrations are repeatedly passed
through the weakly acidic cation exchange resin to selectively elute the nickel
complex and trivalent cobalt ammonia complex on the ion exchange resin. Finally,
a 5% H2SO4 solution is used to completely elute the cobalt complex, while the
cation exchange resin is regenerated, and oxalate is used to recover the cobalt
and nickel metals in the eluent respectively. The ion exchange method has a
simple process and is relatively easy to operate.
3.Biological recycling
Mishra et al. used inorganic acid and acidophilic Thiobacillus ferrooxidans
to leach metals from used lithium-ion batteries, and used S and ferrous ions
(Fe2+) to generate H2SO4, Fe3+ and other metabolites in the leaching medium.
These metabolites help dissolve metals in spent batteries. Research has found
that cobalt biodissolves faster than lithium. As the dissolution process
proceeds, iron ions react with metals in the residue and precipitate, causing
the concentration of ferrous ions in the solution to decrease. As the metal
concentration in the waste sample increases, the growth of cells is prevented
and the dissolution rate slows down. . In addition, a higher solid/liquid ratio
also affects the rate of metal dissolution. Zeng et al. used Thiobacillus
acidophilus to bioleach metal cobalt from used lithium-ion batteries. Different
from Mishra et al., this study used copper as a catalyst to analyze the effect
of copper ions on the bioleaching of LiCoO2 by Thiobacillus acidophilus. . The
results show that almost all cobalt (99.9%) enters the solution after 6 days of
bioleaching when the Cu ion concentration is 0.75g/L, while in the absence of
copper ions, only 43.1% of the cobalt enters the solution after 10 days of
reaction time. Cobalt dissolves. In the presence of copper ions, the cobalt
dissolution efficiency of spent lithium-ion batteries increases. In addition,
Zeng et al. also studied the catalytic mechanism and explained the dissolution
effect of copper ions on cobalt. LiCoO2 and copper ions undergo a cation
exchange reaction to form copper cobaltate (CuCo2O4) on the surface of the
sample, which is easily dissolved by iron ions.
The bioleaching method has low cost, high recovery efficiency, less
pollution and consumption, less impact on the environment, and the
microorganisms can be reused. However, it is difficult to cultivate
high-efficiency microbial fungi, long processing cycle, and control of leaching
conditions are several major problems required by this method.
4.Joint recycling method
Each waste lithium battery recycling process has its own advantages and
disadvantages. Currently, there is research on recycling methods that combine
and optimize multiple processes to give full play to the advantages of various
recycling methods and maximize economic benefits.
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