CN103915661B - A kind of direct recovery the method repairing anode material for lithium-ion batteries - Google Patents

Abstract

The invention discloses a method for directly recovering and repairing anode materials of waste lithium ion batteries, belonging to the field of resource recycling. The method selects the positive electrode material as lithium cobalt oxide or lithium nickel cobalt manganese multi-layered oxide waste positive electrode sheet or positive electrode sheet scraps and defective products; through component analysis, according to the type of binder, the binder is directly destroyed to achieve Clean separation of cathode materials and current collectors; use the principle of heavy liquid separation to separate cathode materials and conductive agents; use SEM, XRD, STEM, XPS and other material analysis methods to study the failure mechanism of cathode materials; if the layered structure is not damaged, use If the chemical composition is repaired by high-temperature calcination, the crystal lattice of the material is disordered and defective, the hydrothermal reaction is used to dissolve and precipitate to repair the layered structure, and to regain the positive electrode material with good charge and discharge performance. The method avoids the dissolving and leaching link, reduces waste liquid generation, and simplifies the technological process.

Description

A method for directly recycling and repairing lithium-ion battery cathode materials

technical field

The invention belongs to the field of resource recycling, and provides a method for directly repairing the anode material of a waste lithium-ion battery by using the subject of material science.

Background technique

Since Sony successfully developed and commercialized lithium-ion batteries in 1990, lithium-ion batteries have a series of advantages such as high working voltage, high specific energy, long cycle life, and good safety. It has been widely used in aerospace, military and medical fields, and is called "the most promising chemical power source". In recent years, the demand for lithium-ion batteries for various purposes has increased year by year, especially in the field of portable electronic products such as mobile phones, notebook computers, cameras and power tools. Lithium-ion batteries, as the preferred power source, have a huge market. Today, when low-carbon economy and energy conservation and emission reduction are vigorously advocated, new energy vehicles will surely become the main development direction of the automotive industry, and the industrialization of hybrid electric vehicles and pure electric vehicles will directly drive the rapid growth of the lithium-ion battery market again. With the widespread application of lithium-ion batteries, the number of used lithium-ion batteries is also increasing year by year, becoming electronic waste that cannot be ignored.

Cathode materials account for a large proportion of the cost of lithium-ion batteries. At present, lithium cobalt oxide is still the main anode material for commercialized lithium-ion batteries in my country. With the expansion of lithium-ion battery applications, cathode materials are moving toward lithium-nickel-cobalt-manganese-based multiple oxidation. Therefore, the recycling and reuse of waste cathode materials can alleviate the shortage of cobalt resources in my country, which is of great strategic significance. In addition, the recycling of waste cathode materials can also greatly save mineral resources and protect the ecological environment. The recycling and reuse of cathode materials for lithium-ion batteries has become an important link in the lithium battery industry with huge economic benefits and broad market prospects.

All countries in the world are developing the recycling technology of cathode materials for lithium-ion batteries. At present, they are all focusing on the use of hydrometallurgical industrial technology to recover metal elements in cathode materials. Xu J Q, Thomas H R, FrancisetR W.A review of processes and technologies for the recycling of Lithium-ionsecondary batteries.Journal of Power Sources,2008,177(2):512-527 summarizes the basic process of lithium-ion battery recycling, that is, the electrode sheet is first broken and separated, and then the battery material is dissolved and leached, separated and recovered in the leachate metal elements, or directly synthesize the positive electrode material from the leaching solution. Domestic recycling of positive electrode materials is still in its infancy, and the relatively mature hydrometallurgical process has published a number of invention patents, such as patent CN101450815A, which uses sulfuric acid and hydrogen peroxide system to leach nickel, cobalt, and manganese elements, and then synthesizes them by treating the leaching solution. Nickel cobalt lithium manganate cathode material. However, the recovery and reuse of positive electrode materials by hydrometallurgical process requires dissolution and leaching, and waste liquid will be generated in each stage, causing serious secondary pollution, and the process is complicated and the cost is high. In addition, as described in patent CN101383442B, NaOH is used to dissolve aluminum to separate deactivated lithium cobaltate, and the positive electrode material is directly supplemented with lithium and roasted to reuse the positive electrode material. Rough development model.

Contents of the invention

The purpose of the present invention is to provide a method for directly reclaiming and repairing the positive electrode material of the waste lithium ion battery. The invention applies material science to the field of resource recycling, avoids the dissolution and leaching link in the existing process, reduces waste liquid generation, simplifies the process flow, does not need or add few chemicals, and does not need to consider the problem of secondary pollution , has a broad application prospect in today's vigorously advocating resource conservation and clean production.

In order to achieve the above object, the present invention adopts following technical scheme:

Fig. 1 is a technical roadmap of the present invention.

As shown in Figure 1, the present invention selects professional equipment to disassemble waste lithium-ion batteries, and sorts the positive electrode material to be lithium cobalt oxide (LiCoO ₂ ) or lithium nickel cobalt manganese multilayer oxide (Li(Ni _1-xy Co _x Mn _y )O ₂ ) positive electrode sheet or battery manufacturer’s positive electrode sheet scraps and defective products; through component analysis, according to the type of binder, directly destroy the binder, and realize the clean separation of the positive electrode material and the current collector; and then Use the principle of heavy liquid separation to separate positive electrode materials and conductive agents with different densities to obtain positive electrode material powder; use SEM, XRD, STEM, XPS, EELS, ICP and other material analysis methods to study the failure mechanism of positive electrode materials; according to different failure mechanisms, layered If the structure is not damaged, directly use high-temperature calcination to repair the chemical composition. If the material lattice is chaotic and defective, use hydrothermal reaction to dissolve and precipitate to repair the layered structure, and regain the positive electrode material with good charge and discharge performance.

A method for directly reclaiming and repairing waste lithium-ion battery cathode materials, said method comprising the steps of:

(1) Dismantling and sorting to obtain the positive electrode sheet whose positive electrode material is lithium cobaltate or lithium-nickel-cobalt-manganese multi-layered oxide, or positive electrode scraps and defective products of the battery manufacturer;

(2) Remove the binder, current collector and conductive agent in sequence to obtain the positive electrode material powder;

(3) Study the failure mechanism of the positive electrode material powder obtained in step (2), and check the chemical composition of the positive electrode material powder. When the failure mechanism is the loss of lithium and transition metals, and the layered structure remains intact, proceed to step (4). When the failure mechanism is Step (4') is performed when the valence state of the transition metal is changed, a phase transition is induced, and the layered structure appears disordered and defective;

(4) According to the composition of the positive electrode material before failure, the compound of the lost metal is mixed into the positive electrode material powder obtained in step (2), and the repaired positive electrode material is obtained by sintering;

(4') According to the composition of the cathode material before failure, the cathode material powder obtained in step (2) is mixed with the dissolved and lost transition metal oxide, and LiOH aqueous solution is added to stir thoroughly, and the cathode material is repaired by hydrothermal reaction.

The positive electrode sheet of lithium ion battery is composed of positive electrode material, conductive agent, binder and current collector. Any positive electrode sheet of any proportion can be used in the present invention, and the positive electrode sheet can be the positive electrode sheet obtained by dismantling and sorting the waste lithium ion battery, or the positive electrode sheet scrap or defective product of the battery manufacturer. It is required that the positive electrode active material of the positive electrode sheet is lithium cobaltate or lithium nickel cobalt manganese multi-layered oxide. Exemplary positive electrode sheet such as the positive electrode sheet of waste lithium ion battery, this positive electrode sheet is that the positive electrode material is evenly rolled on the aluminum foil current collector both sides of thickness about 20 μ m, and the positive electrode material is made of about 85% lithium cobaltate or lithium nickel cobalt manganese Composed of active materials such as multi-layered oxides, 10% acetylene black conductive agent and 5% organic binder. Different manufacturers use different binders for waste positive electrodes, mainly polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF).

In the present invention, the positive electrode material and the current collector are cleaned and separated, and different methods are used to destroy the binder according to the type of the binder.

When the binder is PTFE, a pyrolysis method is used to decompose the binder, thereby realizing the separation of the positive electrode material and the current collector, and achieving the purpose of removing the binder and the current collector. The positive electrode sheet is roasted at high temperature under an inert atmosphere to decompose PTFE, the positive electrode sheet after roasting is taken out, the positive electrode material and the current collector are separated by mechanical friction, and sieved as required to remove the current collector present in the positive electrode material to obtain the positive electrode Mixed powder of material and conductive agent.

The high-temperature calcination is carried out under an inert atmosphere, and the temperature of the high-temperature calcination is 500-600°C, such as 505°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 585°C , 590°C, 595°C, preferably 500~550°C. The time of the high-temperature roasting is 2~5h, such as 2.2h, 2.4h, 2.7h, 2.9h, 3.1h, 3.4h, 3.7h, 3.9h, 4.2h, 4.6h, 4.9h, preferably 2.3~4.5h , further preferably 3h. Due to the poisonous pyrolysis products of PTFE, exhaust gas recovery is required at this time.

When the binder is PVDF, solvent soaking and dissolving is used to make the binder invalid, so as to realize the separation of the positive electrode material and the current collector, and achieve the purpose of removing the binder and the current collector.

When soaking and dissolving, the temperature is controlled at 60~80°C to speed up the dissolution, such as 61°C, 62°C, 64°C, 66°C, 68°C, 70°C, 72°C, 74°C, 76°C, 78°C, 79°C , preferably 61.5~78.5°C. After soaking and dissolving, filter, wash and dry to obtain mixed powder of positive electrode material and conductive agent.

The solvent is selected from any one or a mixture of at least two of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethylsulfoxide, and the mixture For example, a mixture of N,N-dimethylformamide and N,N-dimethylacetamide, a mixture of dimethyl sulfoxide and N-methylpyrrolidone, N,N-dimethylformamide and N,N - Mixtures of dimethylacetamide, mixtures of dimethylsulfoxide and N-methylpyrrolidone, preferably N-methylpyrrolidone. Dirty solvents can be reused by distillation under reduced pressure.

In the present invention, the conductive agent in the positive electrode sheet is removed by a heavy liquid separation method, filtered, washed, and dried to obtain the positive electrode material powder.

Since the density of water is between the conductive agent and the positive electrode material, water can be used as the heavy liquid to separate the conductive agent and the positive electrode material. As a heavy liquid, water is non-toxic and pollution-free, and can be recycled.

An exemplary heavy liquid separation method to remove the conductive agent in the positive electrode sheet is: add the mixed powder of the positive electrode material and the conductive agent to remove the binder and the current collector into the water, stir, stand still, and suspend the conductive agent with a density lower than that of water Above the water, the positive electrode material whose density is higher than that of the water sinks below the water, and the positive electrode material below is flowed out, filtered, and dried to obtain the positive electrode material powder.

Through the above method, the recovery of the positive electrode material can be completed, and the recycled positive electrode material powder can be obtained.

The present invention uses SEM, XRD, STEM, XPS, EELS, ICP and other material analysis methods to study the failure mechanism of positive electrode materials, check the chemical composition of the positive electrode material powder obtained in step (2), determine its specific failure mechanism, and then select a suitable repair method.

Check the chemical composition of the positive electrode material powder obtained in step (2). When the failure mechanism is the loss of lithium and transition metals and the layered structure is well preserved, proceed to step (4): according to the composition of the positive electrode material before failure, in step (2) The compound of the lost metal is mixed into the obtained positive electrode material powder, and the repaired positive electrode material is obtained by sintering. If the positive electrode material before failure is lithium cobalt oxide, it will be repaired as lithium cobalt oxide; if the positive electrode material before failure is lithium-nickel-cobalt-manganese multi-layered oxide, it will be repaired as lithium-nickel-cobalt-manganese multi-layered oxide.

For lithium cobalt oxide or lithium nickel cobalt manganese multi-layered oxide positive electrode materials, the loss of transition metal oxide interlayer lithium and the dissolution loss of transition metal cobalt, nickel, etc. during the charge and discharge process, the chemical composition is repaired by high temperature roasting method. According to the chemical composition analysis of the positive electrode material before failure, according to the composition of the positive electrode material powder obtained in step (3), determine the lost metal elements and the loss amount, and then mix the lost metal elements into the positive electrode material powder obtained in step (2) compound, and sintered to obtain a modified positive electrode material. Lithium loss can be obtained by mixing lithium salt into the positive electrode material powder obtained in step (2), such as Li ₂ CO ₃ , LiOH and the like. The loss of cobalt, nickel and manganese can be obtained by mixing oxides of the metal elements in the positive electrode material powder obtained in step (2), such as cobalt oxides, nickel oxides, and manganese oxides. For example, when both cobalt and nickel are lost, a mixture of cobalt oxide and nickel oxide can be mixed into the positive electrode material powder obtained in step (2). The preparation methods of the cobalt oxide, nickel oxide and manganese oxide are all prior art.

An exemplary preparation method of cobalt oxide is as follows: mixing cobalt salt and precipitant, a precipitation reaction occurs, and the precipitated product is filtered, washed, dried, and then sintered to obtain cobalt oxide. Nickel oxides or manganese oxides can be prepared by replacing the cobalt salts with nickel salts or manganese salts. If a mixed oxide is to be obtained, the corresponding salt is added, and then the salt, the precipitating agent and the complexing agent are mixed for a co-precipitation reaction, and then subsequent reactions are performed to prepare the mixed oxide. The precipitation agent is such as NaOH or Na ₂ CO ₃ , and the complexing agent is such as ammonia water. The drying temperature is, for example, 120° C., and the drying time is, for example, 8 hours. The sintering temperature is, for example, 500-900° C., preferably 700-900° C., more preferably 700° C., and the sintering time is 3-5 hours. XRD results show that the crystal form of the oxide obtained by calcination above 700°C is better, the crystallization is incomplete when the temperature is lower, and the oxide is sintered when the temperature is too high, so the optimal calcination temperature should be controlled at 700°C.

In step (4), the lost metal compound is mixed into the positive electrode material powder, so that the molar ratio of Li/(Ni+Co+Mn) is 1.05~1.15:1, such as 1.06:1, 1.07:1, 1.08:1, 1.09 :1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, preferably 1.08~1.12:1, more preferably 1.1:1. When the positive electrode material is lithium cobalt oxide, both n(Ni) and n(Mn) are 0, and n represents the amount of the substance.

The sintering temperature is 750-950°C, such as 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C, 900°C, 920°C, 940°C, preferably 770-930°C, more preferably 750°C ~870°C, most preferably 850°C.

The calcination time is 10~20h, such as 10.5h, 11h, 11.5h, 12.5h, 13.5h, 14.5h, 15.5h, 16.5h, 17.5h, 18.5h, 19.5h, preferably 10.8~19.7h, more preferably 11.2~18.8h.

Preferably, in step (4), the lost metal compound is mixed into the positive electrode material powder, so that the Li/(Ni+Co+Mn) molar ratio is 1.05~1.15:1, and the repaired positive electrode material is obtained by sintering at 850°C for 10~20h , when the positive electrode material is lithium cobaltate, both n(Ni) and n(Mn) are 0, and n represents the amount of substance.

Check the chemical composition of the positive electrode material powder obtained in step (2). When the failure mechanism is transition metal valence state transition, phase transition, and disorder and defects appear in the layered structure, proceed to step (4'): according to the composition of the positive electrode material before failure , mix the dissolved and lost transition metal oxide into the positive electrode material powder obtained in step (2), add LiOH aqueous solution and stir thoroughly, and hydrothermally react to obtain the repaired positive electrode material. If the positive electrode material before failure is lithium cobalt oxide, it will be repaired as lithium cobalt oxide; if the positive electrode material before failure is lithium-nickel-cobalt-manganese multi-layered oxide, it will be repaired as lithium-nickel-cobalt-manganese multi-layered oxide.

For lithium cobaltate or lithium-nickel-cobalt-manganese multi-layered oxide positive electrode materials, cobalt or nickel equivalent state transition occurs during charge and discharge, causing phase transition and leading to failure. According to the principle of dissolution and re-precipitation, the invention uses hydrothermal reaction to repair the invalid positive electrode material. According to the composition of the positive electrode material powder obtained in step (3), mix the positive electrode material powder obtained in step (2) with a corresponding amount of metal oxide that undergoes valence state transition, add LiOH aqueous solution and stir thoroughly, and move it into a high-pressure reactor. Hydrothermal reaction, using the principle of dissolution and precipitation, to obtain repaired positive electrode materials.

In step (4'), mix the dissolved and lost transition metal oxide into the positive electrode material powder, add LiOH aqueous solution and stir well, so that the molar ratio of Li/(Ni+Co+Mn) is 1.05~1.15:1, for example, 1.06:1, 1.07:1, 1.08:1, 1.09:1, 1.11:1, 1.12:1, 1.13:1, 1.14:1, preferably 1.08~1.12:1, more preferably 1.1:1. When the positive electrode material is lithium cobalt oxide, both n(Ni) and n(Mn) are 0, and n represents the amount of the substance.

The temperature of the hydrothermal reaction is 150-250°C, such as 155°C, 165°C, 175°C, 185°C, 195°C, 205°C, 215°C, 225°C, 235°C, 245°C, preferably 160-240°C, More preferably 170~230°C, most preferably 200°C.

The time of the hydrothermal reaction is 10~20h, such as 10.5h, 11h, 11.5h, 12.5h, 13.5h, 14.5h, 15.5h, 16.5h, 17.5h, 18.5h, 19.5h, preferably 10.8~19.7h , further preferably 11.2~18.8h, most preferably 15h.

The preparation of the oxides of cobalt, nickel and manganese is a prior art.

Preferably, in the step (4'), the positive electrode material powder obtained in the step (2) is mixed with the transition metal oxide lost by dissolution, and the LiOH aqueous solution is added and stirred thoroughly so that the molar ratio of Li/(Ni+Co+Mn) is 1.05~ 1.15:1, moved into a high-pressure reactor, hydrothermally reacted at 200°C for 15 hours, and used the principle of dissolution and precipitation to obtain a repaired positive electrode material. When the positive electrode material is lithium cobaltate, n(Ni) and n(Mn) are both 0, n represents the amount of substance.

Illustrative examples are as follows:

When the positive electrode material before failure is lithium cobaltate (LiCoO ₂ ), the failure mechanism of the positive electrode material is studied by SEM, XRD, STEM, XPS, EELS, ICP and other material analysis methods, and the chemical composition of the positive electrode material powder obtained in step (2) is checked , the failure mechanism is the loss of lithium. According to the composition of the positive electrode material lithium cobaltate before failure, Li ₂ CO ₃ is mixed into the positive electrode material powder obtained in step (2), and the repaired positive electrode material is obtained by sintering; the failure mechanism is lithium and cobalt According to the composition of the positive electrode material lithium cobalt oxide before failure, the cobalt salt solution and NaOH or Na ₂ CO ₃ precipitant are slowly injected into the reactor for precipitation reaction, the precipitate is filtered and washed, vacuum dried at 120°C for 8h, and then 500~ Calcined at 900℃ for 3~5h to obtain cobalt oxide. Then weigh the corresponding Li ₂ CO ₃ and the cobalt oxide and ball mill and mix the positive electrode material powder obtained in step (2), so that the Li/Co molar ratio is 1.05~1.15:1, and bake at 850°C for 10~20h to obtain the repaired positive electrode material .

When the positive electrode material before failure is lithium nickel cobalt manganese multi-layered oxide (Li(Ni _1-xy Co _x Mn _y )O ₂ ), the positive electrode is studied by SEM, XRD, STEM, XPS, EELS, ICP and other material analysis methods Material failure mechanism, check the chemical composition of the positive electrode material powder obtained in step (2), the failure mechanism is the loss of lithium, according to the composition of the positive electrode material lithium nickel cobalt manganese multi-layered oxide before failure, the positive electrode obtained in step (2) Li ₂ CO ₃ is mixed into the material powder, and the repaired positive electrode material is obtained by sintering; the failure mechanism is the loss of lithium, cobalt and nickel, and the cobalt salt and nickel The salt solution is mixed, and then the mixed solution is slowly injected into the reactor with NaOH or Na ₂ CO ₃ precipitating agent and ammonia water complexing agent to undergo co-precipitation reaction, and the precipitate is filtered and washed, vacuum-dried at 120°C for 8 hours, and then roasted at 500-900°C for 3 hours. Cobalt-nickel mixed oxide was prepared in ~5h. Then weigh the corresponding Li ₂ CO ₃ and the cobalt-nickel mixed oxide and mix them with the positive electrode material powder obtained in step (2) by ball milling, so that the molar ratio of Li/(Ni+Co+Mn) is 1.05~1.15:1, and bake at 850°C After 10~20h, a layered structure with enough lithium distributed between the transition metal oxide layers was regenerated.

When the positive electrode material before failure is lithium cobaltate (LiCoO ₂ ), the failure mechanism of the positive electrode material is studied by SEM, XRD, STEM, XPS, EELS, ICP and other material analysis methods, and the chemical composition of the positive electrode material powder obtained in step (2) is checked , the failure mechanism is the transition metal cobalt valence state transition, triggering phase transition, the layered structure is destroyed, and the dissolution loss of Co, according to the composition of the cathode material lithium cobaltate before failure, in the cathode material powder obtained in step (2) Mix in cobalt oxide, add LiOH aqueous solution and stir well so that the Li/Co molar ratio is 1.05~1.15:1, move it into a high-pressure reactor, and conduct a hydrothermal reaction at 200°C for 15 hours. Using the principle of dissolution and precipitation, a repaired positive electrode material is obtained.

When the positive electrode material before failure is lithium nickel cobalt manganese multi-layered oxide (Li(Ni _1-xy Co _x Mn _y )O ₂ ), the positive electrode is studied by SEM, XRD, STEM, XPS, EELS, ICP and other material analysis methods Material failure mechanism, check the chemical composition of the positive electrode material powder obtained in step (2), the failure mechanism is the valence transition of transition metal cobalt and/or nickel, triggering phase transition, and dissolution loss of cobalt and/or nickel, etc., according to the failure mechanism The composition of the lithium-nickel-cobalt-manganese multi-layered oxide of the former positive electrode material is mixed with cobalt and/nickel oxides in the positive electrode material powder obtained in step (2), and the LiOH aqueous solution is added to fully stir, so that Li/(Co+Ni+Mn ) with a molar ratio of 1.05~1.15:1, moved into a high-pressure reactor, and reacted hydrothermally at 200°C for 15 hours. Using the principle of dissolution and precipitation, a repaired positive electrode material was obtained.

The active material is the positive electrode material.

Compared with the prior art, the present invention has the following beneficial effects:

The invention applies the subject of material science to the field of resource recycling, studies the electrochemical performance failure mechanism and repair principle of the positive electrode material in the charging and discharging process from a microscopic perspective, and then guides the recovery and reuse technology from a macroscopic perspective, avoiding the use of acid solution to leach metal elements The process greatly reduces the emission of secondary pollutants, directly recycles and repairs the positive electrode material, avoids the subsequent separation and extraction of metal elements, and simplifies the process. Compared with the existing process technology, the process is shorter, the energy consumption is low, and the environment Friendly, and suitable for recycling lithium cobaltate and lithium nickel cobalt manganese multi-layered oxides.

Description of drawings

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation methods.

Fig. 1: technical roadmap of the present invention;

Figure 2: XRD spectrum of waste Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ cathode material obtained by NMP soaking separation;

Figure 3: XRD pattern of waste Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ positive electrode material separated by high temperature calcination;

Fig. 4: the first charging and discharging curve of the positive electrode material obtained in Repairing Example 1 at 0.1C rate;

Fig. 5: 1C rate charge-discharge cycle curve of positive electrode material obtained in Repairing Example 1;

Fig. 6: XRD spectrum of positive electrode material obtained in Repairing Example 2;

Figure 7: The first charge and discharge curve of the positive electrode material obtained in Repairing Example 2 at 0.1C rate;

Figure 8: 1C rate charge-discharge cycle curve of the positive electrode material obtained in Restoration Example 2.

detailed description

For better illustrating the present invention, facilitate understanding technical scheme of the present invention, typical but non-limiting embodiment of the present invention is as follows:

Example 1

The positive electrode material is Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ Lithium-ion batteries are disassembled, and 100 g of positive electrode sheets with a binder of PVDF are selected, soaked in NMP at 60°C, and wait for activation. The substance powder is separated from the aluminum foil current collector, filtered, washed, and vacuum dried to obtain recovered powder, and the organic solvent NMP can be recycled after being treated. Add the above powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, and dried to obtain the positive electrode material powder. The XRD spectrum is shown in Figure 2. ICP composition analysis shows that the chemical composition of the cathode material contains 7.01% lithium, 20.90% nickel, 20.80% cobalt and 19.86% manganese.

Example 2

The positive electrode material is Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ Lithium-ion batteries are disassembled, and 100g of positive electrode sheets with PTFE as the binder are selected, and the tube atmosphere is protected by N ₂ at 550°C After 3 hours of treatment in the furnace, the tail gas needs to be collected and processed. After the furnace is cooled, the positive electrode sheet is taken out, and the active material is separated from the current collector by mechanical friction. It is sieved with a 400-mesh standard sieve, and the undersieve is taken out, and separated by heavy liquid method. The XRD pattern of the positive electrode material powder is shown in Figure 3. ICP composition analysis shows that the chemical composition of the cathode material contains 6.47% lithium, 18.51% nickel, 18.73% cobalt, and 19.30% manganese.

Example 3

The XRD spectrum of positive electrode material powder recovered in Example 1 shown in Figure ₂ can be seen to correspond to the standard diffraction peak of α-NaFeO, indicating that the recovered positive electrode material powder still has a typical α _- NaFeO structure, which belongs to Space group and hexagonal crystal system. Obvious (006)/(012) and (018)/(110) split peaks can be observed in the XRD pattern, indicating that the recovered cathode material powder still has a good layered structure. Comparing its chemical composition with the theoretical composition of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ , it was found that there was a small loss of lithium content. According to the stoichiometric ratio, Li ₂ CO ₃ was weighed and mixed with recovered powder for ball milling. Li The /(Ni+Co+Mn) molar ratio is 1.1:1, and then placed in a muffle furnace at 850 °C for 10 h to repair the recycled materials. ICP composition analysis shows that the chemical composition of the repaired cathode material powder is 7.18% lithium, 20.34% nickel, 20.24% cobalt, and 19.06% manganese, which are close to the theoretical composition. The repaired positive electrode material, acetylene black and PVDF binder were uniformly mixed at a mass ratio of 85:10:5, and coated on an aluminum foil to prepare a positive electrode sheet. Vinyl carbonate (EC)-dimethyl carbonate (DMC) (volume ratio 1:1) of LiPF ₆ of the positive electrode sheet, lithium sheet, separator and electrolyte 1mol/L in the glove box of argon atmosphere solution, assembled into a CR2032 battery, and tested for charge-discharge cycle performance. In the voltage range of 2.8-4.3V (vs Li/Li ⁺ ), charge and discharge at a constant current density (0.1C) of 18mA/g. Figure 4 is the first cycle charge and discharge curve. It can be seen that the first discharge specific capacity is 160.3mAh/g, and the first discharge efficiency is 88.9%. Figure 5 is the discharge cycle performance curve at a current density (1C) of 180mA/g within the voltage range of 2.8~4.3V (vs Li/Li ⁺ ), and the charge and discharge condition is a constant current charge at a current density of 180mA/g to a voltage of 4.3 V, then charge at a constant voltage of 4.3V until the current density is less than 10mA/g, then discharge at a constant current density of 180mA/g to a voltage of 2.8V, and cycle 100 times. Affected by the ambient temperature, the specific capacity fluctuates periodically. Except for the fluctuation, the single discharge efficiency is above 99.4%. After 100 discharges, the specific capacity is 126.2mAh/g, and the capacity retention rate is 94.3%.

Example 4

The XRD spectrum of the recovered positive electrode material powder in Example 2 shown in Figure 3 shows that the recovered material is also a layered structure, but the (006) peak intensity becomes weaker, indicating that the material lattice is disordered and defective, and analysis methods such as STEM can also prove this point. The chemical composition deviates greatly from the theoretical value, some materials undergo phase transition, and the transition metals cobalt and nickel may also undergo dissolution loss. Cobalt-nickel mixed hydroxides are prepared by co-precipitation, and then roasted at 900°C to form cobalt-nickel mixed oxides. Chemical composition ratio, weigh the corresponding recycled positive electrode material powder, cobalt-nickel mixed oxide, dissolve in a certain concentration of LiOH solution, Li/(Ni+Co+Mn) molar ratio is 1.1:1, 200 ℃ hydrothermal reaction for 20h, Filter and dry to obtain the repaired positive electrode material. The XRD results shown in Figure 6 show that the (006) peak intensity becomes stronger after the hydrothermal reaction repair, and the recovered material recovers a good layered structure. According to the method described in Example 3, it was assembled into a button battery, and the electrochemical performance was tested. Figure 7 shows that in the voltage range of 2.8~4.3V (vs Li/Li ⁺ ), with a current density of 18mA/g (0.1C) Constant current charge and discharge, the first cycle charge and discharge curve, it can be seen that the first discharge specific capacity is 143.7mAh/g, and the first discharge efficiency is 78.4%.

Figure 8 is a discharge cycle performance curve at a current density (1C) of 180mA/g within the voltage range of 2.8~4.3V (vs Li/Li+), and the charge and discharge conditions are the same as in Example 3. After 100 cycles, the discharge specific capacity is 125.6mAh/g, and the capacity retention rate is 98.8%.

Example 5

The positive electrode material is lithium cobaltate (LiCoO ₂ ) lithium ion battery. After dismantling the lithium ion battery, select 100g of the positive electrode sheet whose binder is PVDF, and soak it in N, N-dimethylformamide at 80°C. It is separated from the aluminum foil current collector, filtered, washed, and vacuum-dried to obtain recovered powder, and the organic solvent N, N-dimethylformamide can be recycled after being treated. Add the above powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, and dried to obtain the positive electrode material powder. ICP composition analysis shows that the chemical composition of the cathode material contains 6.46% lithium and 61.35% cobalt. Comparing its chemical composition with the theoretical composition of LiCoO ₂ , it was found that there was a small loss of lithium content. According to the stoichiometric ratio, Li ₂ CO ₃ was weighed and mixed with the recovered positive electrode material powder for ball milling. The Li/Co molar ratio was 1.05:1, and then placed in a 750 ℃ in a muffle furnace for 20 hours to repair the recycled materials. ICP composition analysis shows that the chemical composition of the positive electrode material powder after restoration is 7.06% lithium and 59.82% cobalt, which are close to the theoretical composition.

Example 6

The positive electrode material is lithium cobaltate (LiCoO ₂ ) lithium-ion battery. After dismantling the lithium-ion battery, select 100g of the positive electrode sheet whose binder is PVDF, soak it in N, N-dimethylformamide at 70°C, and wait for the active material powder It is separated from the aluminum foil current collector, filtered, washed, and vacuum-dried to obtain recovered powder, and the organic solvent N, N-dimethylformamide can be recycled after being treated. Add the above powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, and dried to obtain the positive electrode material powder. ICP composition analysis shows that the chemical composition of the cathode material contains 6.51% lithium and 61.3% cobalt. Comparing its chemical composition with the theoretical composition of LiCoO ₂ , it was found that there was a small loss of lithium content. According to the stoichiometric ratio, Li ₂ CO ₃ was weighed and mixed with the recovered positive electrode material powder for ball milling. The Li/Co molar ratio was 1.15:1, and then placed in 950 ℃ in a muffle furnace for 10 h to repair the recycled materials. ICP composition analysis shows that the chemical composition of the positive electrode material powder after restoration is 7.05% lithium and 60.1% cobalt, which are close to the theoretical composition.

Example 7

The positive electrode material is lithium cobalt oxide (LiCoO ₂ ) lithium-ion battery. After dismantling, 100g of positive electrode sheet with PTFE as the binder is selected and treated in a tube atmosphere furnace protected by N ₂ at 500°C for 5 hours. The exhaust gas needs to be collected for treatment. After the furnace is cooled, the positive electrode sheet is taken out, the active material is separated from the current collector by mechanical friction, sieved with a 400-mesh standard sieve, and the under-sieve is taken to obtain a powder. Add the powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, and dried to obtain the positive electrode material powder. ICP composition analysis shows that the chemical composition of the cathode material contains 6.12% lithium and 56.8% cobalt. , comparing its chemical composition with the theoretical value, the transition metal cobalt has been dissolved and lost. STEM and XPS analysis showed that the layered structure was chaotic and defective, and cobalt hydroxide was prepared, and then calcined at 900°C to form cobalt. Oxide, according to the distribution ratio of the chemical composition, weigh the corresponding recovered positive electrode material powder, cobalt oxide, dissolve it in a certain concentration of LiOH solution, make the Li/Co molar ratio 1.05:1, and conduct a hydrothermal reaction at 150°C for 20h. Filter and dry to obtain the repaired positive electrode material. ICP composition analysis shows that the chemical composition of the repaired cathode material powder is 7.08% lithium and 59.9% cobalt, which are close to the theoretical composition.

Example 8

The positive electrode material is lithium cobalt oxide (LiCoO ₂ ) lithium-ion battery. After dismantling, 100g of positive electrode sheet with PTFE as the binder is selected and treated in a tube-type atmosphere furnace protected by N ₂ at 600°C for 2 hours. The tail gas needs to be collected for treatment. After the furnace is cooled, the positive electrode sheet is taken out, the active material is separated from the current collector by mechanical friction, sieved with a 400-mesh standard sieve, and the under-sieve is taken to obtain a powder. Add the powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, and dried to obtain the positive electrode material powder. ICP composition analysis shows that the chemical composition of the cathode material contains 6.11% lithium and 56.8% cobalt. Judging its failure mechanism, comparing its chemical composition with a large deviation from the theoretical value, part of the material undergoes phase transition, and the transition metal cobalt may also undergo dissolution loss, prepare cobalt hydroxide, and then roast at 900°C to form cobalt oxide. According to the distribution ratio of the chemical components, the corresponding recovered positive electrode material powder and cobalt oxide were weighed, dissolved in a certain concentration of LiOH solution, the Li/Co molar ratio was 1.15:1, and the hydrothermal reaction was carried out at 250 °C for 10 h. Filter and dry to obtain the repaired positive electrode material. ICP composition analysis shows that the chemical composition of the positive electrode material powder after restoration is 7.09% lithium and 60.0% cobalt, which are close to the theoretical composition.

Example 9

The positive electrode material is Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ Lithium-ion batteries are disassembled, and 100 g of positive electrode sheets whose binder is PVDF are selected and soaked in NMP at 80 ° C. The substance powder is separated from the aluminum foil current collector, filtered, washed, and vacuum dried to obtain recovered powder, and the organic solvent NMP can be recycled after being treated. Add the above powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, and dried to obtain the positive electrode material powder. ICP composition analysis shows that the chemical composition of the cathode material contains 7.01% lithium, 20.90% nickel, 20.80% cobalt and 19.86% manganese. Judging its failure mechanism, comparing its chemical composition with the theoretical composition of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ , it was found that there was a small loss of lithium content, and Li ₂ CO ₃ was weighed according to the stoichiometric ratio. Mix and ball mill with recycled powder, the molar ratio of Li/(Ni+Co+Mn) is 1.05:1, and then put it in a muffle furnace at 750°C for 20h to repair the recycled material. ICP composition analysis shows that the chemical composition of the repaired cathode material powder is 7.18% lithium, 20.34% nickel, 20.24% cobalt, and 19.06% manganese, which are close to the theoretical composition.

Example 10

The positive electrode material is Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ Lithium-ion batteries are disassembled, and 100 g of positive electrode sheets with a binder of PVDF are selected and soaked in NMP at 70°C. The substance powder is separated from the aluminum foil current collector, filtered, washed, and vacuum dried to obtain recovered powder, and the organic solvent NMP can be recycled after being treated. Add the above powder into water, pour it into a separatory funnel and let it stand for 30 minutes. The acetylene black conductive agent floats above the water, and the positive electrode material sinks to the bottom. The powder at the bottom is flowed out, filtered, washed, and dried to obtain the positive electrode material powder. ICP composition analysis shows that the chemical composition of the cathode material contains 7.01% lithium, 20.90% nickel, 20.80% cobalt and 19.86% manganese. Judging its failure mechanism, comparing its chemical composition with the theoretical composition of Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ , it was found that there was a small loss of lithium and cobalt content, and Li ₂ was weighed according to the stoichiometric ratio. CO ₃ , cobalt oxides and recycled cathode material powders were mixed and ball-milled with a Li/(Ni+Co+Mn) molar ratio of 1.15:1, and then placed in a muffle furnace at 950°C for 10 hours to repair the recycled materials. ICP composition analysis shows that the chemical composition of the repaired cathode material powder is 7.18% lithium, 20.34% nickel, 20.24% cobalt, and 19.06% manganese, which are close to the theoretical composition.

Example 11

The positive electrode material is Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ Lithium-ion batteries are disassembled, and 100g of positive electrode sheets with PTFE as the binder are selected, and the tube atmosphere is protected by N ₂ at 500°C After 5 hours of treatment in the furnace, the tail gas needs to be collected and processed. After the furnace is cooled, the positive electrode sheet is taken out, and the active material is separated from the current collector by mechanical friction, sieved by a 400-mesh standard sieve, and the under-sieve is taken, separated by a heavy liquid method, and the positive electrode material powder is obtained. ICP composition analysis shows that the chemical composition of the cathode material contains 6.27% lithium, 17.57% nickel, 17.76% cobalt and 17.77% manganese. Judging the failure mechanism, the chemical composition deviates greatly from the theoretical value, and the transition metal cobalt and nickel may also undergo dissolution loss. STEM and XPS analysis of it show that the layered structure appears disordered and defective. Prepare cobalt-nickel mixed hydroxides by co-precipitation, and then roast at 900°C to form cobalt-nickel mixed oxides. According to the chemical composition ratio, weigh the corresponding recovered positive electrode material powder and cobalt-nickel mixed oxides, and dissolve them in a certain concentration of LiOH solution , the molar ratio of Li/(Ni+Co+Mn) is 1.05:1, hydrothermal reaction at 150°C for 20h, filtration and drying to obtain the repaired cathode material. ICP composition analysis shows that the chemical composition of the repaired cathode material powder is 7.19% lithium, 19.28% nickel, 19.41% cobalt, and 19.01% manganese, which are close to the theoretical composition.

Example 12

The positive electrode material is Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ Lithium-ion batteries are disassembled, and 100g of positive electrode sheets with PTFE as the binder are selected, and the tube atmosphere is protected by N ₂ at 600°C After 2 hours of treatment in the furnace, the tail gas needs to be collected and processed. After the furnace is cooled, the positive electrode sheet is taken out, and the active material is separated from the current collector by mechanical friction, sieved by a 400-mesh standard sieve, and the under-sieve is taken, separated by a heavy liquid method, and the positive electrode material powder is obtained. ICP composition analysis shows that the chemical composition of the cathode material contains 6.25% lithium, 17.89% nickel, 17.45% cobalt and 17.78% manganese. Judging the failure mechanism, the chemical composition deviates greatly from the theoretical value, some materials undergo phase transitions, and the transition metals cobalt and nickel may also undergo dissolution loss, co-precipitation to prepare mixed hydroxides of cobalt and nickel, and then roasted at 900 ° C to form cobalt-nickel. Mixed oxides, according to the chemical composition distribution ratio, weigh the corresponding recovered positive electrode material powder, cobalt-nickel mixed oxide, dissolve in a certain concentration of LiOH solution, the molar ratio of Li/(Ni+Co+Mn) is 1.15:1, 250°C Hydrothermal reaction was performed for 10 hours, filtered and dried to obtain the repaired positive electrode material. ICP composition analysis shows that the chemical composition of the repaired cathode material powder is 7.15% lithium, 20.05% nickel, 20.44% cobalt, and 18.79% manganese, which are close to the theoretical composition.

The applicant declares that the present invention illustrates the detailed methods of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed methods, that is, it does not mean that the present invention must rely on the above-mentioned detailed methods to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (40)

1. a method for directly reclaiming and repairing the positive electrode material of waste lithium-ion batteries, characterized in that, the method may further comprise the steps: (1) dismantling, sorting to obtain the positive electrode material is lithium cobalt oxide or lithium nickel cobalt manganese multi-layered oxide positive electrode sheet or positive electrode sheet scraps and defective products of battery manufacturers; (2) remove binding agent successively, current collector and conductive agent, obtain positive electrode material powder; (3) Study the failure mechanism of the positive electrode material powder obtained in step (2), and check the chemical composition of the positive electrode material powder. When the failure mechanism is the loss of lithium and transition metals, proceed to step (4). When the failure mechanism is the transition metal valence state transition , triggering phase transition, when disorder and defects appear in the layered structure, step (4'); (4) According to the composition of the positive electrode material before failure, the compound of the lost metal is mixed in the positive electrode material powder obtained in step (2), and the positive electrode material obtained by sintering is repaired; (4') According to the composition of the positive electrode material before failure, the oxide of the transition metal lost is mixed in the positive electrode material powder obtained in step (2), and the LiOH aqueous solution is added to fully stir, and the hydrothermal reaction obtains the repaired positive electrode material. 2. The method according to claim 1, wherein, when the binder in the positive electrode sheet is PTFE, the pyrolysis method is used to decompose the binder, thereby realizing the separation of the positive electrode material from the current collector, and achieving the removal of the binder. The purpose of binder and current collector. 3. The method according to claim 1, characterized in that, the positive electrode sheet is roasted at high temperature under an inert atmosphere to decompose PTFE, the fired positive electrode sheet is taken out, mechanical friction separates the positive electrode material from the current collector, and sieves. The current collector present in the positive electrode material is removed to obtain a mixed powder of the positive electrode material and the conductive agent. 4. The method according to claim 3, wherein the high-temperature calcination is carried out under an inert atmosphere, and the temperature of the high-temperature calcination is 500-600°C. 5. The method according to claim 4, characterized in that the temperature of the high-temperature calcination is 500-550°C. 6. The method according to claim 4, characterized in that the time for the high-temperature calcination is 2-5 hours. 7. The method according to claim 6, characterized in that the time for the high-temperature calcination is 2.3-4.5 hours. 8. The method according to claim 7, characterized in that the time of the high-temperature calcination is 3h. 9. The method according to claim 1, characterized in that, when the binder in the positive electrode sheet is PVDF, the solvent soaking and dissolving is used to make the binder invalid, thereby realizing the separation of the positive electrode material and the current collector, and achieving the removal of the binder. The purpose of binder and current collector. 10. The method according to claim 9, characterized in that the temperature is controlled at 60-80° C. during soaking and dissolving. 11. The method according to claim 10, characterized in that the temperature is controlled at 61.5-78.5°C during soaking and dissolving. 12. The method according to claim 9, wherein the solvent is selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide or dimethylmethylene Any one or a mixture of at least two of sulfones. 13. The method of claim 12, wherein the solvent is selected from N-methylpyrrolidone. 14. The method of claim 9, wherein the solvent is reused by distillation under reduced pressure. 15. The method according to claim 1, wherein the conductive agent in the positive electrode sheet is removed by a heavy liquid separation method, filtered, washed, and dried to obtain the positive electrode material powder. 16. The method according to claim 15, wherein water is selected as the heavy liquid having a density between the conductive agent and the positive electrode material. 17. The method according to claim 15, wherein the heavy liquid separation method for removing the conductive agent in the positive electrode sheet is: adding the positive electrode material and the conductive agent mixed powder for removing the binder and current collector into water, stirring , stand still, the conductive agent with a density less than water floats above the water, the positive electrode material with a density greater than water sinks below the water, and the positive electrode material that sinks to the bottom is flowed out, filtered, and dried to obtain positive electrode material powder. 18. The method as claimed in claim 1, in the step (4), in the positive electrode material powder, the compound of the lost metal is mixed, so that the Li/(Ni+Co+Mn) molar ratio is 1.05～1.15:1, when the positive electrode material In the case of lithium cobaltate, both n(Ni) and n(Mn) are 0. 19. The method according to claim 18, characterized in that the Li/(Ni+Co+Mn) molar ratio is 1.08˜1.12:1. 20. The method of claim 19, wherein the Li/(Ni+Co+Mn) molar ratio is 1.1:1. 21. The method according to claim 1, wherein the sintering temperature is 750-950°C. 22. The method according to claim 21, characterized in that the sintering temperature is 770-930°C. 23. The method according to claim 22, characterized in that the sintering temperature is 750-870°C. 24. The method of claim 23, wherein the sintering temperature is 850°C. 25. The method according to claim 1, characterized in that the sintering time is 10-20 hours. 26. The method according to claim 25, characterized in that the sintering time is 10.8-19.7 hours. 27. The method according to claim 26, characterized in that the sintering time is 11.2-18.8 hours. 28. The method according to claim 1, characterized in that, in step (4), the compound of the lost metal is mixed into the positive electrode material powder, so that the molar ratio of Li/(Ni+Co+Mn) is 1.05～1.15:1 , 850 ° C sintering 10 ~ 20h to get repaired positive electrode material, when the positive electrode material is lithium cobalt oxide, n (Ni) and n (Mn) are both 0. 29. The method as claimed in claim 1, characterized in that, in step (4'), in the positive electrode material powder, the oxides of transition metals that are lost are mixed, and LiOH aqueous solution is added to fully stir, so that Li/(Ni+Co+Mn ) molar ratio is 1.05-1.15:1, when the positive electrode material is lithium cobaltate, both n(Ni) and n(Mn) are 0. 30. The method according to claim 29, wherein the Li/(Ni+Co+Mn) molar ratio is 1.08˜1.12:1. 31. The method of claim 30, wherein the Li/(Ni+Co+Mn) molar ratio is 1.1:1. 32. The method according to claim 1, characterized in that the temperature of the hydrothermal reaction is 150-250°C. 33. The method according to claim 32, characterized in that the temperature of the hydrothermal reaction is 160-240°C. 34. The method according to claim 33, characterized in that the temperature of the hydrothermal reaction is 170-230°C. 35. The method of claim 34, wherein the temperature of the hydrothermal reaction is 200°C. 36. The method according to claim 1, characterized in that the time of the hydrothermal reaction is 10-20 hours. 37. The method according to claim 1, characterized in that the time for the hydrothermal reaction is 10.8-19.7 hours. 38. The method according to claim 37, characterized in that the time of the hydrothermal reaction is 11.2-18.8 hours. 39. The method according to claim 38, wherein the hydrothermal reaction takes 15 hours. 40. The method as claimed in claim 1, characterized in that, in step (4'), in the positive electrode material powder, the oxides of the transition metals that are lost are mixed, and LiOH aqueous solution is added to fully stir, so that Li/(Ni+Co+Mn ) with a molar ratio of 1.05 to 1.15:1, transferred to an autoclave, and hydrothermally reacted at 200°C for 15 hours to obtain a repaired positive electrode material. When the positive electrode material is lithium cobaltate, both n(Ni) and n(Mn) are 0.