Waste paper carbon lithium battery negative electrode material and preparation method thereof, and negative electrode containing waste paper carbon lithium battery negative electrode material

Abstract

The invention provides a waste paper carbon lithium battery negative electrode material, a preparation method thereof and a negative electrode containing the waste paper carbon lithium battery negative electrode material. The method comprises the following steps: (1) crushing waste paper to obtain powdery waste paper with particles less than 1mm, soaking the powdery waste paper in alkali liquor, cleaning to remove pollutants contained in the powdery waste paper, and filtering to obtain a primary waste paper raw material; (2) cleaning the primary waste paper raw material, drying overnight, grinding to obtain clean waste paper powder, and carbonizing the clean waste paper powder at high temperature to obtain waste paper carbon; (3) mixing and fully grinding the waste paper carbon and SuperP, and then adding a binder to obtain slurry, namely the waste paper carbon lithium battery negative electrode material; a copper foil substrate is uniformly coated with the waste paper carbon lithium battery negative electrode material, and a negative electrode is obtained through high-temperature drying. The waste paper is used as the raw material for preparing the negative electrode material of the lithium ion battery, so that waste paper resources can be fully recycled, the production cost of a traditional carbonaceous negative electrode lithium ion battery can be effectively reduced, and high-value utilization of the waste paper is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a waste paper carbon lithium battery negative electrode material and a preparation method thereof, and a negative electrode containing the waste paper carbon lithium battery negative electrode material. Background Art

[0002] The world produces about 420 million tons of waste paper every year, which is equivalent to the amount of paper produced by about 8,000 trees discarded every minute. Conventional methods of waste paper disposal are landfill or incineration, which causes huge environmental pollution and waste of resources. How to effectively reuse waste paper at a high value has become the key to eliminating waste disposal in the future.

[0003] Combining waste paper disposal with the synergistic development of the currently booming lithium-ion battery industry is an ideal waste utilization strategy. Lithium-ion batteries are widely used in the field of electrochemical energy storage. As a key component of lithium-ion batteries, negative electrode materials significantly impact their overall performance. Taking new energy vehicles as an example, the most widely used negative electrode material for automotive batteries is carbon material, which has good capacity retention and excellent coulombic efficiency and will continue to play a dominant role in the future development of the battery industry. The expansion of the new energy vehicle industry has driven a surge in demand for negative electrode materials. Although mainstream graphite negative electrode materials account for 82% of the market share, their preparation relies on non-renewable coke raw materials. Finding more suitable sources of carbon materials has become key to the future development of carbon-based negative electrode lithium batteries.

[0004] Converting waste paper into carbon materials and applying them to the negative electrode of lithium-ion batteries can not only effectively treat waste paper garbage but also further reduce the production cost of lithium-ion batteries. It is a highly competitive means in the field of waste paper recycling in the future. Based on this, this application is proposed. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the prior art and provide a waste paper carbon lithium battery negative electrode material and a preparation method thereof, and a negative electrode containing the waste paper carbon lithium battery negative electrode material, which has ideal coulombic efficiency and good cycle performance in multiple cycles.

[0006] The present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a waste paper carbon lithium battery negative electrode material, comprising the following steps:

[0008] (1) crushing waste paper to obtain powdered waste paper with particles less than 1 mm, soaking the powdered waste paper in an alkaline solution and performing ultrasonic cleaning to remove pollutants contained therein, and filtering to obtain a preliminary waste paper raw material;

[0009] (2) Preliminary waste paper raw materials are ultrasonically cleaned and dried overnight, and then ground to obtain clean waste paper powder, which is then carbonized at high temperature to obtain waste paper carbon;

[0010] (3) Mixing waste paper carbon and Super P, grinding them thoroughly, and then adding a binder to obtain a slurry, which is the waste paper carbon lithium battery negative electrode material. The mass ratio of the waste paper carbon, Super P and binder is 4:3:3 or 5:2:3.

[0011] Furthermore, the alkali solution is a sodium hydroxide solution or a potassium hydroxide solution, and the alkali solution concentration is 1-1.2 mol / L.

[0012] Furthermore, the waste paper is any one of office waste A4 paper, newspapers or packaging boxes.

[0013] Furthermore, in step (2), deionized water is used for repeated ultrasonic cleaning to remove residual alkali solution, and the drying temperature is 80°C.

[0014] Furthermore, in step (2), grinding is performed using a ball mill, the ball mill speed is 1000-1400 r / min, and the grinding time is 15 min.

[0015] Furthermore, in step (2), the high-temperature carbonization is specifically: carbonization in an inert gas environment, the carbonization temperature is 700° C., the heating rate is 5° C. / min, and the carbonization time is 6 h.

[0016] Furthermore, the binder is polyvinylidene fluoride with a mass concentration of 5% using N-methylpyrrolidone as solvent.

[0017] The present invention also provides a waste paper carbon lithium battery negative electrode material prepared by the above preparation method.

[0018] The present invention also provides a negative electrode sheet containing the above-mentioned waste paper carbon lithium battery negative electrode material. The preparation of the negative electrode sheet includes the steps of: uniformly coating the waste paper carbon lithium battery negative electrode material on a copper foil substrate, and continuously drying at 80°C for 8 hours to obtain the negative electrode sheet.

[0019] The present invention has the following beneficial effects:

[0020] 1. The present invention first removes impurities from waste paper through water washing and alkali treatment, then obtains pure hard carbon material through carbonization, and composites the pure hard carbon material with conductive carbon material to form a composite carbon material to improve the conductivity of the material. The waste paper carbon lithium battery negative electrode material is obtained through appropriate proportioning and binder configuration. The assembled battery can achieve an initial coulombic efficiency of 95.43% during charge and discharge tests, and exhibits excellent high voltage stability under different rate tests, with excellent performance.

[0021] 2. The present invention uses waste paper as a raw material for preparing negative electrode materials for lithium-ion batteries. On the one hand, it can fully realize the recycling and utilization of waste paper resources. On the other hand, it can effectively reduce the production cost of traditional carbonaceous negative electrode lithium-ion batteries and realize high-value utilization of waste paper. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 This is the XRD pattern of waste paper carbon prepared in Example 2 of the present invention;

[0024] Figure 2 These are SEM images of the waste paper carbon and the powder after grinding and mixing the waste paper carbon and Super p, prepared in Example 2 of the present invention. (a) and (b) are SEM images of the waste paper carbon, and (c) and (d) are SEM images of the powder after grinding and mixing the waste paper carbon and Super p.

[0025] Figure 3 The first charge and discharge efficiency of the half-cells assembled with the waste paper carbon lithium battery negative electrode materials prepared in Example 1, Example 2, and Comparative Example 1 of the present invention, wherein (a) is Example 1, (b) is Example 2, and (c) is Comparative Example 1;

[0026] Figure 4 The battery rates of half-cells assembled with the waste paper carbon-lithium battery negative electrode materials prepared in Example 1, Example 2, and Comparative Examples 1 to 3 of the present invention at different currents;

[0027] Figure 5 Schematic diagram of 200 half-cell cycles and coulombic efficiency of half-cells assembled with waste paper carbon-lithium battery negative electrode materials prepared in Example 1, Example 2, and Comparative Examples 1 to 3 of the present invention, where (a) is under 0.05 A / g current conditions and (b) is under 1 A / g current conditions. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Example 1:

[0030] (1) Discarded A4 office paper is crushed by a pulverizer to obtain powdered waste paper with particles less than 1 mm, the powdered waste paper is soaked in a 1 mol / L sodium hydroxide solution with water as a solvent, and the pollutants contained therein are removed by ultrasonic cleaning, and the preliminary waste paper raw material is obtained after filtering;

[0031] (2) The preliminary waste paper raw material was repeatedly ultrasonically cleaned three times with deionized water to remove residual sodium hydroxide, and the obtained raw material was placed in a high-temperature oven and dried overnight at 80°C; the dried raw material was passed through a ball mill (the ball mill speed was 1000-1400 r / min) for 15 minutes to obtain clean waste paper powder; a carbonization furnace with a nitrogen atmosphere was used, the carbonization temperature was set to 700°C, the heating rate was 5°C / min, and the time was 6 hours, and the clean waste paper powder was carbonized at high temperature to obtain waste paper carbon (WPC);

[0032] (3) After the waste paper carbon and Super P were mixed and ground thoroughly, a 5% polyvinylidene fluoride (PVDF) solution prepared with N-methylpyrrolidone (NMP) as a solvent was added. The ratio of waste paper carbon, Super P, and 5% PVDF was 4:3:3 to obtain a slurry, which was recorded as slurry 1.

[0033] (4) The slurry 1 was evenly coated on a 4.5 μm copper foil substrate using a 200 μm four-sided coating machine and dried in a forced air drying oven at 80° C. for 8 h to obtain the negative electrode 1.

[0034] Example 2:

[0035] (1) Discarded A4 office paper is crushed by a pulverizer to obtain powdered waste paper with particles less than 1 mm, the powdered waste paper is soaked in a 1 mol / L sodium hydroxide solution with water as a solvent, and the pollutants contained therein are removed by ultrasonic cleaning, and the preliminary waste paper raw material is obtained after filtering;

[0036] (2) The preliminary waste paper raw material was repeatedly ultrasonically cleaned three times with deionized water to remove residual sodium hydroxide, and the obtained raw material was placed in a high-temperature oven and dried overnight at 80°C; the dried raw material was passed through a ball mill (the ball mill speed was 1000-1400 r / min) for 15 minutes to obtain clean waste paper powder; a carbonization furnace with a nitrogen atmosphere was used, the carbonization temperature was set to 700°C, the heating rate was 5°C / min, and the time was 6 hours, and the clean waste paper powder was carbonized at high temperature to obtain waste paper carbon (WPC);

[0037] (3) After the waste paper carbon and Super P were mixed and ground thoroughly, a 5% polyvinylidene fluoride (PVDF) solution prepared with N-methylpyrrolidone (NMP) as a solvent was added. The ratio of waste paper carbon, Super P, and 5% PVDF was 5:2:3 to obtain a slurry, which was recorded as slurry 2.

[0038] (4) Slurry 2 was evenly coated on a 4.5 μm copper foil substrate using a 200 μm four-sided coating machine and dried in a forced air drying oven at 80° C. for 8 h to obtain negative electrode 2.

[0039] Comparative Example 1:

[0040] (1) Discarded A4 office paper is crushed by a pulverizer to obtain powdered waste paper with particles less than 1 mm, the powdered waste paper is soaked in a 1 mol / L sodium hydroxide solution with water as a solvent, and the pollutants contained therein are removed by ultrasonic cleaning, and the preliminary waste paper raw material is obtained after filtering;

[0041] (2) The preliminary waste paper raw material was repeatedly ultrasonically cleaned three times with deionized water to remove residual sodium hydroxide, and the obtained raw material was placed in a high-temperature oven and dried overnight at 80°C; the dried raw material was passed through a ball mill (the ball mill speed was 1000-1400 r / min) for 15 minutes to obtain clean waste paper powder; a carbonization furnace with a nitrogen atmosphere was used, the carbonization temperature was set to 700°C, the heating rate was 5°C / min, and the time was 6 hours, and the clean waste paper powder was carbonized at high temperature to obtain waste paper carbon (WPC);

[0042] (3) After the waste paper carbon and Super P were mixed and ground thoroughly, a 5% polyvinylidene fluoride (PVDF) solution prepared with N-methylpyrrolidone (NMP) as a solvent was added. The ratio of waste paper carbon, Super P, and 5% PVDF was 6:1:3 to obtain a slurry, which was recorded as slurry 3.

[0043] (4) The slurry 3 was evenly coated on a 4.5 μm copper foil substrate using a 200 μm four-sided preparation device and dried in a forced air drying oven at 80° C. for 8 h to obtain the negative electrode 3.

[0044] Comparative Example 2:

[0045] (1) Discarded A4 office paper is crushed by a pulverizer to obtain powdered waste paper with particles less than 1 mm, the powdered waste paper is soaked in a 1 mol / L sodium hydroxide solution with water as a solvent, and the pollutants contained therein are removed by ultrasonic cleaning, and the preliminary waste paper raw material is obtained after filtering;

[0046] (2) The preliminary waste paper raw material was repeatedly ultrasonically cleaned three times with deionized water to remove residual sodium hydroxide, and the obtained raw material was placed in a high-temperature oven and dried overnight at 80°C; the dried raw material was passed through a ball mill (the ball mill speed was 1000-1400 r / min) for 15 minutes to obtain clean waste paper powder; a carbonization furnace with a nitrogen atmosphere was used, the carbonization temperature was set to 700°C, the heating rate was 5°C / min, and the time was 6 hours, and the clean waste paper powder was carbonized at high temperature to obtain waste paper carbon (WPC);

[0047] (3) Adding a 5% polyvinylidene fluoride (PVDF) solution prepared with N-methylpyrrolidone (NMP) as a solvent to the waste paper carbon, the ratio of waste paper carbon to 5% PVDF is 7:3, to obtain a slurry, which is recorded as slurry 4;

[0048] (4) The slurry 4 was evenly coated on a 4.5 μm copper foil substrate using a 200 μm four-sided preparation device, and dried in a forced air drying oven at 80° C. for 8 h to obtain the negative electrode 4.

[0049] Comparative Example 3:

[0050] (1) Discarded A4 office paper is crushed by a pulverizer to obtain powdered waste paper with particles less than 1 mm, the powdered waste paper is soaked in a 1 mol / L sodium hydroxide solution with water as a solvent, and the pollutants contained therein are removed by ultrasonic cleaning, and the preliminary waste paper raw material is obtained after filtering;

[0051] (2) The preliminary waste paper raw material was repeatedly ultrasonically cleaned three times with deionized water to remove residual sodium hydroxide, and the obtained raw material was placed in a high-temperature oven and dried overnight at 80°C; the dried raw material was passed through a ball mill (the ball mill speed was 1000-1400 r / min) for 15 minutes to obtain clean waste paper powder; a carbonization furnace with a nitrogen atmosphere was used, the carbonization temperature was set to 700°C, the heating rate was 5°C / min, and the time was 6 hours, and the clean waste paper powder was carbonized at high temperature to obtain waste paper carbon (WPC);

[0052] (3) After the waste paper carbon and Super P were mixed and ground thoroughly, a 5% polyvinylidene fluoride (PVDF) solution prepared with N-methylpyrrolidone (NMP) as a solvent was added. The ratio of waste paper carbon, Super P, and 5% PVDF was 3:4:3 to obtain a slurry, which was recorded as slurry 5.

[0053] (4) The slurry 5 was evenly coated on a 4.5 μm copper foil substrate using a 200 μm four-sided coating machine and dried in a forced air drying oven at 80° C. for 8 h to obtain the negative electrode 5.

[0054] Performance test analysis:

[0055] The waste paper carbon obtained in step (2) of Example 2 was subjected to X-ray diffraction analysis, and the results are shown in FIG. Figure 1 It can be seen from the XRD spectrum that no diffraction signals other than carbon materials appear in the spectrum signal, which shows the singleness of the obtained carbon material; the (002) crystal plane diffraction peak position of XRD is at 24.02° and it appears as a broadband, which shows that the raw carbon composition is mainly hard carbon. According to the crystal plane diffraction peak position, it can be calculated that the carbon atomic layer spacing is about 0.37nm.

[0056] In this scheme, the waste paper raw materials can be effectively removed from most of the insoluble impurities such as ink and dust after ultrasonic water washing and alkaline washing, and most of the soluble inorganic salts or metal ions therein can be effectively removed through strong alkaline reaction. The waste paper carbon obtained by subsequent carbonization in a nitrogen atmosphere is a pure carbon material.

[0057] The waste paper carbon obtained in step (2) of Example 2 and the powder obtained by grinding and mixing the waste paper carbon and Superp in step (3) were analyzed by SEM electron microscope. The results are as follows: Figure 2 As shown, Figure 2 Figures (a) and (b) are scanning electron microscope images of waste paper raw materials after carbonization. It can be seen from the figure that the fiber structure of the original waste paper is retained inside the carbon powder. The large area of ​​pores composed of fine fibers can provide a large number of lithium ion storage sites to effectively increase the battery capacity: Figure 2 Figures (c) and (d) are microscopic electron microscope images of the composite conductive carbon. It can be seen that after the conductive carbon material SuperP is fully mixed with the waste paper carbon, a good conductive network structure is formed and the pore network formed by the pure waste paper carbon is optimized, further increasing the lithium ion storage sites.

[0058] The negative electrodes 1, 2, 3, 4, and 5 were cut using 10mm electrode scissors to obtain negative electrode sheets with uniform texture. The active material loading of different electrodes was recorded and calculated using an analytical balance. The active material mass was calculated by subtracting the weight of the current collector copper foil of the same area from the weight of the dried electrode sheet and taking the carbon material and the conductive carbon material as the active material ratio. The active material mass was calculated using the ratio scheme adopted in this scheme, that is, (total weight - copper foil weight) * 0.7 = active material mass. It was calculated that the active material masses on the negative electrodes 1, 2, 3, 4, and 5 were 0.57 mg, 0.64 mg, 0.71 mg, 0.74 mg, and 0.51 mg, respectively.

[0059] The above-mentioned negative electrode sheet was used as the negative electrode, the electrolyte was 1.0M LiPF6 dissolved in EC:DEC:EMC (1:1:1VOL%) and 1.0%VC mixed electrolyte, the positive electrode was a 14mm lithium sheet, and it was packaged with a 2032 button battery to prepare half-cells.

[0060] The charge and discharge tests of different half-cells, the battery rate tests at different currents, 200 half-cell cycles at 0.05A / g and 1A / g currents and the coulombic efficiency are shown in the following table. Figure 3 、 4 , 5:

[0061] Figure 3 The first three charge-discharge cycles of electrodes prepared with slurries 1-3 show discharge capacities of 516.3, 590.6, and 335.1 mAh / g, respectively, in Figures (a), (b), and (c). Clear charge-discharge plateaus demonstrate the battery's voltage stability during charge and discharge, allowing for a preliminary comparison of the optimal slurry ratio. The first-cycle Coulombic efficiencies for all three ratios are >95%, demonstrating good charge-discharge reversibility.

[0062] Figure 4 The following are rate diagrams of electrodes prepared from slurries 1-5 at different charge and discharge currents. The capacity and stability of the electrodes were tested by adjusting the current. A comparison shows that the slurry with a 5:2:3 ratio exhibits the best capacity and stability at different currents. However, the electrode prepared from Comparative Example 1 exhibits poor rate and stability performance due to the excessive amount of active material, which leads to electrode expansion and excessive electrode particulate matter. This leads to partial disconnection of the internal conductive network during rolling of the electrode during electrode preparation, forming an electrode dead zone.

[0063] Figure 5 It can be seen that the capacity difference of the half-cell composed of electrodes 1 and 2 is less than 1.5% at any stable voltage and it can still maintain a good capacity performance of >500mAh / g at a high current (1A / g). After charging and discharging at different currents and returning to 0.05A / g, the battery still maintains a capacity close to the initial performance, indicating that the lithium ion insertion and extraction in the electrode is good during the charge and discharge process, and no large amount of lithium loss occurs.

[0064] The present invention adopts a high-temperature carbonization process to carbonize the treated waste paper raw materials to obtain preliminary carbon materials. After verification, it is proved that the main component of the obtained carbon material is hard carbon. Compared with traditional graphite negative electrode lithium batteries, hard carbon has more and wider nanopores and larger interlayer spacing (d-spacing), which reduces the resistance of lithium ions to embedding / ejecting in the material. Also thanks to its open nanopore structure and larger interlayer spacing, lithium ions can be embedded and extracted more quickly. The voltage platform of hard carbon is higher than the lithium deposition point (~0V vs.Li+ / Li). Under fast charging or low temperature conditions, even if the voltage drops rapidly, it is less likely to reach the critical potential for lithium metal precipitation, greatly reducing the risk of dendrite growth due to lithium precipitation, internal short circuit and even thermal runaway. The hard carbon material obtained by carbonization is mixed with SuperP and PVDF binder in a suitable ratio to prepare a negative electrode, which is made of Figure 2 The electron microscope image shows that the hard carbon and SuperP have good dispersion and compatibility; the working potential of the hard carbon negative electrode is close to 0V (vs.Li + / Li), PVDF is extremely stable at this low potential and will not undergo reduction decomposition, thus avoiding electrode structure damage and side reactions caused by binder failure. It also has good tolerance to the electrolyte used in this scheme and is not prone to swelling or degradation in long-term circulation.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a waste paper carbon lithium battery negative electrode material, characterized in that: The following steps are involved: (1) crushing waste paper to obtain powdered waste paper with particles less than 1 mm, soaking the powdered waste paper in an alkaline solution and performing ultrasonic cleaning to remove pollutants contained therein, and filtering to obtain a preliminary waste paper raw material; (2) Preliminary waste paper raw materials are ultrasonically cleaned and dried overnight, and then ground to obtain clean waste paper powder, which is then carbonized at high temperature to obtain waste paper carbon; (3) Mixing waste paper carbon and SuperP, grinding them thoroughly, and then adding a binder to obtain a slurry, which is the waste paper carbon lithium battery negative electrode material. The mass ratio of the waste paper carbon, SuperP and binder is 4:3:3 or 5:2:

3.

2. The method for preparing the waste paper carbon lithium battery negative electrode material according to claim 1, characterized in that: The alkali solution is a sodium hydroxide solution or a potassium hydroxide solution, and the concentration of the alkali solution is 1-1.2 mol / L.

3. The method for preparing the waste paper carbon lithium battery negative electrode material according to claim 1, characterized in that: The waste paper is any one of office discarded A4 paper, newspapers or packaging boxes.

4. The method for preparing a waste paper carbon lithium battery negative electrode material according to claim 1, wherein: In step (2), deionized water is used for repeated ultrasonic cleaning to remove residual alkali solution, and the drying temperature is 80°C.

5. The method for preparing the waste paper carbon lithium battery negative electrode material according to claim 1, characterized in that: In step (2), grinding is performed using a ball mill with a rotation speed of 1000-1400 r / min and a grinding time of 15 min.

6. The method for preparing a waste paper carbon lithium battery negative electrode material according to claim 1, wherein: In step (2), the high-temperature carbonization is specifically: carbonization in an inert gas environment, the carbonization temperature is 700° C., the heating rate is 5° C. / min, and the carbonization time is 6 h.

7. The method for preparing a waste paper carbon lithium battery negative electrode material according to claim 1, characterized in that: The binder is polyvinylidene fluoride with a mass concentration of 5% using N-methylpyrrolidone as a solvent.

8. A waste paper carbon lithium battery negative electrode material prepared by the preparation method according to any one of claims 1 to 7.

9. A negative electrode comprising the waste paper carbon lithium battery negative electrode material according to claim 8, characterized in that: The preparation of the negative electrode comprises the following steps: uniformly coating the waste paper carbon lithium battery negative electrode material on a copper foil substrate, and continuously drying at 80° C. for 8 hours to obtain the negative electrode.

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