Controllable molecular weight oxidized lignin modified phenol-formaldehyde resin-based hard carbon and preparation method and application thereof

Abstract

The application discloses controllable molecular weight oxidized lignin modified phenolic resin based hard carbon and a preparation method and application thereof, and belongs to the technical field of sodium ion negative electrode hard carbon material production. Oxidized lignin and phenolic prepolymer are copolymerized to obtain oxidized lignin phenolic resin, and the oxidized lignin phenolic resin is subjected to curing and high-temperature carbonization treatment to prepare oxidized lignin modified phenolic resin based hard carbon. The application utilizes the depolymerization effect of alkaline hydrogen peroxide oxidation, controls the exposure degree of active functional groups in the process of lignin oxidation pretreatment and lignin and phenolic resin copolymerization, realizes the controllable molecular weight directional regulation of lignin and phenolic resin, and solves the problems of poor storage performance caused by the change of process parameters during the control and regulation of the properties of lignin molecular structure and phenolic resin thermal bonding into hard carbon, and toxic synthesis process.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of sodium ion negative electrode hard carbon material production, more specifically, relates to an oxidized lignin modified phenolic resin based hard carbon with controllable molecular weight and a preparation method and application thereof. BACKGROUND

[0002] Hard carbon has been favored by domestic and foreign researchers and battery enterprises in recent years due to its excellent practicability and high energy density, and is expected to be used in the fields of energy storage systems, mobile power sources and home appliance markets. Hard carbon has reversible sodium storage capacity and low charge-discharge potential, which can endow SIB with high energy density. Different precursors make the sodium storage performance of hard carbon as a sodium ion negative electrode material have great differences, including initial coulombic efficiency (ICE), carbon yield and cycle stability and other electrochemical properties. Phenolic resin is a hard carbon precursor that can produce high-purity carbon, and relevant literature reported that it has good application prospect.

[0003] Benefiting from the high carbon content and adjustable chemical structure of phenolic resin and the mature commercial production technology, phenolic resin is considered to be one of the most promising precursors for commercial sodium storage. The hard carbon prepared from phenolic resin has a low specific surface area and a greater low potential platform capacity. The phenolic resin based hard carbon has the shortcomings of low initial coulombic efficiency, limited cycle capacity and toxicity in the synthesis process.

[0004] Specifically, lignin and its derivatives have abundant groups such as methoxy, phenolic, hydroxyl and aldehyde groups. At the same time, phenolic hydroxyl is a necessary structure in the synthesis process of phenolic resin, and lignin, as a green and sustainable biomass raw material, can replace the toxic components in the synthesis process of phenolic resin. Lignin is the second highest content natural polymer in biomass, and occupies an important position in the energy market dominated by hard carbon negative electrode materials due to its green environmental protection and renewability. However, due to the large molecular weight and complex structure of lignin, these groups are also occupied by inter-unit connections. If lignin is directly added to phenolic resin for physical mixing, not only the phenolic resin cannot be completely mixed and directly cured, but also the reaction uniformity is greatly reduced, and the carbon yield in the high-temperature pyrolysis process will be reduced instead of increased. In the acid pulping process in the pulp and papermaking process, more sodium lignosulfonate by-products are produced. The sulfonate group in the sulfonate lignin has good hydrophilicity, and when considering the selection of lignin categories for chemical reactions, sodium lignosulfonate is a very good choice. Although some lignin materials have achieved some research in the laboratory stage, their sodium storage performance still cannot meet the requirements of industrial application of SIB. SUMMARY

[0005] In view of the above problems existing in the prior art, the technical problems to be solved by the present application are to provide a preparation method of oxidized lignin modified phenolic resin based hard carbon with controllable molecular weight, to realize the directional regulation of the controllable molecular weight of lignin and phenolic resin by regulating the exposure degree of active functional groups in the lignin oxidation pretreatment and the lignin and phenolic resin copolymerization process through the depolymerization of alkaline hydrogen peroxide oxidation, to provide another technical problem to be solved by the present application, and to provide the oxidized lignin modified phenolic resin based hard carbon prepared by the above method, which is more beneficial to the sodium ion battery negative electrode material to exhibit stable and excellent electrochemical performance.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present application are as follows:

[0007] A preparation method of oxidized lignin modified phenolic resin based hard carbon with controllable molecular weight, lignin and phenolic prepolymer are copolymerized to obtain oxidized lignin phenolic resin, and the oxidized lignin phenolic resin based hard carbon is prepared through curing and high temperature carbonization treatment; wherein the oxidized lignin is prepared by oxidizing and degrading lignin with H2O2 and composite alkali, and the directional regulation of the controllable molecular weight of lignin is realized by regulating the oxidation temperature, oxidation time and the addition amount of H2O2 and composite alkali.

[0008] As a preferred, the mass ratio of the oxidized lignin and the phenolic prepolymer is 1:1-50.

[0009] As a preferred, the preparation process of the oxidized lignin is that lignin is dispersed into deionized water, H2O2 and composite alkali are added, and oxidized degradation is carried out to prepare the oxidized lignin.

[0010] As a preferred, the lignin is selected from any one of enzymatic lignin, sulfonate lignin, sulfate lignin and hydrolyzed lignin.

[0011] As a preferred, the preparation method of the phenolic prepolymer is that phenol and barium hydroxide are dissolved in distilled water under the condition of 75 DEG C, and formaldehyde is added in batches, and then the temperature is gradually increased to 83 DEG C for 2h.

[0012] As a preferred, the phenolic prepolymer in the lignin phenolic resin copolymerization stage is any one of thermosetting type and thermoplastic type.

[0013] As a preferred, the mL / g / mL / g of the phenol, barium hydroxide, distilled water and formaldehyde is 50:3:5:24.

[0014] As a preferred, the g / mL of the lignin and deionized water is 1:0-1:4, and the addition amount of H2O2 is 0-8g.

[0015] As preferred, the oxidation temperature is 20-80℃, and the oxidation time is 0-3h.

[0016] As preferred, the composite alkali is selected from any two of ammonia, sodium hydroxide, barium hydroxide, calcium hydroxide, and potassium hydroxide in a ratio of 1:1, and the composite alkali is added in an amount of 0-7.5g.

[0017] As preferred, the copolymerization temperature is 30-85℃, and the copolymerization time is 0.5-2.5h.

[0018] The preparation method of the oxidized lignin modified phenolic resin based hard carbon with controllable molecular weight comprises the following steps:

[0019] (1) lignin is dispersed in deionized water, H2O2 and composite alkali are added, and oxidative degradation is performed to obtain solution A;

[0020] (2) phenol and barium hydroxide are dissolved in distilled water under the condition of 75℃, and formaldehyde is added in batches, and the temperature is gradually increased to 83℃ for reaction to obtain solution B;

[0021] (3) solution A is added to solution B, and stirring is performed at 80℃ to obtain oxidized lignin phenolic resin; the oxidized lignin phenolic resin is solidified into a hard solid state, and after crushing, ball milling and screening, oxidized lignin phenolic resin powder is obtained;

[0022] (4) the oxidized lignin phenolic resin powder prepared in step (3) is carbonized, washed with HCl aqueous solution and distilled water until neutral, dried, and placed in a tube furnace in an argon atmosphere for high-temperature structural reforming at 1300℃ to obtain oxidized lignin phenolic resin based hard carbon.

[0023] As preferred, the concentration of the HCl aqueous solution is 1 mol / L.

[0024] The preparation method of the oxidized lignin modified phenolic resin based hard carbon with controllable molecular weight can prepare oxidized lignin phenolic resin based hard carbon.

[0025] The oxidized lignin phenolic resin based hard carbon is applied to a sodium ion battery negative electrode material.

[0026] Compared with the prior art, the present application has the following beneficial effects:

[0027] 1) The present application utilizes the depolymerization effect of alkaline hydrogen peroxide oxidation, and realizes the controllable molecular weight and directional regulation of lignin and phenolic resin by only regulating the exposure degree of active functional groups in the lignin oxidation pretreatment and the lignin and phenolic resin copolymerization process, which solves the problems of complex lignin molecular structure, difficult reaction active site, toxic phenolic resin synthesis process, and poor carbon storage performance of the phenolic resin before modification.

[0028] 2) The present application utilizes lignin pretreatment to modify phenolic resin raw materials to prepare hard carbon, which has excellent sodium storage performance and low toxicity compared to traditional phenolic resin-based hard carbon preparation methods. Lignin can be quickly degraded to a controllable molecular weight range (molecular weight Mn: 500 or less) at 40℃ under normal pressure, and the generation of toxic free formaldehyde and gas is reduced during the subsequent synthesis of lignan phenolic resin and the pyrolysis of hard carbon; the physicochemical properties of the modified phenolic resin precursor by oxidized lignin are changed, thereby increasing the interlayer spacing of the phenolic resin-based hard carbon, reducing the specific surface area, and increasing the micropore area, so that the phenolic resin-based hard carbon is more conducive to the sodium ion battery negative material to exhibit stable and excellent electrochemical performance;

[0029] 3) The modified phenolic resin hard carbon structure has higher disorder degree and a little microporous structure, which is more conducive to the sodium ion battery negative material to exhibit stable and excellent electrochemical performance;

[0030] 4) The method of the present application is simple to operate and has low energy consumption, and does not require high requirements for the original equipment. It also has reference significance for other types of oxidized modification methods for preparing biomass phenolic resin-based hard carbon. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 XRD patterns of LPRC in Comparative Example 1, PR, LS and OLPRC in Example 23;

[0032] Figure 2 GPC chromatograms and molar mass distribution diagrams of LPR, LS, PR, OLPR and OLS in Example 23; wherein (a) is the GPC chromatogram, and (b) is the molar mass distribution diagram;

[0033] Figure 3 GCS curve diagram of 0.05 Ag -1 ; wherein (a) is the GCD curve diagram of the first three cycles of OLPRC under 0.05 Ag -1 ; and (b) is the GCD curve diagram of the second cycle of all samples under 0.05 Ag 1 . DETAILED DESCRIPTION

[0034] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described below in combination with specific examples. Unless otherwise specified, the technical means used in the following examples are conventional means known to those skilled in the art. If no specific conditions are specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If no manufacturer of the reagent or instrument is specified, it is a conventional product that can be purchased on the market.

[0035] In the present application, phenolic resin is referred to as PR (Phenolic Resin); lignin is referred to as LS (Oxidised lignin); lignin phenolic resin is referred to as LPR (Lignin Phenolic Resin); oxidised lignin phenolic resin is referred to as OLPR (Oxidised Lignin Phenolic Resin); lignin phenolic resin carbon is referred to as LPRC (Lignin phenolic resin hard carbon); oxidised lignin phenolic resin carbon is referred to as OLPRC (Oxidised Lignin phenolic resin hard carbon).

[0036] The test method used in the present application is as follows:

[0037] 1. Molecular structure property test

[0038] X-ray diffraction (XRD) is used to analyze the structure of the hard carbon, with a scan speed of 5° / min; the molecular weight of the sample (GPC) is tested using waters1525 & Agilent PL-GPC220, with water and chloroform as solvents.

[0039] 2. Battery performance test (discharge specific capacity (mAh g -1 ) and initial efficiency)

[0040] 2.1 Battery production

[0041] Preparation of the electrode: the hard carbon material, conductive agent (super-P) and binder (PVDF) are mixed in a mass ratio of 7:1:1, and a slurry is prepared using NMP as a dispersant, the slurry is coated on a copper foil and dried in a forced air drying oven at 80°C for 12h. The dried electrode sheet is punched into a circular electrode sheet with a diameter of 15mm for standby use.

[0042] Assembly of button-type half-cell: the battery assembly is carried out in an argon glove box with a water content and oxygen content of less than 0.01ppm, a battery shell of CR2032 specification is used, the electrolyte is 1mol / L NaPF6 (solvent is a mixed solution of ethylene carbonate: dimethyl carbonate: methyl ethyl carbonate in a volume ratio of 1:1:1), a metal sodium sheet is used as both the counter electrode and the reference electrode, and the separator is a GF / D glass fiber separator. The battery is assembled in the order of positive shell, electrode sheet, separator, sodium sheet, gasket, spring and negative shell from bottom to top.

[0043] 2.2 Performance test

[0044] Constant current charge and discharge test (GCD) is tested on CT-4008Tn battery detection system.

[0045] Comparative Example 1

[0046] 1) Preparation of Solution B

[0047] Dissolve 50 mL of phenol and 3 g of barium hydroxide in 5 mL of distilled water, add 24 g of formaldehyde in batches, and then gradually warm to 83°C for 2 h to obtain Solution B.

[0048] 2) Preparation of Lignin Phenol-Formaldehyde Resin Powder

[0049] Take 5 g of lignin and add it to Solution B, mechanically stir at 80°C for 2 h, and then place it in an oven at 130°C to solidify the lignin phenol-formaldehyde resin into a hard solid state. After crushing, ball milling, and sieving, collect the lignin phenol-formaldehyde resin powder sample.

[0050] 3) Preparation of Lignin Phenol-Formaldehyde Resin Carbon

[0051] First, carbonize the lignin phenol-formaldehyde resin powder sample (2 h at 400°C in a tube furnace), then boil and wash it with 1 mol / L aqueous HCl solution, and then wash it with distilled water until it is neutral and dry. Place it in a tube furnace under an argon atmosphere, and perform high-temperature structural reforming at 1300°C to obtain lignin phenol-formaldehyde resin carbon.

[0052] The following Examples 1-4 are examples of preparing oxidized lignin-modified phenol-formaldehyde resin-based hard carbon by varying the amount of deionized water added.

[0053] Example 1

[0054] 1) Preparation of Solution A

[0055] Disperse 5 g of lignin in 5 mL of deionized water, then add 1 g of 30 wt.% H2O2 and 1 g of a composite base (sodium hydroxide:ammonia water = 1:1, mass ratio, the same below), and then oxidize and degrade at 30°C for 0.5 h to obtain Solution A.

[0056] 2) Preparation of Solution B

[0057] Dissolve 50 mL of phenol and 3 g of barium hydroxide in 5 mL of distilled water at 75°C, add 24 g of formaldehyde in batches, and then gradually warm to 83°C for 2 h to obtain Solution B.

[0058] 3) Preparation of Oxidized Lignin Phenol-Formaldehyde Resin Powder

[0059] Add Solution A to Solution B, mechanically stir at 80°C for 2 h. Then place it in an oven at 130°C to solidify the oxidized lignin phenol-formaldehyde resin into a hard solid state, and after crushing, ball milling, and sieving, collect the sample.

[0060] 4) Preparation of oxidized lignin-modified phenol-formaldehyde resin hard carbon

[0061] First, the oxidized lignin phenol-formaldehyde resin powder was carbonized (400°C for 2h, tube furnace), then washed by boiling with 1 mol / L HCl aqueous solution, and washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace under argon atmosphere for high-temperature structural reorganization at 1300°C to obtain the oxidized lignin-modified phenol-formaldehyde resin hard carbon.

[0062] Example 2

[0063] 5g of lignin was dispersed in 10 mL of deionized water, 1g of 30wt.% H2O2 and 1g of composite alkali (sodium hydroxide:ammonia water = 1:1) were added, and then oxidized and degraded at 30°C for 0.5h to obtain solution A. The subsequent steps were the same as in Example 1.

[0064] Example 3

[0065] 5g of lignin was dispersed in 15 mL of deionized water, 1g of 30wt.% H2O2 and 1g of composite alkali (sodium hydroxide:ammonia water = 1:1) were added, and then oxidized and degraded at 30°C for 0.5h to obtain solution A. The subsequent steps were the same as in Example 1.

[0066] Example 4

[0067] 5g of lignin was dispersed in 20 mL of deionized water, 1g of 30wt.% H2O2 and 1g of composite alkali (sodium hydroxide:ammonia water = 1:1) were added, and then oxidized and degraded at 30°C for 0.5h to obtain solution A. The subsequent steps were the same as in Example 1.

[0068] The molecular structure properties and battery performance of the samples prepared in the above Comparative Example 1 and Examples 1-4 were tested, and the test results are shown in Table 1. The optimal amount of deionized water added is 10 mL, that is, lignin:deionized water is 1:2 (g / mL, same below).

[0069] Table 1 Sodium storage performance of oxidized lignin-modified phenol-formaldehyde resin hard carbon with different amounts of deionized water added

[0070]

[0071]

[0072] The following Examples 5-8 are examples of preparing oxidized lignin-modified phenol-formaldehyde resin-based hard carbon by changing the amount of composite alkali added (the composite alkali is any two of the above preferred ones, and the following examples use sodium hydroxide and ammonia water as examples).

[0073] Example 5

[0074] 1) Preparation of solution A

[0075] 5 g of lignin was dispersed in 10 mL of deionized water, 1 g of 30 wt.% H2O2, 0 g of composite alkali (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 30°C for 0.5 h to obtain solution A.

[0076] 2) Preparation of solution B

[0077] 50 mL of phenol and 3 g of barium hydroxide were dissolved in 5 mL of distilled water at 75°C, 24 g of formaldehyde was added in batches, and then gradually heated to 83°C for 2 h to obtain solution B.

[0078] 3) Preparation of oxidized lignin phenolic resin powder

[0079] Solution A was added to solution B and mechanically stirred at 80°C for 2 h. Then it was placed in an oven at 130°C to solidify the oxidized lignin phenolic resin into a hard solid state, and after crushing, ball milling and sieving, the sample was collected.

[0080] 4) Preparation of oxidized lignin modified phenolic resin hard carbon

[0081] The oxidized lignin phenolic resin powder was first carbonized (400°C for 2 h in a tube furnace), then boiled and washed with 1 mol / L HCl aqueous solution, and then washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace under argon atmosphere for high temperature structural reorganization at 1300°C to obtain oxidized lignin modified phenolic resin hard carbon.

[0082] Example 6

[0083] 5 g of lignin was dispersed in 10 mL of deionized water, 1 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as in Example 5.

[0084] Example 7

[0085] 5 g of lignin was dispersed in 10 mL of deionized water, 1 g of 30 wt.% H2O2, 5 g of composite alkali (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as in Example 5.

[0086] Example 8

[0087] 5 g of lignin was dispersed in 10 mL of deionized water, 1 g of 30 wt.% H2O2, 7.5 g of composite alkali (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as in Example 5.

[0088] The molecular structural properties and battery performance of the samples prepared in Comparative Example 1 and Examples 2, 5-8 were tested, and the test results are shown in Table 2. The optimal amount of added composite base is 2.5 g.

[0089] Table 2 Sodium storage performance of oxidized lignin modified phenol-formaldehyde resin hard carbon with different amounts of added composite base

[0090]

[0091] Examples 9-16 below are examples of preparing oxidized lignin modified phenol-formaldehyde resin based hard carbon with varying amounts of added H2O2.

[0092] Example 9

[0093] 1) Preparation of Solution A

[0094] 5 g of lignin was dispersed in 10 mL of deionized water, 0 g of 30 wt.% H2O2, 2.5 g of composite base (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 30°C for 0.5 h to obtain Solution A.

[0095] 2) Preparation of Solution B

[0096] 50 mL of phenol and 3 g of barium hydroxide were dissolved in 5 mL of distilled water at 75°C, 24 g of formaldehyde was added in batches, and then gradually heated to 83°C for 2 h to obtain Solution B.

[0097] 3) Preparation of oxidized lignin phenol-formaldehyde resin

[0098] Solution A was added to Solution B and mechanically stirred at 80°C for 2 h. The oxidized lignin phenol-formaldehyde resin was then placed in an oven at 130°C to solidify into a hard solid state, and the sample was collected after crushing, ball milling, and sieving.

[0099] 4) Preparation of oxidized lignin modified phenol-formaldehyde resin hard carbon

[0100] The oxidized lignin phenol-formaldehyde resin powder was first carbonized (400°C for 2 h in a tube furnace), then boiled and washed with 1 mol / L HCl aqueous solution, and then washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace in an argon atmosphere for high-temperature structural reforming at 1300°C to obtain oxidized lignin modified phenol-formaldehyde resin hard carbon.

[0101] Example 10

[0102] 5 g of lignin was dispersed in 10 mL of deionized water, 2 g of 30 wt.% H2O2, and 2.5 g of composite base (sodium hydroxide:ammonia water = 1:1) were added, and then oxidized and degraded at 30°C for 0.5 h to obtain Solution A. The subsequent steps were the same as in Example 9.

[0103] Example 11

[0104] 5 g of lignin was dispersed in 10 mL of deionized water, and then 3 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) were added, and then oxidatively degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as those of Example 9.

[0105] Example 12

[0106] 5 g of lignin was dispersed in 10 mL of deionized water, and then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) were added, and then oxidatively degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as those of Example 9.

[0107] Example 13

[0108] 5 g of lignin was dispersed in 10 mL of deionized water, and then 5 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) were added, and then oxidatively degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as those of Example 9.

[0109] Example 14

[0110] 5 g of lignin was dispersed in 10 mL of deionized water, and then 6 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) were added, and then oxidatively degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as those of Example 9.

[0111] Example 15

[0112] 5 g of lignin was dispersed in 10 mL of deionized water, and then 7 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) were added, and then oxidatively degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as those of Example 9.

[0113] Example 16

[0114] 5 g of lignin was dispersed in 10 mL of deionized water, and then 8 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) were added, and then oxidatively degraded at 30°C for 0.5 h to obtain solution A. The subsequent steps were the same as those of Example 9.

[0115] The molecular structural properties and battery performance of the samples prepared in Comparative Example 1 and Examples 6, 9-16 above were tested, and the test results are shown in Table 3. The optimal amount of H2O2 addition was 4 g.

[0116] Table 3 Sodium storage performance of oxidized lignin modified phenolic resin hard carbon with different H2O2 addition amount

[0117]

[0118] Examples 17-20 below are implementation examples for preparing oxidized lignin modified phenolic resin based hard carbon with different oxidation time.

[0119] Example 17

[0120] 1) Preparation of solution A

[0121] 5 g of lignin was dispersed in 10 mL of deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidized and degraded at 30 °C for 0 h to obtain solution A.

[0122] 2) Preparation of solution B

[0123] 50 mL of phenol and 3 g of barium hydroxide were dissolved in 5 mL of distilled water at 75 °C, and then 24 g of formaldehyde was added in batches, and then gradually heated to 83 °C for 2 h to obtain solution B.

[0124] 3) Preparation of oxidized lignin phenolic resin powder

[0125] Solution A was added to solution B and mechanically stirred at 80 °C for 2 h. Then it was placed in an oven at 130 °C to cure the oxidized lignin phenolic resin into a hard solid state, and after crushing, ball milling and sieving, the sample was collected.

[0126] 4) Preparation of oxidized lignin modified phenolic resin hard carbon

[0127] The oxidized lignin phenolic resin powder was first carbonized (400 °C for 2 h in a tube furnace), then boiled and washed with 1 mol / L HCl aqueous solution, and then washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace in an argon atmosphere for high-temperature structural reorganization at 1300 °C to obtain the oxidized lignin modified phenolic resin hard carbon.

[0128] Example 18

[0129] 5 g of lignin was dispersed in 10 mL of deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidized and degraded at 30 °C for 1 h to obtain solution A. The subsequent steps were the same as Example 17.

[0130] Example 19

[0131] 5g of lignin was dispersed in 10mL of deionized water, and then 4g of 30wt.% H2O2 and 2.5g of a compound alkali (sodium hydroxide: ammonia = 1:1) were added. The mixture was then oxidized and degraded at 30°C for 1.5h to obtain solution A. Subsequent steps were the same as in Example 17.

[0132] Example 20

[0133] 5g of lignin was dispersed in 10mL of deionized water, and then 4g of 30wt.% H2O2 and 2.5g of a compound alkali (sodium hydroxide: ammonia = 1:1) were added. The mixture was then oxidized and degraded at 30°C for 2 hours to obtain solution A. Subsequent steps were the same as in Example 17.

[0134] Example 21

[0135] 5g of lignin was dispersed in 10mL of deionized water, and then 4g of 30wt.% H2O2 and 2.5g of a compound alkali (sodium hydroxide: ammonia = 1:1) were added. The mixture was then oxidized and degraded at 30°C for 3 hours to obtain solution A. Subsequent steps were the same as in Example 17.

[0136] The molecular structure properties and battery performance of the samples prepared in Comparative Example 1 and Examples 12, 17-21 were tested, and the test results are shown in Table 4. The optimal oxidation time was 1 hour.

[0137] Table 4. Sodium storage performance of oxidized lignin-modified phenolic resin hard carbon at different oxidation times.

[0138]

[0139]

[0140] Examples 22-27 below are implementation examples of preparing oxidized lignin-modified phenolic resin-based hard carbon by changing the oxidation temperature.

[0141] Example 22

[0142] 1) Preparation of solution A

[0143] Disperse 5g of lignin in 10mL of deionized water, then add 4g of 30wt.% H2O2 and 2.5g of compound alkali (sodium hydroxide: ammonia water = 1:1), and then oxidize and degrade at room temperature (20℃) for 1h to obtain solution A.

[0144] 2) Preparation of solution B

[0145] At 75℃, 50mL of phenol and 3g of barium hydroxide were dissolved in 5mL of distilled water, and 24g of formaldehyde was added in batches. The temperature was then gradually increased to 83℃ and reacted for 2 hours to obtain solution B.

[0146] 3) Preparation of oxidized lignin phenol-formaldehyde resin powder

[0147] Solution A was added to solution B and mechanically stirred at 80 °C for 2 h. Then it was placed in an oven at 130 °C to cure the oxidized lignin phenol-formaldehyde resin into a hard solid state. After crushing, ball milling and sieving, the sample was collected.

[0148] 4) Preparation of oxidized lignin modified phenol-formaldehyde resin hard carbon

[0149] First, the oxidized lignin phenol-formaldehyde resin powder was carbonized (400 °C for 2 h in a tube furnace), then washed by boiling with 1 mol / L HC1 aqueous solution, and washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace under argon atmosphere for high temperature structural reorganization at 1300 °C to obtain the oxidized lignin modified phenol-formaldehyde resin hard carbon.

[0150] Example 23

[0151] 5 g of lignin was dispersed in 10 mL of deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidized and degraded at 40 °C for 1 h to obtain solution A. The subsequent steps were the same as example 21.

[0152] Example 24

[0153] 5 g of lignin was dispersed in 10 mL of deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidized and degraded at 50 °C for 1 h to obtain solution A. The subsequent steps were the same as example 21.

[0154] Example 25

[0155] 5 g of lignin was dispersed in 10 mL of deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidized and degraded at 60 °C for 1 h to obtain solution A. The subsequent steps were the same as example 21.

[0156] Example 26

[0157] 5 g of lignin was dispersed in 10 mL of deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidized and degraded at 70 °C for 1 h to obtain solution A. The subsequent steps were the same as example 21.

[0158] Example 27

[0159] Lignin (5 g) was dispersed in 10 mL deionized water, then 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide: ammonia water = 1:1) was added, and then oxidatively degraded at 80 °C for 1 h to obtain solution A. The subsequent steps were the same as Example 21.

[0160] The molecular structure properties and battery performance of the samples prepared in the above Comparative Example 1 and Examples 18, 22-27 were tested, and the test results are shown in Table 5. The optimal oxidation temperature is 40 °C.

[0161] Table 5 Sodium storage performance of oxidized lignin modified phenolic resin hard carbon of lignin at different oxidation temperatures

[0162]

[0163] In order to analyze the structure-activity relationship of OLPRC, the microstructure thereof was analyzed by X-ray diffraction (XRD) and Raman spectroscopy, as shown in Figure 1 . Figure 1 The XRD patterns of LPRC in Comparative Example 1, PR, LS and OLPRC in Example 23 are shown. The above samples were all heated to 1300 °C under the same pyrolysis conditions, and the characteristic peak positions did not show large shifts. Among them, each sample showed two broad peaks in the range of ~23.5-24.5° and ~42.7-43.5°, respectively, which can correspond to the 002 and 100 planes of the carbon material, indicating that it is a disordered carbon structure. With the addition of OLS, the (002) peak of OLPRC shifts to a lower angle, which is due to the increase in lattice spacing. The d002 of LS, PR, LPRC and OLPR is and With the peak of the oxidation temperature of the precursor LS at 40 °C, the (002) peak position then shifts to a higher angle as the reaction temperature continues to rise, which can indicate that the interlayer spacing of the carbon microcrystalline structure of the hard carbon material gradually decreases. The relatively high interlayer spacing of OLPRC is beneficial to the insertion / extraction and diffusion of sodium, thereby improving the sodium storage performance of the sodium ion battery.

[0164] As can be seen from Figure 2 , Figure 2 the molecular weight polydispersity index (PDI) in b decreases from 2.25 of LS to 1.85 of OLS Figure 2 b), and the molecular weight distribution also narrows, indicating that the depolymerization of LS is intensified and the heterogeneity is partially weakened. But as can be seen from Figure 2 a, the molecular weight becomes smaller and the PDI becomes narrower before and after the reaction, which can indirectly indicate that the alkaline H2O2 oxidation system is beneficial to the polymerization of OLS and PR.

[0165] The molecular weight distribution of the samples prepared in the above comparative examples and examples was tested, and the test results are shown in Table 6.

[0166] Table 6. GPC data of each sample during OLPR synthesis.

[0167]

[0168] As shown in Table 6, the molecular weight of LPR is 1574,6823 g·mol⁻¹. -1 The highest concentration of LS (ortho- and para-osmotic polymers) is mainly due to the large molecular weight of LS itself. Furthermore, the alkaline H₂O₂ oxidation system can reduce the condensation of LS itself, allowing OLS to retain more ortho- and para-osmotic active sites for reaction with PR (proton reductase), while also reducing the self-condensation of materials during the synthesis of OLS and PR. The Mn and Mw of LS and OLS are respectively 1656 g·mol⁻¹. -1 and 3733g.mol -1 Reduced to 489 g.mol -1 and 938g.mol -1 This is attributed to the breakage of some links between lignin monomers (ether bonds in the side chains) under the influence of H2O2 oxidation depolymerization conditions, which in turn reduces the molecular weight of OLPR. The increase in OLS molecular weight and polydispersity with increasing oxidation temperature in Table 1 is due to the longer heating time and higher temperature, which causes the depolymerized lignin fragments to repolymerize (Examples 1-6).

[0169] The sodium storage performance of the LPRC of Comparative Example 1 and the OLPRC obtained in Examples 1-26 was tested (see [reference]). Figure 3 ),Depend on Figure 3 The results show that with the increasing degree of lignin oxidation, the molecular weight of oxidized lignin phenolic resin gradually decreases. The resulting phenolic resin-based hard carbon exhibits increased micropore volume while maintaining stable and excellent sodium storage performance. Among these phenolic resin-based hard carbon materials, OLPRC prepared from pre-oxidized LS exhibits the best performance at 0.05 Ag. -1 It can exhibit the highest reversible capacity of 389.81mAh g. -1 The initial coulomb efficiency is 82%.

[0170] Example 28 (Selection of Lignin Types)

[0171] 1) Preparation of solution A

[0172] Disperse 5g of enzymatically hydrolyzed lignin into 10mL of deionized water, then add 4g of 30wt.% H2O2 and 2.5g of compound alkali (sodium hydroxide: ammonia water = 1:1), and then oxidize and degrade it at 40℃ for 1h to obtain solution A.

[0173] 2) Preparation of solution B

[0174] Dissolve 50 mL of phenol and 3 g of barium hydroxide in 5 mL of distilled water, add 24 g of formaldehyde in batches, and then gradually warm to 83°C for 2 h to obtain solution B.

[0175] 3) Preparation of oxidized lignin phenol-formaldehyde resin powder

[0176] Add solution A to solution B and mechanically stir at 80°C for 2 h. Then place it in an oven at 130°C to solidify the oxidized lignin phenol-formaldehyde resin into a hard solid state, and collect the sample after crushing, ball milling, and sieving.

[0177] 4) Preparation of oxidized lignin modified phenol-formaldehyde resin hard carbon

[0178] First, carbonize the oxidized lignin phenol-formaldehyde resin powder (400°C for 2 h in a tube furnace), then wash it with boiling 1 mol / L HCl aqueous solution, and then wash it with distilled water until it is neutral and dry. Finally, place it in a tube furnace in an argon atmosphere for high-temperature structural reforming at 1300°C to obtain the oxidized lignin modified phenol-formaldehyde resin hard carbon.

[0179] Example 29 (copolymerization temperature of oxidized lignin and phenol-formaldehyde resin prepolymer)

[0180] 1) Preparation of solution A

[0181] Disperse 5 g of lignin in 10 mL of deionized water, then add 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide:ammonia water = 1:1), and then oxidize and degrade at 40°C for 1 h to obtain solution A.

[0182] 2) Preparation of solution B

[0183] Dissolve 50 mL of phenol and 3 g of barium hydroxide in 5 mL of distilled water at 75°C, add 24 g of formaldehyde in batches, and then gradually warm to 83°C for 2 h to obtain solution B.

[0184] 3) Preparation of oxidized lignin phenol-formaldehyde resin powder

[0185] Add solution A to solution B and mechanically stir at 30°C for 2 h. Then place it in an oven at 130°C to solidify the oxidized lignin phenol-formaldehyde resin into a hard solid state, and collect the sample after crushing, ball milling, and sieving.

[0186] 4) Preparation of oxidized lignin modified phenol-formaldehyde resin hard carbon

[0187] The oxidized lignin phenol-formaldehyde resin powder was first carbonized (400 °C for 2 h in a tube furnace), then washed with 1 mol / L aqueous HC1 solution by boiling, and washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace under argon atmosphere for high-temperature structural reorganization at 1300 °C to obtain the oxidized lignin modified phenol-formaldehyde resin hard carbon.

[0188] Example 30 (copolymerization time of oxidized lignin and phenol-formaldehyde prepolymer)

[0189] 1) Preparation of solution A

[0190] 1.5 g of lignin was dispersed in 10 mL of deionized water, 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 40 °C for 1 h to obtain solution A.

[0191] 2) Preparation of solution B

[0192] 50 mL of phenol and 3 g of barium hydroxide were dissolved in 5 mL of distilled water at 75 °C, 24 g of formaldehyde was added in batches, and then gradually heated to 83 °C for 2 h to obtain solution B.

[0193] 3) Preparation of oxidized lignin phenol-formaldehyde resin powder

[0194] Solution A was added to solution B and mechanically stirred at 80 °C for 0.5 h. Then it was placed in an oven at 130 °C to solidify the oxidized lignin phenol-formaldehyde resin into a hard solid state, and after crushing, ball milling and sieving, the sample was collected.

[0195] 4) Preparation of oxidized lignin modified phenol-formaldehyde resin hard carbon

[0196] The oxidized lignin phenol-formaldehyde resin powder was first carbonized (400 °C for 2 h in a tube furnace), then washed with 1 mol / L aqueous HC1 solution by boiling, and washed with distilled water until neutral and dried. Finally, it was placed in a tube furnace under argon atmosphere for high-temperature structural reorganization at 1300 °C to obtain the oxidized lignin modified phenol-formaldehyde resin hard carbon.

[0197] Example 31 (mass ratio of oxidized lignin and phenol-formaldehyde prepolymer)

[0198] 1) Preparation of solution A

[0199] 1.5 g of lignin was dispersed in 10 mL of deionized water, 4 g of 30 wt.% H2O2, 2.5 g of composite alkali (sodium hydroxide:ammonia water = 1:1) was added, and then oxidized and degraded at 40 °C for 1 h to obtain solution A.

[0200] 2) Preparation of solution B

[0201] Dissolve 50 mL phenol and 3 g barium hydroxide in 5 mL distilled water, add 24 g formaldehyde in batches, then gradually warm to 83℃ for 2 h to obtain solution B (the mass of phenol-formaldehyde prepolymer is 75 g by weighing).

[0202] 3) Preparation of oxidized lignin phenol-formaldehyde resin powder

[0203] Add solution A to solution B and mechanically stir at 80℃ for 2 h. Then place in an oven at 130℃ to cure the oxidized lignin phenol-formaldehyde resin into a hard solid state, and collect the sample after crushing, ball milling and sieving.

[0204] 4) Preparation of oxidized lignin modified phenol-formaldehyde resin hard carbon

[0205] First, carbonize the oxidized lignin phenol-formaldehyde resin powder (400℃ for 2 h in a tube furnace), then wash with boiling 1 mol / L HCl aqueous solution, and then wash with distilled water until neutral and dry. Finally, place it in a tube furnace in an argon atmosphere for high-temperature structural reorganization at 1300℃ to obtain oxidized lignin modified phenol-formaldehyde resin hard carbon.

[0206] Test the sodium storage performance of the oxidized lignin modified phenol-formaldehyde resin-based hard carbon prepared in Examples 28-31, as shown in Table 7. The main purpose is to illustrate the effects of reaction conditions during copolymerization of oxidized lignin and phenol-formaldehyde resin, and the selection of lignin raw material on the sodium storage performance of oxidized lignin phenol-formaldehyde resin hard carbon.

[0207] Table 7 Sodium storage performance of oxidized lignin phenol-formaldehyde resin hard carbon synthesized under different copolymerization conditions of lignin, oxidized lignin and phenol-formaldehyde resin

[0208]

[0209] The selection of conditions in Table 7 mainly involves the reaction conditions during the entire reaction process, but the selection of lignin, the copolymerization time and temperature of lignin and phenol-formaldehyde prepolymer have no significant effect on the performance of the prepared oxidized lignin modified phenol-formaldehyde resin-based hard carbon. After comparing the sodium storage performance of lignin, oxidized lignin and phenol-formaldehyde resin copolymerization conditions, it can be determined that the oxidation effect of lignin sulfonate is the best lignin raw material in this experimental system, and the best copolymerization condition of lignin and phenol-formaldehyde resin is Example 23.

[0210] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for preparing controllable molecular weight oxidized lignin modified phenol-formaldehyde resin-based hard carbon, characterized in that, The specific steps are: (1) dispersing lignin into deionized water, adding H2O2 and composite alkali, oxidizing and degrading to obtain solution A; (2) dissolving phenol and barium hydroxide in distilled water at 75°C, adding formaldehyde in batches, gradually heating to 83°C for reaction to obtain solution B; (3) adding solution A to solution B and stirring at 80°C to obtain oxidized lignin phenolic aldehyde resin; solidifying the oxidized lignin phenolic aldehyde resin into a hard solid state, crushing, ball milling and sieving to obtain oxidized lignin phenolic aldehyde resin powder; (4) carbonizing the oxidized lignin phenolic aldehyde resin powder prepared in step (3), washing with HCl aqueous solution and distilled water until neutral, drying, and placing in a tube furnace in an argon atmosphere for high-temperature structural reforming at 1300°C to obtain oxidized lignin phenolic aldehyde resin-based hard carbon.

2. The method for preparing controllable molecular weight oxidized lignin modified phenol-formaldehyde resin-based hard carbon according to claim 1, characterized in that, The mass ratio of the oxidized lignin to the phenolic aldehyde prepolymer is 1:1-50.

3. The method for preparing controllable molecular weight oxidized lignin-modified phenolic resin-based hard carbon according to claim 1, characterized in that, The preparation process of the oxidized lignin is: dispersing lignin into deionized water, adding H2O2 and composite alkali, and oxidizing and degrading to obtain oxidized lignin.

4. The method for preparing controllable molecular weight oxidized lignin-modified phenolic resin-based hard carbon according to claim 3, characterized in that, The g / mL of the lignin to deionized water is 1:1-1:4, and the addition amount of H2O2 is 1-8 g.

5. The method for preparing controllable molecular weight oxidized lignin-modified phenolic resin-based hard carbon according to claim 3, characterized in that, The oxidation temperature is 20-80°C, and the oxidation time is 0.5-3 h.

6. The method for preparing controllable molecular weight oxidized lignin-modified phenolic resin-based hard carbon according to claim 3, characterized in that, The composite alkali is selected from any two of ammonia, sodium hydroxide, barium hydroxide, calcium hydroxide and potassium hydroxide in a ratio of 1:1, and the addition amount of the composite alkali is 1-7.5 g.

7. The method for preparing controllable molecular weight oxidized lignin-modified phenolic resin-based hard carbon according to claim 1, characterized in that, The stirring time of step (3) is 0.5-2.5 h.

8. The preparation method of the oxidized lignin modified phenolic aldehyde resin-based hard carbon with controllable molecular weight according to any one of claims 1-7 to obtain the oxidized lignin phenolic aldehyde resin-based hard carbon.

9. The application of the oxidized lignin phenolic aldehyde resin-based hard carbon according to claim 8 in sodium ion battery negative electrode materials.

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