A phenazine-based polymer cathode material, its preparation method and application

Abstract

This invention relates to the field of secondary battery technology, and discloses a phenazine-based polymer cathode material, its preparation method, and its applications. This material consists of phenazine units linked by flexible methylene chains –(CH2). x A linear polymer formed by bridging. Its preparation method involves a one-step nucleophilic substitution polymerization reaction of 5,10-dihydrophenazine with dibromoalkane under the catalysis of an alkali-alcohol salt. This method requires no precious metal catalyst and has the advantages of simple route and low cost. The polymer is crystalline, with the phenazine units arranged in a long-range ordered manner, constructing a highly efficient carrier transport channel. When used as a positive electrode active material for lithium-ion batteries, it exhibits high specific capacity, excellent rate performance (especially low capacity decay at 10C high rates), and long cycle life, demonstrating significant industrialization potential.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and in particular to a phenazine-based polymer cathode material, its preparation method, and its application. Background Technology

[0002] Against the backdrop of the rapid development of secondary batteries and large-scale energy storage technologies, cathode materials, as core components determining battery energy density, power characteristics, and environmental friendliness, have become crucial drivers for technological upgrades in the industry. Currently, widely used inorganic transition metal oxide cathode materials (such as lithium cobalt oxide and ternary materials) are highly dependent on scarce metal resources like cobalt and nickel. This not only presents challenges such as limited resource reserves and volatile supply chain prices, but their mining and smelting processes also carry significant environmental pressures.

[0003] Organic electrode materials are considered an important direction for the development of next-generation cathode materials due to their advantages such as high abundance of constituent elements, flexible molecular structure design, good environmental compatibility, and high rate capability. Among them, phenazine compounds, with their extended π-electron conjugated system, high density of electrochemically active nitrogen sites, modifiable molecular structure, and complete independence from scarce metals, exhibit outstanding resource sustainability and application potential. However, this field still faces two major bottlenecks: First, performance bottleneck. Existing phenazine polymer cathode materials (including rigid conjugated, network, or donor-acceptor copolymer types) are often designed with an emphasis on pursuing high operating voltage, universality (such as compatibility with multi-ion systems), or constructing special topologies, but generally sacrifice the material's fast charge-discharge capability. Especially under ultra-high rate conditions of 10C and above, there is still considerable room for improvement in their discharge capacity retention. Second, process and cost bottleneck. The synthesis routes of these materials usually rely on noble metal catalysts such as palladium and involve multi-step reactions or complex monomer preparation, resulting in cumbersome processes and high production costs, which seriously hinder their industrialization process.

[0004] To overcome the aforementioned challenges, this invention aims to provide a novel solution. The objective of this invention is to provide a phenazine-based polymer cathode material with a simple synthesis route, low cost, and specifically designed for lithium-ion batteries. This material must simultaneously achieve high specific capacity, extremely low capacity decay, and ultra-long cycle life at ultra-high rates (10C level), thereby overcoming the technical bottleneck of existing technologies that struggle to simultaneously achieve "ultra-high rate performance," "long-term cycle stability," and "economical preparation." Summary of the Invention

[0005] In view of this, the present invention proposes a phenazine-based polymer cathode material, overcoming the shortcomings of existing phenazine polymer cathode materials, such as complex synthesis, high cost, and poor rate performance; and provides a preparation method for the above material, which has the advantages of simple route, mild conditions, readily available raw materials, and low cost, making it suitable for large-scale production; finally, the present invention provides the application of the above phenazine-based polymer cathode material in lithium-ion batteries, and the prepared batteries should exhibit high specific capacity, excellent rate performance, and good cycle stability.

[0006] The technical solution of this invention is implemented as follows: In a first aspect, the present invention provides a phenazine-based polymer cathode material, wherein the phenazine-based polymer comprises the following structure: ; Wherein, R includes -(CH2). x -, x is an integer from 4 to 8; n is the degree of aggregation.

[0007] The phenazine-based polymer prepared in this invention has a highly ordered molecular chain structure and can form a crystalline phase, wherein the phenazine units exhibit long-range ordered arrangement through π-π stacking and other interactions. This material is a polydisperse polymer aggregate, and the number-average molecular weight of the phenazine-based polymer is 5000~50000 g / mol.

[0008] Based on the above technical solutions, preferably, x=4.

[0009] Secondly, the present invention also provides a method for preparing the above-mentioned material, comprising the following steps: 5,10-dihydrophenazine and Br-(CH2) x -Br mixture reacts to obtain the phenazine-based polymer cathode material.

[0010] More preferably, the reaction is a condensation reaction; the reaction temperature is 90~120℃, and the reaction time is 12~72h. After the reaction is complete, the mixture is cooled to room temperature and filtered. The filter cake is washed successively with deionized water, methanol, and dichloromethane until the washing liquid is colorless to obtain the final product.

[0011] More preferably, the condensation reaction is carried out in the presence of an alkali-alcohol salt.

[0012] More preferably, the alkali-alkali metal salt includes at least one of sodium methoxide, sodium tert-butoxide, and potassium tert-butoxide.

[0013] More preferably, the 5,10-dihydrophenazine, Br-(CH2) x The molar ratio of -Br to alkali metal salt is 1:(0.95~1.05):(3~10).

[0014] More preferably, the reaction is carried out under an inert atmosphere.

[0015] More preferably, the reaction solvent for the reaction includes at least one of N,N-dimethylformamide and N,N-dimethylacetamide.

[0016] Thirdly, the present invention provides a positive electrode sheet, the raw materials for which include the above-mentioned phenazine-based polymer positive electrode material, conductive agent and binder.

[0017] Based on the above technical solutions, preferably, the conductive agent is selected from one or more of conductive carbon black, Ketjen black, carbon nanotubes, and Super P, and the binder is selected from polyvinylidene fluoride; the mass ratio of the organic positive electrode active material, the conductive agent and the binder is (6~4):(2~4):2.

[0018] Fourthly, the present invention provides a lithium-ion battery comprising the above-mentioned positive electrode, negative electrode, electrolyte, and separator.

[0019] Based on the above technical solutions, preferably, the negative electrode sheet is selected from lithium metal; the electrolyte includes a metal salt and an organic solvent, wherein the metal salt is selected from one or more of perchlorate, hexafluorophosphate, and difluorosulfonylimide salt; the metal ion in the metal salt is lithium ion; the organic solvent includes one or more of esters, ethers, and sulfones; the separator is selected from one or more of glass fiber separator, cellulose separator, and polypropylene separator; and the current collector of the positive electrode sheet is selected from aluminum-based, nickel-based, or titanium-based current collectors.

[0020] The present invention has the following advantages over the prior art: (1) Based on the design of molecular structure and condensed matter structure, this invention successfully prepared a crystalline aliphatic chain-bridged phenazine-based polymer using a nucleophilic substitution condensation reaction based on carbon sites. In this design, the active phenazine units are connected by flexible aliphatic chains with small molecular weights, which improves the theoretical specific capacity of the material while giving the polymer chains excellent regularity, enabling them to form a crystalline structure. Crystallization promotes the long-range ordered arrangement of electroactive phenazine units, shortening the effective transport distance between phenazine units, thereby facilitating the transport of charge carriers (electrons) and anions in the electrolyte (such as PF6). - It provides a fast and continuous transmission channel, which significantly improves the fast charge and discharge performance of the cathode material.

[0021] (2) Meanwhile, the crystallization characteristics of this polymer cathode material effectively inhibit its dissolution in the electrolyte, significantly reducing the loss of active material and capacity decay during cycling, thereby achieving excellent cycle stability. Therefore, when the polymethylene phenazine polymer provided in this application is used as a cathode for lithium-ion batteries, it simultaneously possesses high specific capacity, high rate capability, and long cycle life.

[0022] (3) The monomer raw materials used in this polymerization system are widely available, inexpensive and easy to obtain, and do not require precious metal catalysts; the reaction conditions are mild and do not require complex synthesis equipment. The entire polymerization process is short and easy to operate, the reaction conditions are mild and easy to control, the post-processing process is simple, the preparation cost is low, and it is easy to achieve the target product, enabling the efficient preparation and large-scale industrial production of phenazine-based polymers. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 The Fourier transform infrared spectra of PDTP and PDPP prepared in Examples 1 and 2 of this invention are shown below. Figure 2 Thermogravimetric analysis diagrams of PDTP and PDPP used in Embodiments 1 and 2 of this invention; Figure 3 The XRD patterns of PDTP and PDPP used in Embodiments 1 and 2 of this invention are shown below. Figure 4 These are electrochemical window test diagrams of PDTP and PDPP used in Examples 1 and 2 of this invention; Figure 5 This is a comparison chart of the specific capacity of lithium-ion batteries assembled using PDTP and PDPP as positive electrode active materials in Examples 1 and 2 of the present invention after 5 cycles at different rates. Figure 6 The graph shows the cycling performance of the PDTP used in Example 1 of this invention at 10°C in an electrolyte (with LiClO4 as the solute). Figure 7 This is a graph showing the cycling performance of the PDPP used in Example 2 of the present invention at 10°C in an electrolyte (with LiClO4 as the solute). Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1: Preparation of Tetramethylenephenazine Polymer (PDTP) In a 250 mL round-bottom flask, 1.8222 g of 5,10-dihydrophenazine (10 mmol), 2.1591 g of 1,4-dibromobutane (10 mmol), and 11.21 g of potassium tert-butoxide (100 mmol) were added, along with 120 mL of anhydrous N,N-dimethylformamide as a solvent. The mixture was stirred and heated thoroughly under nitrogen protection at 120 °C for 48 h. After the reaction was complete, the mixture was cooled to room temperature and filtered. The filter cake was washed successively with deionized water, methanol, and dichloromethane until the washings were colorless, yielding the final product (Mn = 16930 g / mol).

[0027] Example 2: Preparation of hexamethylene phenazine polymer (PDPP) In a 250 mL round-bottom flask, 1.8222 g of 5,10-dihydrophenazine (10 mmol), 2.3176 g of 1,6-dibromohexane (9.5 mmol), and 5.77 g of sodium tert-butoxide (60 mmol) were added, along with 100 mL of anhydrous N,N-dimethylacetamide as a solvent. The mixture was stirred and heated thoroughly under nitrogen protection at 100 °C for 72 h. After the reaction was complete, the mixture was cooled to room temperature and filtered. The filter cake was washed successively with deionized water, methanol, and dichloromethane until the washings were colorless, yielding the final product (Mn = 12830 g / mol).

[0028] Example 3: Preparation of octamethylenephenazine polymer In a 250 mL round-bottom flask, 1.8222 g of 5,10-dihydrophenazine (10 mmol), 2.8562 g of 1,8-dibromooctane (10.5 mmol), and 1.62 g of sodium methoxide (30 mmol) were added, along with 100 mL of anhydrous N,N-dimethylformamide as a solvent. The mixture was stirred and heated thoroughly under nitrogen protection at 90 °C for 12 h. After the reaction was complete, the mixture was cooled to room temperature and filtered. The filter cake was washed successively with deionized water, methanol, and dichloromethane until the washings were colorless, yielding the final product (Mn = 8600 g / mol).

[0029] The theoretical and GPC calibration upper limit can reach about 50,000 g / mol. The polymer Mn obtained in the embodiments of the present invention is 8,600~16,930 g / mol, which falls within this range.

[0030] Comparative Example 1: The difference from Example 1 is that 1,4-dibromobutane was replaced with 2.0189 g of 1,3-dibromopropane (10 mmol), and the other conditions were the same as in Example 1, which will not be repeated here.

[0031] Comparative Example 2: The difference from Example 1 is that 1,4-dibromobutane was replaced with 3.0007 g of 1,10-dibromodecane (10 mmol), and the other conditions were the same as in Example 1, which will not be repeated here.

[0032] Comparative Example 3: Unlike Example 1, this reaction used 1.8222 g of 5,10-dihydrophenazine (10 mmol), 1.9433 g of 1,4-dibromobutane (9 mmol), and 11.21 g of potassium tert-butoxide (100 mmol), and added 120 mL of anhydrous N,N-dimethylformamide to induce a nucleophilic substitution polycondensation reaction. Other conditions were the same as in Example 1 and will not be repeated here.

[0033] Comparative Example 4: Unlike Example 1, this reaction used 1.8222 g of 5,10-dihydrophenazine (10 mmol), 2.1591 g of 1,4-dibromobutane (10 mmol), and 13.4652 g of potassium tert-butoxide (120 mmol), and added 120 mL of anhydrous N,N-dimethylformamide to induce a nucleophilic substitution polycondensation reaction. Other conditions were the same as in Example 1 and will not be repeated here.

[0034] Comparative Example 5: The difference from Example 1 is that 1,4-dibromobutane was replaced with 2.3590 g of p-dibromobenzene (10 mmol), and the other conditions were the same as in Example 1, which will not be repeated here.

[0035] Application Example 1: Fabrication and Performance Testing of PDTP-based Lithium-ion Batteries 1. Electrode paste preparation and positive electrode fabrication Weigh 80.0 mg of the tetramethylene phenazine polymer (PDTP) prepared in Example 1 as the active material, 60.0 mg of Ketjen black and 20.0 mg of Super P conductive carbon black as the composite conductive agent, and 40.0 mg of polyvinylidene fluoride (PVDF) as the binder, and mix them together in a mortar.

[0036] Subsequently, 0.8 mL of N-methylpyrrolidone (NMP) was added to the uniformly mixed powder, and the mixture was ground until a uniform, fine slurry with suitable viscosity was formed. The slurry was uniformly coated onto a clean aluminum foil current collector with a thickness of 15 μm, controlling the wet film thickness to be approximately 200 μm. The coated electrode was then placed in a vacuum drying oven and dried at 120 °C for 24 h. After drying, the electrode was punched into a disc with a diameter of 10 mm using a die.

[0037] 2. Button cell battery assembly CR2032 batteries were assembled in an argon-filled glove box. The aforementioned electrode was used as the positive electrode, a 14.0 mm diameter, 0.45 mm thick lithium sheet as the negative electrode, Celgard 2400 as the separator, and the electrolyte was 1 M LiClO4 EC / DEC (1:1, v / v), with an addition amount of approximately 80 µL per battery. After assembly in the standard sequence, the batteries were sealed at 8 MPa.

[0038] Following the positive electrode preparation, battery assembly, and testing steps described in Application Example 1, lithium-ion batteries were prepared using the materials obtained in Examples 2-3 and Comparative Examples 1-5, and their electrochemical performance was tested according to the following unified procedure: Cyclic voltammetry (CVT) experiments were conducted on simulated batteries using the Chenhua Chi604E battery testing system. The CVT scan rates were 0.2 mV / s, 0.4 mV / s, 0.6 mV / s, 0.8 mV / s, and 1 mV / s, with intervals of 0.2 mV / s. The scan potential range was 2.4 V–4.3 V. Charge-discharge experiments were performed using a Newell CT-4008Tn. The charging termination voltage was 4.3 V, and the discharging termination voltage was 2.4 V. The rate performance test termination voltage was also 2.4 V. The rate performance current densities were 0.3 C, 0.5 C, 1 C, 3 C, 5 C, and 10 C, with a current control accuracy of ±0.01 mA.

[0039] Table 1: Initial specific capacity and specific capacity after 1000 cycles at 10C rate in battery tests with different substituted compounds.

[0040] Comparing Example 1 with Comparative Examples 1-5 respectively, the following conclusions were drawn: Conclusion 1: Carbon chain lengths shorter than C4 significantly reduce the degree of polymerization, thus affecting electrochemical performance. When the substituted compound is 1,3-dibromopropane (C3), the excessively short methylene chain leads to intramolecular cyclization side reactions during nucleophilic substitution significantly prior to chain growth reactions, resulting in a sharp decrease in the degree of polymerization and molecular weight. The product essentially lacks electrochemical activity, with a specific capacity of zero.

[0041] Conclusion 2: A carbon chain length greater than C8 reduces the theoretical specific capacity and electron transport velocity. Using longer alkyl substitutions decreases the initial specific capacity and cycling performance. Compared to C4 short-chain alkyl substitution structures, C10 long-chain alkylene bridging modification increases the proportion of inert alkyl structures, diluting the active redox sites per unit mass by the inert framework, thus reducing the theoretical and actual specific capacity of the material. Simultaneously, the long-chain alkyl increases the spatial distance between adjacent phenazine conjugated units, weakening intermolecular π-π stacking, increasing carrier transition resistance, and increasing electrode electronic impedance.

[0042] Conclusion 3: When the ratio of bromine derivatives is less than that of monomers (0.9), the functional group ratio is unbalanced, the bromine groups are depleted prematurely, and the surplus monomer hydroxyl groups act as end-capping agents to terminate chain growth, resulting in a significant decrease in the degree of polymerization and molecular weight, thus affecting the electrochemical cycle.

[0043] Conclusion 4: When alkali is in excess, the aryl halophene monomer undergoes hydrolysis, and the bifunctional monomer becomes a monofunctional impurity. After being attached to the chain end, it blocks the active site and terminates chain growth, resulting in a significant decrease in the degree of polymerization and molecular weight of the polymer.

[0044] Conclusion 5: Under purely alkaline conditions, dibromobenzene, lacking a strong electron-withdrawing group on its benzene ring, cannot stabilize the Meisenheimer intermediate in nucleophilic substitution reactions and hardly reacts with dihydrophenazine.

[0045] Further tests were conducted on the PDTP and PDPP prepared in Examples 1 and 2 of this invention: like Figure 1 The image shows the infrared spectra of PDTP and PDPP. In the infrared spectra, the region between 2800 and 3000 cm⁻¹... -1 The presence of a strong absorption band due to the CH stretching vibration confirms the introduction of an alkyl group. Because the 1,6-hexene-bridging product has a longer methylene chain, its absorption intensity in this band is higher than that of the 1,4-butylene-bridging product; 730 cm⁻¹ -1 The sharp absorption peak is attributed to the rocking vibration of the methylene CH group, 700–800 cm⁻¹ -1 The region is characterized by the out-of-plane bending vibration of CH, which is generated by the out-of-plane bending vibration of alkyl chain CH.

[0046] like Figure 2 The thermogravimetric spectra of PDTP and PDPP shown indicate that, compared to PDPP modified with long alkyl chains, PDTP with short alkyl-bridged structures exhibits weaker thermal stability: PDPP begins to lose significant thermal weight at 350℃ while retaining 95% of its initial mass, and after heating to 490℃, the residual mass stabilizes at 11%, with subsequent thermal decomposition essentially ceasing; PDTP, due to its shorter alkyl carbon chain length, has a thermal decomposition initiation temperature reduced to 260℃, at which temperature the system retains 95% of its mass, and the rate of thermal weight loss slows significantly when the temperature continues to rise to 430℃, with the thermal stability of the remaining skeleton structure significantly improved.

[0047] like Figure 3 The X-ray diffraction patterns of PDTP and PDPP are shown. Both polymer samples show characteristic diffraction peaks at 2θ≈25°, confirming the existence of π-π stacking interaction between molecules. PDPP has a longer alkyl side chain carbon chain, and the steric hindrance regulates molecular stacking, resulting in a higher peak intensity and a better degree of π-π stacking order.

[0048] like Figure 4As shown, PDTP and PDPP were tested at a uniform scan rate within a 0.5 mV s-1 electrochemical window. -1 At slow scan rates, the two organic cathode materials were compared at 2.4-4.3V (vs. Li). + The / Li) electrochemical window shows reversible oxidation peaks.

[0049] like Figure 5 As shown, the PDTP cathode exhibits 192, 190, 186, 183, 180, and 174 mAh g⁻¹ at rate factors of 0.3C, 0.5C, 1C, 3C, 5C, and 10C, respectively. -1 The discharge capacity indicates excellent rate performance. The specific capacity decay from 0.3C to 10C is less than 10%. This demonstrates that PDTP exhibits high capacity and low rate decay, maintaining a capacity greater than 170 mAh g at a high rate of 10C. -1 The capacity.

[0050] like Figure 6 The figure shows the electrochemical cycle diagram of the PDTP electrode. The PDTP electrode was tested under 10C high-rate charge-discharge conditions, and the discharge specific capacity of the first cycle was 172 mAh g. -1 After 1000 cycles, the specific capacity is 125 mAh g. -1 The capacity retention rate is 72.7%; the long alkyl chain can inhibit the dissolution of active materials in the electrolyte; the phenazine conjugated skeleton has excellent redox reversibility; and there is no rapid degradation phenomenon during high-rate cycling.

[0051] like Figure 7 The figure shows the electrochemical cycle diagram of the PDPP electrode. Under the high-rate test condition of 10C, the initial discharge specific capacity of the PDPP electrode is 152 mAh g. -1 After 1000 charge-discharge cycles, the specific capacity remained at 118 mAh g. -1 The capacity retention rate is 77.6%; the long alkyl bridging structure effectively inhibits the dissolution of active components, the conjugated phenazine skeleton has stable electrochemical reversibility, and the cycle decay is gradual.

[0052] 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 within the protection scope of the present invention.

Claims

1. A phenazine-based polymer cathode material, characterized in that, The phenazine-based polymer comprises the following structure: ； Wherein, R includes -(CH2). x - where x is an integer from 4 to 8; n is the degree of polymerization; and the number-average molecular weight of the phenazine-based polymer is 5000 to 50000 g / mol.

2. A method for preparing the phenazine-based polymer cathode material as described in claim 1, characterized in that, Includes the following steps: 5,10-dihydrophenazine and Br-(CH2) x -Br mixture reacts to obtain the phenazine-based polymer cathode material.

3. The preparation method according to claim 2, characterized in that, The reaction is a condensation reaction; the reaction temperature is 90~120℃, and the reaction time is 12~72h.

4. The preparation method according to claim 3, characterized in that, The condensation reaction is carried out in the presence of an alkali-alcohol salt.

5. The preparation method according to claim 4, characterized in that, The alkali-alkali metal salt includes at least one of sodium methoxide, sodium tert-butoxide, and potassium tert-butoxide.

6. The preparation method according to claim 2, characterized in that, The 5,10-dihydrophenazine, Br-(CH2) x The molar ratio of -Br to alkali metal salt is 1:(0.95~1.05):(3~10).

7. The preparation method according to claim 2, characterized in that, The reaction was carried out under an inert atmosphere.

8. A positive electrode sheet, characterized in that, The raw materials for preparing the positive electrode sheet include the phenazine-based polymer positive electrode material as described in claim 1, a conductive agent, and a binder.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the positive electrode, negative electrode, electrolyte, and separator as described in claim 8.

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