Lithium titanate negative electrode slurry of lithium slurry battery and preparation method of lithium titanate negative electrode slurry

Abstract

The invention provides lithium slurry battery lithium titanate negative electrode slurry and a preparation method thereof.The lithium slurry battery lithium titanate negative electrode slurry comprises a lithium titanate negative electrode active material, an electrolyte and a conductive agent.The method comprises the steps that firstly, the spherical conductive agent and the lithium titanate negative electrode active material are mixed to obtain solid powder with uniform components, and then the electrolyte is added into the solid powder; the electrode slurry suspension prepared by the method is good in stability and high in conductivity. In addition, the internal relation among the settling performance, the rheological property and the conductivity performance of the slurry of different conductive additive types is researched systematically. According to comprehensive evaluation of the three types of indexes, the conductive agent with good slurry suspension performance is screened out, and on the basis, the rule that the settling performance, the rheological property and the conductivity of the slurry change along with the solid content of the active substance under different conductive agents is further studied. A set of systematic screening mechanism for the electrode paste conductive agent of the lithium paste battery is established on the basis of the influence rule of different conductive agent components on the electrode paste, and application and development of the lithium paste battery in the field of energy storage are further promoted.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of chemical energy storage, and relates to a lithium slurry battery lithium titanate negative electrode slurry and a preparation method thereof. BACKGROUND

[0002] A lithium slurry battery is a new type of electrochemical energy storage technology, which uses a suspension of electrode active solid particles and conductive particles dispersed in an electrolyte as an electrode, and the electrode suspension is circulated between a battery reactor and an external storage container. The lithium slurry battery has the advantages of independent output power and energy storage capacity, high energy density, low cost, good cycling performance, high safety of the battery system, etc., and has become a research hotspot in the energy storage field. The lithium slurry battery uses electrode slurry as the main material for electrochemical reaction. The electrode slurry is a solid-liquid mixed system formed by dispersing electrode active materials and conductive agents in an electrolyte, and the quality of the electrode slurry determines whether it can achieve good electrochemical performance.

[0003] However, the system energy efficiency and electrochemical performance of the battery still have great room for improvement. The poor stability, conductivity and flowability of the electrode slurry suspension of the core working component of the battery system result in low energy efficiency. The physicochemical properties of the active material and the conductive agent have important influence on the stability, conductivity and electrochemical performance of the lithium slurry suspension. The lithium slurry battery is still in the research and development stage. Previous patents (such as CN106033821 B, CN115863541 A, etc.) focus on adding dispersants or optimizing the preparation process to obtain a slurry suspension with uniform composition. The conductive agents mentioned are common conductive agents on the market, such as carbon fibers, Ketjen black, carbon nanotubes and graphene, etc. There are many types, and their morphology, specific surface area and particle size differ greatly. The influence of different conductive agents on the stability of the slurry suspension is not clear. Since different types of conductive agents have a great influence on the electrode slurry of the lithium slurry battery, without understanding the influence of different types of conductive agents (one of the components of the slurry, which is composed of active materials, conductive agents and electrolyte) on the slurry, studying the influence of other additional dispersants or preparation processes on the slurry not only consumes a long time, but also is not accurate. There is no clear screening mechanism for the influence of conductive agents on the electrode slurry of the lithium slurry battery and the evaluation method. SUMMARY

[0004] To solve the above problems, the present application provides a kind of lithium slurry battery lithium titanate negative slurry and its preparation method, first, active material is carbon-coated and carbon nanotube doped composite modification, to improve the conductivity of slurry suspension.Then determine the key factor of the influence of conductive agent on lithium slurry battery electrode slurry-sedimentation performance, rheological property and conductivity, conductive agent type selection is carried out.Based on the better conductive agent, further study the sedimentation performance, rheological property and conductivity of slurry under different conductive agent, the rule of variation with active material solid content.Thus, the influence of active material and conductive agent on lithium slurry suspension is determined.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] A kind of lithium slurry battery lithium titanate negative slurry, the lithium titanate negative slurry is composed of the following weight percentage components, lithium titanate negative active material 5%-30%, electrolyte 70%-94% and conductive agent I 0.5%-4%;

[0007] The lithium titanate negative active material is prepared by carbon-coated lithium titanate and conductive agent II, and the mass fraction of conductive agent II in carbon-coated lithium titanate is 0.5%-3%;

[0008] The conductive agent I is spherical conductive agent SP.

[0009] The present application also provides a preparation method of the lithium slurry battery lithium titanate negative slurry, comprising the following steps:

[0010] (1) add lithium titanate powder into sucrose solution, and uniformly mix by high-energy solid-liquid phase in a defoaming machine to obtain slurry A;

[0011] (2) spray dry and calcine slurry A to obtain carbon-coated lithium titanate;

[0012] (3) mix carbon-coated lithium titanate and conductive agent II uniformly to obtain slurry B;

[0013] (4) spray dry slurry B to obtain lithium titanate negative active material;

[0014] (5) screen conductive agent I by screening mechanism of lithium slurry battery electrode slurry conductive agent;

[0015] (6) mix conductive agent I and lithium titanate negative active material to obtain solid powder with uniform composition, and add electrolyte into the solid powder to obtain lithium slurry battery lithium titanate negative slurry.

[0016] Further, in step (1), the mass ratio of lithium titanate to sucrose is (8-13):1, the rotation speed of high-energy solid-liquid phase mixing in a defoaming machine is 1000-4000, and the time is 10min-60min.

[0017] Further, the inlet temperature of the spray drying in the step (2) is 130-200 DEG C, the outlet temperature is 40-80 DEG C, the calcination temperature is 650-950 DEG C, and the holding time is 1.5-4 h.

[0018] Further, the conductive agent II in the step (3) is a linear or network conductive agent, including one or a mixture of at least two of carbon nanotubes, graphene, carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB or nano activated carbon.

[0019] Further, the inlet temperature of the spray drying in the step (4) is 130-200 DEG C, and the outlet temperature is 40-80 DEG C.

[0020] Further, the mixing and dispersing device in the step (6) is a mixer without any stirring paddle in the material tank, has a uniformly distributed star rotor, and the material tank is installed at an angle, the mixing speed and time are both controlled in a stepwise manner, the mixing speed is greater than 500 rpm and less than 1500 rpm each time, and the mixing time is greater than 100 s and less than 800 s each time.

[0021] Further, the screening mechanism of the lithium slurry battery electrode slurry conductive agent I in the step (5) comprises the following steps:

[0022] S1, find out the key factors of different conductive agent types on the lithium slurry battery electrode slurry - slurry settling performance, rheological property and conductivity;

[0023] S2, fix the proportion of active material, conductive agent and electrolyte in the slurry, take the conductive agent type as the variable, and obtain the action law of different conductive agent types on the slurry settling performance, rheological property and conductivity;

[0024] S3, according to the comprehensive evaluation of the three types of indexes, the conductive agent with excellent slurry performance is screened out;

[0025] S4, on the basis of step S3, fix the content of the conductive agent, change the content of the active material, and obtain the law of the slurry settling performance, rheological property and conductivity of the slurry under different types of conductive agents with the change of the active material solid content, so as to screen out the conductive agent I.

[0026] Further, the different conductive additive types include carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB and carbon nanotube CNT.

[0027] Another object of the present application is to provide a set of screening mechanism of lithium slurry battery electrode slurry conductive agent, to clarify the action law of the conductive agent type of lithium slurry battery electrode slurry on the key parameters of the electrode slurry to determine the specific conductive agent screening.

[0028] Lithium slurry battery electrode slurry is usually composed of electrolyte, active material and conductive agent, and the content of active material in unit volume is high, which is an effective way to improve the energy density of flow battery. In the slurry, the active material and the conductive agent are dispersed in the electrolyte to form a conductive network. However, it is difficult to obtain stable slurry suspension due to the high density of ordinary electrode materials and poor conductive network of slurry suspension. The present application improves the quality of lithium slurry battery lithium titanate negative electrode slurry by modifying the active material and establishing a systematic screening mechanism for lithium slurry battery electrode slurry conductive agent.

[0029] Compared with the prior art, the present application has the following advantages: 1. The active material is modified by carbon coating and carbon nanotube doping to improve the conductivity of the slurry suspension. 2. A systematic screening mechanism for lithium slurry battery electrode slurry conductive agent is established based on the influence of different conductive agent compositions on electrode slurry. Based on common lithium slurry battery different conductive additive types including carbon fiber VGCF, Cabot CABOT, carbon black SP, carbon black KB and carbon nanotube CNT, the internal relationship between slurry sedimentation performance, rheological property and conductivity of different conductive additive types is studied. According to the comprehensive evaluation of the three indexes, the conductive agent with good slurry suspension performance is selected. 3. On the basis of obtaining better conductive agent, the slurry sedimentation performance, rheological property and conductivity performance change with the solid content of active material under different conductive agents. The influence of the physicochemical properties of active material and conductive agent on lithium slurry suspension is determined. 4. By modifying the active material and establishing a systematic screening mechanism for lithium slurry battery electrode slurry conductive agent, the quality of lithium slurry battery lithium titanate negative electrode slurry is improved. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0031] Figure 1 Carbon-coated and conductive agent-doped lithium titanate.

[0032] Figure 2 The reactor picture for testing the performance of lithium titanate slurry.

[0033] Figure 3 The electrochemical performance of carbon-coated lithium titanate and carbon nanotube-doped reactor test.

[0034] Figure 4 The electrochemical performance of lithium titanate raw material reactor test.

[0035] Figure 5 Electrochemical performance of carbon-coated lithium titanate reactor test.

[0036] Figure 6 Electrochemical performance of carbon nanotube-doped lithium titanate reactor test.

[0037] Figure 7 Electrochemical performance of carbon nanotube-doped lithium titanate reactor test.

[0038] Figure 8 Settling performance of 15% lithium titanate - 1% different conductive agents.

[0039] Figure 9 Rheological performance of 15% lithium titanate - 1% different conductive agents.

[0040] Figure 10 Rheological performance of 15% lithium titanate - 1% different conductive agents (G' / G" and critical strain plot).

[0041] Figure 11 Conductivity performance of 15% lithium titanate - 1% different conductive agents.

[0042] Figure 12 Conductivity performance of 15% lithium titanate - 1% different conductive agents (partial enlargement).

[0043] Figure 13 Change in solid content of each layer of 15% lithium titanate - 1% different conductive agents at 0h, 3h, 6h.

[0044] Figure 14 Settling performance of different solid content lithium titanate - 1% SP / CNT.

[0045] Figure 15 Conductivity performance of different solid content lithium titanate - 1% SP / CNT.

[0046] Figure 16 Rheological performance of different solid content lithium titanate - 1% SP / CNT.

[0047] Figure 17 Digital photo of settling effect of 15% lithium titanate - 1% different conductive agents.

[0048] Figure 18 Digital photo of settling effect of different solid content lithium titanate - 1% CNT.

[0049] Figure 19 Digital photo of settling effect of different solid content lithium titanate - 1% SP.

[0050] Figure 20The settling effect comparison digital photo of 10% / 15% lithium titanate-1% CNT and 10% / 15% lithium titanate-1% SP.

[0051] Table 1 is the conductivity record value of 15% lithium titanate-1% different conductive agent 24h

[0052] Table 2 is the change record table of solid content of 15% lithium titanate-1% different conductive agent at 0h, 3h, 6h DETAILED DESCRIPTION

[0053] The application will be further described in conjunction with specific examples. It should be understood that the following examples are only used to illustrate the application and not used to limit the scope of the application, and those skilled in the art can make some non-essential improvements and adjustments according to the content of the above application.

[0054] Example 1

[0055] I. Preparation of lithium titanate negative active material

[0056] (1) A certain amount of sucrose was dissolved in deionized water, then lithium titanate was added in an amount of 10 times the mass of sucrose, and high-energy solid-liquid mixing was performed by using a defoaming machine (2000 rpm, 30 min) to obtain slurry A;

[0057] (2) Slurry A was spray dried at an inlet temperature of 150°C and an outlet temperature of 70°C, and then calcined at 850°C for 3h to obtain carbon-coated lithium titanate material;

[0058] (3) The above carbon-coated lithium titanate material and carbon nanotube CNT conductive agent were mixed uniformly at a mass ratio of 98:2 to obtain slurry B;

[0059] (4) Slurry B was spray dried at an inlet temperature of 150°C and an outlet temperature of 50°C to obtain lithium titanate negative active material, as shown in Figure 1 .

[0060] II. Preparation of lithium titanate negative slurry

[0061] (5) The conductive agent and lithium titanate negative active material were mixed in a mass ratio of 1:15 in a mixer, the mixing equipment used was a mixer without any stirring paddle in the material tank, with a uniformly distributed star-shaped rotor, and the material tank was installed at an angle, the mixing speed and time were controlled in a stepwise manner, the mixing speed was 700 rpm and 1200 rpm, and the mixing time was 300 s and 600 s, respectively, to obtain a solid powder with uniform composition.

[0062] (6) Add electrolyte to the above solid powder at a solid-liquid mass ratio of 16:84, and continue mixing in a mixer at a mixing speed of 600 rpm and 1000 rpm for 300 s and 150 s respectively to obtain lithium titanate anode slurry.

[0063] III. Electrochemical Performance Testing of Lithium Titanate Anode Slurry

[0064] According to Figure 2 As shown, the reactor was assembled, with lithium metal as the negative electrode, and charged and discharged at 0.1C.

[0065] IV. Screening of Conductive Agents for Slurry

[0066] 1. Sedimentation effect of different conductive agent slurries: 1% conductive agent (carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB, and carbon nanotubes CNT) was used to prepare lithium titanate anode slurries with 15% lithium titanate anode active material and 84% electrolyte. 13 ml of each slurry was placed in a 15 ml test tube, and the sedimentation amount was recorded at 0 h, 1 h, 2 h, and 3 h. For example... Figure 8 and Figure 17 As shown, it can be seen that:

[0067] As time increases, the sedimentation effect of slurries containing different conductive agents (1%) is CNT>SP>CABOT>KB>VGCF.

[0068] 2. Rheological properties of slurries with different conductive agents: 1% conductive agent (carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB, and carbon nanotubes CNT) was used to prepare lithium titanate anode slurries with 15% lithium titanate anode active material and 84% electrolyte. Rheological tests were performed on a rheometer. Figure 9 and Figure 10 As shown, we can conclude that:

[0069] 1) The viscosity of slurries with different conductive agents decreases as the shear rate increases;

[0070] 2) The viscosity of the slurries containing different conductive agents (1%) is in the following order: CNT > SP > CABOT > KB > VGCF;

[0071] 3) The critical strain (γF) points appear in the following order from left to right: VGCF, KB, CABOT, SP, CNT. The further to the right the critical strain point appears, the better the settling performance. This is consistent with the results observed visually of the settling effects of different conductive agent slurries, as seen from the rheological data.

[0072] 4) Higher viscosity results in better settling performance: CNT has the highest viscosity and settles the slowest. VGCF has the lowest viscosity and settles the fastest.

[0073] 3. Conductivity of different conductive agent slurries: 1% of conductive agent (carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB and carbon nanotube CNT) was respectively mixed with 15% lithium titanate negative active material, 84% electrolyte to prepare lithium titanate negative slurry, 30ml of each was taken in 50ml test tube, and the conductivity value within 100min was recorded every 10min, as shown in Table 1, and the following conclusions were drawn: Figure 11 、 Figure 12 and Table 1, and the following conclusions were drawn:

[0074] 1) The conductivity of the slurry with CNT is much higher than that of the slurry with other conductive agents, indicating that the slurry with CNT conductive agent has the strongest conductivity;

[0075] 2) The conductivity increases with time, indicating that there is a sedimentation phenomenon.

[0076] Table 1: Conductivity of 15% lithium titanate-1% different conductive agent

[0077]

[0078] 4. Solid content change of different conductive agent slurries: 1% of conductive agent (carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB and carbon nanotube CNT) was respectively mixed with 15% lithium titanate negative active material, 84% electrolyte to prepare lithium titanate negative slurry, 30ml of each was taken in 50ml test tube, and the slurry at the upper, middle and lower positions was taken on aluminum foil at 0h, 3h, 6h, the original mass m1 was recorded, then it was placed in an oven for 24h, and the mass m2 was recorded again, and the solid content change of different conductive agent slurries was calculated, as shown in Table 2, and the following conclusions were drawn: Figure 13 and Table 2, and the following conclusions were drawn:

[0079] 1) The solid content of the upper layer decreases with time, the solid content of the lower layer increases with time, and the change trend of the middle layer is inconsistent;

[0080] 2) The solid content of the upper, middle and lower layers of the conductive agent CNT slurry changes the least with time, indicating that this slurry is not easy to settle. The solid content of the upper layer of the conductive agent VGCF slurry increases and then decreases with time, and finally remains basically unchanged;

[0081] 3) The middle layer solids content initially increases and then decreases over time, indicating that initially the upper layer settling velocity is greater than the lower layer settling velocity, but later the upper layer settling velocity becomes less than the lower layer settling velocity, meaning that the conductive agent VGCF slurry has the fastest settling velocity. For the conductive agent KB slurry, the upper layer settling velocity is greater than the lower layer settling velocity within 6 hours, and the change is large, indicating a relatively fast settling velocity. For the conductive agent CABOT slurry, the upper layer settling velocity is greater than the lower layer settling velocity within 6 hours, and the change is small, indicating a slow settling velocity. For the conductive agent SP slurry, the upper layer settling velocity is greater than the lower layer settling velocity within 6 hours, and the solids content of the lower and middle layers is relatively close, indicating a relatively slow settling velocity.

[0082] Table 2 shows the changes in solid content of each layer at 0h, 3h, and 6h for 15% lithium titanate-1% different conductive agents.

[0083]

[0084] 5. Sedimentation effect of lithium titanate slurries with different solid contents: Lithium titanate anode active materials of 10%, 15%, 20%, and 25% were prepared with 1% conductive agent (CNT and SP), 89%, 84%, 79%, and 74% electrolyte, respectively, to prepare lithium titanate anode slurries. 13 ml of each slurry was placed in a 15 ml test tube, and the sedimentation amount was recorded at 0 h, 1 h, 2 h, and 3 h. Figure 14 , Figure 18 , Figure 19 and Figure 20 As shown, we can conclude that:

[0085] As the solid content increases, the sedimentation effect of the slurry with added SP conductive agent gradually improves; the slurry with added CNT conductive agent shows no obvious sedimentation.

[0086] 6. Conductivity of lithium titanate slurries with different solid contents: Lithium titanate anode active materials of 10%, 15%, 20%, and 25% were prepared with 1% conductive agent (CNT and SP), 89%, 84%, 79%, and 74% electrolyte, respectively, to form lithium titanate anode slurries. 30 ml of each slurry was placed in a 50 ml test tube, and the conductivity was measured every 10 minutes. The conductivity values ​​within 100 minutes were recorded. Figure 15 As shown, we can conclude that:

[0087] The conductivity of CNT-containing slurry increases with increasing solid content. The conductivity of SP-containing slurry decreases with increasing solid content.

[0088] 7. Rheological properties of lithium titanate slurries with different solid contents: Lithium titanate anode active materials of 10%, 15%, 20%, and 25% were prepared into lithium titanate anode slurries with 1% conductive agent (CNT and SP), 89%, 84%, 79%, and 74% electrolyte, respectively. Rheological tests were performed on a rheometer.Figure 16 As shown, we can conclude that:

[0089] Solid content has a significant impact on the rheological properties of suspensions. Different systems exhibit the same trend in terms of solid content: viscosity increases with increasing solid content, and decreases with increasing shear rate.

[0090] Based on the analysis in sections 1-7 above, the following are the results regarding the sedimentation performance of different types of conductive agents in lithium-ion battery slurry: CNT > SP > CABOT > KB > VGCF; in terms of rheological properties, the viscosity order is CNT > SP > CABOT > KB > VGCF; and in terms of electrical conductivity, CNT > KB > CABOT > SP > VGCF. CNT exhibits significantly higher values ​​for both conductivity and viscosity than other conductive agents. However, for lithium-ion batteries, the electrode slurry flows between the storage tank and the battery reactor via a sealed pipeline driven by a pump during operation, thus requiring good slurry flowability. CNT conductive agent slurry has excessive viscosity and poor flowability, making it unsuitable for slurry flow testing. SP conductive agent slurry demonstrates superior sedimentation performance compared to CABOT, KB, and VGCF, while also possessing moderate conductivity and viscosity. Considering both the stability and flowability of the slurry suspension, the spherical conductive agent SP was ultimately selected as the conductive agent for the slurry.

[0091] Example 2

[0092] I. Preparation of Lithium Titanate Anode Active Material

[0093] (1) Dissolve a certain amount of sucrose in deionized water, then add lithium titanate at 8 times the mass of sucrose, and use a degassing machine to mix the solid and liquid phases at high energy (3500 rpm, 15 min) until uniform, to obtain slurry A;

[0094] (2) Slurry A was spray-dried at an inlet temperature of 150°C and an outlet temperature of 80°C, and then calcined at 800°C for 3.5 hours to obtain carbon-coated lithium titanate material.

[0095] (3) The carbon-coated lithium titanate material and carbon nanotubes are mixed evenly at a mass ratio of 99:1 to obtain slurry B;

[0096] (4) Spray dry slurry B with an inlet temperature of 180°C and an outlet temperature of 60°C to obtain lithium titanate anode active material.

[0097] II. Preparation of Lithium Titanate Anode Slurry

[0098] (5) The conductive agent SP and lithium titanate negative electrode active material are added to the mixer at a mass ratio of 3:27. The mixing equipment is a mixer without any stirring paddle in the material tank, with a uniformly distributed star rotor and the material tank is installed at an angle. The mixing speed and time are controlled in a step manner. The mixing speed is 800 rpm and 1400 rpm for 300 s and 660 s respectively to obtain a solid powder with uniform composition.

[0099] (6) Add electrolyte to the above solid powder at a solid-liquid mass ratio of 30:70, and continue mixing in a mixer at a mixing speed of 600 rpm and 800 rpm for 300 s and 150 s respectively to obtain lithium titanate anode slurry.

[0100] Example 3

[0101] I. Preparation of Lithium Titanate Anode Active Material

[0102] (1) Dissolve a certain amount of sucrose in deionized water, then add lithium titanate at 13 times the mass of sucrose, and use a degassing machine to mix the solid and liquid phases at high energy (1000 rpm, 60 min) until uniform, to obtain slurry A;

[0103] (2) Slurry A was spray-dried at an inlet temperature of 130°C and an outlet temperature of 45°C, and then calcined at 700°C for 4 hours to obtain carbon-coated lithium titanate material.

[0104] (3) The carbon-coated lithium titanate material and carbon nanotube / carbon black SP conductive agent are mixed evenly at a mass ratio of 97:3 to obtain slurry B, wherein the mass ratio of carbon nanotube / carbon black SP is 1:2.

[0105] (4) Spray dry slurry B with an inlet temperature of 195°C and an outlet temperature of 80°C to obtain lithium titanate anode active material.

[0106] II. Preparation of Lithium Titanate Anode Slurry

[0107] (5) The conductive agent SP and lithium titanate negative electrode active material are added to the mixer at a mass ratio of 4:10. The mixing equipment is a mixer without any stirring paddle in the material tank, with a uniformly distributed star rotor and the material tank is installed at an angle. The mixing speed and time are controlled in a step manner. The mixing speed is 800 rpm and 1300 rpm for 300 s and 600 s respectively to obtain a solid powder with uniform composition.

[0108] (6) Add electrolyte to the above solid powder at a solid-liquid mass ratio of 30:70, and continue mixing in a mixer at a mixing speed of 600 rpm and 800 rpm for 300 s and 150 s respectively to obtain lithium titanate anode slurry.

[0109] Example 4

[0110] I. Preparation of Lithium Titanate Anode Active Material

[0111] (1) Dissolve a certain amount of sucrose in deionized water, then add lithium titanate at 11 times the mass of sucrose, and use a degassing machine to mix the solid and liquid phases at high energy (3000 rpm, 20 min) until uniform, to obtain slurry A;

[0112] (2) Slurry A was spray-dried at an inlet temperature of 150°C and an outlet temperature of 55°C, and then calcined at 950°C for 1.5 hours to obtain carbon-coated lithium titanate material.

[0113] (3) The carbon-coated lithium titanate material and the graphene / carbon nanotube conductive agent were mixed evenly at a mass ratio of 99.5:0.5 to obtain slurry B, wherein the mass ratio of graphene / carbon nanotube was 0.25:0.25.

[0114] (4) Spray dry slurry B at an inlet temperature of 160°C and an outlet temperature of 70°C to obtain lithium titanate anode active material.

[0115] II. Preparation of Lithium Titanate Anode Slurry

[0116] (5) Add the conductive agent and lithium titanate negative electrode active material into the mixer at a mass ratio of 0.5:25 and mix at a mixing speed of 700 rpm and 1400 rpm for 300 s and 700 s respectively to obtain a solid powder with uniform composition.

[0117] (6) Add electrolyte to the solid powder at a solid-liquid mass ratio of 25.5:74.5 and continue mixing in a mixer. The mixing equipment is a mixer without any stirring paddles in the material tank, with a uniformly distributed star rotor and the material tank is installed at an angle. The mixing speed and time are controlled in a step manner. The mixing speed is 600 rpm and 1000 rpm for 600 s and 120 s respectively to obtain lithium titanate anode slurry.

[0118] Comparative Example 1

[0119] Compared to Example 1, the slurry was prepared by directly mixing lithium titanate raw material, electrolyte, and conductive agent. In other words, the lithium titanate was not carbon-coated or doped with conductive agent. The remaining steps were the same as in Example 1, as detailed below:

[0120] (1) The conductive agent and lithium titanate raw material are added to the mixer at a mass ratio of 1:15 and mixed at a mixing speed of 700 rpm and 1200 rpm for 300 s and 600 s respectively to obtain a solid powder with uniform composition.

[0121] (2) Add electrolyte to the solid powder at a solid-liquid mass ratio of 16:84, and continue mixing in a mixer at a mixing speed of 600 rpm and 1000 rpm for 300 s and 150 s respectively to obtain lithium titanate anode slurry.

[0122] The primary purpose of Comparative Example 1 was to investigate the influence of active materials on slurry performance. Unlike lithium-ion batteries, lithium slurry battery electrode suspensions contain a large amount of electrolyte, in which active materials and conductive agents are suspended. Therefore, the ability of active particles, conductive agents, and active particles and conductive agents to connect and form a conductive network is crucial. Lithium titanate itself has poor conductivity and a spherical shape, which is not conducive to building a conductive network in the slurry system. Therefore, carbon coating is used to enhance conductivity, and linear or mesh-like conductive agents are used for doping to increase conductivity. Experimental results show that lithium titanate slurries without carbon coating and conductive agent doping exhibit significantly deteriorated initial efficiency, discharge capacity, and cycle life. See details below. Figure 3 and Figure 4 .

[0123] Comparative Example 2

[0124] Compared to Example 1, lithium titanate only underwent carbon coating, while the remaining steps were the same as in Example 1. The specific steps are as follows:

[0125] (1) Dissolve a certain amount of sucrose in deionized water, then add lithium titanate at 10 times the mass of sucrose, and use a degassing machine to mix the solid and liquid phases at high energy (2000 rpm, 30 min) until uniform, to obtain slurry A;

[0126] (2) Slurry A was spray-dried at an inlet temperature of 150°C and an outlet temperature of 70°C, and then calcined at 850°C for 3 hours to obtain carbon-coated lithium titanate material.

[0127] (3) The conductive agent and carbon-coated lithium titanate material are added to the mixer at a mass ratio of 1:15 and mixed at 700 rpm and 1200 rpm for 300 s and 600 s respectively to obtain a solid powder with uniform composition.

[0128] (4) Add electrolyte to the solid powder at a solid-liquid mass ratio of 16:84, and continue mixing in a mixer at a mixing speed of 600 rpm and 1000 rpm for 300 s and 150 s respectively to obtain lithium titanate anode slurry.

[0129] The main purpose of Comparative Example 2 was to investigate the effect of active materials on slurry performance. Lithium titanate material itself has poor conductivity and a spherical shape, which is not conducive to constructing a conductive network in the slurry system. This study investigated the effect of carbon coating without carbon nanotube doping. Experimental results showed that carbon coating alone resulted in electrochemical performance inferior to Example 1, but significantly improved performance compared to unmodified lithium titanate raw material. See details below. Figure 3 and Figure 5 .

[0130] Comparative Example 3

[0131] Compared to Example 1, lithium titanate only underwent carbon nanotube doping, while the remaining steps were the same as in Example 1. The specific steps are as follows:

[0132] (1) Lithium titanate material and carbon nanotube (CNT) conductive agent are mixed evenly at a mass ratio of 98:2 to obtain slurry B;

[0133] (2) Spray drying of slurry B with an inlet temperature of 150°C and an outlet temperature of 50°C to obtain carbon nanotube-doped lithium titanate material.

[0134] (3) The conductive agent and carbon nanotube-doped lithium titanate material were added to the mixer at a mass ratio of 1:15 and mixed at 700 rpm and 1200 rpm for 300 s and 600 s respectively to obtain a solid powder with uniform composition.

[0135] (4) Add electrolyte to the solid powder at a solid-liquid mass ratio of 16:84, and continue mixing in a mixer at a mixing speed of 600 rpm and 1000 rpm for 300 s and 150 s respectively to obtain lithium titanate anode slurry.

[0136] The main purpose of Comparative Example 3 was to investigate the effect of active materials on slurry performance. It examined the effect of carbon nanotube doping alone, and also compared the effects of carbon nanotube doping and carbon coating. The experimental results showed that carbon nanotube doping alone resulted in electrochemical performance inferior to Comparative Example 2, indicating that carbon coating is more effective than carbon nanotube doping. (See details in [link to Comparative Example 3]). Figure 3 , Figure 5 and Figure 6 .

[0137] Comparative Example 4

[0138] Compared with Example 1, lithium titanate is first doped with carbon nanotubes and then coated with carbon. The remaining steps are the same as in Example 1. The specific steps are as follows:

[0139] (1) Lithium titanate material and carbon nanotube (CNT) conductive agent are mixed evenly at a mass ratio of 98:2 to obtain slurry B;

[0140] (2) Spray drying of slurry B with an inlet temperature of 150°C and an outlet temperature of 50°C to obtain carbon nanotube-doped lithium titanate material.

[0141] (3) Dissolve a certain amount of sucrose in deionized water, and then add the above carbon nanotube-doped lithium titanate material at 10 times the mass of sucrose. After uniform mixing of solid and liquid phases using a degassing machine (2000 rpm, 30 min), slurry A is obtained.

[0142] (4) Spray drying of slurry A at an inlet temperature of 150℃ and an outlet temperature of 70℃, followed by calcination at 850℃ for 3 hours to obtain lithium titanate anode active material.

[0143] The main purpose of Comparative Example 4 was to investigate the effect of lithium titanate modification process on slurry performance. Experimental results showed that performing carbon nanotube doping followed by carbon coating yielded worse results than either carbon coating alone or carbon nanotube doping alone. (See details below.) Figure 5 and Figure 6 , Figure 7 .

[0144] This invention modifies the active material by carbon coating and carbon nanotube doping to improve the conductivity of the slurry suspension. Compared with the technical solutions of Comparative Examples 1-4, the technical solution of this invention is superior.

[0145] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A lithium titanate anode slurry for lithium-ion batteries, characterized in that, The lithium titanate anode slurry is composed of the following components by weight percentage: 5%-30% lithium titanate anode active material, 70%-94% electrolyte, and 0.5%-4% conductive agent I; The lithium titanate anode active material is prepared by carbon-coated lithium titanate and conductive agent II, wherein the conductive agent II accounts for 0.5%-3% of the mass of carbon-coated lithium titanate; The conductive agent I is a spherical conductive agent SP.

2. The method for preparing lithium titanate anode slurry for lithium slurry batteries according to claim 1, characterized in that... Includes the following steps: (1) Lithium titanate powder is added to sucrose solution and mixed evenly with solid-liquid phase using a degassing machine to obtain slurry A; (2) Spray drying and calcination of slurry A were performed to obtain carbon-coated lithium titanate; (3) Mix carbon-coated lithium titanate and conductive agent II evenly to obtain slurry B; (4) Spray dry slurry B to obtain lithium titanate anode active material; (5) Conductive agent I was obtained by screening through the screening mechanism of conductive agents for lithium slurry battery electrode slurry; (6) Mix the conductive agent I and the lithium titanate anode active material to obtain a solid powder with uniform composition. Add electrolyte to the solid powder to obtain lithium titanate anode slurry for lithium slurry batteries.

3. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, In step (1), the mass ratio of lithium titanate to sucrose is (8-13):1, the high-energy mixing speed of the solid-liquid phase in the degassing machine is 1000-4000, and the time is 10min-60min.

4. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, In step (2), the inlet temperature of the spray dryer is 130℃-200℃ and the outlet temperature is 40℃-80℃.

5. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, In step (2), the calcination temperature is 650℃-950℃, and the holding time is 1.5 h-4 h.

6. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, In step (3), the conductive agent II is a linear or network conductive agent, including one or a mixture of at least two of the following: carbon nanotubes, graphene, carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB, or nano-activated carbon.

7. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, In step (4), the inlet temperature of the spray dryer is 130℃-200℃ and the outlet temperature is 40℃-80℃.

8. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, In step (6), the mixing equipment used is a mixer without any stirring paddles in the material tank. It has a uniformly distributed star rotor and the material tank is installed at an angle. The mixing speed and time are controlled in a step-like manner. The mixing speed is greater than 500 rpm and less than 1500 rpm each time, and the mixing time is greater than 100 s and less than 800 s each time.

9. The method for preparing lithium titanate anode active material for lithium slurry batteries according to claim 2, characterized in that, The screening mechanism for conductive agent I in lithium slurry battery electrode slurry in step (5) includes the following steps: S1. Identify the key factors affecting the lithium slurry battery electrode slurry of different conductive agent types: slurry settling properties, rheological properties and conductivity. S2. With the proportions of active substances, conductive agents and electrolytes in the slurry fixed, and the type of conductive agent as the variable, the effects of different types of conductive agents on the sedimentation performance, rheological properties and conductivity of the slurry are obtained. S3. Based on the comprehensive evaluation of the three types of indicators, conductive agents with excellent slurry performance are selected. S4. Based on step S3, fix the conductive agent content, change the active material content, and obtain the law of change of slurry sedimentation performance, rheological properties and conductivity with the solid content of active material under different types of conductive agents, so as to screen out conductive agent I.

10. The method for preparing the lithium titanate anode active material for lithium slurry batteries according to claim 9, characterized in that, The different types of conductive additives include carbon fiber VGCF, Cabot CABOT, carbon black SP, Ketjen black KB, and carbon nanotubes CNT.

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