A washing method for reducing residual alkali on the surface of positive electrode material and improving yield

Abstract

The present invention provides a washing method for reducing residual alkali on the surface of a positive electrode material and improving the yield. The washing method comprises the following steps: (1) adding a water washing agent to a water washing container, starting stirring, adding a positive electrode material, washing and stirring to obtain a slurry; (2) injecting the slurry obtained in step (1) into a filter press for filter pressing, circulating the obtained filtrate between the water washing container and the filter press through a circulation system, filtering while circulating, and drying the filter cake after the filter pressing to obtain the positive electrode material. The present invention controls the residual alkali content by controlling the water temperature, the water-to-material ratio and the circulation time of the filtrate during the water washing process, thereby not only controlling the residual alkali content but also achieving a yield of more than 99%.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries and relates to a washing method for reducing residual alkali on the surface of a positive electrode material and improving yield. Background Art

[0002] Cathode materials are a core, critical component of lithium-ion batteries. Their properties directly determine their energy density, cycle performance, and safety. They account for approximately 40% of battery costs, directly impacting battery cost. Driven by the new energy vehicle industry's demand for increased range and national policies, high-nickel ternary cathode materials have become the mainstream technology for cathode materials, with their share increasing annually. With the maturity of high-nickel ternary technology and the rising prices of nickel, cobalt, and lithium, cost, while ensuring performance, is becoming a growing concern.

[0003] Due to the low primary sintering temperature of high-nickel products and the difficulty of Ni oxidation, high-nickel cathode materials contain relatively high levels of residual LiOH and Li2CO3 in their first-fired form. Excessive residual lithium can lead to problems such as jelly-like slurry, electrode scaling, increased internal resistance, and flatulence during battery production. Excessive residual alkali can easily lead to excessive lithium loss, decreased capacity, and poor cycling performance. Therefore, during cathode material preparation, it is necessary not only to remove residual lithium from the surface of high-nickel cathode materials but also to control the residual lithium level. There are two most effective methods for removing residual lithium from high-nickel surfaces. The first involves introducing additives during the first or second sintering coating process, but this method often fails to achieve the desired effect. The second method involves removing residual alkali during the water washing process, which involves introducing additives or weak acids. This method primarily removes residual alkali in the water washing tank. While water washing can remove residual alkali on the surface, it is difficult to control the amount of residual alkali in the cathode material and can result in material loss, yields below 99%, and increased production costs.

[0004] CN108878863A discloses a method for improving the residual alkalinity on the surface of a ternary positive electrode material for a lithium ion battery, comprising the following steps: x Co y Mn z A powdered nickel-cobalt-manganese layered cathode material containing O2 is mixed with water and centrifuged to obtain a washed powder material. A lithium source is added to anhydrous ethanol and mixed evenly, and the washed powder material is then added and mixed evenly. The material is evaporated completely, dried, and sintered to obtain a ternary cathode material for a lithium-ion battery. This invention uses an ethanol system to replenish lithium and perform a secondary sintering after washing to replace the lithium lost during the washing process. This method involves multiple steps, requiring the use of organic solvents in industrial production and increasing material losses with each additional step.

[0005] CN112186156A discloses a method for washing a high-nickel cathode material, a product thereof, and uses thereof. The method comprises mixing the high-nickel cathode material with a boric acid solution, reacting the solution, and sintering the solution to obtain the washed high-nickel cathode material. The method uses vacuum filtration for solid-liquid separation, and neither specifies a residual alkali control range nor addresses yield issues. This method is clearly a conventional water washing method, with a yield of less than 99%. Summary of the Invention

[0006] The present invention aims to provide a washing method that reduces residual alkali on the surface of positive electrode materials and improves yield. The method controls the residual alkali content by controlling the water temperature, water-to-material ratio, and filtrate circulation time during the washing process. A portion of the residual alkali is removed in the washing tank, while another portion is removed by repeatedly rinsing the filter cake with the filtrate. By adding a filtrate circulation cleaning system and controlling drying process parameters, the residual alkali content can be controlled while also achieving a yield exceeding 99%. During the initial filtration process, most of the material forms a filter cake, while a small portion is lost with the filtrate. Once the filter cake is formed, the filtrate is filtered again, and the remaining portion of the material in the filtrate is retained on the filter cake. Repeating this process several times not only removes the residual alkali but also improves the yield of the positive electrode material. During the drying process, stirring is performed at low temperatures. Due to the relatively wet material, dust is reduced and the water loss rate is high. Stirring is stopped at high temperatures, resulting in a static drying process and low dust generation. This also ensures a high material yield.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a washing method for reducing residual alkali on the surface of a positive electrode material and improving yield, the washing method comprising the following steps:

[0009] (1) Add a water washing agent to a water washing container, start stirring, add a positive electrode material, and wash and stir to obtain a slurry;

[0010] (2) The slurry obtained in step (1) is pumped into a filter press by a diaphragm pump for filter pressing. The obtained filtrate is circulated between a water washing container and a filter press through a circulation system, and filter pressing is performed while circulating. After the filter pressing is stopped, the filter cake is dried to obtain a positive electrode material.

[0011] Without adding water washing steps, equipment, and raw materials, the present invention removes residual alkali on the surface of high-nickel cathode materials for lithium batteries by controlling the water temperature, water-to-material ratio, and filtrate circulation time during the water washing process, and can control the content of residual alkali. During the entire water washing process, the filtrate is repeatedly rinsed through the pipeline, water washing tank, and filter cake by the filtrate circulation cleaning system to control material loss. At the same time, during drying, the material loss is controlled by using the method of high temperature without stirring and low temperature with stirring, so that the yield can reach over 99.0%.

[0012] Preferably, the water washing agent in step (1) includes water.

[0013] Preferably, the conductivity of the water washing agent is ≤2 μS / cm.

[0014] Preferably, the temperature of the water washing agent is 15 - 25 °C, such as 15 °C, 20 °C, or 25 °C, etc.

[0015] Preferably, the water washing container includes a water washing tank.

[0016] Preferably, the chemical formula of the cathode material in step (1) is Li a Ni x Co y M 1-x-y O2, where 1.02 ≤ a ≤ 1.07, 0.70 ≤ x < 0.96, 0 < y < 0.3, and M includes any one or at least two combinations of Mn, Al, Ti, Zr, Y, Sr, Mo, or W.

[0017] Preferably, the mass ratio of the water washing agent to the cathode material in step (1) is (0.4 - 2):1, such as: 0.4:1, 0.5:1, 1:1, 1.5:1, or 2:1, etc.

[0018] Preferably, the water washing stirring time in step (1) is 1 - 30 s, such as: 1 s, 2 s, 5 s, 10 s, or 60 s, etc.

[0019] Preferably, the filtrate circulation time in step (2) is 10 - 30 min, such as: 10 min, 15 min, 20 min, 25 min, or 30 min, etc.

[0020] Preferably, the solid content of the filtrate is ≤0.5%.

[0021] Preferably, the water content of the filter cake in step (2) is ≤10%.

[0022] Preferably, the residual alkali content of the filter cake is 0.3 - 0.6%, such as: 0.3%, 0.4%, 0.5%, or 0.6%, etc.

[0023] Preferably, the drying treatment in step (2) includes placing the filter cake in a drying device with a dust collection system and a stirring device for drying, the dust collector is always kept on, low-temperature stirring is turned on at low temperatures, and the stirring device is turned off at high temperatures, and the dried positive electrode material is obtained after drying.

[0024] Preferably, the low temperature is 80-100°C, for example, 80°C, 85°C, 90°C, 95°C or 100°C.

[0025] Preferably, the low-temperature stirring speed is 1 to 10 rpm, for example, 1 rpm, 2 rpm, 5 rpm, 8 rpm or 10 rpm.

[0026] Preferably, the low-temperature stirring time is 70 to 100 min, for example, 70 min, 80 min, 90 min or 100 min.

[0027] Preferably, the high temperature is 120-150°C, for example, 120°C, 130°C, 140°C or 150°C.

[0028] Preferably, the drying time is 30 to 60 minutes, for example, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0029] Preferably, the moisture content of the dried positive electrode material is 0.05-0.15%, for example, 0.05%, 0.08%, 0.1%, 0.12% or 0.15%.

[0030] Preferably, the residual alkali content of the dried positive electrode material is 0.3-0.6%, for example, 0.3%, 0.4%, 0.5% or 0.6%.

[0031] Preferably, the mass proportion of lithium carbonate in the dried positive electrode material is 0.05-0.20%, for example, 0.05%, 0.08%, 0.1%, 0.15% or 0.20%.

[0032] Preferably, the yield of the dried positive electrode material is 99.0-99.9%, for example, 99.0%, 99.2%, 99.5%, 99.7% or 99.9%.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention removes residual alkali from the surface of high-nickel positive electrode materials for lithium batteries without increasing the number of washing steps, equipment, or raw materials by controlling the water temperature, water-to-material ratio, and filtrate circulation time during the washing process, thereby controlling the residual alkali content. Throughout the washing process, a filtrate circulation cleaning system repeatedly flushes the pipes, washing tank, and filter cake with filtrate to control material loss. Furthermore, during drying, a high-temperature, no-stirring, low-temperature, stirring method is used to control material loss, resulting in a yield exceeding 99.0%. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a process flow chart of the washing method described in Example 1, wherein 1-water pipe for cleaning, 2-water pipe for washing, 3-first storage tank, 4-water washing tank, 5-filter press, 6-second storage tank, 7-drying tank, 8-dust collecting device.

[0036] Figure 2 This is a SEM image of the positive electrode material described in Example 1 of the present invention before water washing.

[0037] Figure 3 This is a SEM image of the cathode material after drying described in Example 1 of the present invention.

[0038] Figure 4 3 is a comparison chart of the charge and discharge capacity of the positive electrode material before washing and after drying according to Example 1 of the present invention. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] Example 1

[0041] Li 1.03 Ni 0.90 Co 0.045 Mn 0.05 W 0.005 Taking O2 as an example, this embodiment provides a washing method for reducing residual alkali on the surface of the positive electrode material and improving the yield. The process flow chart of the washing method is as follows: Figure 1 As shown, 1 is a cleaning water pipe, 2 is a water washing water pipe, 3 is a first storage tank, 4 is a water washing tank, 5 is a filter press, 6 is a second storage tank, 7 is a drying tank, and 8 is a dust collecting device. The washing method specifically includes the following steps:

[0042] (1) Place water at 25°C, weighing 2000 kg, and having a conductivity of 1.0 μS / cm in a stirring tank, turn on the stirring paddle, and measure 2000 kg of the above-mentioned positive electrode material into the stirring tank while stirring. After the measurement is completed, stir for 50 seconds to obtain a slurry;

[0043] (2) The slurry was pumped into the filter press with a diaphragm pump. The filtrate circulation system was turned on at the same time as the filtration. After 20 minutes of circulation, the filtration was continued and air-dried. The solid content of the filtrate, the moisture content of the filter cake and the residual alkali content were tested. The filter cake was placed in a drying tank for drying. The low temperature was set to 90°C, the stirring speed was 3 rpm, and the drying time was 80 minutes. The high temperature was set to 120°C, the stirring paddle was turned off, and the drying time was 40 minutes. The water content, total residual alkali, Li2CO3 content, capacity of the positive electrode material and yield were tested.

[0044] The SEM image of the positive electrode material before washing is as follows Figure 2 As shown, the SEM image after drying is as follows Figure 3 As shown, the charge and discharge capacity comparison of the positive electrode material before washing and after drying is shown in FIG. Figure 4 As shown by Figure 2-4 By comparison, it can be seen that the water washing method described in the present application reduces the residual alkali on the surface of the positive electrode material while improving its electrochemical performance.

[0045] Example 2

[0046] Li 1.03 Ni 0.90 Co 0.045 Mn 0.05 W 0.005 Taking O2 as an example, this embodiment provides a washing method for reducing residual alkali on the surface of the positive electrode material and improving the yield, and the washing method specifically comprises the following steps:

[0047] (1) Place water at 25°C, weighing 2000 kg, and having a conductivity of 1.5 μS / cm in a stirring tank, turn on the stirring paddle, and measure 1000 kg of the above-mentioned positive electrode material into the stirring tank while stirring. After the measurement is completed, stir for 5 seconds to obtain a slurry;

[0048] (2) The slurry was pumped into the filter press with a diaphragm pump. The filtrate circulation system was turned on at the same time as the filtration. After 10 minutes of circulation, the filtration was continued and air-dried. The solid content of the filtrate, the moisture content of the filter cake and the residual alkali content were tested. The filter cake was placed in a drying tank for drying. The low temperature was set to 95°C, the stirring speed was 1 rpm, and the drying time was 90 minutes. The high temperature was set to 120°C, the stirring paddle was turned off, and the drying time was 40 minutes. The moisture content, total residual alkali, Li2CO3 content, capacity of the positive electrode material and yield were tested.

[0049] Example 3

[0050] Li 1.03 Ni 0.70 Co 0.10 Mn 0.19 Al0.01 Taking O2 as an example, this embodiment provides a washing method for reducing residual alkali on the surface of the positive electrode material and improving the yield, and the washing method specifically comprises the following steps:

[0051] (1) Place water at 25°C, weighing 2000 kg, and having a conductivity of 0.5 μS / cm in a stirring tank, turn on the stirring paddle, and measure 2000 kg of the above-mentioned positive electrode material into the stirring tank while stirring. After the measurement is completed, stir for 20 seconds to obtain a slurry;

[0052] (2) The slurry was pumped into the filter press with a diaphragm pump. The filtrate circulation system was turned on at the same time as the filtration. After 10 minutes of circulation, the filtration was continued and air-dried. The solid content of the filtrate, the moisture content of the filter cake and the residual alkali content were tested. The filter cake was placed in a drying tank for drying. The low temperature was set to 85°C, the stirring speed was 7 rpm, the drying time was 100 minutes, and the high temperature was set to 140°C. The stirring paddle was turned off and the drying time was 50 minutes. The moisture content, total residual alkali, Li2CO3 content, capacity of the positive electrode material and yield were tested.

[0053] Example 4

[0054] Li 1.03 Ni 0.70 Co 0.10 Mn 0.19 Al 0.01 Taking O2 as an example, this embodiment provides a washing method for reducing residual alkali on the surface of the positive electrode material and improving the yield, and the washing method specifically comprises the following steps:

[0055] (1) Place water at a temperature of 18°C, weighing 1000 kg, and having a conductivity of 0.5 μS / cm in a stirring tank, turn on the stirring paddle, and measure 2000 kg of the above-mentioned positive electrode material into the stirring tank while stirring. After the measurement is completed, stir for 50 seconds to obtain a slurry;

[0056] (2) The slurry was pumped into the filter press with a diaphragm pump. The filtrate circulation system was turned on at the same time as the filtration. After 25 minutes of circulation, the filtration was continued and air-dried. The solid content of the filtrate, the moisture content of the filter cake and the residual alkali content were tested. The filter cake was placed in a drying tank for drying. The low temperature was set to 80°C, the stirring speed was 10 rpm, and the drying time was 70 minutes. The high temperature was set to 130°C, the stirring paddle was turned off, and the drying time was 50 minutes. The moisture content, total residual alkali, Li2CO3 content, capacity of the positive electrode material and yield were tested.

[0057] Example 5

[0058] The only difference between this embodiment and embodiment 1 is that stirring is also started at high temperature, and the stirring speed is 10 rpm. Other conditions and parameters are exactly the same as those in embodiment 1.

[0059] Example 6

[0060] The only difference between this embodiment and embodiment 1 is that the stirring time (i.e., water washing and stirring) after the metering in step (1) is 5 minutes, and the other conditions and parameters are exactly the same as those in embodiment 1.

[0061] Example 7

[0062] The only difference between this embodiment and embodiment 1 is that the weight of water is changed to 1500 kg and the weight of material is changed to 500 kg.

[0063] Comparative Example 1

[0064] The only difference between this comparative example and Example 1 is that the filtrate circulation system is not turned on, and the other conditions and parameters are exactly the same as those in Example 1.

[0065] The test results obtained in Examples 1-7 and Comparative Examples 1-2 are shown in Table 1:

[0066] Table 1

[0067]

[0068]

[0069] As can be seen from Table 1, according to Examples 1-4, the residual alkali content of the positive electrode material obtained by the washing method of the present invention is 0.3-0.6%, the mass proportion of lithium carbonate in the positive electrode material is 0.05-0.2%, the yield of the positive electrode material after drying can reach more than 99%, and the capacity can be increased by more than 5 mAh / g compared with the burned product. The residual alkali is controlled within a beneficial range and a high yield is guaranteed.

[0070] From the comparison between Example 1 and Example 5, it can be seen that in the washing method of the present invention, stirring is stopped at a high temperature during the drying process, the drying process is in a static state, less dust is generated, and a higher yield of the material can be ensured.

[0071] By comparing Example 1 and Example 6, it can be seen that the time of water washing and stirring will affect the residual alkali on the surface of the positive electrode material. In the conventional washing method, the washing time is generally 5-10 minutes, but in the washing method described in this application, the washing time needs to be controlled within 1 minute. Because the washing time is too long, the amount of residual alkali on the surface of the material will drop significantly, which will lead to a decrease in material performance.

[0072] From the comparison between Example 1 and Example 7, it can be seen that in the washing method of the present invention, the water-to-material ratio needs to be controlled at (0.4-2):1. If the water-to-material ratio is too high, it will also lead to excessive loss of residual alkali on the surface of the positive electrode material, affecting its performance.

[0073] From the comparison between Example 1 and Comparative Example 1, it can be seen that the present invention removes the residual alkali on the surface of the positive electrode material by circulating the filtrate, which can control the content of the residual alkali while improving the yield of the positive electrode material and controlling the loss of the material.

[0074] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A washing method for reducing residual alkali on the surface of positive electrode materials and improving yield, characterized in that: The washing method comprises the following steps: (1) Adding a water washing agent into a water washing container, starting stirring, adding a positive electrode material, and washing and stirring to obtain a slurry; the washing and stirring time is 1 to 60 seconds; the water washing agent is water; (2) The slurry obtained in step (1) is pumped into a filter press for filter pressing, and the obtained filtrate is circulated between the water washing container and the filter press through a circulation system, and the filter pressing is performed while circulating. After the filter pressing is stopped, the filter cake is dried to obtain the positive electrode material; The drying treatment in step (2) includes placing the filter cake in a drying device with a dust collection system and a stirring device for drying, the dust collector is always kept in an on state, low-temperature stirring is turned on at low temperatures, and the stirring device is turned off at high temperatures, and the dried positive electrode material is obtained after drying; the low-temperature temperature is 80~100℃; the high-temperature temperature is 120~150℃; the residual alkali content of the filter cake is 0.3~0.6%.

2. The washing method according to claim 1, wherein The conductivity of the water lotion is ≤2µS / cm.

3. The washing method according to claim 1, wherein The temperature of the water lotion is 15-25°C.

4. The washing method according to claim 1, wherein The water washing container includes a water washing tank.

5. The washing method according to claim 1, wherein The chemical formula of the cathode material described in step (1) is Li a Ni x Co y M 1-x-y O2, where 1.02 ≤ a ≤ 1.07, 0.70 ≤ x < 0.96, 0 < y < 0.3, and M includes any one or a combination of at least two of Mn, Al, Ti, Zr, Y, Sr, Mo, or W.

6. The washing method according to claim 1, wherein The mass ratio of the water washing agent and the positive electrode material in step (1) is (0.4~2):

1.

7. The washing method according to claim 1, wherein The filtrate circulation time in step (2) is 10 to 30 minutes.

8. The washing method according to claim 1, wherein The solid content of the filtrate is ≤0.5%.

9. The washing method according to claim 1, wherein The moisture content of the filter cake in step (2) is ≤10%.

10. The washing method according to claim 1, wherein The low-temperature stirring speed is 1-10 rpm.

11. The washing method according to claim 1, wherein The low temperature stirring time is 70 to 100 minutes.

12. The washing method according to claim 1, wherein The drying time is 30 to 60 minutes.

13. The washing method according to claim 1, wherein The moisture content of the dried positive electrode material is 0.05-0.15%.

14. The washing method according to claim 1, wherein The residual alkali content of the dried positive electrode material is 0.3-0.6%.

15. The washing method according to claim 1, wherein The mass proportion of lithium carbonate in the dried positive electrode material is 0.05-0.20%.

16. The washing method according to claim 1, wherein The yield of the dried positive electrode material is 99.0-99.9%.

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