A potassium and phosphate dual-doped lithium-rich layered positive electrode material and preparation method thereof

Abstract

The present invention relates to a lithium-rich layered positive electrode material doped with potassium and phosphate, the chemical formula of which is Li 1‑x K x (Li a Ni b Co c Mn d ) 2‑y (PO 4 ) y ,a+b+c+d=1,1>x>0,2>y>0. The ultrafast heating rate and reaction kinetics of Joule heat enable the dual-doped lithium-rich layered materials to be synthesized within seconds, greatly reducing energy consumption and improving production efficiency. + and (PO 4 ) 3‑ The dual doping can effectively inhibit the irreversible release of oxygen and the irreversible transformation of the structure during the cycle of the material.

Description

Technical Field

[0001] The invention relates to the field of lithium-rich layered positive electrode materials and preparation methods thereof, in particular to a potassium- and phosphate-doped lithium-rich layered positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have been widely used in portable electronic products, electric vehicles and large energy storage devices. With the rapid expansion of market demand, the development of lithium-ion batteries with high energy density, long cycle life and low cost has become a top priority. Among all the components of lithium-ion batteries, the positive electrode plays a vital role in determining the cost and energy density of the entire battery. At present, the mainstream positive electrode materials in the market include LiMn2O4, LiCoO2, LiFePO4, LiNi x Co y Mn z O2 (x + y + z = 1), its specific capacity is less than 200mAh / g, which seriously limits the improvement of the energy density of lithium-ion batteries. Compared with the above positive electrode materials, lithium-rich layered positive electrode materials (xLiMO2 · (1-x) Li2MnO3 (M = Ni, Co, Mn)) can provide a specific capacity of more than 250mAh / g, and its ultra-high specific capacity is due to the common redox mechanism of transition metals and oxygen. In addition, due to the low cobalt or cobalt-free content, compared with other positive electrode materials, it also shows a lower cost advantage. Although lithium-rich layered materials show the above advantages, the problem of rapid capacity and voltage decay has hindered its further commercial development. At present, researchers believe that there are two main reasons for the occurrence of the above problems. One is that the irreversible release of oxygen leads to serious interfacial side reactions and triggers the redox reaction of transition metals at low voltage. The second is the irreversible transformation of the layered structure to the spinel phase during the cycle. In order to solve this problem, researchers have proposed various strategies to suppress the capacity and voltage decay of the material. Among them, ion doping is the most widely used and effective strategy. The doped ions can inhibit the irreversible release of oxygen and the structural transformation, greatly improving the cycle stability of lithium-rich layered materials. Currently, a variety of ions have been used as dopants, including cations (Al 3+ ,Ti 4+ ,Ru 4+ ,La 3+ ), anion (Cl - ,S 2- ,F - ). However, the above doping preparation process is very complicated and the heat treatment process takes several hours, resulting in huge energy consumption and manufacturing costs.

[0003] Therefore, there is a need for a potassium and phosphate dual-doped lithium-rich layered positive electrode material and a preparation method thereof. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing doping methods that are cumbersome and time-consuming, and to provide a method for rapidly synthesizing a lithium-rich layered positive electrode material doped with potassium and phosphate using Joule heat and a preparation method thereof. On the one hand, the ultra-high heating rate of Joule heat and the ultra-fast reaction kinetics ensure that the dual-doped lithium-rich layered material can be successfully synthesized within seconds. On the other hand, dual doping with potassium and phosphate can improve the structural stability of the material and improve the cycle performance of the lithium-rich layered material.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A potassium and phosphate doped lithium-rich layered cathode material, the chemical formula of which is Li 1-x K x (Li a Ni b Co c Mn d ) 2-y (PO4) y ,a+b+c+d=1,1>x>0,2>y>0.

[0007] A method for preparing a lithium-rich layered positive electrode material doped with potassium and phosphate, comprising: m Co k Ni n The CO3 precursor is mixed with lithium salt and KH2PO4 according to the chemical formula ratio through ball milling. A small amount of anhydrous ethanol is added during the ball milling process. After the ball milling is completed, it is placed in a 60°C vacuum oven for drying and ground into powder, where m+k+n=1; then Joule heat treatment is carried out. During the Joule heat treatment process, the reaction temperature reaches 660°C through ultra-fast heating, and the reaction temperature is maintained for 60 seconds. After grinding evenly, the powder is placed on a nickel foil substrate for secondary calcination, and the current and voltage are adjusted to a temperature of 970°C. After 45 seconds, the power is disconnected.

[0008] Furthermore, Mn m Co k Ni n The CO3 precursor was prepared by coprecipitation (compared with other precursor preparation methods, such as sol-gel method and solid phase ball milling method, the Mn m Co k Ni n CO3, lithium salt and KH2PO4 are intercalation reaction mechanisms during the calcination process, and their reaction path and reaction kinetics are faster, ensuring that the positive electrode material can be successfully prepared within seconds).

[0009] Further, the lithium salt refers to Li2CO3.

[0010] The Joule heat used in this application is the heat generated by current passing through the conductor when a voltage is applied across the two ends of the conductor sheet. The conductor sheet can be an aluminum sheet, a nickel sheet, a cobalt sheet, or the like.

[0011] The heating rate, cooling rate and reaction temperature can be measured by a thermal infrared imager, and the reaction temperature can be adjusted by adjusting the current and voltage.

[0012] The present invention has the beneficial effects:

[0013] (1) The ultrafast heating rate and reaction kinetics of Joule heat enable the synthesis of dual-doped lithium-rich layered materials within seconds, greatly reducing energy consumption and improving production efficiency.

[0014] (2) K + and (PO4) 3- The dual doping can effectively inhibit the irreversible release of oxygen and the irreversible transformation of the structure during the cycle. Compared with the poor capacity retention rate of the undoped material (the capacity retention rate after 150 cycles is 67%) and the rapid voltage decay (the voltage drop after 150 cycles is 0.40V), the dual doped material shows a higher capacity retention rate (the capacity retention rate after 150 cycles is 84%) and a slower voltage decay (the voltage drop after 150 cycles is 0.30V). BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Li prepared in Example 1 and Example 2 of the present invention 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2、Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 X-ray diffraction (XRD) patterns of lithium-rich layered materials;

[0016] Figure 2 Li prepared in Example 2 of the present invention 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Transmission electron microscopy (TEM) images of lithium-rich layered materials;

[0017] Figure 3Li prepared in Example 2 of the present invention 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 High-resolution transmission electron microscopy (TEM) image of lithium-rich layered materials;

[0018] Figure 4 Li prepared in Example 2 of the present invention 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Fourier transform (FFT) image corresponding to the high-resolution transmission electron microscopy (TEM) image of lithium-rich layered materials;

[0019] Figure 5 Li prepared in Example 2 of the present invention 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 EDS mapping of lithium-rich layered materials;

[0020] Figure 6 Li prepared in Example 1 and Example 2 of the present invention 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2、Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Capacity cycling performance diagram of lithium-rich layered materials;

[0021] Figure 7 Li prepared in Example 1 and Example 2 of the present invention 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2、Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Voltage cycling performance diagram of lithium-rich layered materials. DETAILED DESCRIPTION

[0022] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0023] Example 1: Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 Li-rich layered materials (Li 1-x K x (Li a Ni b Co c Mn d ) 2-y (PO4) y ,a=0.2,b=0.13,c=0.13,d=0.54,x=0,y=0)

[0024] Step 1: 0.9388 g of Mn 4 / 6 Co 1 / 6 Ni 1 / 6 CO3(Mn m Co k Ni n CO3, m=4 / 6, k=1 / 6, n=1 / 6) and 0.4601g of Li2CO3 were mixed by ball milling, and a small amount of anhydrous ethanol was added during the ball milling process. After the ball milling, it was placed in a vacuum oven at 60°C for drying and ground into powder.

[0025] Step 2: In this embodiment, nickel foil is used as a conductor sheet for rapid heating, and the size is 2*5cm 2 The precursor powder obtained in step 1 was placed on a nickel foil substrate, and then the current and voltage were adjusted to a temperature of 660°C. After 60 seconds, the power supply was disconnected. After grinding evenly, the powder was placed on a nickel foil substrate for secondary calcination. The current and voltage were adjusted to a temperature of 970°C. After 45 seconds, the power supply was disconnected. After grinding evenly, Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 lithium-rich layered materials.

[0026] For this embodiment, Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 material was subjected to XRD test, such as Figure 1 As shown, Li of this embodiment 1.2 Ni 0.13 Co0.13 Mn 0.54 The O2 material completely matches the standard diffraction peaks of the lithium-rich layered material and does not have any additional impurity peaks, indicating that pure lithium-rich layered materials have been successfully synthesized.

[0027] For this embodiment, Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 O2 materials were tested for electrochemical properties, such as Figure 6-7 As shown, undoped Li 1.2 Ni 0.13 Co 0.13 Mn 0.54 The O2 material showed poor capacity retention, with a capacity retention of only 67% after 150 cycles. 1.2 Ni 0.13 Co 0.13 Mn 0.54 The O2 material also exhibits severe voltage decay, with a voltage drop of 0.40 V after 150 cycles.

[0028] Example 2: Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Lithium-rich layered materials (Li 1-x K x (Li a Ni b Co c Mn d ) 2-y (PO4) y ,a=0.2,b=0.13,c=0.13,d=0.54,x=0.01,y=0.01)

[0029] Step 1: 0.9388 g of Mn 4 / 6 Co 1 / 6 Ni 1 / 6 CO3(Mn m Co k Ni n CO3, m=4 / 6, k=1 / 6, n=1 / 6), 0.4601g of Li2CO3 and 0.0137g of KH2PO4 were mixed by ball milling, and a small amount of anhydrous ethanol was added during the ball milling process. After the ball milling, it was placed in a vacuum oven at 60°C for drying and ground into powder.

[0030] Step 2: In this embodiment, nickel foil is used as a conductor sheet for rapid heating, and the size is 2*5cm 2 The precursor powder obtained in step 1 was placed on a nickel foil substrate, and then the current and voltage were adjusted to a temperature of 660°C. After 60 seconds, the power supply was disconnected. After grinding evenly, the powder was placed on a nickel foil substrate for secondary calcination. The current and voltage were adjusted to a temperature of 970°C. After 45 seconds, the power supply was disconnected. After grinding evenly, Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Lithium-rich layered materials.

[0031] For this embodiment, Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 The material was subjected to XRD test, such as Figure 1 As shown, Li of this embodiment 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 The material completely matches the standard diffraction peaks of lithium-rich layered materials and does not have any additional impurity peaks, indicating that K + and (PO4) 3- The dual doping does not affect the main structure of the material.

[0032] For this embodiment, Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 Materials were subjected to TEM tests, such as Figure 2-4 As shown, Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 The material shows a typical (003) crystal plane of lithium-rich layered structure. In addition, EDS mapping test was performed on the material, such as Figure 5 As shown, Ni, Co, Mn, K, and P are evenly distributed on the material, indicating that K +and (PO4) 3- It has been successfully incorporated into the material.

[0033] For this embodiment, Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 The materials were tested for electrochemical properties, such as Figure 6-7 As shown, compared with the undoped material, Li 1.19 K 0.01 Ni 0.13 Co 0.13 Mn 0.54 O 1.99 (PO4) 0.01 The material exhibits better capacity retention and slower voltage decay, for example: 84% capacity retention and 0.30V voltage drop after 150 cycles.

[0034] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A potassium and phosphate dual-doped lithium-rich layered positive electrode material, characterized in that: Its chemical formula is Li 1-x K x (Li a Ni b Co c Mn d ) 2-y (PO4) y , a+b+c+d=1, 1>x>0, 2>y>0; the lithium-rich layered positive electrode material is prepared by the following steps: Mn m Co k Ni n The CO3 precursor is mixed with Li2CO3 and KH2PO4 according to the chemical formula ratio through ball milling. A small amount of anhydrous ethanol is added during the ball milling process. After the ball milling, it is placed in a 60°C vacuum oven for drying and ground into powder, where m+k+n=1; then Joule heat treatment is carried out. During the Joule heat treatment process, the reaction temperature reaches 660°C through ultra-fast heating. The power supply is disconnected at the reaction temperature for 60 s. After the powder is evenly ground, it is placed on a nickel foil substrate for secondary calcination. The current and voltage are adjusted to a temperature of 970°C. After 45 s, the power supply is disconnected and the powder is evenly ground.

2. The method for preparing a potassium and phosphate dual-doped lithium-rich layered positive electrode material according to claim 1, characterized in that: Mn m Co k Ni n The CO3 precursor is mixed with Li2CO3 and KH2PO4 according to the chemical formula ratio through ball milling. A small amount of anhydrous ethanol is added during the ball milling process. After the ball milling, it is placed in a 60°C vacuum oven for drying and ground into powder, where m+k+n=1; then Joule heat treatment is carried out. During the Joule heat treatment process, the reaction temperature reaches 660°C through ultra-fast heating. The power supply is disconnected at the reaction temperature for 60 s. After the powder is evenly ground, it is placed on a nickel foil substrate for secondary calcination. The current and voltage are adjusted to a temperature of 970°C. After 45 s, the power supply is disconnected and the powder is evenly ground.

3. The method for preparing a potassium and phosphate dual-doped lithium-rich layered positive electrode material according to claim 2, characterized in that: The Mn m Co k Ni n The CO3 precursor was prepared by co-precipitation method.

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